Abstract
Objective
To investigate the association between the presence of spinal cord injury (SCI) on biomechanical variables by comparing individuals with SCI and able-bodied individuals during the sit-to-stand (STS) task assisted by a walker device. Specifically, we compared the upper-extremity joint angles and moments, trunk forward tilt angle, vertical forces of the instrumented walker, and ground reaction forces between groups.
Design
Case–control study.
Setting
Department of Orthopedics and Traumatology, UNICAMP-Brazil.
Participants
Six individuals with SCI and fourteen able-bodied individuals.
Main outcome measures
Kinematics and kinetics of the shoulder, elbow, and wrist joints; trunk forward tilt angle, vertical walker forces, and ground reaction forces (GRF) were analyzed during the STS task in two phases: before and after the seat-off event.
Results
A higher peak elbow flexion angle and higher vertical walker forces were observed before the seat-off, whereas the lower peak vertical GRF was found, after the seat-off, in the SCI group compared with the control group.
Conclusions
SCI affects kinematics and kinetics variables during the STS task compared to able-bodied controls. Individuals with SCI adopted different standing-up strategies that affected the distribution of the forces in the upper and lower extremities of the human body.
Keywords: Spinal cord injury, Sit-to-stand, Walker, Upper extremity
Introduction
Standing up or sit-to-stand (STS) is one of the most important tasks and a functional prerequisite for daily activities as it is a precursor to walking (1). STS is a physically demanding task that requires adequate control and coordination of the lower and upper extremities segments to maintain balance and equilibrium (2) while the body’s center of mass is being moved forward and upward.
The biomechanics of the STS task has been studied in healthy individuals (2–9) and in individuals with total knee arthroplasty, where higher hip joint forces were reported (10). A previous study described that to reduce its demands on lower extremity joints, the use of hands during the STS task yields a reduced hip moment by about 50% (11). Individuals presenting impairments in the lower extremities typically need assistive devices (e.g. walkers) to perform STS tasks due to muscle weakness. Weak, or perhaps paralyzed, muscles in individuals with spinal cord injury (SCI), may have a compromised ability to rise from a seated position. Previous studies reported that more than half of the individuals with SCI need an assistive device to perform the STS task as they relied on the upper extremity to help control the movement, due to a reduced sensorimotor response (12,13). During activities of daily living, such as transfers and wheelchair propulsion, individuals with SCI rely more on the upper limbs which can result in pain, especially in the shoulder and wrist joints (14,15). Although the biomechanics of the STS task in individuals with SCI has been previously reported (12,13,16–19), where a greater initial hip angle was found to assist in bending the body forward (19) to use the linear momentum of the trunk (18), and higher forces from the upper extremities are needed to lift the body during the STS task (16,17), none of these studies used an instrumented walker to quantify the forces acting in the body where the sensor was embedded in handle grips instead of mounted underneath only at the right walker handle (16) or bars instrumented with strain gauges (17). Moreover, simple marker sets have been typically adopted, in these studies, where the analysis is limited to the shoulder joint. Additionally, fixed bars were used (17,18) which contrary to the walker frame might alter the forces needed to lift the body upward due to the more unstable nature of the walker. These studies may also be considered either case reports (17,18) with one or two participants or a single group study with no healthy control group (16). To perform the STS task, adequate postural control is needed where the load between the upper and lower extremities should be equally distributed, optimizing the standing-up strategy. To understand how to perform this efficiently, a control group of healthy individuals is necessary as their proprioception sense of position and movement of the body in space have not deteriorated. Therefore, there is a need for a study which considers both individuals with SCI and a comparable group of control individuals to provide reference data during STS tasks using an instrumented walker. Such a study would enable making inferences about the effect of SCI on STS tasks while partly addressing the limitations of previous studies.
