The influence of hip muscle strength on gait in individuals with a unilateral transfemoral amputation

Daniel Walter Werner Heitzmann; Julien Leboucher; Julia Block; Michael Günther; Cornelia Putz; Marco Götze; Sebastian Immanuel Wolf; Merkur Alimusaj

doi:10.1371/journal.pone.0238093

. 2020 Sep 2;15(9):e0238093. doi: 10.1371/journal.pone.0238093

The influence of hip muscle strength on gait in individuals with a unilateral transfemoral amputation

Daniel Walter Werner Heitzmann ^1,^2,^*, Julien Leboucher ¹, Julia Block ^1,², Michael Günther ³, Cornelia Putz ^1,², Marco Götze ¹, Sebastian Immanuel Wolf ¹, Merkur Alimusaj ^1,²

Editor: Yih-Kuen Jan⁴

PMCID: PMC7467296 PMID: 32877428

Abstract

Introduction

A unilateral transfemoral amputation (TFA) has a major impact on function. A leg-length discrepancy is the primary structural change, accompanied by the loss of lower-limb muscle volume and function. Prostheses can help individuals with a TFA to regain function, but such individuals still do not reach the functional level of unimpaired peers and exhibit gait deviations. This study gives insight into the causality between residual limb strength and gait deviations in individuals with a TFA.

Methods

A convenient sample of 13 male individuals with a TFA (38.0 ± 12.6y; 179.7cm ± 6.5cm; 82.9kg ± 12.4kg) was recruited for this study. One participant with TFA was excluded, as he differed from the rest of the cohort, in residual limb length and the use of walking aids. A cohort of 18 unimpaired subjects served as a reference group (REF; nine females; 44y ± 13y; 174cm ± 9cm; 71kg ± 12kg). All participants underwent a conventional clinical gait analysis using a marker based 3D motion capture system and force platforms. Kinematics and kinetics were determined utilizing standard modelling methods. All subjects underwent a strength test, using a custom-made device to determine isometric moments of the hip joint in abduction, adduction, extension, and flexion. Peak values for maximum isometric moments for each movement direction and selected kinematic and kinetic values were derived from the results. Differences between subjects with TFA and unimpaired were compared using a Mann-Whitney U Test and associations between groups by Spearman’s rank correlation.

Results

The participants with a TFA showed a significantly lower maximum isometric moment for hip abduction (0.85 vs. 1.41 Nm/kg p < .001), adduction (0.87 vs. 1.37 Nm/kg p = .001) and flexion (0.93 vs. 1.63 Nm/kg p = .010) compared to the reference group. Typically reported gait deviations in people with a TFA were identified, i.e. significant lower cadence and increased step width. We further identified altered coronal plane hip and trunk kinematics, with significantly higher ranges of motion during involved side stance-phase. Gait kinetics of individuals with a TFA showed significantly lower peak values during stance for hip abduction, adduction and extension moments in comparison to the reference group. We identified a moderate negative correlation between maximum isometric moment for hip abduction and trunk obliquity range of motion (ρ = -0.45) for participants with a TFA, which was not significant (p = 0.14).

Conclusion

We showed that there are strength deficits in individuals with TFA and, that there are moderate correlations between gait deviations, i.e. lateral trunk lean during involved side stance and isometric hip abductor moment. The relation between maximum moments during gait and the corresponding maximum isometric moment may therefore be helpful to detect strength related compensation mechanisms. However, the moderate, non-significant correlation between lateral trunk lean and isometric hip abductor moment was the only one which corresponded directly to a gait deviation. Thus results must be interpreted with care. This study suggests that gait deviations in individuals with TFA are multifactorial and cannot be exclusively explained by their strength deficits. Future studies should explore the relationship between strength with kinematics and kinetics during gait in this population.

Introduction

Unilateral lower-limb amputation has a major impact on individuals’ body integrity, perception and physical capabilities. A leg-length discrepancy between the involved and sound side represents the primary structural change, accompanied by the loss of functional levers, e.g., the foot lever. The amputation also has further impact on lower-limb muscle function. Muscle insertions distal to the amputation site are lost, making part of the lower limb musculature ineffective. Some further musculoskeletal comorbidities following lower-limb amputation are: low back pain, osteoarthritis, reduced bone density and volume loss and atrophy of involved muscles [1]. These changes related to muscle function lead to a deficit in muscle strength, as reported in previous studies investigating individuals with a transtibial amputation (TTA) [2–8] and transfemoral amputation (TFA) [5, 7, 9–12]. Although the impact on muscle function is obvious, it remains unclear how the deficit in strength relates to function and, more specifically, to walking. It has been shown that adequate strength is needed in both the residual and sound limb to improve walking ability in people with TTA [4]. Furthermore, it was also concluded in a review that the evidence of a relationship between muscle strength and walking ability remains insufficient in people with a lower limb amputation [13].

Via ultrasound imaging, involved side atrophy of the anterior thigh muscles was detected in individuals with TTA [6]. This led to altered walking biomechanics and residual limb muscle activation patterns after a TTA [6]. Also in individuals with TFA, muscle atrophy of the hip abductors was identified using MRI imaging [14]. However, neither study associated the functional muscular changes with measurements of muscle strength. In addition to these specific changes, general differences of the muscles are prevalent following amputation at both levels, e.g. larger amounts of fat embedded in the residual limb. Such fatty muscle degeneration was found, when residual limb muscles were compared to the corresponding muscles of the uninvolved side [15, 16].

The prosthetic socket may also have an influence on residual limb strength. The interface formed by the residual limb and the socket provides a semi-articulate coupling between the residuum and the prosthesis, due to incongruent movement between socket and stump influenced by soft tissue and socket fit. This results in a pseudo joint, which will not transfer loads through the lower extremity as in an unimpaired person, possibly leading to altered muscle loads. So, residual limb muscles in those with TFA will not be exposed to the same level of exercise, as lower limb muscles in unimpaired persons. In contrast to this, a more rigid fixation of the residual limb with the prosthesis, i.e. by osseointegration, or bone anchored prostheses, in individuals with TFA can have a positive effect on muscle strength [17].

Several studies have shown a general increase in function in people with lower limb amputation when they exercise, and they therefore demonstrated an increase in lower limb strength. Isometric strength training led to increased residual limb volume, improved suspension of the prosthetic socket, and gave a mean increase in walking speed by 13% when comparing results before and after the intervention [18]. Similar effects were reported for an isokinetic strengthening program with some participants doubling their walking distance after the program [19]. Individuals with TTA who frequently participate in sports activities were stronger than their non-active peers, reaching strength magnitudes almost as large as an unimpaired control group, while inactive individuals with TTA were significantly weaker [20].

Besides general function, walking and gait deviations are often associated with lower limb strength deficits. Excessive coronal plane movement of the trunk is one well known example of a gait deviation which is induced by a strength deficit [21]. It is commonly attributed to weakness of the hip abductors. Indeed, there is a relationship between the hip abductor strength and irregularities in trunk movements in several different pathological conditions [22–24]. Such deviations have also been reported in individuals with TFA [25, 26]. To date, it has not been shown that coronal plane trunk deviations in those subjects with TFA are caused primarily by weak hip abductors as these deviations may also be related to other factors, such as socket related issues. Leg length discrepancy is another potential cause for trunk deviation in people with TFA. A prosthetic leg length discrepancy could be due to one or a number of factors: Pistoning of the residual limb within the socket, the compression of elastic prosthetic feet or intentionally shortened prosthetic legs to guarantee clearance in swing.

To determine how muscle strength and walking are related in individuals with TFA we measured isometric strength, utilizing a custom made testing rig [11]. Following the ideas of Fosang et al. and Dallmeijer et al., who used a similar approach in individuals with cerebral palsy, we wanted to compare the maximum isometric joint moments (MIM) of people with TFA with the corresponding joint moments during walking as determined by conventional clinical gait analysis (CGA) [27–29]. We developed the following hypotheses for this study: Firstly, that people with TFA would have lower isometric moments on the involved side than those in the reference group; secondly, we expected to find similar gait deviations in individuals with TFA, as previously described in the literature, i.e. deviations in trunk movement. Finally, we expected to find correlations between maximum isometric joint moments and parameters of gait kinematics and kinetics, in that we expected weaker participants with TFA would show greater deviations during walking.

Material and methods

The parameters investigated here were the hip MIM, temporal spatial parameters, kinematics, and kinetics during walking. For MIM, at least two valid repeated measurements were collected for each of the four movement directions flexion, extension, abduction, and adduction. The trial with the highest MIM was used for subsequent analysis. From the CGA data, maximum hip moments as well as ranges of motion of trunk, pelvis, and hips in all three planes and temporal-spatial parameters (step length, step time, walking speed, cadence, and step width) were calculated. Group averages were analysed for the residual side only. For the reference group both limbs were used for calculating the group average. Methodological details are specified in the following paragraphs.

Participants

This study was approved by the Institutional Review Board (Ethikkommission der Medizinischen Fakultät Heidelberg; reference number S-302/2007). Recruitment was conducted at the in-house prosthetics and orthotics department. Prior to the assessment, written informed consent was obtained from all participants. A total of 13 male participants with TFA (38.0 ± 12.6y; 179.7cm ± 6.5cm; 82.9kg ± 12.4kg; details in Table 1) completed CGA and subsequently underwent a strength assessment in which the maximum isometric hip joint moment for abduction, adduction, flexion, and extension of the hip on the involved side were measured. The OpTIMo device [11] was utilized for this assessment and will be described in a following section (Isometric muscle strength measurements OpTIMo).

Table 1. Detailed information of the participants with a transfemoral amputation (TFA) and their current prostheses.

Person with TFA	cause for amputation	height [cm]	mass^* [kg]	age [y]	residual limb length	prosthetic knee	prosthetic foot	K-Level	amputation dates back [y]
1	tumor	172	62	33	long	C-Leg ¹	C-Walk ¹	3	10
2	tumor	186	81	47	medium	C-Leg ¹	C-Walk ¹	3	29
3	trauma	171	61	25	medium	C-Leg ¹	C-Walk ¹	4	7
4	trauma	175	85	52	medium	C-Leg ¹	Axtion ¹	3	26
5	trauma	183	100	23	long	C-Leg ¹	C-Walk ¹	3	8
6	trauma	176	87	51	medium	C-Leg ¹	C-Walk ¹	4	34
7	trauma	188	93	18	medium	C-Leg ¹	C-Walk ¹	3	1
8	trauma	190	93	34	short	3R60 ¹	Dynamic Motion ¹	2	18
9	bone abscess	187	96	42	long	C-Leg ¹	Variflex LP ²	3	2
10	congenital deformity	173	87	37	long	C-Leg ¹	C-Walk ¹	4	31
11	trauma	177	76	53	long	Rheo Knee ²	Ceterus ²	3	3
12	trauma	181	87	27	medium	C-Leg ¹	C-Walk ¹	3	2
13	trauma	178	70	53	medium	3A2000 ³	Soleus ⁴	4	27

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residual limb length in relation to the thigh length of sound side (<1/3 short, ≥1/3<2/3 medium, ≥ 2/3 long),

* body mass includes the mass of the prosthesis; Participant No.8 was excluded for further analysis, as his activity level, residual limb length and the use of walking aids differed considerably from the rest of the participants with TFA.

¹ = Otto Bock, Duderstadt, Germany;

² = Össur, Reykjavik, Iceland;

³ = Streifeneder, Emmering, Germany;

⁴ = College Park Inc., Warren, USA.

Prior to assessment, participants underwent a clinical examination to check their eligibility for the study. Inclusion criteria were: at least one year since amputation, able to perform a single leg stance on the sound side for at least five seconds without any assistance, sufficient residual limb length to attach the transducer strap during OpTIMo measurements, and no residual limb problems, e.g., pressure sores, edema, or pain within the last three months. Participants with TFA were classified from K-Level 2 to 4, according to the Medicare level functional classification system (MFCL) [30]. Only one participant (No. 8) was classified as K-Level 2, had a short residual limb and typically used crutches while walking outdoors (Table 1). During CGA he walked without the use of crutches. He further reported using the prosthesis less than three hours per day, while all others reported to use it more than three hours per day. He furthermore showed a strength deficit according to a modified Medical Research Council (UK) scale of 3+ (active movement against gravity with minor resistance) for hip abduction and flexion [31]. All other subjects showed normal strength with 5 out of 5 on this scale. Participant No. 8 was excluded from further analysis, due to these differences in prosthetic usage, residual limb length and the use of walking aids, when compared to the rest of the cohort. All participants reported that they were satisfied with their current prosthesis. Their habitual sockets were all total contact, ischial containment sockets without the use of liners. Participants had all obtained their sockets at the in-house prosthetics and orthotics department. Alignment of the socket was in accordance to Long’s line in the coronal plane and considered possible hip flexion contractures in the sagittal plane [32, 33]. According to the documentation, none of the participants showed a hip-flexion contracture of the involved side. Prosthetic length was adjusted to achieve a levelled pelvis. This was controlled by equal height of the posterior superior iliac spines during quiet standing, with both limbs equally loaded. Prosthetic components were aligned according to the manufacturer recommendations and checked via L.A.S.A.R Posture device (Laser Assisted Static Alignment Reference, Otto Bock, Duderstadt, Germany), which projects the vertical component of the ground reaction force as reference either laterally or anteriorly onto the subjects lower limbs [34].

A group of 18 unimpaired subjects served as a reference group (REF; nine female; 44y±13y; 174cm±9cm; 71kg±12kg). The REF group underwent both OpTIMo testing and CGA. MIM and CGA moments were normalized to body mass.

