Evaluation of a Powered Ankle-Foot Prosthetic System During Walking

Greater than recommended stiffness and power setting of a stance-phase powered leg prosthesis can improve step-to-step transition work and effective foot length ratio during walking in people with transtibial amputation

People with unilateral transtibial amputation (TTA) using a passive-elastic prosthesis exhibit lower positive affected leg trailing work (ALtrail Wpos) and a greater magnitude of negative unaffected leg leading work (ULlead Wneg) during walking than non-amputees, which may increase joint pain and osteoarthritis risk in the unaffected leg. People with TTA using a stance-phase powered prosthesis (e.g., BiOM, Ottobock, Duderstadt, Germany) walk with increased ALtrail Wpos and potentially decreased magnitude of ULlead Wneg compared to a passive-elastic prosthesis. The BiOM includes a passive-elastic prosthesis with a manufacturer-recommended stiffness category and can be tuned to different power settings, which may change ALtrail Wpos, ULlead Wneg, and the prosthesis effective foot length ratio (EFLR). Thirteen people with TTA walked using 16 different prosthetic stiffness category and power settings on a level treadmill at 0.75-1.75 m/s. We constructed linear mixed effects models to determine the effects of stiffness category and power settings on ALtrail Wpos, ULlead Wneg, and EFLR and hypothesized that decreased stiffness and increased power would increase ALtrail Wpos, not change and decrease ULlead Wneg magnitude, and decrease and not change prosthesis EFLR, respectively. We found there was no significant effect of stiffness category on ALtrail Wpos but increased stiffness reduced ULlead Wneg magnitude, perhaps due to a 0.02 increase in prosthesis EFLR compared to the least stiff category. Furthermore, we found that use of the BiOM with 10% and 20% greater than recommended power increased ALtrail Wpos and decreased ULlead Wneg magnitude at 0.75-1.00 m/s. However, prosthetic power setting depended on walking speed so that use of the BiOM increased ULlead Wneg magnitude at 1.50-1.75 m/s compared to a passive-elastic prosthesis. Ultimately, our results suggest that at 0.75-1.00 m/s, prosthetists should utilize the BiOM attached to a passive-elastic prosthesis with an increased stiffness category and power settings up to 20% greater than recommended based on biological ankle values. This prosthetic configuration can allow people with unilateral transtibial amputation to increase ALtrail Wpos and minimize ULlead Wneg magnitude, which could reduce joint pain and osteoarthritis risk in the unaffected leg and potentially lower the metabolic cost of walking.

Design and preliminary verification of a novel powered ankle-foot prosthesis: From the perspective of lower-limb biomechanics compared with ESAR foot

A novel powered ankle-foot prosthesis is designed. The effect of wearing the novel prosthesis and an energy-storage-and-return (ESAR) foot on lower-limb biomechanics is investigated to preliminarily evaluate the design. With necessary auxiliary materials, a non-amputated subject (a rookie at using prostheses) is recruited to walk on level ground with an ESAR and the novel powered prostheses separately. The results of the stride characteristics, the ground reaction force (GRF) components, kinematics, and kinetics in the sagittal plane are compared. Wearing the powered prosthesis has less prolongation of the gait cycle on the unaffected side than wearing the ESAR foot. Wearing ESAR or proposed powered prostheses influences the GRF, kinematics, and kinetics on the affected and unaffected sides to some extent. Thereinto, the knee moment on the affected side is influenced most. Regarding normal walking as the reference, among the total of 15 indexes, the influences of wearing the proposed powered prosthesis on six indexes on the affected side (ankle's/knee's/hip's angles, hip's moment, and Z- and X-axis GRF components) and five indexes on the unaffected side (ankle's/knee's/hip's angles and ankle's/hip's moments) are slighter than those of wearing the ESAR foot. The influences of wearing the powered prosthesis on two indexes on the unaffected side (knee's moment and X-axis GRF component) are similar to those of wearing the ESAR foot. The greatest improvement of wearing the powered prosthesis is to provide further plantarflexion after reaching the origin of the ankle joint before toe-off, which means that the designed powered device can provide further propulsive power for the lifting of the human body's centre of gravity during walking on level ground. The results demonstrate that wearing the novel powered ankle-foot prosthesis benefits the rookie in recovering the normal gait more than wearing the ESAR foot.