Hence, the objective of this study was to investigate the association between the presence of SCI on biomechanical variables by comparing individuals with SCI and able-bodied individuals during the STS task assisted by a walker device. We hypothesized that as the SCI individuals rely more on the upper extremity during the STS task, higher values would be found mainly in the shoulder and wrist joints compared with able-bodied individuals. The findings of this study can be used by clinicians and caregivers to optimize the forces acting in the SCI population mainly in the upper limb during the STS task, aiming to improve their quality of life.
Methods
Participants
Six paraplegic individuals (SCI Group) were recruited to take part in this study (Table 1). The sample size adopted in this study is comparable with previous studies with similar designs (16–18). The inclusion criteria encompassed individuals with complete SCI, classified as American Spinal Injury Association (AIS) Impairment Scale A, aged 18 years or older, and capable of performing the STS task. All individuals in the SCI group used a wheelchair for daily locomotion. In addition, fourteen able-bodied individuals who met the inclusion criteria, which required them to be 18 years or older and without any musculoskeletal or neurological injury (age: 35.4 ± 10.5 years, height: 1.7 ± 0.1 m, body mass: 75.9 ± 12.8 kg), were assigned to the Control Group. Before the data collection, each individual read and signed a consent form approved by the University Ethics Committee. All individuals were recruited from the ambulatory of Spinal Cord Injury Rehabilitation of the Department of Orthopedics and Traumatology.
Table 1.
Individual characteristics of the SCI group.
| Subject | Age (year) | Height (m) | Body mass (kg) | Diagnosis | Severity (AIS) | Post-injury time (years) |
|---|---|---|---|---|---|---|
| S1 | 32 | 1.86 | 94.81 | T3 | A | 13 |
| S2 | 23 | 1.69 | 50.38 | T4 | A | 2 |
| S3 | 31 | 1.88 | 63.10 | T6 | A | 4 |
| S4 | 27 | 1.78 | 66.71 | T6 | A | 2 |
| S5 | 38 | 1.86 | 71.74 | T9 | A | 4 |
| S6 | 38 | 1.70 | 53.14 | T10 | A | 20 |
AIS = American Spinal Injury Association Impairment Scale.
Data collection
Plug-in-gait marker set protocol was adopted and the three-dimensional trajectory of each marker was captured with a 12-camera motion capture system at 100 Hz (Vero 1.3, Vicon Motion Systems Ltd., Oxford, Oxford Metrics Group, UK). Force signals were collected at 1000 Hz with two force plates and an instrumented walker (AMTI, Watertown, United States). Both kinematic and kinetic data were simultaneously recorded with Vicon Nexus (Vicon Motion Systems Ltd., Oxford, Oxford Metrics Group, UK).
For the data collection, a chair without a backrest, or armrests were used. During the test, each individual in the Control and SCI group was asked to perform the STS task while sitting in the chair and placing a foot on each force plate, while ensuring that both feet were parallel. Additionally, an instrumented walker was used where the height was adjusted based on the individual’s preference (20,21) (Fig. 1). The Control group was asked to perform the STS task using an instrumented walker such that they bear more weight on their arms rather on their legs, simulating a paraplegic individual. This was done to understand what strategy the Control group would adopt to optimize the STS task strategy and to prevent future injuries if they did not have the appropriate assistance in their lower extremities. All individuals with SCI were classified as an AIS A before the data collection by an experienced physiotherapist (Table 1). To complete the task, the individuals in the SCI group required ankle-foot orthoses (AFO) associated with electrical functional stimulation (FES) with charge-balanced pulses of 300 μs at 25 Hz (22) on the quadricep muscles. The amplitude of the stimulation was adapted for each individual to provide an appropriate joint locking. All individuals have been participating in FES therapy sessions twice a week. Both individuals in the Control and SCI group were asked to perform the STS task comfortably, with as many attempts as necessary to complete the task.
Figure 1.
(A) Set up protocol displaying an individual in the SCI group during the experiment. (B) Animation showing the STS cycle divided into two phases: before seat-off (left) and after (right) seat-off. Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/yscm.