Gait analysis

For CGA, skin mounted markers were placed on all subjects (with TFA and REF) on anatomical landmarks according to the Plugin-Gait (Vicon, Oxford, UK) lower body marker set. Additional markers on the subjects’ shoulder girdle (spinous process of the 7^th cervical vertebrae, left and right acromion, and incisura jugularis) were used to observe trunk motion in relation to the global reference frame [35]. Participants were asked to walk on a 10m-long walkway at self-selected speed. A 12-camera system (Vicon, Oxford, UK) operating at 120 Hz and two force plates operating at 1080Hz (Kistler Instruments, Winterthur, Switzerland) were used to record data. Joint kinematics and joint kinetics were calculated using the conventional inverse dynamics approach with the Plugin-Gait software (PiG, Vicon, Oxford, UK) [36–39]. Joint internal moments were averaged across 5–10 trials with valid force plate hits. Prosthetic feet ankle markers were placed onto the foot cosmesis where the lateral malleolus is mimicked. The knee marker was placed on the axis of rotation for single axis joints and the upper, anterior axis for the two polycentric joints (Otto Bock 3R60 and Streifeneder 3A2000; Table 1). A thigh marker was placed laterally onto the socket. As kinetics were investigated during stance-phase while walking, it was decided to use standard CGA routines which do not allow for corrections of centres of gravity position, moments of inertia, or mass distribution of the prostheses. As shown by Pamies-Vila et al., the changes of the anthropometric body segment parameters have little effects on gait analysis results during stance [40].

Isometric muscle strength measurements

The OpTIMo device, used to determine isometric hip moments, consists of a rigid frame with a force transducer (Biovision, Wehrheim, Germany). During testing, the subject stood and was supported at the pelvis inside this frame (Fig 1A). Reflective markers on the pelvis and the sound limb were left in place during measurements.

Fig 1 — (A) Schematic representation, (B) Bird’s eye view of the OpTIMo device with the different pulling directions during isometric tests. (1 = Pelvic Support; 2 = Frame; 3 = Force Transducer; / Modified Picture of [11] with permission).

The force transducer was attached via a strap and a lightly padded cuff to the thigh of the REF or to the residual limb, respectively. Individuals with TFA did not wear a socket during OpTIMo measurement. The cuff was placed at a similar height between groups, which was the upper third of the thigh or residual limb, respectively. The position of the force transducer and cuff was adjusted for each hip MIM direction (flexion, extension, abduction, and adduction / Fig 1B). During measurements, a vertical position of the thigh was obtained. Prior to measuring each motion direction, subjects had the opportunity to perform submaximal test trials with to become familiar with the setup and protocol. The number of trials for familiarization was not standardized. After familiarization with the test, participants performed two repetitions for each motion direction. The trials with the highest MIM for each direction were used for further analysis. Participants were verbally encouraged during the trial to pull on the force transducer strap with their maximum voluntary contraction for about 10 seconds. Transducer force data (16 bit resolution at 1080Hz) and marker trajectories (120 Hz) were captured simultaneously. To avoid fatigue becoming a confounding factor, participants were allowed to rest between measurements. Participants were instructed to pull the transducer strap only in the direction the hip was being tested (flexion-extension and adduction-abduction) to avoid combined movements, e.g., hip abduction with adjunctive hip flexion. Participants were asked to constantly increase force during the trial and to attempt to hold their maximum for at least two seconds. The average force within this 2-second plateau was used for further data processing. The hip joint centres were determined by Davis regression equations [36] on the basis of the pelvic marker trajectories, similar to CGA routines (i.e., Plugin Gait, Vicon, Oxford, UK). The direction of force was determined by two markers and their associated trajectories, on the force transducer strap. The lever arm was defined by a vector from the calculated hip joint centre to a marker on the cuff. The isometric hip joint moment was subsequently calculated as the cross product of lever arm and force vector. A detailed description of the OpTIMo method can be found in Heitzmann et al. [11].

Statistics

A Shapiro-Wilk Test was used to test for normal distribution of data. As some of the tested outcome variables were non-normally distributed, we chose non-parametric statistics (Mann-Whitney U Test for independent samples) to compare between groups (REF vs. TFA) and correlations between parameters within the participants with TFA (Spearman’s rank correlation). To account for corrections for multiple comparisons (14 in CGA parameters and 4 in MIM) we applied a Bonferroni correction and adapted the levels of significance for MIM comparisons to p < .0125 and for CGA parameter comparisons to p < .0036.

Correlations with a Spearman’s ρ of 0.40–0.59 were classified as moderate, 0.60–0.79 as strong, and 0.80–1.0 as very strong correlations. The level of significance for correlations was corrected to p < .0036 to account for testing across the coronal and sagittal plane CGA and MIM parameters.

Results

We detected differences between the REF group and the group with TFA. In addition to the difference between groups in sex, we saw a significantly higher mean mass for the participants with TFA (p = .025). There were no statistical significant differences in height (p = .087) and age (p = .346) between groups.

The participants with TFA had a significantly lower MIM for hip abduction and adduction and hip flexion than the REF. They reached only 60% of the mean REF value in MIM abduction (p < .001), 63% in MIM adduction (p = .001) and 57% in MIM flexion (p = .010). There was no significant difference in hip extension MIM, with participants with TFA reaching 85% of the MIM of REF (p = .215). For temporal spatial parameters, individuals with TFA showed a comparable step length to REF. They walked slightly, but not significantly slower and had a significant decrease in cadence (p < .001) and step width (p < .001) (see Table 2).

Table 2. Results for the maximum isometric moments (MIM) and conventional clinical gait analysis (CGA).

		Participants
		with trans femoral amputation (TFA)				without impairment (REF)				TFA vs. REF
		(N = 12 mean of involved limb)				(N = 18 mean of both limbs)				TFA vs. REF
				95% CI				95% CI
		mean	±SD	LB	UB	mean	±SD	LB	UB
Hip MIM (N m/kg)	abd.	.85	(±0.25)	.69	1.01	1.41	(±0.41)	1.21	1.62	p < .001*
	add.	.87	(±0.36)	.64	1.10	1.37	(±0.42)	1.16	1.58	p = .001*
	ext.	1.11	(±0.33)	.90	1.32	1.30	(±0.39)	1.11	1.50	p = .215
	flex.	.93	(±0.40)	.68	1.18	1.63	(±0.73)	1.27	1.99	p = .010*
CGA Temporal spatial parameter	step length (m)	.73	(±0.08)	.68	.79	0.75	(±0.07)	.72	.79	p = .602
	Speed(m/s)	1.22	(±0.22)	1.08	1.36	1.44	(±0.17)	1.35	1.52	P = .008
	cadence (steps/min)	99	(±9.94)	93	105	114	(±8.79)	110	119	p < .001*
	step width (cm)	14.4	(±3.63)	12.1	16.7	6.9	(±2.85)	5.4	8.3	p < .001*
CGA kinematics hip pelvis & trunk ranges 0–100% gait cycle (in degrees)	hip abd. & add.	8.5	(±3.25)	6.5	10.6	13.7	(±3.09)	12.2	15.3	p < .001*
	hip flex. & ext.	44.1	(±6.20)	40.2	48.0	47.4	(±4.36)	45.2	49.6	p = .134
	pelvic obliquity	7.9	(±2.82)	6.1	9.7	9.5	(±2.23)	8.4	10.6	p = .104
	pelvic tilt	8.2	(±1.69)	7.1	9.3	2.4	(±1.27)	1.8	3.1	p < .001*
	trunk obliquity	5.9	(±2.11)	4.6	7.3	2.7	(±0.83)	2.3	3.2	p < .001*
	trunk tilt	3.9	(±0.98)	3.2	4.5	2.0	(±0.76)	1.6	2.4	p < .001*
CGA maximum hipmoments in stance (N m/kg)	abd.	.59	(±0.19)	.47	.71	0.88	(±0.18)	.79	.96	p = .001*
	add.	.06	(±0.04)	.04	.08	0.16	(±0.10)	.10	.21	p = .009
	ext.	.46	(±0.16)	.35	.56	1.07	(±0.26)	.94	1.19	p < .001*
	flex.	1.06	(±0.29)	.88	1.25	0.88	(±0.21)	.77	.98	p = .059

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TFA = transfemoral amputation; REF = group of unimpaired peers which served as a reference; CI = 95% confidence interval of the mean; LB = lower bound; UB = upper bound; SD = standard deviation; level of significance for CGA parameters p < 0.0036; for MIM p < 0.0125

For CGA kinematic results, participants with TFA showed a significant lower hip abduction and adduction range of motion on the involved side during walking. Furthermore, they showed significantly greater ranges for pelvic tilt, trunk obliquity and trunk tilt (see Table 1 / kinematics hip pelvis & trunk ranges 0–100% gait cycle). Additionally, they leant their trunk towards the involved side during single limb support, which was associated with an involved side pelvic drop and increased involved side hip abduction in stance (see Fig 2 and S1 Fig).

Fig 2 — The participant with TFA presents a lean of the trunk to the involved side with a linked pelvic drop and increased hip abduction on the involved side.

When compared to REF, participants with TFA had significantly lower peak internal hip abduction and adduction moments and a lower peak hip extension moment during the stance phase.

We detected significant strong, to very strong correlations between the hip MIMs in the different movement directions (abduction, adduction, extension, and flexion) in both groups (S2 Table). For hip abduction and adduction, MIMs in individuals with TFA showed a strong but not significant correlation. We saw no significant correlations between MIM and CGA parameters for the coronal or sagittal plane, in those with TFA. However, while not significant, we saw a moderately negative correlation between hip abduction MIM and trunk obliquity range (ρ = -0.45; p = 0.14) in participants with TFA. Lastly, a moderately negative correlation was found for TFA hip adduction MIM and hip adduction moments during walking (ρ = -0.63; p = 0.03), but also a moderately positive correlation between hip flexion MIM and the corresponding moments during gait (ρ = 0.49; p = 0.11). There was no correlation between peak hip abduction moments in stance and the corresponding abduction MIM (ρ = -0.032; p = 0.92), nor did we find a correlation between peak hip extension moment in stance and the extension MIM (ρ = 0.042; p = 0.90) for participants with TFA.

Discussion

Our data shows that those individuals with TFA have significantly lower MIM values for hip abduction, adduction, and flexion than the REF group, which supports our first hypothesis that people with TFA show significant strength deficits on the involved side. These findings are generally in line with the literature, e.g. hip joint muscles strength deficit in people with TFA of up to 35% when compared to unimpaired peers [7, 10, 41].

In addition, we detected several gait deviations in the cohort with TFA. A significantly higher mean range in trunk obliquity (mean 5.9±2.11°) over the entire gait cycle was seen in comparison to REF (2.7±0.83°) (Table 2, S1 Fig). This was accompanied by an increased hip abduction, indicated by the decreased range in abduction and adduction (Table 2, S1 Fig). The participants with TFA appear to avoid hip adduction. Instead, they possibly shifted their mass by means of the increased lateral trunk obliquity to the involved side. This compensation may explain the decreased hip internal abduction moments on the involved side in participants with TFA (S1 Fig), as has been observed in people with TFA [25, 26, 42, 43]. Occasionally this pattern in people with TFA is referred to as being a Trendelenburg gait pattern. However, we do believe that this not correct, as Trendelenburg’s original publication described a different pattern, i.e. a pelvic drop on the swinging limb, in a different pathology [21]. In contrast to Trendelenburg’s explanations, we monitored a coronal plane pelvic drop in the affected side single-support-phase with a linked pelvic lift on the contralateral side, and an accompanied trunk lean to the affected side (Fig 2). Tazawa et al. indicated that subjects with a subjectively ‘good’ walking pattern showed a smaller lateral trunk displacement [43]. Altered trunk and hip kinematics exhibited in persons with TFA have been attributed to weak hip musculature [14, 25, 42]. This connection may explain the observed, non-significant, moderate negative correlation between hip abduction MIM and trunk obliquity range-of-motion. This correlation indicates that weaker people with TFA have the tendency to show a greater trunk range-of-motion during walking than their stronger piers. However, it should be noted that this is the exact opposite trend observed in the unimpaired population (S2 Fig), showing a moderate positive correlation. The only significant and strong, to very strong correlations were found between the MIMs of different movement directions with each other (S2 Table and Scatterplots S3 and S4 Figs). Thus, a weaker person shows generally lower hip MIM values, which was true in both TFA and REF groups.

Peak to peak ranges in MIM were significantly smaller in participants with TFA (Fig 3). In theory, one could imagine these peak to peak values as a working range. If this working range would be surpassed by moments occurring during gait, this may lead to gait deviations. In typically developing children, the hip MIMs were about 2 to 3 times as high as the moments during walking [27]. At the same time their ankle moments during walking exceed their ankle MIM [27]. Therefore, the model of the peak to peak MIM values building a “working range” certainly has limitations and does not fully explain the relationship between monitored strength deficits and gait deviations in people with TFA. In REF and individuals with TFA, we observed MIM values 1.5 to 2 times higher than the peak moments during gait. This was also true for participants with TFA as they had generally reduced moments during walking, which led to a similar ratio. Although, the aforementioned “working range” model and the relationship between isometric moments and moments during walking are not fully understood, those with TFA may pursue a similar ratio of MIM and peak moments during walking as REF, potentially to reach comparable “headroom” as their unimpaired peers. The price for this strategy may be gait deviations which lead to reduced moments during walking. However, this is a conjecture and we cannot fully support this theory with the data collected in this study. Likewise, it was concluded that more work is required to understand how the MIM measurements relate to moments during walking [10]. Additionally, participants with TFA walked considerably, but not significantly slower, which makes comparisons of kinetics difficult.