A comprehensive dataset on biomechanics and motor control during human walking with discrete mechanical perturbations

Background

Humans have a remarkable capability to maintain balance while walking. There is, however, a lack of publicly available research data on reactive responses to destabilizing perturbations during gait.

Methods

Here, we share a comprehensive dataset collected from 10 participants who experienced random perturbations while walking on an instrumented treadmill. Each participant performed six 5-min walking trials at a rate of 1.2 m/s, during which rapid belt speed perturbations could occur during the participant's stance phase. Each gait cycle had a 17% probability of being perturbed. The perturbations consisted of an increase of belt speed by 0.75 m/s, delivered with equal probability at 10%, 20%, 30%, 40%, 50%, 60%, 70%, or 80% of the stance phase. Data were recorded using motion capture with 25 markers, eight inertial measurement units (IMUs), and electromyography (EMG) from the tibialis anterior (TA), soleus (SOL), lateral gastrocnemius (LG), rectus femoris (RF), vastus lateralis (VL), vastus medialis (VM), biceps femoris (BF), and gluteus maximus (GM). The full protocol is described in detail.

Results

We provide marker trajectories, force plate data, EMG data, and belt speed information for all trials and participants. IMU data is provided for most participants. This data can be useful for identifying neural feedback control in human gait, biologically inspired control systems for robots, and the development of clinical applications.

Gait quality in prosthesis users is reflected by force-based metrics when learning to walk on a new research-grade powered prosthesis

Introduction

Powered prosthetic feet require customized tuning to ensure comfort and long-term success for the user, but tuning in both clinical and research settings is subjective, time intensive, and the standard for tuning can vary depending on the patient's and the prosthetist's experience levels.

Methods

Therefore, we studied eight different metrics of gait quality associated with use of a research-grade powered prosthetic foot in seven individuals with transtibial amputation during treadmill walking. We compared clinically tuned and untuned conditions with the goal of identifying performance-based metrics capable of distinguishing between good (as determined by a clinician) from poor gait quality.

Results

Differences between the tuned and untuned conditions were reflected in ankle power, both the vertical and anterior-posterior impulse symmetry indices, limb-force alignment, and positive ankle work, with improvements seen in all metrics during use of the tuned prosthesis.

Discussion

Notably, all of these metrics relate to the timing of force generation during walking which is information not directly accessible to a prosthetist during a typical tuning process. This work indicates that relevant, real-time biomechanical data provided to the prosthetist through the future provision of wearable sensors may enhance and improve future clinical tuning procedures associated with powered prostheses as well as their long-term outcomes.

The development of rating scales to evaluate experiential prosthetic foot preference for people with lower limb amputation

BACKGROUND

Selection of a foot is an important aspect of prosthetic prescription and vital to maximizing mobility and functional goals after lower limb amputation. Development of a standardized approach to soliciting user experiential preferences is needed to improve evaluation and comparison of prosthetic feet.

OBJECTIVE

To develop rating scales to assess prosthetic foot preference and to evaluate use of these scales in people with transtibial amputation after trialing different prosthetic feet.

DESIGN

Participant-blinded, repeated measures crossover trial.

SETTING

Veterans Affairs and Department of Defense Medical Centers, laboratory setting.

PARTICIPANTS

Seventy-two male prosthesis users with unilateral transtibial amputation started, and 68 participants completed this study.

INTERVENTIONS

Participants trialed three mobility-level appropriate commercial prosthetic feet briefly in the laboratory.

