Daily Steps and Stepping Cadence Increase One-Year Following Prosthesis Osseointegration in People with Lower-Limb Amputation

Abstract

Purpose:

People with lower-limb loss participate in less physical activity than able-bodied individuals, which increases the mortality risk and incidence of metabolic syndromes. This study evaluated the effect of lower-limb prosthesis osseointegration on physical activity, including daily steps and stepping cadence.

Methods:

Free-living walking activity was assessed from 14 patients scheduled to undergo prosthesis osseointegration at two time points (within 2 weeks prior to osseointegration surgery and 12-months following). Daily step count, stepping time, number of walking bouts, average step cadence per bout, maximum step cadence per bout, and time spent in bands of step cadence were compared before and after osseointegration.

Results:

Twelve months after prosthesis osseointegration, participants increased daily steps, daily stepping time, average step cadence, and maximum cadence per walking bout compared to pre-osseointegration. The daily time spent at a purposeful (40–59 steps/min) and brisk (≥ 100 steps/min) cadence were increased after prosthesis osseointegration.

Conclusions:

Participants engaged in more daily steps, higher stepping cadence, and longer bouts at higher cadence one year following osseointegration compared to when using a socket prosthesis. As a novel intervention that is becoming more common, it is important to understand walking activity outcomes as these are critical for long-term health.

1. Introduction

Lower-limb amputation (LLA) can negatively impact multiple dimensions of an individual’s health, including greater levels of disability [1] and reduced quality of life [2]. One of the primary factors for this negative impact stems from prosthesis dissatisfaction, with approximately 30% of prosthesis users self-reporting the socket to cause a worsened quality of life [3,4]. Collectively, these challenges related to disability, quality of life, and prosthesis discomfort have direct and indirect influences on reduced walking activity compared to individuals without amputation [5].

People with a LLA take an average of 1700 to 4800 daily steps during free-living activity, well below the lowest recommendation target for people with disabilities (≥5500 daily steps) [6–8]. Low walking activity is correlated with decreased mobility [9] and increases the incidence of sedentary diseases [10], which can complicate the recovery and healing process following LLA. Walking is the most common form of human movement [11]; therefore, daily step count is an important metric for monitoring walking activity. However, it is crucial to evaluate not only total daily steps, but also average step cadence [12]. Cadence is a measure of walking intensity, with higher cadence indicating a higher metabolic equivalent and higher intensity of walking [12]. Prior work in healthy adults has described step cadence categories as non-movement (0 steps/minute), incidental movement (1–19 steps/minute), sporadic movement (20–39 steps/minute), purposeful (40–59 steps/minute), slow walking (60–79 steps/minutes), medium walking (80–99 steps/minute), brisk walking (100–119 steps/minute), or faster locomotion (120+ steps/minute) [12]. Able-bodied individuals in the U.S. spend approximately 30 minutes/day at step cadences of 60+ steps/minute during free-living activity [12]. Importantly, step cadence outcomes can capture changes in intensity of walking following an intervention, which may not be reflected in the average number of total daily steps. Additionally, lower free-living step cadence is related to higher fall rates [13], suggesting that cadence is an important metric related to safe walking. Therefore, it is important to identify interventions that may increase daily steps and step cadence following LLA.

Prosthesis osseointegration is a surgical intervention that creates a direct connection between the residual bone and prosthetic limb through a bone-anchored implant, eliminating the need for a socket [14]. Osseointegration is an elective, secondary procedure offered primarily to individuals with LLA who experience failure with multiple socket prostheses due to severe pain, swelling, and discomfort at the residual limb-socket interface [14]. Prosthesis osseointegration has been shown to improve quality of life [15–17] and physical function [16–18], likely due to reduction in pain in the residual limb and other complications of socket use. Established improvements in clinical outcomes such as the Six-Minute Walk Test and Timed-Up-and Go demonstrate improved walking capacity [16,17]; however, no study has evaluated if engagement in free-living walking activity (i.e., daily steps and step cadence) improves following prosthesis osseointegration.

The purpose of the current study was to evaluate walking activity one-year post-osseointegration compared to pre-osseointegration in people with transfemoral and transtibial amputations. We compared average free-living daily step count, stepping time, number of walking bouts, average step cadence per bout, maximum step cadence per bout, and time spent in previously described walking step cadence bands (1–19 steps/min, 20–39 steps/min, 40–59 steps/min, 60–79 steps/min, 80–99 steps/min, 100+ steps/min). We hypothesized that individuals with a LLA would increase their overall daily step count, with improvements in all step cadence outcomes one-year post-osseointegration compared to pre-osseointegration.