In addition to the strength status of the involved side, other confounding factors will influence gait quality in individuals with TFA. Such factors could be technical characteristics of their prosthesis such as socket design, prosthetic alignment, potential leg length discrepancies and prosthetic components. The lack of any significant correlation that corresponded directly to a gait deviation supports our suggestion that gait deviations in our TFA cohort are multifactorial. Especially, in our opinion, the socket plays a crucial role. The interactions between the residual limb and the socket will result in a pseudo-joint, independent of the chosen socket design. A reduced power transmission between the stump and the socket may cause the observed muscle weakness to manifest a more pronounced functional deficit. We believe there is an accumulation of these two factors, i.e. the structural changes of the limb and the reduced power transmission. Some socket designs may be even more prone to increased residual limb-socket interactions, when compared to others. For example, it is well accepted that quadrilateral sockets do not stabilize the femur in the coronal plane and therefore will more likely cause increased residual limb movement during walking, compared to other designs, e.g. ischial containment sockets [44, 45]. Decreased medio-lateral stability of the residuum, along with other cofounding factors like strength deficits of the hip abductors and a leg length discrepancy, was identified as a potential cause for a lateral trunk motion [46]. The strength status of people with TFA is therefore of high clinical relevance. Strength deficits may force people with TFA into compensation mechanisms during walking, which should be distinguished from those induced by the socket, the prosthetic components, or leg length induced gait alterations. Moreover, the affected side ground contact in a person with TFA is different than in an unimpaired person. In people with TFA the affected side hip joint is the only joint which can be volitionally controlled and therefore used to adjust the loads introduced to the prosthetic limb. Thus, gait deviations in this population may be a response to unwanted loads introduced to the involved side, and may serve as an option to readjust loads. Another indicator, that coronal plane gait deviations cannot purely be attributed to hip strength deficits, is that a lateral trunk lean can be also present in amputations below the knee. So, there is a high plausibility that not all gait deviations, in particular of the pelvis and trunk can entirely be lead back to weaknesses of the hip.

Hence, the origins for strength deficits in people with TFA and their gait deviations, partially attributed to these strength deficits, cannot be fully clarified in this study. For example, the hip abductors are not directly damaged by the transfemoral amputation per se. However, the muscle balance between abductors and adductors is disturbed. The adductors’ moment arm is reduced, which leads to increased residual limb abduction, which will affect the abductor moment arm. As a result, the altered muscle loads may be insufficient to maintain strength of the hip abductors. As stated earlier, the altered biomechanics of prosthetic gait in subjects with TFA may induce a weakening of certain muscle groups, while possibly also preserving strength of other muscle groups. This hypothesis is partly supported by the hip extension MIM results in our TFA group. It is noteworthy that we detected no significant strength deficit in hip extension MIM in individuals with TFA, which, to our knowledge, has not been reported previously. This was the only MIM parameter where we did not find a significant weakness, which could be explained by the fact that the hip extensors are important to provide propulsion and an upright posture in those with TFA but also to stabilize the prosthetic knee joint in early stance, mainly in conventional, non-microprocessor controlled prosthetic knee joints. The subjects seem to utilize an increased internal hip extension moment, which may be sufficient to preserve strength in the hip extensors of our, higher active cohort with TFA. This is also in line that hip extensors, of both the involved, and the sound side, compensate for the loss of function of the involved side [47]. Reduced hip extension power on the involved side has further a negative impact on preferred walking speed [48]. So, individuals with TFA seem to utilize their hip extensors more than other muscle groups of the residual limb.

In the context of this study, we must also report its main limitations. Prosthetic alignment was controlled in the in-house workshop but was not quantified furthermore. Although the prosthetic leg length was checked, in that the pelvis was levelled in quite standing, the prosthesis may be shorter in single limb support, e.g. due to pistoning or due to compression of elastic prosthetic feet. As mentioned previously, deficits in alignment and leg length discrepancies lead to gait deviations, also of the trunk. Socket comfort was not determined in this study [49]. A socket that does not fit comfortably could aggravate gait deviations, e.g. the occurrence of an increased pistoning or a reduced loading to avoid pain. However, all participants reported being satisfied with their current socket and prosthesis in general. Generally any convenient sample, of either unimpaired or TFA participants, is limiting. The sample size in this study was small and may have influenced the results, in particular significance levels of correlations between MIM and GCA parameters. However, we do believe that the moderate correlation between abduction MIM and lateral trunk motion could be an indication that strength is one of the cofounding factors in lateral trunk displacement of individuals with TFA during walking. The rather high activity level or K-Level of our TFA group may also influence results. Low activity individuals with TFA (i.e. K-level 1 and 2) may show even greater deficits in strength and larger deviations in gait. The differences in age and gender between REF and TFA groups may also represent a limitation. In this context, it is remarkable that the potentially “stronger” participants with TFA (younger and only male participants) are still significantly weaker in three out of four of the hips MIM in comparison to REF. People with TFA walked slower. This difference was not significant. However, it is noticeable and may bias the interpretation of kinetics.

Conclusion

The relation between maximum moments during gait and the corresponding MIM might be helpful in detecting strength related compensation mechanisms. However, during walking compensation mechanisms may also be induced, e.g. by the socket, prosthetic leg length or prosthetic component related, that contribute to the net functional deficit. Though, we have demonstrated that there are moderate correlations between gait deviations, i.e. later trunk lean onto the involved side and hip abductor MIM. However, this was not significant and was the only correlation that corresponded directly to a gait deviation. This supports our suggestion that gait deviations in our cohort of individuals with TFA are multifactorial. Future studies should investigate additional influential factors e.g. by comparing different socket designs and further explore the relationship between MIM and kinematics and kinetics during gait.

Supporting information

S1 Table. Self-reported health status and sports activities of the participants with TFA.

# = nothing specified.

(DOCX)

Click here for additional data file.^{(47.7KB, docx)}

S2 Table. Correlations of sagittal and coronal plane gait parameters with their corresponding maximum isometric moments (MIM) of the hip.

Values Spearman's rho with its corresponding p-value; level of significance was set to p < .0036; * = statistical significant correlation; # = moderate, + = strong, ! = very strong; correlations with a Spearman’s ρ of 0.40–0.59 were classified as moderate, 0.60–0.79 as strong, and 0.80–1.0 as very strong correlations).

(DOCX)

Click here for additional data file.^{(54.3KB, docx)}

S1 Fig. Trunk, pelvic and hip coronal and sagittal kinematics as well as coronal and sagittal hip kinetics (internal moments) of both investigated cohorts.

Red, solid line = mean kinematics and kinetics during walking of participants with TFA walking @ 1.22 (±0.22) m/s; red, dashed line = standard deviation of the TFA mean; grey, dashed line = mean moments during walking of REF @ 1.44(±0.17) m/s; grey band = standard deviation of the REF mean; FS = foot strike; oFO opposite foot of; oFS = opposite foot strike; FO = foot off; DS = double support.

(TIF)

Click here for additional data file.^{(966.7KB, tif)}

S2 Fig. Scatterplot of the isometric trunk obliquity range of motion vs. hip abduction moment during the gait cycle.

(TIF)

Click here for additional data file.^{(434KB, tif)}

S3 Fig. Scatterplot of isometric coronal plane hip moment against each other.

(TIF)

Click here for additional data file.^{(471.6KB, tif)}

S4 Fig. Scatterplot of isometric sagittal plane hip moment against each other.

(TIF)

Click here for additional data file.^{(477KB, tif)}

Acknowledgments

The authors would like to thank all study participants. Their contribution is highly appreciated. We further like to thank Dr. Alan R. De Asha for editing the manuscript.

Abbreviations

CGA: Conventional clinical gait analysis
MFCL: Medicare 5-level functional classification system
MIM: Maximum isometric joint moment
OpTIMo: Device for testing isometric moments (OpTIMo = Optical Testing Isometric Moment)
REF: unimpaired subjects served as a reference group
TFA: transfemoral amputation
TTA: transtibial amputation

Data Availability

All relevant data are within the manuscript and its Supporting Information files.

Funding Statement

This study was supported by Bundesministerium für Arbeit und Soziales (BMAS) - Referat Orthopädische Hilfmittel in the form of a grant awarded to DWWH, JB, SIW and MA (Title 684 02) and Deutsche Forschungsgemeinschaft (DFG) in the form of a grant awarded to DWWH, JL, JB, CP, SIW, and MA within the project ‘Biomechanik des Prothesengangs’ (project no. 322886417). Guenther Bionics GmbH also provided support in the form of a salary for MG. The specific roles of this author are articulated in the ‘author contributions’ section. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

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PLoS One. doi: 10.1371/journal.pone.0238093.r001

Decision Letter 0

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4 Dec 2019

PONE-D-19-24706

The influence of hip muscle strength on gait in individuals with a unilateral transfemoral amputation – a prospective cohort study

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4. Please include a copy of Table 3 which you refer to in your text on page 20.

Additional Editor Comments (if provided):

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Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

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2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: No

Reviewer #2: Yes

Reviewer #3: Yes

**********

3. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

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4. Is the manuscript presented in an intelligible fashion and written in standard English?

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Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: No

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5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: The manuscript reports results from a study examining the changes in gait kinematics and joint moments that occur in a cohort of participants with transfemoral amputations (pTFA), and their relationship to isometric joint moments. To do this, the authors use an isometric force measurement rig in conjunction with marker based clinical gait analysis to compare maximum isometric joint moments (MIM) with joint moments and kinematics measured during walking. The experiment design appears solid (although clarifications are needed), and the results show consistent reductions in maximum isometric moment for hip abduction, adduction, and flexion, correlations between isometric and gait joint moments, and a moderate correlation between isometric hip abduction moment and trunk movement. As the authors point out in the discussion, many of the findings agree with previous studies looking at isometric moment generation or gait kinetics/kinematics in pTFA, although here the authors are also able to examine relationships between the two metrics.

Overall the manuscript is well written. There are a variety of minor issues that require correction or clarification in the manuscript but most are relatively easily addressed. Clearly this is a rich dataset with a wide number of measures obtained during testing, particularly during gait. It looks like table 2 lists all of the measures examined but it would be helpful for the reader if they were stated more explicitly in the methods, possibly as a list of the planned study measures before they are detailed in the main text. The nonparametric statistical testing for group differences is appropriate, however, it is not clear whether corrections for multiple comparisons were applied to help control for false positive results given the number of tests.

The Discussion is quite long, which is not necessarily a problem, although there are a number of associations made between pTFA and other populations (e.g. hip luxation, cereberal palsy, Legg Calve’ Perthes, etc.), for which the rationale is not always clear given the inherent differences between such groups.

Page 6 (lines 116-121), The point the authors are trying to make with Sherk et al. is not very clear.

Page 12 (line 249), please clarify why adjustments for the characteristics of the prosthesis were not made when calculating joint kinetics. This would seem likely to have an impact on the measures.

Page 13 (line 266), references Figure 1C which is not present in Figure 1.

(line 271), notes that marker trajectories were measured during isometric testing but their use is not clarified later on.

(line 287) indicates that the “best trial” was used. Please clarify how this was defined.

Figure 3, The content of the figure is not clear and the caption does not explain all elements of what is being presented. For example, the titles suggest an x vs. y comparison of the title variables in the plots but the independent variable appears to be gait cycle (although abbreviations are not defined). Shading and dotted lines are not defined in the caption. Please also doublecheck the phrasing ‘none continual scalar’.

Page 19, reports the spearman correlations between various metrics in TFA but it is unclear how the levels of correlation relate to controls, which are not presented.

Page 22 (lines 425-427), if the participants maximum isometric joint moment was being measured in the study (which generally speaking should be the largest moment that can be generated), it is unclear how/why moments generated during gait would necessarily exceed it.

Figure S1 caption, please indicate what the ranges correspond to.

Other minor comments and suggested edits (insertions/deletions in brackets),

Please verify that past tense grammar is consistent throughout the manuscript

Page 4 (line 84), “… might [be] helpful…”

Page 6 (line 127), “…Additional[ly]…”

(line 132), “…compromise[d]…”

(line 135), “…who [was] utilizing…”

Page 7 (line 156), “…walking [is] coronal plane…”

(line 159), “…and [] irregularities…”

(line 161), “…TFA [out] of a ….”

(line 164), “…this may [also] be related to…”

Page 8 (line 179), “…role of [muscle] strength…”

Page 9 (line 190), delete “of the department”

Page 16 (line 325-326), “…vie [of] each side…present[ed]…”, “conjunct” spelling?

Page 21 (line 390), “…patter[n]…”

Page 22 (line 426), “…if this [] working…”

Page 23 (line 445), “…socket do[es] not…”

Reviewer #2: The goal of the manuscript is to examine the influence of hip muscle strength on walking biomechanics for persons with transfemoral amputation. The authors hypothesize that: “people with [transfemoral amputation] TFA will show lower isometric moments on the involved side than those in reference a group (REF); we expect correlations between maximum isometric joint moments and gait kinematics of the hip, pelvis, and trunk; and, further, we expect correlations between maximum hip joint moments in gait with those tested isometrically.” The authors prove their hypothesis and show that persons with transfemoral amputation have reduced hip muscle strength as compared to healthy individuals, but do not attempt to decouple the effects of reduced hip muscle strength and differences in leg length due to the transfemoral prosthesis for the gait deviations observed. It is recommended that the authors perform additional analyses to examine the role of the transfemoral prosthesis on the gait deviations observed rather than ignoring this confounding factor.

Major:

In the discussion and conclusion, the authors link decreased hip ab/adduction moment to changes in hip and trunk kinematics. While this may be a factor, the reviewer does not believe it is the cause of the kinematic changes. Most prosthetists make create a transfemoral prosthetic system that causes the prosthetic limb to be longer than the sounds limb so that during walking the user compresses the prosthetic foot during stance. This can lead poor hip alignment during standing and during the stance phase of walking if the user does not meaningfully progress onto the prosthesis during this time. Additionally, this longer prosthetic leg can lead to hip hiking during swing. Did the authors examine the trunk obliquity and hip alignment during a static trial? Additionally, the authors could examine the effective leg-length throughout walking by examining a vector from the hip joint center to the center-of-pressure under the foot. Such a vector should be compared to the sound limb to see if the effective limb length is the same. This would allow the authors to make a more concrete statement about how the subjects interact with the prosthesis and if the observed hip and trunk kinematic changes are due to leg length changes or due to weak hip musculature.

The introduction and discussion are clunky. The authors often introduce a source and then explain what the study concluded (or the inverse). For example:

“Pröbsting et al. gathered studies on changes in the musculoskeletal system as a result of lower-limb amputation [1]. They categorized these musculoskeletal changes as follows: low back pain, osteoarthritis, reduced bone density, and muscle atrophy.”

This type of referencing occurs 15+ times throughout the introduction and reduces the readability of the article. It is encouraged for the authors to concisely revise the introduction and discussion. An example for the previous quote would be:

“Noted musculoskeletal comorbidities following lower-limb amputation are: low back pain, osteoarthritis, reduced bone density, and muscle atrophy [1].”