MAIN OUTCOME MEASURES

"Activity-specific" rating scales were developed to assess participants' ability with a given prosthetic foot to perform typical mobility activities (eg, walking at different speeds, on inclines, and stairs) and "global" scales to rate overall perceived energy required to walk, satisfaction, and willingness to regularly use the prosthetic foot. Foot preference was determined by comparing the rating scale scores, after laboratory testing.

RESULTS

The greatest within-participant differences in scores among feet were observed in the "incline" activity, where 57% ± 6% of participants reported 2+ point differences. There was a significant association (p < .05) between all "activity-specific" rating scores (except standing) and each "global" rating score.

CONCLUSIONS

The standardized rating scales developed in this study could be used to assess prosthetic foot preference in both the research and clinical settings to guide prosthetic foot prescription for people with lower limb amputation capable of a range of mobility levels.

Effects of a Powered Ankle-Foot Prosthesis and Physical Therapy on Function for Individuals With Transfemoral Limb Loss: Rationale, Design, and Protocol for a Multisite Clinical Trial

BACKGROUND

Powered ankle-foot prosthetic devices can generate net positive mechanical work during gait, which mimics the physiological ankle. However, gait deviations can persist in individuals with transfemoral limb loss because of habit or lack of rehabilitation. Prosthetic research efforts favor the design or evaluation of prosthetic componentry and rarely incorporate any type of rehabilitation, despite evidence suggesting that it is critical for minimizing gait imbalances. Given the accelerated rate of innovation in prosthetics, there is a fundamental knowledge gap concerning how individuals with transfemoral limb loss should learn to correctly use powered ankle-foot devices for maximum functional benefit. Because of the recent advances in prosthetic technology, there is also a critical unmet need to develop guidelines for the prescription of advanced prosthetic devices that incorporate both physical and psychological components to identify appropriate candidates for advanced technology.

OBJECTIVE

The primary goal of this investigation is to examine the roles of advanced prosthetic technology and a device-specific rehabilitative intervention on gait biomechanics, functional efficacy, and pain in individuals with transfemoral limb loss. The secondary goal is to develop preliminary rehabilitation guidelines for advanced lower limb prosthetic devices to minimize gait imbalances and maximize function and to establish preliminary guidelines for powered ankle-foot prosthetic prescription.

METHODS

This prospective, multisite study will enroll 30 individuals with unilateral transfemoral limb loss. At baseline, participants will undergo a full gait analysis and assessment of function, neurocognition, cognitive load, subjective preferences, and pain using their current passive prosthesis. The participants will then be fitted with a powered ankle-foot device and randomized into 2 equal groups: a powered device with a device-specific rehabilitation intervention (group A) or a powered device with the current standard of practice (group B). Group A will undergo 4 weeks of device-specific rehabilitation. Group B will receive the current standard of practice, which includes basic device education but no further device-specific rehabilitation. Data collection procedures will then be repeated after 4 weeks and 8 weeks of powered ankle use.

RESULTS

This study was funded in September 2017. Enrollment began in September 2018. Data collection will conclude by March 2024. The initial dissemination of results is expected in August 2024.

CONCLUSIONS

The projected trends indicate that the number of individuals with limb loss will dramatically increase in the United States. The absence of effective, evidence-based interventions may make individuals with transfemoral limb loss more susceptible to increased secondary physical conditions and degenerative changes. With this expected growth, considerable resources will be required for prosthetic and rehabilitation services. Identifying potential mechanisms for correcting gait asymmetries, either through advanced prosthetic technology or rehabilitative interventions, can provide a benchmark for understanding the optimal treatment strategies for individuals with transfemoral limb loss.

TRIAL REGISTRATION

ClinicalTrials.gov NCT03625921; https://clinicaltrials.gov/study/NCT03625921.

INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID)

DERR1-10.2196/53412.