2. Materials and Methods

2.1. Participants

Subjects with unilateral lower-limb (transtibial or transfemoral) amputation were enrolled in the current study. Each patient underwent prosthesis osseointegration as a secondary procedure due to complications with their traditional socket prosthesis. Inclusion criteria for osseointegration surgery and current study, included: existing LLA due to traumatic, congenital, or cancer etiologies, minimum age of 18 years old, and a history of severe socket-related skin and residual limb problems that contribute to mobility limitations. Potential participants were excluded in this study if they had amputation of vascular etiology, demonstrated a risk of substance abuse, had an unstable heart condition, had acute systemic infection, were decisionally impaired, or were seeking active cancer treatment. Patients were approached during a clinical visit by the research team and the study was explained both verbally and in writing. Each patient provided written informed consent prior to the onset of data collection. All protocols and procedures were approved by the University of Colorado Multiple Institutional Review Board and adhered to the 1964 declaration of Helsinki and its later amendments [19]. For this study, 14 patients were included. This sample size was determined from a two-tailed a priori power analyses (α = 0.05) of subjects needed to detect differences with at least 95% power.

All patients received a titanium press-fit implant (OTN Implant BV, The Netherlands) that was implanted by the same orthopedic surgeon (JWS). Transfemoral implants were placed in two surgical stages. The first surgical stage involved the intramedullary implantation of a femoral prosthesis, followed by 6-weeks of non-weight bearing. The second surgical stage created a stoma through an incision into the skin and soft tissue at the distal end of the residual limb and secured the transcutaneous component into the implant. Transtibial implants were placed in a single surgical stage, followed by 6-weeks of non-weight bearing. Each participant then underwent the same 3-week rehabilitation protocol consisting of daily intervention sessions that began two days following the second surgical stage, directed by the same physical therapist (GL). The rehabilitation protocol involved static and dynamic load bearing exercises, biomechanical education of gait and movement, and individualized range of motion and strength exercises with functional progress up to community walking on level surfaces with obstacles using two assistive devices in a two-point gait pattern. Rehabilitation continued within the patient’s home community with the supervision of a physical therapist of their choosing, with oversight by our team (DHM). This consisted of progressing ambulation and functional mobility through gradually decreasing support of bilateral assistive devices prior to walking with no assistive device with good symmetrical walking pattern and minimal pain over a 3–6 week period. This protocol is largely representative of standard of clinical practice in this novel population [20].

2.2. Experimental Collection

Free-living walking activity was monitored over 10 days using a triaxial accelerometer (activPAL^™ (PAL Technologies Ltd, Glasgow, UK)). The activPAL^™ was waterproofed via transparent medical dressing and affixed to the midline of the intact-limb anterior thigh, one-third of the way between the hip and knee. Data were collected at two time points relative to the first stage of the osseointegration surgery (within two weeks prior (using socket prosthesis) and 12-months following). For both collections, a valid data collection period included a minimum of four days (three weekdays and one weekend) with 24 hours of wear-time per day.

2.3. Data Analysis

Stepping data were sampled at 20-Hz and extracted as an event file with 1-minute epochs using proprietary software (PALanalysis v8.11.8.75, PAL Technologies, Glasgow UK). Following inspection to ensure sufficient device wear time, data were analyzed to calculate activity (stepping, sitting, standing, lying) and cadence bouts using a customized MATLAB script (R2022a, MathWorks, Natick, MA). Individual stepping bouts were determined as consecutive 1-minute epochs with non-zero steps. Stepping cadence was then calculated as the total steps within each individual bout (steps/minute) and categorized as incidental movement (1–19 steps/min), sporadic movement (20–39 steps/min), purposeful steps (40–59 steps/min), slow walking (60–79 steps/min), medium walking (80–99 steps/min), or brisk walking (≥ 100 steps/min) [12].

2.4. Statistical Analyses

Dependent variables consisted of three primary categories: 1) activity (total daily step count, number of sit-to-stand transitions) and time in activity (sitting, standing, stepping, lying), 2) the number and duration of stepping bouts (including purposeful and brisk), and 3) cadence (including during purposeful and brisk bouts). All variables were examined with the Shapiro-Wilk test for normality and Levene’s test for homogeneity of variance. Normally distributed variables were compared before and after prosthesis osseointegration using paired t-tests, with corrections made for unequal variances. Other variables were compared non-parametrically using Mann-Whitney U tests. The level of significance for all tests was set at α = 0.05 with a Holm-Bonferroni correction for multiple comparisons within each category and statistical analyses were performed using JMP Pro 16 (SAS Institute, Cary, NC).