Make sure to check the grammar and punctuation throughout the manuscript. The reviewer has listed several grammar and punctuation items that need to be addressed in the introduction but did not do so for the entire manuscript.

Minor:

This is not a prospective study as there was not an extended period of time that the subjects were examined over. Please remove such wording from the title and the manuscript.

Make sure to have continuous past tense throughout the manuscript

Introduction:

Line 91: need a comma instead of and between “integrity” and “perception”

Line 102: “this” to “muscles strength” as in the previous sentence you refer to muscle atrophy, amputation and strength

Line 109: “Medial” instead of ventral? The reviewer does not know what the ventral side of the thigh is.

Line 114: add “muscles” to the end of the sentence.

Line 127: “Addition” to “Additionally,”

Line 132: “compromise” to “compromised”

Line 138: “Additionally”

Line 156-157: “A well-known example of how strength deficits impact walking are probably coronal plane gait deviations of the trunk, as described by Trendelenburg [23].” Is not a definitive sentence.

Line 178-179: Remove: “We are confident that by using this approach we will gain better insight into the role of strength in people with TFA and their compensation mechanisms in gait.”

Methods:

How much does the K2 subject skew the results? Should he/she be eliminated from subsequent analyses? This subject, as reported, does not spend as much time on the prosthesis as the other subjects and is the only subject collected that was classified as K2.

Lines 190-191: remove “of the department”

Line 217: Define the acronym MRC

Lines 221-222: Were these sockets different than their daily use sockets? If they were, how much do you think this affects the gait outcomes of the manuscript?

Line 225: Define the acronym LASAR

Lines 249-250: How does not adjusting for the prosthetic inertial parameters affect the joint kinetics? And how does this affect the comparisons the authors make between able-bodied and persons with transfemoral amputation?

Line 266: a comma is needed

Line 288-291: The reviewer does not understand the how this portion is relevant. What was being correlated to provide a high correlation?

Line 289: put (ICC) after interclass correlation coefficient

Line 294: Please define PTFA acronym.

Results:

Why compare peak-to-peak maximum isometric moments? This would seem to penalize persons with amputation or hip musculature weakness more. Additionally, this does not provide an accurate characterization of the musculature which is only active in one direction. It is strongly recommended to separate out different motions as is reported in Lines 352 to 355 of the discussion and to not use the peak-to-peak range.

Line 313: include “during walking” to the end of the topic sentence.

Table 2: It is encouraged to not statistically compare gait parameters between the persons with amputation and healthy individuals as they had a significantly different gait velocity. It has been shown that differences in gait velocity cause differences in lower limb kinematics and kinetics (see Zelik and Kuo 2010).

Figure 3: Please update the healthy line color as the reviewer cannot see the mean line.

Figure 3 caption: please include the mean walking velocities for the persons with amputation and healthy individuals.

Line 322: this was not a significant finding. why report without significance?

Can the authors include a table with the variables correlated, the correlation values and the significance of the correlation values?

Discussion:

Line 350: “Individuals”

Lines 355-358: The reviewer does not see the relevance in reporting the ranges in the MIM. See comment above.

Line 363: “und” to “and”

Lines 368 to 438: Paragraph may want to be broken up to improve readability. Also, the authors refer to many different clinical populations (ex: children with Legg Calve´ Perthes disease, persons with cerebral palsy). This provides un-useful information as many clinical populations may suffer from different co-morbidities which makes the population unique and less relatable to each other.

Lines 411-420: Seems to be reiteration of the results with no real discussion going on. Additionally, are all the correlation values significant that are cited?

Line 425: “In theory one could imagine these peak to peak values as a working range and if this this working range will be surpassed by moments occurring during gait this may induce gait deviations or even make it impossible to walk.” These peak to peak ranges are exceeded during human running (see Riddick et al. 2018) for healthy individuals. The reviewer does not feel that this hypothesis can be supported as human locomotion exceeds these thresholds. It is recommended to temper the language.

The review thinks that the Author’s statement of: “Strength deficits may force individuals with TFA into compensation mechanisms, which should be distinguished from socket or prosthesis-induced gait alterations. External factors inducing the significant strength deficits in people with TFA cannot be fully identified in this study.” is the crux of the article and should be stated earlier in the discussion than line 462.

Line 466-467: “The hip abductors are not directly weakened by the transfemoral amputation itself.” is a misleading statement. The hip abduction muscles may not loose muscle mass during the amputation BUT the thigh muscles are “tacked down” onto the femur or may not even be attached. In the former case, the muscle loses the moment arm at which it acts, effectively making it weaker to perform the necessary task.

Line 470-481: Why do the authors interpret non-significant results as significant results?

Conclusion:

The authors state that this information may be helpful for rehabilitation. The authors should discuss such implication in the discussion.

Reviewer #3: This manuscript investigates potential correlations of strength gait deviations, as well as compared a cohort of people with transfemoral amputation to people without amputation. The topic of this article is interesting because if we could see a gait deviation and then address it with rehabilitation (e.g., strength or balance), it would help people with amputation walk with less deviations. I have a series of comments below that reference major and minor concerns, and I have highlighted some of them with line numbers but did not highlight every instance that is repeated throughout the manuscript.

General questions: Is maximal strength important with over ground preferred walking speed, or is it more important to show how much of their overall capacity they need to use to walk compared with non-amputees? Is there a greater reserve strength for non-amputees? Maybe a deviation is chosen to save available muscle fibers and reserve capacity to respond to perturbations or minimize energy expenditure.

Major Comments

Abstract:

Line 51: Is this a prospective study? A prospective study identifies a population and then follows them and tries to make predictions about what will happen, whereas here you are trying to make correlations between gait deviations and strength deficits.

Lines 51-53: Aside from the prospective study comment, I like this statement because it is clear about what you did in this study.

Introduction:

Line 95: This is something done many times throughout the manuscript, and may just be a personal preference on my part, but other authors should be cited while their findings are prominent. “Probsting…” sentence adds nothing. Then line 104, “Ostchega et al….” did not prove a relationship, the results or findings of a study show something, the authors just write it up. Also, there are very few proven relationships, there is more evidence for some things than others, but one study (and multiple studies) does not prove a relationship.

Line 102: Unless you plan on talking about other forms of mobility, such as transfers, just say “this relates to walking.”

Throughout the introduction there could be more standalone paragraphs, and rather than listing findings from study after study, the information could be synthesized or summarized. This relates to my comment above about authors not showing anything, but the overall data collected from many studies.

Lines 173 and 174: There should not be methods in the introduction.

Lines 182-183: Should hypothesized directionality of correlations, not just state there will be correlations.

Methods:

Line 213-215: I am not sure if participant 8 should be included in the data analysis, especially since he is a K2 ambulator and then he walked without crutches during his motion analysis. Walking without crutches is not his normal or preferred, and therefore the gait speed and mechanics are not preferred, whereas the participants were using preferred mechanics.

Lines 267-268: Did you standardize the amount of test trials for participants to try the OpTIMo?

Lines 284: General questions about OpTIMo, how widespread is this device clinically or in research? Is it a research-only device? How does it compare to typical clinical force dynamometry measures with patients laying down?

Line 287: What makes a trial the best?

Line 295: Why not look at the sound side too? Could be interesting when comparing to affected side and unaffected participants.

Statistics look right.

Results:

Line 310-311: All the differences were significant except for the step length.

Figure 3: Should label x and y axes rather than leave that to the title. Also, I do not know what FS, FO, oFS, and oFO are, I assume they are foot strike and foot off, but do not know.

Lines 342-345: What does negative and positive correlations mean in your results?

Discussion:

General comment: Should not repeat results, especially with p-values, in the discussion section, they should be in the results section alone.

Line 375: Remove distinguished, that is your spin and unnecessary.

Line 382: The results from Cappozzo agree with your results, do not confirm your results, and if anything, your results confirm their finding.

Lines 409-421: Listing many results in the discussion section, could be synthesized with the literature better.

Minor Comments

Abstract:

Line 47: Awkward wording “on the person concerned”

Line 59: should be “Kinematics” not “Kinematic”

Line 59: Could say determined, not derived, unless you derived equations.

Line 72: Could say “were identified, i.e. significantly lower speed,…”

Introduction:

Line 91: Could say “body integrity, perception…”

Line 98: “clear atrophy” does not make sense, atrophy alone works

Line 98: I recommend saying amputated or affected side, rather than ipsilateral side. I understand ipsilateral but I am not sure every reader will, it is more clear to say something like amputated, affected or involved.

Line 102: “particularly” does not add anything, like most adverbs

Line 126: What do you mean by “redundant”?

Line 127: Could say “Additionally, the…”

Line 128: What do you mean by “finite coupling”?

Line 130: Could say “Gholizadeh et al. underline the problems in…”

Line 138: Could say “Additionally, new…”

Line 164: Lower case i in ischial

Methods:

Line 193: clinical gait analysis can be replaced with CGA because the acronym is already listed in the beginning

Line 225: Is the L.A.S.A.R. posture device widely known? I am not sure if it should be explained more or you could stop the sentence with “recommendations.”

Line 240: What was the collection rate for the force plates?

Results:

Line 315: “in the patients” is awkward wording

Lines 320-321: “For CGA…the patient group.” is not a clear sentence, could be written better.

Line 325: Why is this schematic “exemplary”?

In table 2, Kg should be kg, and it should be N m and not Nm because they are 2 separate words.

Line 339: Should say “with TFA hip MIM of…” and not “with TFA Hip MIMof…”

Discussion:

Line 390: pattern, not patter

Line 445: Say For example, no E.g. to lead a sentence

Line 445: does rather than do

Line 449-452: Not a clear sentence.

Line 452: stabilize rather than stabile

Line 501: address rather than tackle deficits, tackle is in American football or Rugby rather deficits of our patients/clients

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Reviewer #2: No

Reviewer #3: No

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PLoS One. 2020 Sep 2;15(9):e0238093. doi: 10.1371/journal.pone.0238093.r002

Author response to Decision Letter 0

5 Jun 2020

General response from the authors: We would like to thank all reviewers for their time and effort when reviewing this manuscript. The input of the reviewers substantially helped us to improve the manuscript. We have tried to answer all raised questions adequately. Further we tried to shorten the manuscript and be more concise in describing effects. We excluded one critical patient from the cohort and added additional calculations (REF correlations and scatterplots of the correlated parameters). We do apologize for the almost unreadable tracked changes version, due to the many changes. We further involved a native speaker and fellow researcher in the field of prosthetics and orthotics for language editing of the manuscript. Also, since we did rewrite major parts of the manuscript, some of the specific critique of the reviewers may not apply any more, as we deleted or changed the sentence concerned. We apologize when this is sometime annoying. We hope for a positive feedback of the reviewers.

Reviewer #1: The manuscript reports results from a study examining the changes in gait kinematics and joint moments that occur in a cohort of participants with transfemoral amputations (pTFA), and their relationship to isometric joint moments. To do this, the authors use an isometric force measurement rig in conjunction with marker based clinical gait analysis to compare maximum isometric joint moments (MIM) with joint moments and kinematics measured during walking. The experiment design appears solid (although clarifications are needed), and the results show consistent reductions in maximum isometric moment for hip abduction, adduction, and flexion, correlations between isometric and gait joint moments, and a moderate correlation between isometric hip abduction moment and trunk movement. As the authors point out in the discussion, many of the findings agree with previous studies loing at isometric moment generation or gait kinetics/kinematics in pTFA, although here the authors are also able to examine relationships between the two metrics.

Response from the authors: We thank the reviewer for the thorough summary and hope that we can answer all raised questions sufficiently.

Response from the authors: We would like to thank the reviewer for the valuable comment. We moved the lines 285 to 295 in the original submission to the beginning of the methods section to clarify early in the text which are the main outcomes. We further corrected the level of significance for gait analysis parameters to p < 0.0036 and for the maximum isometric moment to p < 0.0125. The correction had minor effects on the results. Although, the level of significance is low after correction, all the main effects are unchanged and still significant. We hope this is sufficient.

Response from the authors: We shortened the discussion and deleted the paragraph which referred to different pathologies.

Page 6 (lines 116-121), The point the authors are trying to make with Sherk et al. is not very clear.

Response from the authors: We would like to thank the reviewer for that comment. We agree that this part was not quite clear. We shortened this part and combined it with the reference to Putz et al. . We hope that this helps for clarification.

Page 12 (line 249), please clarify why adjustments for the characteristics of the prosthesis were not made when calculating joint kinetics. This would seem likely to have an impact on the measures.

Response from the authors: Thank you for that comment. Adjustments would mainly influence results of joint kinetics during swing phase. We added information that we only investigated kinetics during stance and that correction for the persons/prosthesis characteristics would have a negligible influence onto joint kinetics during stance. This was added in the methods section, at the end of the subsection gait analysis.

Page 13 (line 266), references Figure 1C which is not present in Figure 1.

Response from the authors: We apologise for that. This was a mistake and supposes to say “B.” we corrected this. Thank you for making us aware of this mistake.

(line 271), notes that marker trajectories were measured during isometric testing but their use is not clarified later on.

Response from the authors: We would like to thank the reviewer for that comment. We explained the use of the trajectories and the biomechanical model behind OpTIMo in the following paragraph. We used marker trajectories on the pelvis to determine the hip joint centre, similar to CGA methods. Markers on the strap and on the thigh were used to determine the lever and force orientation. This used to be part of the subsection “Data Analysis” in the original submission, which we included in subsection “Isometric muscle strength measurements (OpTIMo)”. We hope this is sufficient.

(line 287) indicates that the “best trial” was used. Please clarify how this was defined.

Response from the authors: It was the trial with the highest isometric moment (MIM). We added this information in the methods section at the beginning, where we also summarized all main outcome parameters.

Response from the authors: We agree with the reviewer and changed the figure. We hope it is clearer now. We also added more information in the caption for clarification.

Page 19, reports the spearman correlations between various metrics in TFA but it is unclear how the levels of correlation relate to controls, which are not presented.