Data analysis
Maximum values of the flexion angle of the shoulder, elbow, and wrist joints, and trunk forward tilt angle, flexion internal moments of the shoulder, elbow, and wrist joints calculated by an inverse dynamics approach, and the maximal vertical force of the instrumented walker and the ground reaction forces (GRF) were analyzed during the STS cycle that was divided in two phases: before seat-off and after seat-off event. The STS cycle was defined as the time between when the vertical position of the center of mass of the body starts to move downward (or the initiation of forward lean) to the maximum vertical position of the center of mass (or standing fully upright). Additionally, the time the buttock left the chair, defined as a seat-off event, was based on the lowest position of the center of mass of the body. We considered the biomechanical variables at the sagittal plane and only the right side of the body were analyzed, assuming symmetry(23). Kinematic and kinetic signals were filtered with a fourth-order lowpass Butterworth filter with a 10 Hz cut-off frequency. All the calculations were performed in Visual 3D software (C-Motion Inc., Germantown, USA).
The STS cycle was time normalized (0–100%) and the average of a minimum of three trials was considered for further analysis. The kinetics data were spatially normalized by body mass for between-group comparisons. The outcome variables extraction was performed by custom-made software written in Python language version 3.10.10 using the SciPy Stack (https://www.scipy.org).
Statistical analysis
Descriptive statistics (mean and standard deviation) were employed to present anthropometric and demographic characteristics. The normality of the data was assessed with Shapiro-Wilk’s tests. Student’s t-test or Mann–Whitney tests were used to investigate the differences between groups before and after the seat-off. The significance level was set to a Bonferroni-corrected value for multiple comparisons of 0.005, to minimize the chance of type I errors. All statistical analyses were performed in Python version 3.10.10.
Results
The distribution of the peak joint angles, moments, and forces of the Control and SCI group is shown in Fig. 2. A higher peak elbow flexion angle (P = 0.002) and higher vertical walker forces (P = 0.003) were observed before the seat-off, whereas a lower peak vertical GRF was found (P < 0.001), after the seat-off, in the SCI compared with the Control group.
Figure 2.
Boxplot showing the distribution of the peak values of the shoulder, elbow, and wrist angles, the trunk segment angle, the shoulder, elbow, and wrist moments, and the vertical walker and vertical GRF forces for the Control and SCI groups during the STS cycle that was divided into two phases: before seat-off and after seat-off. * P < 0.005. Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/yscm.
Discussion
The aim of this study was to investigate the association between the presence of SCI on biomechanical variables by comparing individuals with SCI and able-bodied individuals during the STS task. We hypothesized that during the STS task, the SCI group would increase the loading in the upper extremity. Overall, before the seat-off, the individuals with SCI presented higher elbow flexion angle and vertical walker forces compared with the Control group. After the seat-off, a lower peak value was found in the vertical GRF in the SCI in relation to the Control group.
The upper extremity’s effort in individuals with SCI has been analyzed in previous studies; however, they are limited to the gait task (24–26). Before performing a gait task, it is first necessary to stand up. This movement places a high demand on the upper limbs as it has been reported that more than half of the individuals with SCI rely on their upper extremities to stand up (12) thus, the STS task should also be investigated carefully. A previous study reported that during the STS task, individuals with gross muscle weakness tend to increase the flexion of the trunk as a compensatory mechanism to reduce the needs on the lower limb muscles (27). As the individuals with SCI presented a higher flexion angle of the elbow joint before the seat-off, this could be adopted to compensate for the muscle weakness in the lower extremities, which resulted in the higher value of the vertical walker forces. In fact, to lift the body upward and keep in the upright position, a higher force is required mainly in the shoulder joint to compensate for the weakness in the lower limb (14). Moreover, different strategies of the wrist position on the walker could be adopted mainly by the Control group, which may explain the high variability among the individuals. Although during the STS task, the control individuals were instructed to perform similar movement patterns to the SCI group, they still put more weight on their lower limbs as higher values of the vertical GRF were found. Therefore, future studies standardizing the position of the hands on the walker and better control of the loading applied by able-bodied individuals are necessary.
