Use of Perturbation-Based Gait Training in a Virtual Environment to Address Mediolateral Instability in an Individual With Unilateral Transfemoral Amputation

Reporting of Rehabilitation Outcomes in the Traumatic Lower Limb Amputation Literature: A Systematic Review

OBJECTIVE

To synthesize the outcomes reported in the rehabilitation and community literature for adults with traumatic lower limb amputation (LLA).

DATA SOURCES

The search strategy was conducted in 3 databases (Medline, EMBASE, and CINAHL) from inception to April 2022.

STUDY SELECTION

To be eligible, articles could be of any design but were required to have at least 50% adult individuals with traumatic LLA and had to report on interventions and outcomes in either a rehabilitation or community setting.

DATA EXTRACTION

The extracted outcomes were classified using Dodd's framework, which is designed for organizing research outcomes. Heterogeneity was observed in the outcome measures (OMs) used for evaluation. Two reviewers independently conducted the data extraction, which was verified by a third reviewer.

DATA SYNTHESIS

Of the 7,834 articles screened, 47 articles reporting data on 692 individuals with traumatic LLA, met our inclusion criteria. Four core areas encompassing 355 OMs/indicators were identified: life effect (63.4%), physiological/clinical (30.1%), resource use (5.1%), and adverse events (1.4%). Physical functioning (eg, gait, mobility) was the most frequently reported outcome domain across studies, followed by nervous system outcomes (eg, pain) and psychiatric outcomes (eg, depression, anxiety). Domains such as global quality of life and role/emotional functioning were seldomly reported.

CONCLUSION

The study provides a list of outcome indicators explicitly published for adults with traumatic LLA, highlighting inconsistent reporting of outcome indicators. The lack of a standardized set of OMs is a barrier to performing meta-analyses on interventions, preventing the identification of effective care models and clinical pathways. Developing a core outcome set that includes OMs relevant to the needs of the traumatic LLA population may address these issues.

Fall Prevention Training for Service Members With an Amputation or Limb Salvage Following Lower Extremity Trauma

INTRODUCTION

Recent military conflicts have resulted in a significant number of lower extremity injuries to U.S. service members that result in amputation or limb preservation (LP) procedures. Service members receiving these procedures report a high prevalence and deleterious consequences of falls. Very little research exists to improve balance and reduce falls, especially among young active populations such as service members with LP or limb loss. To address this research gap, we evaluated the success of a fall prevention training program for service members with lower extremity trauma by (1) measuring fall rates, (2) quantifying improvements in trunk control, and (3) determining skill retention at 3 and 6 months after training.

MATERIALS AND METHODS

Forty-five participants (40 males, mean [±SD] age, 34 ± 8 years) with lower extremity trauma (20 with unilateral transtibial amputation, 6 with unilateral transfemoral amputation, 5 with bilateral transtibial amputation, and 14 with unilateral LP procedures) were enrolled. A microprocessor-controlled treadmill was used to produce task-specific postural perturbations which simulated a trip. The training was conducted over a 2-week period and consisted of six 30-minute sessions. The task difficulty was increased as the participant's ability progressed. The effectiveness of the training program was assessed by collecting data before training (baseline; repeated twice), immediately after training (0 month), and at 3 and 6 months post-training. Training effectiveness was quantified by participant-reported falls in the free-living environment before and after training. Perturbation-induced recovery step trunk flexion angle and velocity was also collected.

RESULTS

Participants reported reduced falls and improved balance confidence in the free-living environment following the training. Repeated testing before training revealed that there were no pre-training differences in trunk control. The training program improved trunk control following training, and these skills were retained at 3 and 6 months after training.

CONCLUSION

This study showed that task-specific fall prevention training reduced falls across a cohort of service members with diverse types of amputations and LP procedures following lower extremity trauma. Importantly, the clinical outcome of this effort (i.e., reduced falls and improved balance confidence) can lead to increased participation in occupational, recreational, and social activities and thus improved quality of life.