Response from the authors: We added correlations of the REF group in the supplement. We added also scatterplots to substantiate the results. After excluding participant no 8 from the analysis we noted significant correlations first found did not persist. Therefore there have been some changes in the discussion where we discuss the relation more moderately. Also, high correlation coefficients in REF group may suggest that there are more relationships (e.g. abd. MIM vs. abd. CGA -0.649 p = 0.004) However, we are critical, as the scatterplots do not suggest clearly that there is a clinical relevant relation in that group(see the plots below). We hope this answers all raised questions of the reviewer.

Response from the authors: We would like to thank the reviewer for the comment. We added information in the manuscript that the relationship between the isometric moments and the moments during gait is not straight forward and still subject to research. Fosang et al. also found that dynamic moments exceeded isometric moments, particularly in the ankle joint. We changed parts of the discussion, added the results of Fosang and weakened the conclusions of the first version of the manuscript. We hope this is sufficient.

Figure S1 caption, please indicate what the ranges correspond to.

Response from the authors: We added the information and also modified the figure slightly to show which gait phases we refer to. We hope this is sufficient for clarification.

Other minor comments and suggested edits (insertions/deletions in brackets),

Please verify that past tense grammar is consistent throughout the manuscript

Page 4 (line 84), “… might [be] helpful…”

Response from the authors: Changed

Page 6 (line 127), “…Additional[ly]…”

Response from the authors: This sentence was changed, deleted during rewriting the manuscript.

(line 132), “…compromise[d]…”

Response from the authors: This sentence was changed, deleted during rewriting the manuscript.

(line 135), “…who [was] utilizing…”

Response from the authors: This sentence was changed, deleted during rewriting the manuscript.

Page 7 (line 156), “…walking [is] coronal plane…”

Response from the authors: This sentence was rewritten during rewriting the manuscript.

(line 159), “…and [] irregularities…”

Response from the authors: Changed

(line 161), “…TFA [out] of a ….”

Response from the authors: This sentence was rewritten during rewriting the manuscript.

(line 164), “…this may [also] be related to…”

Response from the authors: Changed

Page 8 (line 179), “…role of [muscle] strength…”

Response from the authors: The sentence was deleted upon request of the 2nd reviewer, which we agreed to.

Page 9 (line 190), delete “of the department”

Response from the authors: Changed

Page 16 (line 325-326), “…vie [of] each side…present[ed]…”, “conjunct” spelling?

Response from the authors: Changed. We replaced conjunct by linked.

Page 21 (line 390), “…patter[n]…”

Response from the authors: This sentence was rewritten during rewriting the manuscript.

Page 22 (line 426), “…if this [] working…”

Response from the authors: This sentence was rewritten during rewriting the manuscript.

Page 23 (line 445), “…socket do[es] not…”

Response from the authors: Changed.

Response from the authors: We would like to thank the reviewer for his valuable comments and the summary. We try to respect the reviewer comments and change the manuscript accordingly. We absolutely agree with the reviewer that a leg length discrepancy could be as well one of the cofounding factors which cause gait deviations in people with TFA. We did add the influence of leg length at several points in the manuscript.

Major:

Response from the authors:

We would like to thank the reviewer for the comments. We absolutely agree with the reviewer that a leg length discrepancy will certainly influence whole body movement, including the trunk. We also named this very briefly at the end of the discussion in the previous version of the manuscript (Line 485 in the original submission: “A leg-length discrepancy could also lead to an increased lateral trunk lean.”). To emphasise that trunk movement is one of the possible causes for later trunk displacement we rewrote parts of the introduction and discussion to underline that a leg length discrepancy could be one of these factors. Further we tried to clarify how prosthetic alignment is performed in our facility. We aim for a levelled pelvis during steady standing, with both limbs equally loaded. We also respect the reviewers believe that strength may not be the main influence of lateral trunk movement in people with TFA. However, in this study the emphasis was on strength and the influence onto gait. It is a common belief that strength, in particular hip abductor strength is the only cause for lateral trunk movements in people with TFA. This somehow biased belief is also one reason we conducted this study, as this theory was never proved. We found out that there may be some connection, but we could not deliver true evidence. This underlines the “multifactorial” causes of gait deviations in people with TFA, of which one factor is also the leg length. Other calculations, as suggested by the reviewer will be subject of future research. We would like to thank the reviewer for the inspiration and hope that this sufficiently addresses the critique of the reviewer.

The introduction and discussion are clunky. The authors often introduce a source and then explain what the study concluded (or the inverse). For example:

“Noted musculoskeletal comorbidities following lower-limb amputation are: low back pain, osteoarthritis, reduced bone density, and muscle atrophy [1].”

Response from the authors: We agree with the reviewer and would like to thank him for making us aware of these shortcomings. We edited and shortened the introduction and the discussion and hope the readability is improved.

Response from the authors: We would like to thank the reviewer for his efforts. A native speaker and fellow researcher edited the manuscript and we tried to make sure to avoid mistakes and hope we covered all issues.

Minor:

This is not a prospective study as there was not an extended period of time that the subjects were examined over. Please remove such wording from the title and the manuscript.

Response from the authors: Changed

Make sure to have continuous past tense throughout the manuscript

Response from the authors: We involved a native speaker for editing and hope we found all shortcomings in language

Introduction:

Line 91: need a comma instead of and between “integrity” and “perception”

Response from the authors: Changed

Line 102: “this” to “muscles strength” as in the previous sentence you refer to muscle atrophy, amputation and strength

Response from the authors: This sentence was modified during the rewriting the manuscript.

Line 109: “Medial” instead of ventral? The reviewer does not know what the ventral side of the thigh is.

Response from the authors: Ventral refers to the front. In this case, it refers to the thigh muscles in the front. We changed ventral to anterior, as this may be more commonly used.

Line 114: add “muscles” to the end of the sentence.

Response from the authors: This sentence was modified during the rewriting the manuscript.

Line 127: “Addition” to “Additionally,”

Response from the authors: This sentence was modified during the rewriting the manuscript.

Line 132: “compromise” to “compromised”

Response from the authors: This sentence was modified during the rewriting the manuscript.

Line 138: “Additionally”

Response from the authors: This sentence was deleted during rewriting the manuscript.

Response from the authors: We agree with the reviewer and the sentence was rewritten

Line 178-179: Remove: “We are confident that by using this approach we will gain better insight into the role of strength in people with TFA and their compensation mechanisms in gait.”

Response from the authors: We agree. The sentence was deleted.

Methods:

Response from the authors: Following this comment and a comment of another reviewer, the influence of this particular subject was questioned. The subject had a lower functional level and used crutches while walking outside. It was consequently decided to remove the subject from the group to recalculate results.

Lines 190-191: remove “of the department”

Response from the authors: It is removed

Line 217: Define the acronym MRC

Response from the authors: We defined the acronym MRC (Medical Research Council)

Lines 221-222: Were these sockets different than their daily use sockets? If they were, how much do you think this affects the gait outcomes of the manuscript?

Response from the authors: The participants used their habitual sockets, which they obtained in our in-house prosthetics and orthotics department. We added this information in the methods.

Line 225: Define the acronym LASAR

Response from the authors: LASAR stand for “Laser Assisted Static Alignment Reference”. This information was added ion the manuscript. Further we added the reference of Blumentritt et al. who developed this system and defined the acronym.

Response from the authors: This was also a request by the 1st reviewer. We added information which underline that such adjustments lead to negligible differences in the calculated joint kinetics, which was confirmed by Pàmies-Vilà et al. [1].

Line 266: a comma is needed

Response from the authors: added

Line 288-291: The reviewer does not understand the how this portion is relevant. What was being correlated to provide a high correlation?

Response from the authors: This refers to the methodology paper which describes the OpTIMo Method in detail [2]. We detected a good reproducibility in this paper with the poorest ICC being 0.765 for hip abduction for the day-to-day variability. As we refer to the methodology paper earlier, we decided to delete this sentence.

Line 289: put (ICC) after interclass correlation coefficient

Response from the authors: We decided to delete this sentence.

Line 294: Please define PTFA acronym.

Response from the authors: We apologize for that mistake. We used the acronym PTFA (people with a trans-femoral amputation) in an earlier version of the manuscript. The acronym was changed in the course of the internal review and this is just a “left-over”. We deleted it in this sentence and refer to people with TFA. Thank you for making us aware of this shortcoming.

Results:

Response from the authors: We agree with the reviewer and do not report peak to peak values any more. We changed the paragraph accordingly.

Line 313: include “during walking” to the end of the topic sentence.

Response from the authors: Added

Response from the authors: We agree with the reviewer. The differences in speed are noticeable and may be of clinical relevance. We added information that there is a noticeable difference in walking speed in the results and in the limitations (at the end of the discussion).

Figure 3: Please update the healthy line color as the reviewer cannot see the mean line.

Response from the authors: We changed the graphs accordingly.

Figure 3 caption: please include the mean walking velocities for the persons with amputation and healthy individuals.

Response from the authors: We added this information.

Line 322: this was not a significant finding. why report without significance?

Response from the authors: We removed this sentence as results are shown in the table.

Can the authors include a table with the variables correlated, the correlation values and the significance of the correlation values?

Response from the authors: Yes, we can and we added a table with the correlation in the supplement.

Discussion:

Line 350: “Individuals”

Response from the authors: Changed

Lines 355-358: The reviewer does not see the relevance in reporting the ranges in the MIM. See comment above.

Response from the authors: The sentences which reported ranges were deleted.

Line 363: “und” to “and”

Response from the authors: We do apologize for that mistake. Changed.

Response from the authors: We agree with the reviewer and have deleted the parts referring to trunk deviations during walking in other pathologies than people with a lower limb amputation.

Lines 411-420: Seems to be reiteration of the results with no real discussion going on. Additionally, are all the correlation values significant that are cited?

Response from the authors: We tried to shorten this paragraph, to avoid repetition. We added the p-values to the correlation coefficient.

Response from the authors: We agree with the reviewer and tampered the language as this is a theory which cannot be proven by the collected data. Unfortunately we could not find the reference the reviewer is citing (maybe the Reviewer is referring to “Soft tissues store and return mechanical energy in human running” Riddick, Kuo 2016, but we are not certain). But we added aspects of the publication of Fosang et al. who also described that moments during walking are surpassing MIM in some instances, i.e. the ankle moment during walking.

Response from the authors: We agree with the reviewer and we state this earlier in the discussion now.

Response from the authors: We would like to thank the reviewer for that comment. Unfortunately we do not have information on the amputation technique performed in our cohort, as this could be another cofounding factor. For example, if a myodesis (tacking down the muscle to the bone) or a myoplasty (suture agonists and antagonists) was performed. We changed this sentence including the moment arm and the changed ratio of agonists and antagonists in a TFA. We hope this is clearer now.

Line 470-481: Why do the authors interpret non-significant results as significant results?

Response from the authors: We tried to rephrase and reformulate these sentences. We just found it peculiar that all muscle groups of the hip showed significant strength deficits in MIM except the hip extensors and tried to find an explanation for that, as this was the only non-significant MIM. Literature and clinical evidence suggests that the extensors play an important role in walking of people with TFA. This made us thinking whether or not there might be a training effect, due to the changed biomechanics which prevents the extensors form losing as much strength as the other muscle groups. We hope this is clearer now.

Conclusion:

The authors state that this information may be helpful for rehabilitation. The authors should discuss such implication in the discussion.

Response from the authors: Due to the lack of arguments supporting this hypothesis, we decided to delete the sentence.

Response from the authors: we would like to thank the reviewer for these remarks.

Response to the general questions above: For normal walking in unimpaired people somebody will most likely not need their maximum effort. So, one of our aims was to prove the second question: “how much of their overall capacity they need to use to walk compared with non-amputees” Is there a greater reserve strength for non-amputees? Yes, we were able to show this, e.g. in Figure 2 the horizontal lines representing the MIM in the according direction can be understood as a “Working Range” or “Reserve”.

“Maybe a deviation is chosen to save available muscle fibers and reserve capacity to respond to perturbations or minimize energy expenditure? „We have a similar concept. See the sentences in the discussion: “The strength status of people with TFA is highly clinically relevant. Strength deficits may force individuals with TFA into compensation mechanisms during walking, which should be distinguished from socket-, prosthetic-component, or prosthesis-leg length induced gait alterations.”

We hope the changes and the revised manuscript help to clarify all raised questions.

Major Comments

Abstract:

Response from the authors: We agree with the reviewer and deleted the parts which refer to a prospective study.

Lines 51-53: Aside from the prospective study comment, I like this statement because it is clear about what you did in this study.

Response from the authors: We would like to thank the reviewer for the encouraging comment and we deleted the prospective study comment.

Introduction:

Response from the authors: We would like to thank the reviewer for this remark and follow the suggestions in the revised version of the manuscript.

Line 102: Unless you plan on talking about other forms of mobility, such as transfers, just say “this relates to walking.”

Response from the authors: Changed

Response from the authors: We tried to rewrite larger parts of the introduction as well of the discussion. We tried to synthesize the statements from other studies and bring them better in the context of our results. Lastly we tried to structure the introduction in several thematic paragraphs. We hope the critique will be milder in the revised manuscript. Although we have to admit that we cited many studies, as we wanted to draw a picture of the many factors which could lead to gait deviations.

Lines 173 and 174: There should not be methods in the introduction.

Response from the authors: We agree with the authors and deleted the part referring explicitly to the method.

Lines 182-183: Should hypothesized directionality of correlations, not just state there will be correlations.

Response from the authors: We agree with the reviewer and tried to rephrase the sentence and describe in which directions we expect relationships.

Methods:

Response from the authors: We agree with the reviewer that this participant differs from the other participant. Therefore, we excluded patient no8 from the analysis and recalculated the results.

Lines 267-268: Did you standardize the amount of test trials for participants to try the OpTIMo?

Response from the authors: Yes we did. Each participant performed two repetitions for each motion direction with maximal force. Number of trials for getting familiar with the system, with submaximal force was not standardised. We added this information in the methods section.