Given the substantial weight-bearing loads associated with assistive devices (28), the risk of injury because of their usage, particularly, in the upper extremity joints is always a concern. Hence, the biomechanical assessment of the STS task in individuals with SCI emerges as a pivotal tool in rehabilitation, providing valuable insights for clinicians to quantify changes in the functional abilities of SCI patients over time as well as to develop rehabilitation programs to optimize their movement, improve muscle strength, and coordination, to recover their independence and enhance the overall quality of life. In this study, the higher values of the elbow angle and vertical walker forces found in the SCI population, compared to able-bodied individuals, suggest a potential increased risk of upper extremity injury. In fact, previous studies have reported the association of shoulder pain and dysfunction with increased stress on the shoulder joint during upper-extremity ambulation (29,30). Therefore, the increased elbow angle and weight-bearing walker forces may increase the injury risk in SCI individuals. Moreover, due to the reduced sensorimotor response, individuals with SCI tend to rely more on the upper extremities for enhanced control during the STS task (12,13). The results of the present study indicate that the biomechanical assessment can be a valuable tool to detect the presence of excessive loads and functional impairments during the STS task in SCI populations. Therefore, clinicians could use the results of these assessments to improve the rehabilitation program of SCI patients, with an emphasis on maximizing movement quality and independence while maintaining stability and safety during the STS task.
There are limitations in this study that need to be highlighted. First, the Control group individuals presented higher values for the vertical GRF and lower values of instrumented walker forces after the seat-off, indicating that they bear more weight in their lower limbs compared to individuals with SCI during this time. Although this factor could partly explain the observed differences between individuals with SCI and controls, as proprioception sense deficits may occur following SCI (31), we believe the higher elbow flexion angle and the vertical walker force observed in individuals with SCI, suggest that they still rely more in their upper extremity. Second, even though the individuals with SCI performed the STS task wearing their own AFO combined with FES stimulation, the individuals in the Control Group did not follow the same procedure as they were not familiar with it, which could alter the final result. Nevertheless, future studies should also be performed to investigate if the orthoses and the stimulation influence the STS task in able-bodied individuals to compare with individuals with SCI. Lastly, to prevent injuries in the upper extremity in individuals with SCI, based on our results, the rehabilitation program should be focused toward reducing the forces applied to the upper extremity. Although these individuals use FES stimulation to perform the STS task, they still rely more on the upper extremity as a greater arm support was found. Thus, future studies are necessary to guide these individuals with SCI to redistribute the loads properly between the upper and lower extremities while optimizing their postural control strategy to perform the STS task.
Conclusion
The results of the present study indicate that SCI affects both kinematics and kinetics data, compared to controls, during the STS task. In fact, the higher vertical walker forces combined with the higher elbow flexion angle before the seat-off and with the lower vertical GRF values after the seat-off, suggest that individuals with SCI rely to a greater extent on their upper extremities during the STS task, presumably to better control their balance. Although the present findings provide valuable insights into the movement strategies adopted by individuals with SCI that can be useful to optimize the rehabilitation and injury prevention programs, future studies are needed to yield more conclusive findings.
Disclaimer statements
Funding This work as supported by the Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP/Brazil), grants 2019/06604-1 and 2016/50253-0.
Conflict of interest None.