3. Results

3.1. Participants

Demographic information for the enrolled participants are provided in Table 1. The number of valid days of free-living activity did not change between timepoints (pre: 7.6 ± 1.5 days, post: 8.2 ± 1.4 days; P = 0.365).

Table 1.

Patient demographics.

Sex	5F/9M
Age	51.4 ± 11.4 years
BMI	27.0 ± 5.7 kg/m2
Amputation Level	10 transfemoral/4 transtibial
Time Since Amputation (years)	15.1 ± 10.6 years

3.2. Walking activity

Twelve months after prosthesis osseointegration, the average number of daily steps and the stepping time were increased (P = 0.001 and P = 0.013, respectively) (figure 1). There were no differences in the number of sit-to-stand transitions or in lying, sitting, or standing time after prosthesis osseointegration. Individual activity before and after osseointegration is described in table 2.

Figure 1.

Distribution of walking activity before (black box) and after (white box) prosthesis osseointegration (Pre-OI and Post-OI, respectively). * indicates statistical difference (α ≤ 0.05). + indicates an individual outlier outside of 25^th and 75^th percent quartile range of the sample data.

Table 2.

Individual free-living walking activity before and 12-months following prosthesis osseointegration (Pre-OI and Post-OI, respectively) for each patient within the cohort. Stepping activity was collected and averaged across a 10-day period

	Daily Steps		Sit-to-Stand		Stepping Time (min)		Lying Time (min)		Sitting time (min)		Standing Time (min)
OI ID	Pre-OI	Post-OI	Pre-OI	Post-OI	Pre-OI	Post-OI	Pre-OI	Post-OI	Pre-OI	Post-OI	Pre-OI	Post-OI
1	2939.4	5102.7	35.9	46.0	49.7	83.7	618.1	609.0	388.9	471.5	246.5	298.2
2	3456.0	4376.9	34.3	34.7	50.8	52.7	657.3	457.5	223.0	785.9	131.5	124.7
3	2309.3	3584.8	26.2	25.0	38.4	55.6	578.1	574.3	341.2	336.2	176.1	156.0
4	3785.6	6009.1	60.6	48.7	52.4	84.6	569.3	656.1	475.7	447.5	204.9	241.8
5	3633.6	6810.4	56.0	54.7	55.6	90.4	427.2	435.7	614.9	531.2	308.9	414.7
6	8572.0	8437.8	36.8	33.8	119.8	108.6	500.7	539.0	381.9	439.8	454.1	378.0
7	5178.8	4778.2	53.1	40.0	69.9	60.5	506.8	599.4	600.9	518.4	190.4	142.3
8	3458.9	4840.0	42.1	40.9	46.3	65.3	554.2	520.0	527.8	585.8	241.3	261.5
9	103.8	1289.0	12.8	27.6	2.3	20.4	488.7	537.9	888.6	757.8	17.7	95.2
10	5336.5	5179.5	44.0	44.3	94.2	81.9	448.5	510.3	324.6	277.8	410.2	399.8
11	4318.5	5282.9	36.1	47.1	76.5	80.1	402.5	328.3	510.1	668.5	423.5	373.0
12	2932.9	6158.0	32.6	35.8	49.4	87.6	519.0	461.7	589.7	496.3	187.0	304.9
13	6053.1	7658.6	52.9	56.1	85.8	110.6	512.7	465.4	504.3	568.0	230.1	312.3
14	4627.8	4885.0	31.0	34.2	59.9	62.4	617.6	554.5	404.0	576.0	186.5	201.4
Mean ± 1 S.D.	4050.4± 1957.7	5313.8± 1743.5	39.6± 12.9	40.6± 9.4	60.8± 27.9	74.6± 23.8	528.6± 75.0	517.8± 84.0	484.0± 163.7	532.9± 142.5	243.5± 120.2	264.6± 107.4

3.3. Bouts

The average duration of stepping bouts was increased 12-months after prosthesis osseointegration (P = 0.014) (figure 2).

Figure 2.