Response from the authors: We would like to thank the reviewer for these questions and feel complimented for the interest in this device. 1st: The OpTIMo device is a development of the local laboratory and is not used elsewhere, to our knowledge. However there are other research group combining force-transducers or hand held dynamometers with optical marker data to obtain joint centres, length and orientation of the lever to calculate joint moments. 2nd: OpTIMo is a research only device and was specifically developed to collect strength data during conventional gait analysis. 3rd: We have not compared results of the device with other strength measurement methods. The idea is that we determine hip joint centres in a similar way as in conventional gait analysis, therefore marker on the pelvis have to be visible, which would not be possible with a person in supine position. Further we specifically wanted the people to stand upright during the test, as we believe that this position is closer to the function of walking, as we are aiming for a comparison of walking and isometric strength.

Line 287: What makes a trial the best?

Response from the authors: We added the requested information. It was the trial with the highest MIM.

Line 295: Why not look at the sound side too? Could be interesting when comparing to affected side and unaffected participants.

Response from the authors: In this study we aimed for the involved side as this clearly has a changed muscle configuration. We would like to thank the reviewer for that comment and the inspiration. This comparison was not in the scope of our study, but sound side measurements could potentially be performed in the future.

Statistics look right.

Response from the authors: As there were a few legitimate questions raised by the other reviewers we changed statistics according to their requests.

Results:

Line 310-311: All the differences were significant except for the step length.

Response from the authors: We do apologise for this avoidable mistake and changed it accordingly.

Figure 3: Should label x and y axes rather than leave that to the title. Also, I do not know what FS, FO, oFS, and oFO are, I assume they are foot strike and foot off, but do not know.

Response from the authors: We changed to figure for clarification as we realised that the term “vs.” may cause the reader to interpret the graphs as a plot of one value vs. the other. In this case it is a time series normalized to the gait cycle with the scalar, isometric moments as vertical lines for reference.

Lines 342-345: What does negative and positive correlations mean in your results?

Response from the authors: It depends on the data. In trunk motion, higher value means greater gait deviation (i.e. we expect a reduction of trunk movement, with greater abduction MIM). In case of MIM we obtained a positive correlation, as greater values in one MIM will lead to greater values in another MIM. The sign is somehow secondary, as it is not really helpful to determine whether or not there is a correlation it merely gives an insight if we are looking at a rising or falling slope.

Discussion:

General comment: Should not repeat results, especially with p-values, in the discussion section, they should be in the results section alone.

Response from the authors: Deleted

Line 375: Remove distinguished, that is your spin and unnecessary.

Response from the authors: Deleted

Line 382: The results from Cappozzo agree with your results, do not confirm your results, and if anything, your results confirm their finding.

Response from the authors: Changed

Lines 409-421: Listing many results in the discussion section, could be synthesized with the literature better.

Response from the authors: We have rewritten larger parts of the discussion in order to synthesis literature references better.

Minor Comments

Abstract:

Line 47: Awkward wording “on the person concerned”

Response from the authors: Deleted

Line 59: should be “Kinematics” not “Kinematic”

Response from the authors: Changed

Line 59: Could say determined, not derived, unless you derived equations.

Response from the authors: Thank you for this comment, we changed it accordingly

Line 72: Could say “were identified, i.e. significantly lower speed,…”

Response from the authors: Added

Introduction:

Line 91: Could say “body integrity, perception…”

Response from the authors: Changed

Line 98: “clear atrophy” does not make sense, atrophy alone works

Response from the authors: This sentence was deleted in the course of rewriting the introduction.

Response from the authors: This sentence was deleted in the course of rewriting the introduction. We further avoided the word ipsilateral throughout the manuscript.

Line 102: “particularly” does not add anything, like most adverbs

Response from the authors: Deleted

Line 126: What do you mean by “redundant”?

Response from the authors: We agree with the reviewer that redundant was not precise and changed it to superfluous

Line 127: Could say “Additionally, the…”

Response from the authors: Changed

Line 128: What do you mean by “finite coupling”?

Response from the authors: We changed it to “somewhat stiff coupling”

Line 130: Could say “Gholizadeh et al. underline the problems in…”

Response from the authors: Changed

Line 138: Could say “Additionally, new…”

Response from the authors: Changed

Line 164: Lower case i in ischial

Response from the authors: This sentence was deleted.

Methods:

Line 193: clinical gait analysis can be replaced with CGA because the acronym is already listed in the beginning

Response from the authors: Apologies. We changed this accordingly.

Line 225: Is the L.A.S.A.R. posture device widely known? I am not sure if it should be explained more or you could stop the sentence with “recommendations.”

Response from the authors: The L.A.S.A.R. posture device is widely known. We added a very brief description and a reference. So, the interested reader has the possibility to get additional information on the device.

Line 240: What was the collection rate for the force plates?

Response from the authors: We were not sure if the reviewer is referring to the sampling rate or the number of trials capured to calculate a mean. We added both in the methods section.

Results:

Line 315: “in the patients” is awkward wording

Response from the authors: We changed this sentence.

Lines 320-321: “For CGA…the patient group.” is not a clear sentence, could be written better.

Response from the authors: We totally agree with the reviewer and changed the sentence to: “During walking, the participants with TFA showed significantly lower peak internal hip abduction and adduction moments in stance, as well as peak hip extension moment in stance when compared to REF.” >> We hope this improves readability and is clearer.

Line 325: Why is this schematic “exemplary”?

Response from the authors: We removed the word exemplary and added the information that the schematics show a representative trial.

In table 2, Kg should be kg, and it should be N m and not Nm because they are 2 separate words.

Response from the authors: Apologies for overseeing these mistakes. We thank the reviewer for making us aware of it. We changed it. Also Nm in the figures were changed to N m.

Line 339: Should say “with TFA hip MIM of…” and not “with TFA Hip MIMof…”

Response from the authors: Changed

Discussion:

Line 390: pattern, not patter

Response from the authors: Changed

Line 445: Say For example, no E.g. to lead a sentence

Response from the authors: Changed! Thank you, we were not aware of this rule.

Line 445: does rather than do

Response from the authors: Changed

Line 449-452: Not a clear sentence.

Response from the authors: This sentence was deleted in the course of rewriting the manuscript.

Line 452: stabilize rather than stabile

Response from the authors: This sentence was deleted in the course of rewriting the manuscript.

Line 501: address rather than tackle deficits, tackle is in American football or Rugby rather deficits of our patients/clients

Response from the authors: This sentence was deleted in the course of rewriting the manuscript.

1. Pàmies-Vilà R, Font-Llagunes JM, Cuadrado J, Alonso FJ. Analysis of different uncertainties in the inverse dynamic analysis of human gait. Mechanism and Machine Theory. 2012;58:153-64. doi: https://doi.org/10.1016/j.mechmachtheory.2012.07.010.

2. Heitzmann DW, Guenther M, Becher B, Alimusaj M, Block J, van Drongelen S, et al. Integrating strength tests of amputees within the protocol of conventional clinical gait analysis: a novel approach. Biomedizinische Technik Biomedical engineering. 2013;58(2):195-204. doi: 10.1515/bmt-2012-0036. PubMed PMID: 23454713.

Attachment

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PLoS One. doi: 10.1371/journal.pone.0238093.r003

Decision Letter 1

Yih-Kuen Jan

3 Jul 2020

PONE-D-19-24706R1

The influence of hip muscle strength on gait in individuals with a unilateral transfemoral amputation

PLOS ONE

Dear Dr. Heitzmann,

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We look forward to receiving your revised manuscript.

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Yih-Kuen Jan, PhD

Academic Editor

PLOS ONE

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Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #1: (No Response)

Reviewer #2: (No Response)

Reviewer #3: All comments have been addressed

**********

2. Is the manuscript technically sound, and do the data support the conclusions?

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

**********

3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

**********

4. Have the authors made all data underlying the findings in their manuscript fully available?

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

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5. Is the manuscript presented in an intelligible fashion and written in standard English?

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

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6. Review Comments to the Author

Reviewer #1: The revised manuscript has been extensively rewritten in response to the reviewers’ comments. The literature in the introduction is now presented in a more synthesized form, the statistical analyses have been revised to account for multiple comparisons, and the discussion has largely been re-written to better relate the results to the literature and discuss the impact of potential confounds. In doing so, the clarity of the manuscript has been improved. A few minor issues remain, which should be addressed prior to publication.

The methods indicate that Spearman’s rank correlation was used, but in some places the results refer to “linear correlations” (e.g., Line 505 and S2_Figure). If the references to a linear correlation are correct, please include in the methods. In not, I would suggest removing the reference to ‘linear’ and the line fits in S2_Figure, since the spearman rank correlation characterizes the monotonic relationship between two variables, which is less restrictive than assuming a linear relationship.

Lines 278-280, suggest revising to read, “The level of significance for correlations was corrected to p < .0036 to account for testing across the coronal and sagittal plane CGA and MIM parameters.”

Lines 293 & 297, I believe the table being referenced is Table 2.

Line 336, the labels (and definitions) for FS, oFO, oFS, and FO are not in the revised figure and can be removed.

Line 376 references S2_Fig when stating that “…pelvic drop of the none-involved side was not present in our TFA group…”. Please clarify how S2_Fig shows this.

Lines 451-0452, suggest revising to read, “For example, the affected side ground contact in a person with TFA is different than in an unimpaired person.”

Lines 454-455, the phrase “adapt the introduced”, seems incomplete. Suggest revising.

Lines 455-457, suggest revising to read, “Another indicator that coronal plane gait deviations cannot purely be attributed to hip strength deficits is that a lateral trunk lean can also present in amputations below the knee.”

Lines 460-461, the phrase “…the reasons behind the strength deficits and the commonly, to strength deficits attributed gait deviations…” seems incomplete. Suggest revising.

Line 468, suggest revising to read, “may induce a weakening of certain muscle groups…”

Line 491, suggest revising to read, “participants reported being satisfied with…”

Lines 507-509 state that “Over the course of this study, an additional hypothesis was developed, i.e. that people with TFA should not have a maximum hip moment below a certain threshold to avoid gait deviations.”. There does not appear to be any indication of a threshold effect in the results. Please clarify how the current data/analyses directly test this hypothesis.

Lines 515-518, suggest revising to read, “However, during walking compensation mechanisms may also be induced, e.g. by the socket, prosthetic leg length or prosthetic component related, that contribute to the net functional deficit.”

Other minor comments and suggested edits (insertions/deletions in brackets),

Line 80, “…reduced bone density and also [] volume loss…”

Line 97, “Larger amounts of fat embedded in the residual limb[] muscles…”

Line 174, “…aids differ[red] considerably from…”

Line 290, “For temporal spatial parameters[,] individuals…”

Line 294, “For CGA kinematic results[,] participants with…”

Line 339, “…extension, and flexion) in [] both…”

Line 340, “For hip abduction and adduction[,] MIMs in individuals…”

Line 372-373, “However, the patter[n] described by…”

Line 376, “…pelvic drop of the non[]-involved side…”

Line 378, “…described a different patter[n] in a different pathology…”

Line 381, “…with TFA show[,] in contrast to Trendelenburg[,] a coronal plane…”

Line 389, “Although not clearly detailed[,] this muscle…”

Line 415, “…individuals with TFA)[,] we observed…”

Line 443, “…it may be advisable to [guarantee] passive

Line 480, “…has negative impact on[] the preferred…”

Line 481, “Consequentially, there seem[s] to be…”

Reviewer #2: First off, I would like to thank the authors for taking time to improve their manuscript. This has really shown through in the introduction which has a better flow than in the previous version. My comments are mostly dedicated to updating the phrasing throughout the manuscript and restructuring of the discussion to make the manuscript more concise and link similar ideas together.

Minor:

Abstract:

Line 37: please update “convenience” to “convenient”

Line 45: please update “abduction, adduction[,] extension[,] and flexion” with the commas suggested

Line 56: consider updating “with significantly higher ranges of motion on the involved side” to “with significantly higher ranges of motion during involved side stance phase”. I suggest adding “stance phase” to the sentence as the trunk is not a part of the involved side.

Introduction:

Line 81: Delete “, as described by Probsting et al.” as this is implicit with the citation.

Line 87: Change “conversely” to “furthermore” as the authors are adding to the argument established in the previous sentence.

Lines 97-99: Consider deleting the last sentence of this paragraph as it distracts from the points that the author has established about muscle strength and atrophy.

Lines 107-112: Consider updating: “In contrast to this, a more rigid fixation of the residual limb with the prosthesis, i.e. by osseointegration, or bone anchored prostheses, in individuals with TFA may have a positive effect on muscle strength. This hypothesis was supported in a study by Leijendekkers et al. who measured muscle volume. In the monitored subject with TFA the hip abductor muscle volume increased in the sound limb by 5.5% and in the residual limb by 7.4% during 12 months after implanting the bone-anchored prosthesis [16].”

to:

“In contrast to this, a more rigid fixation of the residual limb with the prosthesis, i.e. by osseointegration, or bone anchored prostheses, in individuals with TFA can have a positive effect on muscle strength [16].”

Methods:

The methods overall read nicely.

Page 11: Thank you for including more information regarding you TFA population and the procedure for prosthetic/socket fit.

Line 219: Consider deleting “following Kadaba et al. and Davis et al.” as this information is included in the citations.

Line 224: “was” to “were”

Line 230: consider adding the following commas to the sentence: “The OpTIMo device[,] used to determine isometric hip moment[s][,] consist of a rigid frame….”

Lines 278-279: consider deleting “as well” as it makes the sentence clunky

Results:

The results read nicely.

Line 290: add a comma between “parameters” and “individuals”

Line 294: add a comma between “results” and “participants”

Discussion:

The following are recommendation to make the discussion more concise and to bring together similar ideas that were throughout the discussion.

Line 356: consider deleting “TTA” and updating the sentence to “persons with TFA” because it does not make sense to connect the results with persons with TTA as they are a completely different population.

Lines 357-361: consider deleting these two sentences as it has you have already summarized these results in the previous sentence.