Quantitative methods used to evaluate balance, postural control, and the fear of falling in lower limb prosthesis users: A systematic review

Problems with balance, postural control, and fear of falling are highly prevalent in lower limb prosthesis users, with much research conducted to understand these issues. The variety of tools used to assess these concepts presents a challenge when interpreting research outcomes. This systematic review aimed to provide a synthesis of quantifiable methods used in the evaluation of balance, postural control, and fear of falling in lower limb prosthesis users with an amputation level at or proximal to the ankle joint. A systematic search was conducted in CINAHL, Medline, AMED, Cochrane, AgeLine, Scopus, Web of Science, Proquest, PsycINFO, PsycArticles, and PubPsych databases followed by additional manual searching via reference lists in the reviewed articles databases. Included articles used quantitative measure of balance or postural control as one of the dependent variables, lower limb prosthesis users as a sample group, and were published in a peer-reviewed journal in English. Relevant assessment questions were created by the investigators to rate the assessment methods used in the individual studies. Descriptive and summary statistics are used to synthesize the results. The search yielded (n = 187) articles assessing balance or postural control (n = 5487 persons in total) and (n = 66) articles assessing fear of falling or balance confidence (n = 7325 persons in total). The most used test to measure balance was the Berg Balance Scale and the most used test to measure fear of falling was the Activities-specific Balance Confidence scale. A large number of studies did not present if the chosen methods were valid and reliable for the lower limb prosthesis users. Among study limitations, small sample size was common.

Virtual Reality-Based Rehabilitation to Restore Motor Function in People With Amputation: A Systematic Literature Review

ABSTRACT

Virtual reality is an emerging technology with accumulating research and clinical evidence in the field of physical rehabilitation. This study aimed to systematically identify and examine the effects of virtual reality on motor function outcomes in patients with amputation to inform clinical decision making on amputation rehabilitation and inform further research endeavors. Five databases were searched, including PubMed, CINAHL, PsycINFO, Embase, and Scopus. After screening for 1052 records, 10 clinical studies were included in this review: four randomized controlled trials, three pre-post single-arm studies, and three case studies; all studies had fair to good methodological quality. Seven studies were for lower extremity amputation, and three were for upper extremity amputation. Results reveal the positive effects of virtual reality on improving motor function in prosthesis training, including balance, gait, and upper extremity outcomes. Participants also report enjoyment during virtual reality intervention as measured by subjective experience. However, it is unclear whether virtual reality can induce better therapeutic outcomes than conventional rehabilitation, given the limited number of controlled studies and conflicting results reported in the included studies. More properly designed randomized controlled trials with adequately powered sample sizes are warranted to elucidate the benefits of virtual reality-based rehabilitation in the amputation population.

Testing and evaluation of lower limb prosthesis prototypes in people with a transfemoral amputation: a scoping review on research protocols

BACKGROUND

When developing new lower limb prostheses, prototypes are tested to obtain insights into the performance. However, large variations between research protocols may complicate establishing the potential added value of newly developed prototypes over other prostheses.

OBJECTIVE

This review aims at identifying participant characteristics, research protocols, reference values, aims, and corresponding outcome measures used during prosthesis prototype testing on people with a transfemoral amputation.

METHODS

A systematic search was done on PubMed and Scopus from 2000 to December 2020. Articles were included if testing was done on adults with transfemoral or knee disarticulation amputation; testing involved walking with a non-commercially available prototype leg prosthesis consisting of at least a knee component; and included evaluations of the participants' functioning with the prosthesis prototype.

RESULTS

From the initial search of 2027 articles, 48 articles were included in this review. 20 studies were single-subject studies and 4 studies included a cohort of 10 or more persons with a transfemoral amputation. Only 5 articles reported all the pre-defined participant characteristics that were deemed relevant. The familiarization time with the prosthesis prototype prior to testing ranged from 5 to 10 min to 3 months; in 25% of the articles did not mention the extent of the familiarization period. Mobility was most often mentioned as the development or testing aim. A total of 270 outcome measures were identified, kinetic/kinematic gait parameters were most often reported. The majority of outcome measures corresponded to the mobility aim. For 48% of the stated development aims and 4% of the testing aims, no corresponding outcome measure could be assigned. Results indicated large inconsistencies in research protocols and outcome measures used to validate pre-determined aims.

CONCLUSIONS

The large variation in prosthesis prototype testing and reporting calls for the development of a core set of reported participant characteristics, testing protocols, and specific and well-founded outcome measures, tailored to the various aims and development phases. The use of such a core set can give greater insights into progress of developments and determine which developments have additional benefits over the state-of-the-art. This review may contribute as initial input towards the development of such a core set.

Viability, task switching, and fall avoidance of the simplest dynamic walker

Walking humans display great versatility when achieving task goals, like avoiding obstacles or walking alongside others, but the relevance of this to fall avoidance remains unknown. We recently demonstrated a functional connection between the motor regulation needed to achieve task goals (e.g., maintaining walking speed) and a simple walker's ability to reject large disturbances. Here, for the same model, we identify the viability kernel-the largest state-space region where the walker can step forever via at least one sequence of push-off inputs per state. We further find that only a few basins of attraction of the speed-regulated walker's steady-state gaits can fully cover the viability kernel. This highlights a potentially important role of task-level motor regulation in fall avoidance. Therefore, we posit an adaptive hierarchical control/regulation strategy that switches between different task-level regulators to avoid falls. Our task switching controller only requires a target value of the regulated observable-a "task switch"-at every walking step, each chosen from a small, predetermined collection. Because humans have typically already learned to perform such goal-directed tasks during nominal walking conditions, this suggests that the "information cost" of biologically implementing such controllers for the nervous system, including cognitive demands in humans, could be quite low.