References
- 1.Bobbert MF, Kistemaker DA, Vaz MA, Ackermann M.. Searching for strategies to reduce the mechanical demands of the sit-to-stand task with a muscle-actuated optimal control model. Clin Biomech. 2016;37:83–90. [DOI] [PubMed] [Google Scholar]
- 2.Jeon W, Jensen JL, Griffin L.. Muscle activity and balance control during sit-to-stand across symmetric and asymmetric initial foot positions in healthy adults. Gait Posture. 2019;71:138–144. [DOI] [PubMed] [Google Scholar]
- 3.Kerr KM, White JA, Barr DA, Mollan RAB.. Analysis of the sit-stand-sit movement cycle in normal subjects. Clin Biomech. 1997;12:236–245. [DOI] [PubMed] [Google Scholar]
- 4.Schofield JS, Parent EC, Lewicke J, Carey JP, El-Rich M, Adeeb S.. Characterizing asymmetry across the whole sit to stand movement in healthy participants. J Biomech. 2013;46:2730–2735. [DOI] [PubMed] [Google Scholar]
- 5.Janssen WG, Bussmann HB, Stam HJ.. Determinants of the sit-to-stand movement: A review. Phys Ther. 2002;82:866–879. [PubMed] [Google Scholar]
- 6.Shepherd RB, Gentile AM.. Sit-to-stand: functional relationship between upper body and lower limb segments. Hum Mov Sci. 1994;13:817–840. [Google Scholar]
- 7.Kralj A, Jaeger RJ, Munih M.. Analysis of standing up and sitting down in humans: definitions and normative data presentation. J Biomech. 1990;23:1123–1138. [DOI] [PubMed] [Google Scholar]
- 8.Galli M, Cimolin V, Crivellini M, Campanini I.. Quantitative analysis of sit to stand movement: Experimental set-up definition and application to healthy and hemiplegic adults. Gait Posture. 2008;28:80–85. [DOI] [PubMed] [Google Scholar]
- 9.Millington PJ, Myklebust BM, Shambes GM.. Biomechanical analysis of the sit-to-stand motion in elderly persons. Arch Phys Med Rehabil. 1992;73:609–617. [PubMed] [Google Scholar]
- 10.Su FC, Lai KA, Hong WH.. Rising from chair after total knee arthroplasty. Clin Biomech. 1998;13(3):176–181. [DOI] [PubMed] [Google Scholar]
- 11.Arborelius UP, Wretenberg P, Lindberg F.. The effects of armrests and high seat heights on lower-limb joint load and muscular activity during sitting and rising. Ergonomics. 1992;35:1377–1391. [DOI] [PubMed] [Google Scholar]
- 12.Saensook W, Mato L, Manimmanakorn N, Amatachaya P, Sooknuan T, Amatachaya S.. Ability of sit-to-stand with hands reflects neurological and functional impairments in ambulatory individuals with spinal cord injury article. Spinal Cord. 2018;56:232–238. [DOI] [PubMed] [Google Scholar]
- 13.Khuna L, Mato L, Amatachaya P, Thaweewannakij T, Amatachaya S.. Increased lower limb loading during sit-to-stand is important for the potential for walking progression in ambulatory individuals with spinal cord injury. Malaysian J Med Sci. 2019;26:99–106. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 14.Gellman H, Sie I, Waters RL.. Late complications of the weight-bearing upper extremity in the paraplegic patient. Clin Orthop Relat Res. 1988;233:135–135. [PubMed] [Google Scholar]
- 15.Pentland WE, Twomey LT.. The weight-bearing upper extremity in women with long term paraplegia. Paraplegia. 1991;29:521–530. [DOI] [PubMed] [Google Scholar]
- 16.Kamnik R, Bajd T, Kralj A.. Functional electrical stimulation and arm supported sit-to-stand transfer after paraplegia: A study of kinetic parameters. Artif Organs. 1999;23:413–417. doi: 10.1046/j.1525-1594.1999.06367.x. [DOI] [PubMed] [Google Scholar]
- 17.Bahrami F, Riener R, Jabedar-Maralani P, Schmidt G.. Biomechanical analysis of sit-to-stand transfer in healthy and paraplegic subjects. Clin Biomech. 2000;15:123–133. [DOI] [PubMed] [Google Scholar]