Ankle and Foot Arthroplasty and Prosthesis: A Review on the Current and Upcoming State of Designs and Manufacturing

The foot and ankle serve vital roles in weight bearing, balance, and flexibility but are susceptible to many diverse ailments, making treatment difficult. More commonly, Total Ankle Arthroplasty (TAA) and Total Talus Replacement (TTR) are used for patients with ankle degeneration and avascular necrosis of the talus, respectively. Ankle prosthesis and orthosis are also indicated for use with lower limb extremity amputations or locomotor disability, leading to the development of powered exoskeletons. However, patient outcomes remain suboptimal, commonly due to the misfitting of implants to the patient-specific anatomy. Additive manufacturing (AM) is being used to create customized, patient-specific implants and porous implant cages that provide structural support while allowing for increased bony ingrowth and to develop customized, lightweight exoskeletons with multifunctional actuators. AM implants and devices have shown success in preserving stability and mobility of the joint and achieving fast recovery, as well as significant improvements in gait rehabilitation, gait assistance, and strength for patients. This review of the literature highlights various devices and technologies currently used for foot and ankle prosthesis and orthosis with deep insight into improvements from historical technologies, manufacturing methods, and future developments in the biomedical space.

A Scientometric Analysis and Visualization of Prosthetic Foot Research Work: 2000 to 2022

This study aims to highlight recent research work on topics around prosthetic feet through a scientometric analysis and historical review. The most cited publications from the Clarivate Analytics Web of Science Core Collection database were identified and analyzed from 1 January 2000 to 31 October 2022. Original articles, reviews with full manuscripts, conference proceedings, early access documents, and meeting abstracts were included. A scientometric visualization analysis of the bibliometric information related to the publications, including the countries, institutions, journals, references, and keywords, was conducted. A total of 1827 publications met the search criteria in this study. The related publications grouped by year show an overall trend of increase during the two decades from 2000 to 2022. The United States is ranked first in terms of overall influence in this field (n = 774). The Northwestern University has published the most papers on prosthetic feet (n = 84). Prosthetics and Orthotics International has published the largest number of studies on prosthetic feet (n = 151). During recent years, a number of studies with citation bursts and burst keywords (e.g., diabetes, gait, pain, and sensor) have provided clues on the hotspots of prosthetic feet and prosthetic foot trends. The findings of this study are based on a comprehensive analysis of the literature and highlight the research topics on prosthetic feet that have been primarily explored. The data provide guidance to clinicians and researchers to further studies in this field.

A low-power ankle-foot prosthesis for push-off enhancement

Passive ankle-foot prostheses are light-weighted and reliable, but they cannot generate net positive power, which is essential in restoring the natural gait pattern of amputees. Recent robotic prostheses addressed the problem by actively controlling the storage and release of energy generated during the stance phase through the mechanical deformation of elastic elements housed in the device. This study proposes an innovative low-power active prosthetic module that fits on off-the-shelf passive ankle-foot energy-storage-and-release (ESAR) prostheses. The module is placed parallel to the ESAR foot, actively augmenting the energy stored in the foot and controlling the energy return for an enhanced push-off. The parallel elastic actuation takes advantage of the amputee's natural loading action on the foot's elastic structure, retaining its deformation. The actuation unit is designed to additionally deform the foot and command the return of the total stored energy. The control strategy of the prosthesis adapts to changes in the user's cadence and loading conditions to return the energy at a desired stride phase. An early verification on two transtibial amputees during treadmill walking showed that the proposed mechanism could increase the subjects' dorsiflexion peak of 15.2% and 41.6% for subjects 1 and 2, respectively, and the cadence of about 2%. Moreover, an increase of 26% and 45% was observed in the energy return for subjects 1 and 2, respectively.