Line 362-363: Why do the authors think that there was no strength deficit in hip extension as there were deficits the other directions? The authors have an explanation for this later in the discussion. I would recommend that they move lines 472-482 to the end of this paragraph. Please update some of these sentences as to not use the [author] et al…. (explanation). Updating the sentence structure will make the sentences clear and concise.

Line 367: consider updating “range” to “range-of-motion”

Lines 371-378: Consider deleting these sentences as they do not add meaningful content to the author’s discussion as these sentences are dedicated to a population with a different pathology – which is stated in the last sentence fragment.

Line 369: Consider adding the following to the end of the sentence: “, as has been observed in people with TFA [24,25,42,45]”. The authors can then delete the sentence from lines 379-380.

Lines 383-391: It is suggested not to use the phrasing: [author] et al. showed….. this style of writing makes these sentences difficult to read. This information may be able to be summarized concisely. For example: “Altered trunk and hip kinematics exhibited in persons with TFA have been attributed to weak hip musculature [13,24,42].”

The authors could then move lines 398-403 after this statement as it connects very well. In my opinion, the authors should have the caveat in this paragraph that such a correlation was not observed in the healthy population. The S2 Figure (which I like) shows that less strength in the REF group would have a reduced trunk obliquity (p=0.02).

For instance: (the following is a suggestion for the authors, linking these statements together eliminates the reader having to go back and forth between paragraphs separated by another paragraph)

Altered trunk and hip kinematics exhibited in persons with TFA have been attributed to weak hip musculature [13,24,42]. This connection may explain the observed, non-significant, moderate negative correlation between hip abduction MIM and trunk obliquity range-of-motion. This correlation indicates that weaker people with TFA have the tendency to show a greater trunk range-of-motion during walking than their stronger piers. However, it should be noted that this is the exact opposite trend that was observed in the healthy population (S2 Fig.).

This may lead to lines 403-406 may be able to be appended (with some editing) to the paragraph from lines 392-397.

Lines 409-410: consider update the start of the sentence to: “In typically developing children, the hip MIM…”

Line 426: consider updating “contradictable” to “difficult”

Lines 441-443: This sentence is very similar to the previous. It is recommended to end the sentence on line 441 with two citations [44,45] to eliminate the redundancy. I recommend then moving lines 445-447 after this sentence because it directly connects.

For example:

“For example, it is well accepted that quadrilateral sockets do not stabilize the femur in the coronal plane and therefore will more likely cause increased residual limb movement during walking, compared to other designs, e.g. ischial containment sockets [44, 45]. Decreased medio-lateral stability residuum and the femur, as a cause for a lateral trunk motion, along with other cofounding factors, like strength deficits of the hip abductors the socket [46]. The strength status of people with TFA is therefore of high clinical relevance.”

This recommendation does remove “So, in socket design it may be advisable to grantee passive stability and a very good force transmission, while not restricting the remaining muscles.” however, the proposed change does capture the importance of socket design.

499: “K_level” to “K-level”

Conclusion:

Looks good!

Reviewer #3: The authors made significant improvements to the manuscript. Overall, the writing is better and the authors have addressed my and other reviewer's comments. There a few minor issues to revise before being ready for publication.

Slight formatting issues with table 1, column width is too narrow.

Line 28: I am assuming you mean mass, not weight.

Line 443: grantee, incorrect word?

Repeated use of consequentially, a different word or phrase in few instances to improve readability

Check for consistent spacing after periods, fluctuates between 0 to 2 spaces

Check - versus _ in regards to K-levels (e.g., lines 498-499)

Thank you for addressing our comments.

**********

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Reviewer #1: Yes: Scott A. Beardsley

Reviewer #2: No

Reviewer #3: No

While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/. PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email PLOS at figures@plos.org. Please note that Supporting Information files do not need this step.

PLoS One. 2020 Sep 2;15(9):e0238093. doi: 10.1371/journal.pone.0238093.r004

Author response to Decision Letter 1

4 Jul 2020

Response to the Reviewer: We would like to thank the reviewer for the encouraging words and the many valuable suggestions. This was more than helpful and we appreciate the time and effort the reviewer put into their response.

Response to the Reviewer: We would like to thank the reviewer for the very valuable input. The reviewer is correct; we used Spearman’s rank correlation. So, we deleted passages which referred to a “linear” behaviour. As the reviewer is also questioning the hypothesis formulated in this paragraph, we decided to delete it completely. We agree with the reviewer that this hypothesis was a bit too motivated and was partly based on the results including one participant, which we excluded in the course of the previous review. We further deleted the lines in S2_Fig. which did suggest that we tested for a linear relationship.

Response to the reviewer: We would like to thank the reviewer for this suggestion, which we changed accordingly in the new manuscript (now Lines 272-274)

Lines 293 & 297, I believe the table being referenced is Table 2.

Response to the reviewer: Correct! We apologise for this mistake, and changed the reference to table 2.

Line 336, the labels (and definitions) for FS, oFO, oFS, and FO are not in the revised figure and can be removed.

Response to the reviewer: The abbreviations for the discrete gait events are still present in the figure. They may not be as obvious as before, because we added the sub-phases underneath. So, we did not change the caption of the figure.

Line 376 references S2_Fig when stating that “…pelvic drop of the none-involved side was not present in our TFA group…”. Please clarify how S2_Fig shows this.

Response to the reviewer: We would like to thank the reviewer for noticing. This is a mistake and it should say “Fig. 2” not “S2 Fig.”. This part of the discussion was further rewritten.

Lines 451-0452, suggest revising to read, “For example, the affected side ground contact in a person with TFA is different than in an unimpaired person.”

Response to the reviewer: Thank you. We changed this sentence to: “Moreover, the affected side ground contact in a person with TFA is different than in an unimpaired person.” (Now in line 416-417)

Lines 454-455, the phrase “adapt the introduced”, seems incomplete. Suggest revising.

Response to the reviewer: Thank you. We revised this sentence to: “Thus, gait deviations in this population may be a response to unwanted loads introduced to the involved side, and may serve as an option to readjust loads.” (Now in line 419-421)

Response to the reviewer: Thank you. We changed this sentence according to your suggestion (Now in line 421-422).

Lines 460-461, the phrase “…the reasons behind the strength deficits and the commonly, to strength deficits attributed gait deviations…” seems incomplete. Suggest revising.

Response to the reviewer: Thank you. Yes, this sentence was incomplete and we revised it to: “Hence, the origins for strength deficits in people with TFA and their gait deviations, partially attributed to these strength deficits, cannot be fully clarified in this study.” (now in line 425-426)

Line 468, suggest revising to read, “may induce a weakening of certain muscle groups…”

Response to the reviewer: Changed

Line 491, suggest revising to read, “participants reported being satisfied with…”

Response to the reviewer: Changed

Response to the reviewer: We deleted this paragraph completely. As stated earlier, we agree with the reviewer that this hypothesis was a bit too motivated and was partly based on the results including one participant, which we excluded in the course of the previous review.

Response to the reviewer: Thank you. We changed this sentence according to your suggestion (now in line 470-471)

Other minor comments and suggested edits (insertions/deletions in brackets),

Line 80, “…reduced bone density and also [] volume loss…”

Response to the reviewer: Changed

Line 97, “Larger amounts of fat embedded in the residual limb[] muscles…”

Response to the reviewer: Changed

Line 174, “…aids differ[red] considerably from…”

Response to the reviewer: Changed

Line 290, “For temporal spatial parameters[,] individuals…”

Response to the reviewer: Changed

Line 294, “For CGA kinematic results[,] participants with…”

Response to the reviewer: Changed

Line 339, “…extension, and flexion) in [] both…”

Response to the reviewer: Changed

Line 340, “For hip abduction and adduction[,] MIMs in individuals…”

Response to the reviewer: Changed

Line 372-373, “However, the patter[n] described by…”

Response to the reviewer: Changed

Line 376, “…pelvic drop of the non[]-involved side…”

Response to the reviewer: Changed

Line 378, “…described a different patter[n] in a different pathology…”

Response to the reviewer: Changed

Line 381, “…with TFA show[,] in contrast to Trendelenburg[,] a coronal plane…”

Response to the reviewer: Changed

Line 389, “Although not clearly detailed[,] this muscle…”

Response to the reviewer: Changed

Line 415, “…individuals with TFA)[,] we observed…”

Response to the reviewer: Changed

Line 443, “…it may be advisable to [guarantee] passive

Response to the reviewer: Apologies for overseeing the wrong autocorrect result. We changed this.

Line 480, “…has negative impact on[] the preferred…”

Response to the reviewer: Changed

Line 481, “Consequentially, there seem[s] to be…”

Response to the reviewer: Changed

Response to the reviewer: We would like to thank the reviewer for the inspiring words. We also like to thank the reviewer for invested time and effort.

Minor:

Abstract:

Line 37: please update “convenience” to “convenient”

Response to the reviewer: Changed

Line 45: please update “abduction, adduction[,] extension[,] and flexion” with the commas suggested

Response to the reviewer: Changed

Response to the reviewer: We like to thank the reviver for this valuable suggestion. We agree to this remark and changed the sentence accordingly (now in line 54-55)

Introduction:

Line 81: Delete “, as described by Probsting et al.” as this is implicit with the citation.

Response to the reviewer: Deleted

Line 87: Change “conversely” to “furthermore” as the authors are adding to the argument established in the previous sentence.

Response to the reviewer: Changed

Lines 97-99: Consider deleting the last sentence of this paragraph as it distracts from the points that the author has established about muscle strength and atrophy.

Response to the reviewer: We partly disagree with the reviewer and didn’t delete this. We have rewritten the sentences as the fatty degeneration is part of the structural change and muscle atrophy of the residual limb (now in line 94-97).

to:

Response to the reviewer: Thank you for the valuable suggestion which wraps up the information very well. We have changed this accordingly (now in line 104-107).

Methods:

The methods overall read nicely.

Response to the reviewer: Thank you very much!

Page 11: Thank you for including more information regarding you TFA population and the procedure for prosthetic/socket fit.

Response to the reviewer: We appreciate that the reviewer is recognising that such details are important to us. Thank you!

Line 219: Consider deleting “following Kadaba et al. and Davis et al.” as this information is included in the citations.

Response to the reviewer: Deleted

Line 224: “was” to “were”

Response to the reviewer: Changed

Line 230: consider adding the following commas to the sentence: “The OpTIMo device[,] used to determine isometric hip moment[s][,] consist of a rigid frame….”

Response to the reviewer: Changed

Lines 278-279: consider deleting “as well” as it makes the sentence clunky

Response to the reviewer: Thank you for the suggestion. This shortcoming was also recognized by the 1st reviewer and we changed the sentence according to his suggestion.

Results:

The results read nicely.

Response to the reviewer: Thank you!

Line 290: add a comma between “parameters” and “individuals”

Response to the reviewer: Changed. This was also identified by the 1st reviewer.

Line 294: add a comma between “results” and “participants”

Response to the reviewer: Changed. This was also identified by the 1st reviewer.

Discussion:

The following are recommendation to make the discussion more concise and to bring together similar ideas that were throughout the discussion.

Response to the reviewer: Thank you, we appreciate your suggestions.

Response to the reviewer: Deleted.

Lines 357-361: consider deleting these two sentences as it has you have already summarized these results in the previous sentence.

Response to the reviewer: We agree with the reviewer and deleted the partly redundant information.

Response to the reviewer: We agree with the reviewer and moved the sentence accordingly.

Please update some of these sentences as to not use the [author] et al…. (explanation). Updating the sentence structure will make the sentences clear and concise.

Response to the reviewer: We tried to delete most of the criticised sentences.

Line 367: consider updating “range” to “range-of-motion”

Response to the reviewer: Changed

Response to the reviewer: We partly agree with the reviewer, that this is partly an off-topic. However, the pattern seen in people with TFA is often described as a Trendelenburg gait pattern, in particular in our community. We try to emphasis with these sentences that this is actually not correct. We deleted redundant parts of this section and tried to make it more concise. We hope that the reviewer is accepting our changes (see lines 359 following)

Line 369: Consider adding the following to the end of the sentence: “, as has been observed in people with TFA [24,25,42,45]”. The authors can then delete the sentence from lines 379-380.

Response to the reviewer: Thank you for the suggestion. We changed this accordingly (now in line 356-358)

Response to the reviewer: Thank you for the suggestion. We tried to take this into account. The paragraph was changed accordingly (now in line 366-367).

The authors could then move lines 398-403 after this statement as it connects very well.

Response to the reviewer: We moved the section as suggested.

In my opinion, the authors should have the caveat in this paragraph that such a correlation was not observed in the healthy population. The S2 Figure (which I like) shows that less strength in the REF group would have a reduced trunk obliquity (p=0.02).

For instance: (the following is a suggestion for the authors, linking these statements together eliminates the reader having to go back and forth between paragraphs separated by another paragraph)

Response to the reviewer: We absolutely agree with the reviewer changed the section as suggested. This was very helpful and will improve readability. Thank you!

This may lead to lines 403-406 may be able to be appended (with some editing) to the paragraph from lines 392-397.

Response to the reviewer: Changed, shortened and edited accordingly.

Lines 409-410: consider update the start of the sentence to: “In typically developing children, the hip MIM…”

Response to the reviewer: Changed

Line 426: consider updating “contradictable” to “difficult”

Response to the reviewer: Changed

For example:

Response to the reviewer: We would like toWe took over most of the suggestions of the reviewer.

499: “K_level” to “K-level”

Response to the reviewer: Changes

Conclusion:

Looks good!

Response to the reviewer: Thank you!

Response to the reviewer: We thank the reviewer for these kind words. We also acknowledge the efforts und time of the reviewer. Thank you!

Slight formatting issues with table 1, column width is too narrow.

Response to the reviewer: We adapted this. We guess that such issues will be taken care of by the editorial office and the formatting of the tables will be adjusted to fit to their layout.

Line 28: I am assuming you mean mass, not weight.

Response to the reviewer: We apologize, but we do not know exactly which line the reviewer was referring to. We searched the document and changed weight to mass.

Line 443: grantee, incorrect word?

Response to the reviewer: Apologies for the typo, this supposed to say “guarantee”. This section was shortened and rewritten and this part was deleted.