Dynamic balancing responses in unilateral transtibial amputees following outward-directed perturbations during slow treadmill walking differ considerably for amputated and non-amputated side

BACKGROUND

Due to disrupted motor and proprioceptive function, lower limb amputation imposes considerable challenges associated with balance and greatly increases risk of falling in presence of perturbations during walking. The aim of this study was to investigate dynamic balancing responses in unilateral transtibial amputees when they were subjected to perturbing pushes to the pelvis in outward direction at the time of foot strike on their non-amputated and amputated side during slow walking.

METHODS

Fourteen subjects with unilateral transtibial amputation and nine control subjects participated in the study. They were subjected to perturbations that were delivered to the pelvis at the time of foot strike of either the left or right leg. We recorded trajectories of center of pressure and center of mass, durations of in-stance and stepping periods as well as ground reaction forces. Statistical analysis was performed to determine significant differences in dynamic balancing responses between control subjects and subjects with amputation when subjected to outward-directed perturbation upon entering stance phases on their non-amputated or amputated sides.

RESULTS

When outward-directed perturbations were delivered at the time of foot strike of the non-amputated leg, subjects with amputation were able to modulate center of pressure and ground reaction force similarly as control subjects which indicates application of in-stance balancing strategies. On the other hand, there was a complete lack of in-stance response when perturbations were delivered when the amputated leg entered the stance phase. Subjects with amputations instead used the stepping strategy and adjusted placement of the non-amputated leg in the ensuing stance phase to make a cross-step. Such response resulted in significantly larger displacement of center of mass.

CONCLUSIONS

Results of this study suggest that due to the absence of the COP modulation mechanism, which is normally supplied by ankle motor function, people with unilateral transtibial amputation are compelled to choose the stepping strategy over in-stance strategy when they are subjected to outward-directed perturbation on the amputated side. However, the stepping response is less efficient than in-stance response.

Inclusion of a Military-specific, Virtual Reality-based Rehabilitation Intervention Improved Measured Function, but Not Perceived Function, in Individuals with Lower Limb Trauma

INTRODUCTION

Lower extremity injury is common in the military and can lead to instability, pain, and decreased function. Military service also places high physical demands on service members (SMs). Standard treatment interventions often fail to align with these unique demands. Thus, the goal of the study was to evaluate the effectiveness of a military-specific virtual reality-based rehabilitation (VR) intervention supplemental to standard care (SC) in improving military performance in SMs with lower extremity injuries.

MATERIALS AND METHODS

As part of an institutional review board-approved randomized control trial, SMs receiving care at an advanced rehabilitation center were randomized to receive either SC or VR in addition to SC (VR+SC). Participants were evaluated before treatment and ∼3 weeks later using a previously developed and validated military-specific assessment. Perceived improvement in physical function was measured using a Global Rating of Change (GROC) questionnaire. A repeated measures ANOVA was used to evaluate the effects of adding VR on the military-specific assessment measures. Linear regression was used to determine the relationship between perceived improvement, measured improvement, and VR volume.

RESULTS

The VR+SC group was able to traverse a greater distance in the assessment following the VR intervention. There was no significant difference in GROC between groups. For the VR+SC group, change in distance completed was not correlated with GROC, but GROC was correlated with VR volume.

CONCLUSION

VR improved the distance that participants were able to traverse in the assessment. However, the VR+SC group demonstrated a disconnect between their perceived functional improvement as measured by the GROC and functional improvement as measured by the change in the distance completed. Rather, the perceived improvement appears to be more correlated with the volume of VR received. The way in which the treatment progression is structured and communicated may influence how patients perceive their change in physical function.