Full body musculoskeletal model for simulations of gait in persons with transtibial amputation

This paper describes the development, properties, and evaluation of a musculoskeletal model that reflects the anatomical and prosthetic properties of a transtibial amputee using OpenSim. Average passive prosthesis properties were used to develop CAD models of a socket, pylon, and foot to replace the lower leg. Additional degrees of freedom (DOF) were included in each joint of the prosthesis for potential use in a range of research areas, such as socket torque and socket pistoning. The ankle has three DOFs to provide further generality to the model. Seven transtibial amputee subjects were recruited for this study. 3 D motion capture, ground reaction force, and electromyographic (EMG) data were collected while participants wore their prescribed prosthesis, and then a passive prototype prosthesis instrumented with a 6-DOF load cell in series with the pylon. The model's estimates of the ankle, knee, and hip kinematics comparable to previous studies. The load cell provided an independent experimental measure of ankle joint torque, which was compared to inverse dynamics results from the model and showed a 7.7% mean absolute error. EMG data and muscle outputs from OpenSim's Static Optimization tool were qualitatively compared and showed reasonable agreement. Further improvements to the muscle characteristics or prosthesis-specific foot models may be necessary to better characterize individual amputee gait. The model is open-source and available at (https://simtk.org/projects/biartprosthesis) for other researchers to use to advance our understanding and amputee gait and assist with the development of new lower limb prostheses.

Therapeutic benefits of lower limb prostheses: a systematic review

BACKGROUND

Enhancing the quality of life of people with a lower limb amputation is critical in prosthetic development and rehabilitation. Yet, no overview is available concerning the impact of passive, quasi-passive and active ankle-foot prostheses on quality of life.

OBJECTIVE

To systematically review the therapeutic benefits of performing daily activities with passive, quasi-passive and active ankle-foot prostheses in people with a lower limb amputation.

METHODS

We searched the Pubmed, Web of Science, Scopus and Pedro databases, and backward citations until November 3, 2021. Only English-written randomised controlled trials, cross-sectional, cross-over and cohort studies were included when the population comprised individuals with a unilateral transfemoral or transtibial amputation, wearing passive, quasi-passive or active ankle-foot prostheses. The intervention and outcome measures had to include any aspect of quality of life assessed while performing daily activities. We synthesised the participants' characteristics, type of prosthesis, intervention, outcome and main results, and conducted risk of bias assessment using the Cochrane risk of bias tool. This study is registered on PROSPERO, number CRD42021290189.

RESULTS

We identified 4281 records and included 34 studies in total. Results indicate that quasi-passive and active prostheses are favoured over passive prostheses based on biomechanical, physiological, performance and subjective measures in the short-term. All studies had a moderate or high risk of bias.

CONCLUSION

Compared to passive ankle-foot prostheses, quasi-passive and active prostheses significantly enhance the quality of life. Future research should investigate the long-term therapeutic benefits of prosthetics devices.

Microprocessor-Controlled Prostheses for a Bilateral Transtibial Amputee with Gait Analysis and Satisfaction: A 1-Year Followup Case Report

Bilateral amputees are disadvantaged as they lack healthy leg support. We present the rare case of a bilateral transtibial amputee (BTA), in which we compared the first South Korean-made microprocessor-controlled prosthesis (MPA) to a conventional prosthetic ankle (CPA) with gait analysis and a patient questionnaire for long-term outcomes. A 70-year-old man presented with bilateral transtibial amputations from injury. Assessments were performed after wearing an MPA for 1 month and 1 year with three-dimensional gait analysis. Satisfaction, mobility, and pain were evaluated using the Korean version of the Prostheses Evaluation Questionnaire (K-PEQ). The spatiotemporal parameters of both sides showed increased stability from the CPA to 1 month (mMPA) and 1 year (yMPA). We observed an increased single support time, decreased step width, and almost normal stance-swing time ratio. In kinematic parameters, the ankle range of motion (ROM) was bilaterally increased at mMPA and yMPA. Unfortunately, the MPA gait showed insufficient ankle plantarflexion during the terminal stance that failed to generate push-up power. As the MPA adaptation time increased, the symmetry ratio improved to a balanced value. The questionnaire-based investigations of satisfaction, mobility, and pain revealed excellent results. The MPA proved helpful for ankle mobility in the BTA, and the questionnaire showed good satisfaction and mobility in varied terrain.