Average overall duration of bouts of walking before (black) and after (white) prosthesis osseointegration (Pre-OI and Post-OI, respectively). * indicates statistical difference (α ≤ 0.05). + indicates an individual outlier outside of 25^th and 75^th percent quartile range of the sample data.

3.4. Cadence

The maximum and average step cadence per bout were both increased after prosthesis osseointegration (P < 0.001 and P = 0.001, respectively) (figure 3). No other differences in cadence bands were found before and after prosthesis osseointegration.

Figure 3.

Maximum and average walking cadence before (black) and after (white) prosthesis osseointegration (Pre-OI and Post-OI, respectively). * indicates statistical difference (α ≤ 0.05).

4. Discussion

In this longitudinal study, wearable activity monitor data were used to characterize walking activity for people with LLA before and after prosthesis osseointegration. Step counts prior to prosthesis osseointegration were similar in comparison with participants using socket prosthesis in previous studies [6–8]. Our results demonstrated a 31.2%, or 1264 step, increase in average daily step count during free-living activity 12 months after prosthesis osseointegration. Consistent with our hypothesis, the increase in daily step count was accompanied by an increase in average step cadence. These data indicate a meaningful change in walking activity for people undergoing osseointegration as a secondary procedure after failed use of a socket-based prosthesis. For this cohort, meaningful change is supported by consistent anecdotal statements from patients that the most significant impact prosthesis osseointegration has on their lives is improved independence. As a novel intervention that is becoming more common, it is important for clinicians, patients, and researchers to understand expectations for walking activity outcomes as a critical factor in long-term patient health after prosthesis osseointegration.

Walking activity in daily living provides important information regarding a person’s physical function, which is different than traditional in-clinic measures of functional capacity. Accelerometer-based walking activity outcomes are direct measures of free-living community activity and do not always correlate with clinical measures of functional capacity [21]. While early data for lower-limb prosthesis osseointegration has shown improvement in clinical measures of functional capacity [17,18,22], to our knowledge, changes in daily walking activity after osseointegration have not been reported. For people with LLA, it has been shown that walking activity is explained by factors such as cardiovascular health, pre-amputation walking behavior, amputation etiology (traumatic vs. non-traumatic), age, socioeconomic characteristics, BMI, and prosthesis characteristics, in addition to functional capacity [6,23]. As a result, it cannot be assumed that improved functional capacity alone will result in increased walking performance. Thus, the finding at 12 months following prosthesis osseointegration of 5313 steps per day on average is novel and important.

People with LLA are known to have limited walking activity compared to healthy people of similar age [6]. Previous studies with accelerometer-based walking activity monitoring have shown that people with LLA typically have step counts that can be as low as 1721 to 4785 daily steps on average (1721 ± 1524 [7]; 4217 ± 3027 [24]; 4785 ± 1868 [8]), which our current cohort aligns with prior to osseointegration (4050 ± 1958). The value of 5000 steps has been suggested as an important clinical threshold to distinguish sedentary from non-sedentary lifestyle, which our cohort surpassed 12-months following prosthesis osseointegration (5313 ± 1743) [12,25]. Furthermore, progressively lower daily step counts below 6000 steps/day are linked to higher mortality risk for adults over age of 60 [26]. Most participants (8/14) in this current sample met a threshold of over 6000 daily steps 12-months after prosthesis osseointegration, which is a significant finding pertaining to the effect of osseointegration on an individual’s overall health. However, some patients (6/14) within this cohort walked less than 6000 steps per day 12-months after osseointegration. As there are likely many reasons that may contribute to why some patients did not reach this threshold (e.g., secondary comorbidities, additional disabilities beyond amputation (e.g., spinal cord injury) [27], post operative pain, complications after osseointegration, age, work status, etc.), continued study of walking activity in relation to rehabilitation interventions after lower-limb prosthesis osseointegration is needed to understand how various rehabilitation factors facilitate and maintain walking activity.

Another novel finding for this sample is the amount of time spent in stepping bouts after prosthesis osseointegration. Prior evidence shows a very low percentage of time during an average day is typically spent walking for people with LLA. For example, Miller, et. al. found that adults living with LLA for at least a year spent on average 77% of their daily wake time sitting, 16% of time in standing activity, and 6% of time in walking activity [28]. Thus, it is important to identify clinical interventions to effectively decrease sedentary behavior and increase walking activity for people with LLA. Interestingly, the amount of standing and walking combined for the current sample increased by 35 minutes per day from immediately before to 12 months after prosthesis osseointegration. For walking time alone, there was an increase in the duration of 14 minutes per day, with the longest walking bouts increasing on average by 4 minutes. Thus, in addition to total daily steps and anecdotal evidence of improved independence, prosthesis osseointegration also promotes an overall more active lifestyle, which has numerous long-term health benefits.