Margins of stability of persons with transtibial or transfemoral amputations walking on sloped surfaces

Gait is a complex motor skill. However, most falls in humans occur during gait, and people with lower limb amputation have an increased risk of falls. Thus, this study evaluated the stability of persons with unilateral amputation by quantifying the margin of stability (MoS) during gait, to contribute to understanding the strategies adopted by these people to reduce falls. The participants were divided into 3 groups: persons with transtibial amputations (n = 12, 32.27 ± 10.10 years, 76.9 ± 10.3 kg, 1.74 ± 0.06 m); persons with transfemoral amputations (n = 13, 32.21 ± 8.34 years, 72.55 ± 10.23 kg, 1.73 ± 0.05 m); and controls (n = 15, 32.2 ± 10.17 years, 75.4 ± 9.25 kg, 1.75 ± 0.05 m), who walked for 4 min on a level and sloped (8% down and up) treadmill. The pelvic and foot marker kinematic data were used to estimate the center of mass and base of support, and from these, the MoS was estimated. Although both groups of persons with amputations showed higher values for the ML MoS than did the control group (transtibial: 8.81 ± 1.79, 8.97 ± 1.74, 8.79 ± 1.76, transfemoral: 10.15 ± 2.03, 10.60 ± 1.98, 10.11 ± 1.75, control: 8.13 ± 1.30, 7.18 ± 1.85, 8.15 ± 1.57, level, down, and up, respectively), only the transfemoral group presented a significant higher value compared to the control group. Our findings suggest that the documented limitations in persons with amputations, especially with transfemoral amputation, are exacerbated in situations that require more skills, such as walking on sloped surfaces, triggering protective mechanisms.

How persons with transtibial amputation regulate lateral stepping while walking in laterally destabilizing environments

BACKGROUND

Persons with lower limb amputation often experience decreased physical capacity, difficulty walking, and increased fall risk. To either prevent or recover from a loss of balance, one must effectively regulate their stepping movements. It is therefore critical to identify how well persons with amputation regulate stepping. Here, we used a multi-objective control framework based on Goal Equivalent Manifolds to identify how persons with transtibial amputation (TTA) regulate lateral stepping while walking without and with lateral perturbations.

RESEARCH QUESTION

When walking in destabilizing environments, do otherwise healthy persons with TTA exhibit greater difficulty regulating lateral stepping due to impaired control? Or do they instead continue to use similar strategies to regulate lateral stepping despite their amputation?

METHODS

Eight persons with unilateral TTA and thirteen able-bodied (AB) controls walked in a virtual environment under three conditions: no perturbations, laterally oscillating visual field, and laterally oscillating treadmill platform. We analyzed step-to-step time series of step widths and absolute lateral body positions. We computed means, standard deviations and Detrended Fluctuation Analysis scaling exponents for each time series and computed how much participants directly corrected step width and position deviations at each step. We compared our results to computational predictions to identify the underlying causes of our experimental findings.

RESULTS

All participants exhibited significantly increased variability, decreased scaling exponents, and tighter direct control when perturbed. Simulations from our stepping regulation models revealed that people responded to the increased variability produced by the imposed perturbations by tightening their control of both step width and lateral position. Participants with TTA exhibited only a few minor differences from AB in lateral stepping regulation, even when subjected to substantially destabilizing lateral perturbations.

SIGNIFICANCE

Since control of stepping is intrinsically multi-objective, developing effective interventions to reduce fall risk in persons with amputation will likely require strategies that adopt multi-objective approaches.

The Effects of Prosthesis Inversion/Eversion Stiffness on Balance-Related Variability During Level Walking: A Pilot Study

Prosthesis features that enhance balance are desirable to people with transtibial amputation. Ankle inversion/eversion compliance is intended to improve balance on uneven ground, but its effects remain unclear on level ground. We posited that increasing ankle inversion/eversion stiffness during level-ground walking would reduce balance-related effort by assisting in recovery from small disturbances in frontal-plane motions. We performed a pilot test with an ankle-foot prosthesis emulator programmed to apply inversion/eversion torques in proportion to the deviation from a nominal inversion/eversion position trajectory. We applied a range of stiffnesses to clearly understand the effect of the stiffness on balance-related effort, hypothesizing that positive stiffness would reduce effort while negative stiffness would increase effort. Nominal joint angle trajectories were calculated online as a moving average over several steps. In experiments with K3 ambulators with unilateral transtibial amputation (N = 5), stiffness affected step-width variability, average step width, margin of stability, intact-foot center of pressure variability, and user satisfaction (p ≤ 0.05, Friedman's test), but not intact-limb evertor average, intact-limb evertor variability, and metabolic rate (p ≥ 0.38, Friedman's test). Compared to zero stiffness, high positive stiffness reduced step-width variability by 13%, step width by 3%, margin of stability by 3%, and intact-foot center of pressure variability by 14%, whereas high negative stiffness had opposite effects and decreased satisfaction by 63%. The results of this pilot study suggest that positive ankle inversion stiffness can reduce active control requirements during level walking.