- 18.Jovic J, Fraisse P, Coste CA, Bonnet V, Fattal C.. Improving valid and deficient body segment coordination to improve FES-assisted sit-to-stand in paraplegic subjects. In: 2011 IEEE International Conference on Rehabilitation Robotics, Zurich, Switzerland; 2011: 1–5. doi: 10.1109/ICORR.2011.5975369. [DOI] [PubMed] [Google Scholar]
- 19.Mao HF, Huang HP, Lu TW, Wang TM, Wu CH, Hu JS.. Balance control and energetics of powered exoskeleton-assisted Sit-to-stand movement in individuals with paraplegic spinal cord injury. Arch Phys Med Rehabil. 2018;99:1982–1990. [DOI] [PubMed] [Google Scholar]
- 20.Gagnon D, Nadeau S, Gravel D, Noreau L, Larivière C, Gagnon D.. Biomechanical analysis of a posterior transfer maneuver on a level surface in individuals with high and low-level spinal cord injuries. Clin Biomech. 2003;18:319–331. doi: 10.1016/S0268-0033(03)00016-0. [DOI] [PubMed] [Google Scholar]
- 21.Potten YJM, Seelen HAM, Drukker J, Reulen JPH, Drost MR.. Postural muscle responses in the spinal cord injured persons during forward reaching. Ergonomics. 1999;42:1200–1215. [DOI] [PubMed] [Google Scholar]
- 22.De Abreu DCC, Cliquet A, Rondina JM, Cendes F.. Electrical stimulation during gait promotes increase of muscle cross-sectional area in quadriplegics: A preliminary study. Clin Orthop Relat Res. 2009;467:553–557. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 23.Magnan A, McFadyen BJ, St-Vincent G.. Modification of the sit-to-stand task with the addition of gait initiation. Gait Posture. 1996;4:232–241. [Google Scholar]
- 24.Baniasad M, Farahmand F, Arazpour M, Zohoor H.. Role and significance of trunk and upper extremity muscles in walker-assisted paraplegic gait: A case study. Top Spinal Cord Inj Rehabil. 2018;24:18–27. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 25.Khodadadi M, Baniasad MA, Arazpour M, Farahmand F, Zohoor H.. Designing instrumented walker to measure upper-extremity’s efforts: a case study. Assist Technol. 2019;31:267–275. [DOI] [PubMed] [Google Scholar]
- 26.Baniasad M, Farahmand F, Arazpour M, Zohoor H.. Kinematic and electromyography analysis of paraplegic gait with the assistance of mechanical orthosis and walker. J Spinal Cord Med. 2019;43(6):854–861. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 27.Doorenbosch CAM, Harlaar J, Roebroeck ME, Lankhorst GJ.. Two strategies of transferring from sit-to-stand; the activation of monoarticular and biarticular muscles. J Biomech. 1994;27:1299–1307. [DOI] [PubMed] [Google Scholar]
- 28.Haubert LL, Gutierrez DD, Newsam CJ, Gronley JAK, Mulroy SJ, Perry J.. A comparison of shoulder joint forces during ambulation with crutches versus a walker in persons with incomplete spinal cord injury. Arch Phys Med Rehabil. 2006;87:63–70. [DOI] [PubMed] [Google Scholar]
- 29.Akbar M, Balean G, Brunner M, Seyler TM, Bruckner T, Munzinger J, Grieser T, Gerner HJ, et al. Prevalence of rotator cuff tear in paraplegic patients compared with controls. J Bone Jt Surg. 2010;92:23–30. [DOI] [PubMed] [Google Scholar]
- 30.Bayley JC, Cochran TP, Sledge CB.. The weight-bearing shoulder. The impingement syndrome in paraplegics. J bone Jt Surg Br. 1987;69:676–678. [PubMed] [Google Scholar]
- 31.Chisholm AE, Qaiser T, Williams AMM, Eginyan G, Lam T.. Acquisition of a precision walking skill and the impact of proprioceptive deficits in people with motor-incomplete spinal cord injury. J Neurophysiol. 2019;121:1078–1084. [DOI] [PubMed] [Google Scholar]