Design optimization of powered ankle prosthesis to reduce peak power requirement

The aim of the prosthetic devices is to replicate the able-bodied angle-torque profile of a healthy human during locomotion. A lightweight and energy-efficient ankle joint is able to lower the actuator peak power and/or energy consumption per gait cycle, while adequately fulfilling the profile matching constraints. This study presents the design optimization of the prosthetic ankle joint containing an elastic element and actuator coupled with a rigid triangular part. The dimensions of the ankle joint triangular part were optimized to minimize actuator peak power and maximize spring energy within its elastic limits. As a result of series simulation tests, at 1.1 and 1.6 m/s walking speeds, the simulation of dorsi/plantar flexion shows up to 78.8% and 66.98% reduction in motor peak power compared to a direct drive system, respectively. Low power ankle-prosthetic device that closely matches the angle-torque profile of a healthy human's ankle, is one of the key parameters for the cost-effectiveness of lower limb prostheses.

Design and Evaluation of a Knee Flexion Assistance Exoskeleton for People with Transtibial Amputation

People with below-knee amputation walk with asymmetric gaits that over time can lead to further musculoskeletal disorders and decreased quality of life. While prosthesis technology is improving, prosthetic ankles may be fundamentally limited in their ability to restore healthy walking patterns because they do not assist the residual knee joint. The knee on the residual limb has muscular deficits due to the loss of the gastrocnemius, a biarticular muscle that crosses both the ankle and knee. Here we present the design, development, and preliminary evaluation of a robotic knee exoskeleton for people with transtibial amputation. The device is intended to restore gastrocnemius-like flexion moments to the knee on the residual limb. The exoskeleton uses a custom offboard actuation and control system to allow for a simple and lightweight design with high torque capabilities. A preliminary walking experiment with one person with transtibial amputation was conducted. The exoskeleton provided a range of knee flexion torque profiles and had an RMS tracking error of 1.9 Nm across four assistance conditions. This device will be used in future studies to explore the effects of providing knee flexion assistance to people with transtibial amputation during walking. Long term, findings from studies with this exoskeleton could motivate future assistive device designs that improve walking mechanics and quality of life for people with limb loss.

Functional Mobility Training With a Powered Knee and Ankle Prosthesis

Limb loss at the transfemoral or knee disarticulation level results in a significant decrease in mobility. Powered lower limb prostheses have the potential to provide increased functional mobility and return individuals to activities of daily living that are limited due to their amputation. Providing power at the knee and/or ankle, new and innovative training is required for the amputee and the clinician to understand the capabilities of these advanced devices. This protocol for functional mobility training with a powered knee and ankle prosthesis was developed while training 30 participants with a unilateral transfemoral or knee disarticulation amputation at a nationally ranked physical medicine and rehabilitation research hospital. Participants received instruction for level-ground walking, stair climbing, incline walking, and sit-to-stand transitions. A therapist provided specific training for each mode including verbal, visual, and tactile cueing along with patient education on the functionality of the device. The primary outcome measure was the ability of each participant to demonstrate independence with walking and sit-to-stand transitions along with modified independence for stair climbing and incline walking due to the use of a handrail. Every individual was successful in comfortable ambulation of level-ground walking and 27 out of 30 were successful in all other functional modes after participating in 1–3 sessions of 1–2 h in length (3 terminated their participation before attempting all activities). As these prosthetic devices continue to advance, therapy techniques must advance as well, and this paper serves as education on new training techniques that can provide amputees with the best possible tools to take advantage of these powered devices to achieve their desired clinical outcomes.