Healthy individuals are more maneuverable when walking slower while navigating a virtual obstacle course

INTRODUCTION

Maintaining stability, especially in the mediolateral direction, is important for successful walking. Navigating in the community, however, may require people to reduce stability to make quick lateral transitions, creating a tradeoff between stability and maneuverability. Walking slower can improve stability during steady state walking, but there remains a need to better understand how walking speed influences maneuverability. This study investigated how walking at different speeds influenced how individuals modulate both stability and maneuverability in a virtual obstacle course.

METHODS

Fifteen healthy adults walked on a treadmill in a virtual environment for 6 trials each at typical and slower speed. Participants made repeated transitions between virtual sets of arches displayed in any of 4 lanes. Participants were instructed to walk under the arches and hit as few arches as possible. To quantify stability, mean step width and mean lateral margin of stability (Mean MOS) were calculated and averaged for ipsilateral and contralateral steps. To quantify maneuverability, the number of arches hit when entering or exiting each arch set was calculated and averaged for each condition.

RESULTS

Participants exhibited high levels of variability in their stepping patterns. Mean MOS and mean step width were significantly greater for the typical speed than slower speed for the ipsilateral steps (p < 0.001). Participants hit more arches during the typical speed than during the slow speed (p = 0.039).

CONCLUSION

When walking at the slower speed, healthy individuals exhibited decreased stability of ipsilateral steps, but increased maneuverability and better transition performance.

Step-to-Step Ankle Inversion/Eversion Torque Modulation Can Reduce Effort Associated with Balance

Below-knee amputation is associated with higher energy expenditure during walking, partially due to difficulty maintaining balance. We previously found that once-per-step push-off work control can reduce balance-related effort, both in simulation and in experiments with human participants. Simulations also suggested that changing ankle inversion/eversion torque on each step, in response to changes in body state, could assist with balance. In this study, we investigated the effects of ankle inversion/eversion torque modulation on balance-related effort among amputees (N = 5) using a multi-actuated ankle-foot prosthesis emulator. In stabilizing conditions, changes in ankle inversion/eversion torque were applied so as to counteract deviations in side-to-side center-of-mass acceleration at the moment of intact-limb toe off; higher acceleration toward the prosthetic limb resulted in a corrective ankle inversion torque during the ensuing stance phase. Destabilizing controllers had the opposite effect, and a zero gain controller made no changes to the nominal inversion/eversion torque. To separate the balance-related effects of step-to-step control from the potential effects of changes in average mechanics, average ankle inversion/eversion torque and prosthesis work were held constant across conditions. High-gain stabilizing control lowered metabolic cost by 13% compared to the zero gain controller (p = 0.05). We then investigated individual responses to subject-specific stabilizing controllers following an enforced exploration period. Four of five participants experienced reduced metabolic rate compared to the zero gain controller (−15, −14, −11, −6, and +4%) an average reduction of 9% (p = 0.05). Average prosthesis mechanics were unchanged across all conditions, suggesting that improvements in energy economy might have come from changes in step-to-step corrections related to balance. Step-to-step modulation of inversion/eversion torque could be used in new, active ankle-foot prostheses to reduce walking effort associated with maintaining balance.

Control of locomotor stability in stabilizing and destabilizing environments

To develop effective interventions targeting locomotor stability, it is crucial to understand how people control and modify gait in response to changes in stabilization requirements. Our purpose was to examine how individuals with and without incomplete spinal cord injury (iSCI) control lateral stability in haptic walking environments that increase or decrease stabilization demands. We hypothesized that people would adapt to walking in a predictable, stabilizing viscous force field and unpredictable destabilizing force field by increasing and decreasing feedforward control of lateral stability, respectively. Adaptations in feedforward control were measured using after-effects when fields were removed. Both groups significantly (p<0.05) decreased step width in the stabilizing field. When the stabilizing field was removed, narrower steps persisted in both groups and subjects with iSCI significantly increased movement variability (p<0.05). The after-effect of walking in the stabilizing field was a suppression of ongoing general stabilization mechanisms. In the destabilizing field, subjects with iSCI took faster steps and increased lateral margins of stability (p<0.05). Step frequency increases persisted when the destabilizing field was removed (p<0.05), suggesting that subjects with iSCI made feedforward adaptions to increase control of lateral stability. In contrast, in the destabilizing field, non-impaired subjects increased movement variability (p<0.05) and did not change step width, step frequency, or lateral margin of stability (p>0.05). When the destabilizing field was removed, increases in movement variability persisted (p<0.05), suggesting that non-impaired subjects made feedforward decreases in resistance to perturbations.