Also related to walking activity is the intensity of walking, which can be measured indirectly through step cadence [12]. In the current sample, average walking cadence improved from 16 steps/minute before osseointegration to 20 steps per minute one year after prosthesis osseointegration, which includes all levels of stepping activity from incidental to brisk walking (1–100+ steps/min). The current sample of participants improved in walking bouts of both purposeful and brisk walking, based on this cadence band classification. For example, one year after prosthesis osseointegration, participants spent on average 4.5 minutes per day walking at brisk cadence (compared to 1.2 minutes/day walking at a brisk cadence before osseointegration), which compares favorably to the average of about 5 minutes for typical adults without amputation [12]. However, there was still room for improvement as slow walking bouts improved only slightly, from 6.5 minutes average duration to 8.3 minutes average duration. In comparison, the average for typical adults without amputation is 16 minutes per day for average slow walking bouts. Nonetheless, greater walking intensity is important for both weight management and reduce insulin resistance, which are two important clinical factors relevant to this population to prevent future vascular pathologies caused by sedentary lifestyle. As with step count, the influence of rehabilitation intervention on step cadence is warranted to better understand how to optimize outcomes following prosthesis osseointegration.

Several limitations could influence the inferences made from this study. As a novel intervention with only one current prosthesis with full market approval by the FDA, there are a limited number of people who have undergone osseointegration of a lower-limb prosthesis. Although our sample size was powered to detect statistical significance, we did not include baseline physical activity levels as an inclusion criterion. As such, there was considerable heterogeneity in patient functional values at baseline. This may explain the potential ceiling effect in our results that higher functioning patients at baseline demonstrated less improvements in physical activity after osseointegration. Secondly, it is also known that commercially available wearable activity monitors have variable outputs in step counts [29]. The data from the activPAL monitor in this study are likely somewhat different from studies using other activity monitors. However, the activPal device has been shown to accurately measure step counts in adults, including those with LLA [30,31], and the use of a 24-hour wear time for inclusion as a valid day provides confidence that all walking activity was being measured in this pre-post study design. Third, the minimum valid data collection period of four days (three weekdays, one weekend day) did not control for collection periods over multiple weekends. It is possible that varying collection periods across a different number of weekends could influence daily stepping activity. However, as there was no difference in the number of valid days before or after prosthesis osseointegration, we do not think this posed a significant influence on our findings. Finally, after completion of the 3-week rehabilitation in our clinic, patients’ rehabilitation protocols were personalized to their recovery and completed in their home-based clinics. Although the overall protocol was standardized and was overseen by our team (DHM), it is possible that the tailoring of rehabilitation modalities to meet recovery needs could have an influence on outcomes. Future work, including a control group, is needed to elucidate this effect.

In conclusion, people who had undergone osseointegration of a lower-limb prosthesis took more daily steps, had higher daily step cadence, and longer bouts of walking 12 months following prosthesis osseointegration compared to immediately prior to surgery. The average daily step count at 12 months indicated that people on average moved to more active lifestyles. Overall, these data suggest that average daily step count, walking bouts, and step cadence during free-living walking activity are promising measures to capture physical function performance following osseointegration of a lower-limb prosthesis.

Figure 4.

Mean ± 1 S.D. accumulated minutes per day within individual step cadence categories based on steps per minute (SPM) before (black) and after (white) prosthesis osseointegration (Pre-OI and Post-OI, respectively). * indicates statistical difference (α ≤ 0.05).

Implications for Rehabilitation.

• People with lower-limb loss participate in less physical activity than able-bodied individuals, which increases the mortality risk and incidence of metabolic syndromes.

• Daily step count, walking bouts, and step cadence during free-living walking activity are promising measures to capture physical functional performance in patients with lower-limb amputation.

• This study shows that patients with osseointegrated prostheses increase their stepping activity, including daily steps, number of bouts, and stepping cadence compared to when using a socket prosthesis, which has positive implications on overall patient health.

• As a novel intervention that is becoming more common, it is important for clinicians, patients, and researchers to understand expectations for walking activity outcomes as a critical factor in long-term patient health after prosthesis osseointegration.