Repeated use of consequentially, a different word or phrase in few instances to improve readability

Response to the reviewer: Yes, we seem to like this word too much. We changed the manuscript accordingly.

Check for consistent spacing after periods, fluctuates between 0 to 2 spaces

Response to the reviewer: We checked spacing.

Check - versus _ in regards to K-levels (e.g., lines 498-499)

Response to the reviewer: Changed

Thank you for addressing our comments.

Response to the reviewer: Your comments are appreciated and help to improve the manuscript considerably.

Attachment

Submitted filename: Response to Reviewers.docx

Click here for additional data file.^{(26.9KB, docx)}

PLoS One. doi: 10.1371/journal.pone.0238093.r005

Decision Letter 2

Yih-Kuen Jan

28 Jul 2020

PONE-D-19-24706R2

The influence of hip muscle strength on gait in individuals with a unilateral transfemoral amputation

PLOS ONE

Dear Dr. Heitzmann,

Please submit your revised manuscript by Sep 11 2020 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

Please include the following items when submitting your revised manuscript:

A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'.
A marked-up copy of your manuscript that highlights changes made to the original version. You should upload this as a separate file labeled 'Revised Manuscript with Track Changes'.
An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'.

We look forward to receiving your revised manuscript.

Kind regards,

Yih-Kuen Jan, PhD

Academic Editor

PLOS ONE

[Note: HTML markup is below. Please do not edit.]

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

Reviewer #1: All comments have been addressed

Reviewer #2: All comments have been addressed

Reviewer #3: All comments have been addressed

**********

2. Is the manuscript technically sound, and do the data support the conclusions?

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

**********

3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

**********

4. Have the authors made all data underlying the findings in their manuscript fully available?

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

**********

5. Is the manuscript presented in an intelligible fashion and written in standard English?

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

**********

6. Review Comments to the Author

Reviewer #1: (No Response)

Reviewer #2: I would like to commend the authors on re-writing their manuscript. This manuscript represents a significant knowledge contribution in terms of how strength deficits can affect walking performance for persons with transfemoral amputation. Below I have listed some minor comments regarding word choice and punctuation.

Line 67: “later” to “lateral”

Line 89: comma between “imaging” and “involved”

Line 90-91: suggest to update the sentence to: “This led to altered walking biomechanics and residual limb muscle activation patterns after a TTA [6]”

Line 118: “Beside” to “Besides”

Line 137: comma between “secondly” and “we”

Line 139: Replace semicolon with period and comma between “Finally” and “we”

line 147: comma between “data” and “maximum”

line 192: comma between “documentation” and “none”

line 220: consider updating the start of this sentence to: “As shown by Pamies-Vila et al., changes of the…”

line 242: comma between “measurements” and “a”

Discussion:

The flow of the discussion has improved greatly! Thank you for taking time and updating this section.

Line 378: “will” to “would”

Line 378: comma between “gait” and “this”

line 386 “lead” to “led”

line 392: “conclude” to “concluded”

line 403: “transition” to “transmission”

Line 403-404: recommend updating the wording of this sentence to: “A reduced power transmission between the stump and the socket may cause the observed muscle weakness to manifest a more pronounced functional deficit.”

Line 406: “transition” to “transmission”

Line 412: comma between “discrepancy” and “was”

Reviewer #3: The authors addressed reviewers comments during this second review, so thank for continued improvements on this manuscript. Readability and clarity have been improved. There are a few more minor changes to be made:

Abstract:

Line 64: "i.e. later[al] trunk"

Line 68: "between later[al]"

Introduction:

Line 92: "ultrasound imaging[,] involved"

Line 149: "movement; [f]inally we"

Methods:

Looks good, no suggested changes.

Results:

Looks good, no suggested changes.

Discussion:

Line 357: "First and foremost" is colloquial, could say "Our data shows that..."

Line 443: "it was conclud[ed]..."

Line 464: Remove 'A' at start of "A decreased..."

Line 465: Remove comma after "factors"

Line 466: Add comma after "discrepancy"

Conclusion:

Looks good, no suggested changes.

Thank you again for your continued work on this manuscript!

**********

7. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: Yes: Scott A. Beardsley

Reviewer #2: No

Reviewer #3: No

While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/. PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email PLOS at figures@plos.org. Please note that Supporting Information files do not need this step.

PLoS One. 2020 Sep 2;15(9):e0238093. doi: 10.1371/journal.pone.0238093.r006

Author response to Decision Letter 2

28 Jul 2020

Reviewer #1: (No Response)

Response from the Authors: We would like to thank the reviewer once again for the input. It helped considerably to increase the quality of the manuscript.

Response from the Authors: We would like to thank reviewer for the positive words.

Line 67: “later” to “lateral”

Response from the Authors: Changed

Line 89: comma between “imaging” and “involved”

Response from the Authors: Changed

Line 90-91: suggest to update the sentence to: “This led to altered walking biomechanics and residual limb muscle activation patterns after a TTA [6]”

Response from the Authors: Changed

Line 118: “Beside” to “Besides”

Response from the Authors: Changed

Line 137: comma between “secondly” and “we”

Response from the Authors: We added a comma

Line 139: Replace semicolon with period and comma between “Finally” and “we”

Response from the Authors: Changed

line 147: comma between “data” and “maximum”

Response from the Authors: We added a comma

line 192: comma between “documentation” and “none”

Response from the Authors: We added a comma

line 220: consider updating the start of this sentence to: “As shown by Pamies-Vila et al., changes of the…”

Response from the Authors: We changed the start accordingly

line 242: comma between “measurements” and “a”

Response from the Authors: We added a comma

Discussion:

The flow of the discussion has improved greatly! Thank you for taking time and updating this section.

Response from the Authors: We would like to thank the reviewer for these positive words. This was also an effort of the reviewer. Thank you for helping to improve the manuscript.

Line 378: “will” to “would”

Response from the Authors: Changed

Line 378: comma between “gait” and “this”

Response from the Authors: We added a comma

line 386 “lead” to “led”

Response from the Authors: Changed

line 392: “conclude” to “concluded”

Response from the Authors: Changed

line 403: “transition” to “transmission”

Response from the Authors: Changed, we further updated the sentence as suggested.

Response from the Authors: Thank you for this suggestion, we updated the sentence as suggested.

Line 406: “transition” to “transmission”

Response from the Authors: Changed

Line 412: comma between “discrepancy” and “was”

Response from the Authors: We also thank the reviewers for their time and effort. Without their help we would not come to this stage of the manuscript.

Abstract:

Line 64: "i.e. later[al] trunk"

Line 68: "between later[al]"

Response from the Authors: Changed. Apologies for these typos

Introduction:

Line 92: "ultrasound imaging[,] involved"

Response from the Authors: Changed

Line 149: "movement; [f]inally we"

Response from the Authors: We changed this sentence in accordance to the suggestion of reviewer 2.

Methods:

Looks good, no suggested changes.

Response from the Authors: Thank you.

Results:

Looks good, no suggested changes.

Response from the Authors: Thank you.

Discussion:

Line 357: "First and foremost" is colloquial, could say "Our data shows that..."

Response from the Authors: We would like to thank the reviewer for that suggestion and changed the sentence accordingly.

Line 443: "it was conclud[ed]..."

Response from the Authors: Changed

Line 464: Remove 'A' at start of "A decreased..."

Response from the Authors: Changed

Line 465: Remove comma after "factors"

Response from the Authors: Deleted

Line 466: Add comma after "discrepancy"

Response from the Authors: Added

Conclusion:

Looks good, no suggested changes.

Response from the Authors: Thank you!

Thank you again for your continued work on this manuscript!

Response from the Authors: It was our pleasure. Thanks

Attachment

Submitted filename: Response to Reviewers.docx

Click here for additional data file.^{(18.6KB, docx)}

PLoS One. doi: 10.1371/journal.pone.0238093.r007

Decision Letter 3

Yih-Kuen Jan

11 Aug 2020

The influence of hip muscle strength on gait in individuals with a unilateral transfemoral amputation

PONE-D-19-24706R3

Dear Dr. Heitzmann,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

Within one week, you’ll receive an e-mail detailing the required amendments. When these have been addressed, you’ll receive a formal acceptance letter and your manuscript will be scheduled for publication.

An invoice for payment will follow shortly after the formal acceptance. To ensure an efficient process, please log into Editorial Manager at http://www.editorialmanager.com/pone/, click the 'Update My Information' link at the top of the page, and double check that your user information is up-to-date. If you have any billing related questions, please contact our Author Billing department directly at authorbilling@plos.org.

If your institution or institutions have a press office, please notify them about your upcoming paper to help maximize its impact. If they’ll be preparing press materials, please inform our press team as soon as possible -- no later than 48 hours after receiving the formal acceptance. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information, please contact onepress@plos.org.

Kind regards,

Yih-Kuen Jan, PhD

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

Reviewer #1: All comments have been addressed

Reviewer #2: All comments have been addressed

Reviewer #3: All comments have been addressed

**********

2. Is the manuscript technically sound, and do the data support the conclusions?

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

**********

3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

**********

4. Have the authors made all data underlying the findings in their manuscript fully available?

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

**********

5. Is the manuscript presented in an intelligible fashion and written in standard English?

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

**********

6. Review Comments to the Author

Reviewer #1: (No Response)

Reviewer #2: I would like to thank the authors once again for their continued work through this review process. The authors have a well written and scientifically sound manuscript. I have included a few minor suggestions. I feel that this manuscript is ready for publication.

Make sure that there is consistent punctuation after e.g. and i.e. Sometimes the authors include a comma after these abbreviations and sometimes not.

Line 220: comma after “al.”

Line 221: “effects” to “effect”, “in” to “on”

Line 371: remove “was”

Line 404: there is an extra period

Reviewer #3: The authors have made the necessary changes to the manuscript and now have an article that is ready for publication. Thank you for your efforts!

**********

7. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: Yes: Scott A. Beardsley

Reviewer #2: No

Reviewer #3: No

PLoS One. doi: 10.1371/journal.pone.0238093.r008

Acceptance letter

Yih-Kuen Jan

25 Aug 2020

PONE-D-19-24706R3

The influence of hip muscle strength on gait in individuals with a unilateral transfemoral amputation

Dear Dr. Heitzmann:

I'm pleased to inform you that your manuscript has been deemed suitable for publication in PLOS ONE. Congratulations! Your manuscript is now with our production department.

If your institution or institutions have a press office, please let them know about your upcoming paper now to help maximize its impact. If they'll be preparing press materials, please inform our press team within the next 48 hours. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information please contact onepress@plos.org.

If we can help with anything else, please email us at plosone@plos.org.

Thank you for submitting your work to PLOS ONE and supporting open access.

Kind regards,

PLOS ONE Editorial Office Staff

on behalf of

Dr. Yih-Kuen Jan

Academic Editor

PLOS ONE

Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

S1 Table. Self-reported health status and sports activities of the participants with TFA.

# = nothing specified.

(DOCX)

Click here for additional data file.^{(47.7KB, docx)}

S2 Table. Correlations of sagittal and coronal plane gait parameters with their corresponding maximum isometric moments (MIM) of the hip.

(DOCX)

Click here for additional data file.^{(54.3KB, docx)}

S1 Fig. Trunk, pelvic and hip coronal and sagittal kinematics as well as coronal and sagittal hip kinetics (internal moments) of both investigated cohorts.

(TIF)

Click here for additional data file.^{(966.7KB, tif)}

S2 Fig. Scatterplot of the isometric trunk obliquity range of motion vs. hip abduction moment during the gait cycle.

(TIF)

Click here for additional data file.^{(434KB, tif)}

S3 Fig. Scatterplot of isometric coronal plane hip moment against each other.

(TIF)

Click here for additional data file.^{(471.6KB, tif)}

S4 Fig. Scatterplot of isometric sagittal plane hip moment against each other.

(TIF)

Click here for additional data file.^{(477KB, tif)}

Attachment

Submitted filename: TFA_strength_gait_2019.pdf

Click here for additional data file.^{(65KB, pdf)}

Attachment

Submitted filename: Response to Reviewers.docx

Click here for additional data file.^{(82.9KB, docx)}

Attachment

Submitted filename: Response to Reviewers.docx

Click here for additional data file.^{(26.9KB, docx)}

Attachment

Submitted filename: Response to Reviewers.docx

Click here for additional data file.^{(18.6KB, docx)}

Data Availability Statement

All relevant data are within the manuscript and its Supporting Information files.

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PERMALINK

The influence of hip muscle strength on gait in individuals with a unilateral transfemoral amputation

Daniel Walter Werner Heitzmann

Julien Leboucher

Julia Block

Michael Günther

Cornelia Putz

Marco Götze

Sebastian Immanuel Wolf

Merkur Alimusaj

Roles

Abstract

Introduction

Methods

Results

Conclusion

Introduction

Material and methods

Participants

Table 1. Detailed information of the participants with a transfemoral amputation (TFA) and their current prostheses.

Gait analysis

Isometric muscle strength measurements

Fig 1. OpTIMo (Optical Testing Isometric Moment) device to determine isometric hip moments in the study participants.

Statistics

Results

Table 2. Results for the maximum isometric moments (MIM) and conventional clinical gait analysis (CGA).

Fig 2. Schematic coronal plane views presented during left and right single support (representative trial of a participant with TFA and a REF participant).

Discussion

Fig 3. Sagittal and coronal plane hip moments during walking (plotted against the gait cycle) in comparison to the corresponding isometric moments collected during isometric muscle tests.

Conclusion

Supporting information

Acknowledgments

Abbreviations

Data Availability

Funding Statement

References

Decision Letter 0

Yih-Kuen Jan

Roles

Author response to Decision Letter 0

Decision Letter 1

Yih-Kuen Jan

Roles

Author response to Decision Letter 1

Decision Letter 2

Yih-Kuen Jan

Roles

Author response to Decision Letter 2

Decision Letter 3

Yih-Kuen Jan

Roles

Acceptance letter

Yih-Kuen Jan

Roles

Associated Data

Supplementary Materials

Data Availability Statement

ACTIONS

PERMALINK

RESOURCES

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