Energy storage and stress-strain characteristics of a prosthetic foot: a priori design and analysis with experiments

This work proposes an experimentally validated numerical approach for a systematic a priori evaluation of the energy storage and stress-strain characteristics of a prosthetic foot during the stance phase of walking. Boundary conditions replicating the rocker based inverted pendulum model were incorporated. The mechanically complex Ottobock Solid Ankle Cushioned Heel (SACH) foot was opted as the test device. A non-linear finite element (FE) model of the device was developed inclusive of its sources of non-linearity. A custom rig was fabricated to investigate the prosthetic foot's mechanics in a gait analysis facility and experimentally validate the finite element approach. The numerical and experimental outcomes showed fair agreement, with the centre of pressure at the foot-floor interface deviating by 1.56 mm at the instance of highest strain. The magnitude and the distribution of the energy stored and a series of stress and strain parameters were analyzed for the test device using the proposed approach. The novel methodology proposed may act as an effective tool for the design, analysis, and prescription of energy storage and return prosthetic feet.

Biomechanical Impacts of Toe Joint With Transfemoral Amputee Using a Powered Knee-Ankle Prosthesis

Transfemoral amputees are currently forced to utilize energetically passive prostheses that provide little to no propulsive work. Among the several joints and muscles required for healthy walking, the ones most vital for push-off assistance include the knee, ankle, and metatarsophalangeal (MTP) joints. There are only a handful of powered knee-ankle prostheses (also called powered transfemoral prostheses) in literature and few of them comprise a toe-joint. However, no one has researched the impact of toe-joint stiffness on walking with a power transfemoral prosthesis. This study is aimed at filling this gap in knowledge. We conducted a study with an amputee and a powered transfemoral prosthesis consisting of a spring loaded toe-joint. The prosthesis's toe-joint stiffness was varied between three values: 0.83 Nm/deg, 1.25 Nm/deg, and infinite (rigid). This study found that 0.83 Nm/deg stiffness reduced push-off assistance and resulted in compensatory movements that could lead to issues over time. While the joint angles and moments did not considerably vary across 1.25 Nm/deg and rigid stiffness, the latter led to greater power generation on the prosthesis side. However, the 1.25 Nm/deg joint stiffness resulted in the least power production from the intact side. We, thus, concluded that the use of a stiff toe-joint with a powered transfemoral prosthesis can reduce the cost of transport of the intact limb.

Toward Developing a Powered Ankle-Foot Prosthesis With Electromyographic Control to Enhance Functional Performance: A Case Study in a U.S. Service Member

The only commercially available ankle-foot prosthesis with powered propulsion lacks ruggedization and other capabilities for service members seeking to return to duty and/or other physically demanding activities. Here, we evaluated a ruggedized powered ankle-foot prosthesis with electromyographic control ("Warrior Ankle"; WA) in an experienced male user of the predicate (Empower) prosthesis. The participant (age = 56 years, mass = 86.8 kg, stature = 173 cm) completed a 650 m simulated hike with varying terrain at a fixed, self-selected speed in the WA and predicate prosthesis, with and without a 22.8 kg weighted vest ("loaded" and "unloaded," respectively). Peak dorsiflexion and plantarflexion angles were extracted from each gait cycle throughout the simulated hike (∼500 prosthetic-side steps). The participant walked faster with the WA (1.15 m/s) compared to predicate (0.80 m/s) prosthesis. On the prosthetic side, peak dorsiflexion angles were larger for the WA (loaded: 27.9°; unloaded: 26.9°) compared to the predicate (loaded: 19.4°; unloaded: 21.3°); peak plantarflexion angles were similar between prostheses and loading conditions [WA (loaded: 15.5°; unloaded: 14.9°), predicate (loaded: 16.9°; unloaded: 14.8°). The WA better accommodated the varying terrain profile, evidenced by greater peak dorsiflexion angles, as well as dorsiflexion and plantarflexion angles that more closely matched or exceeded those of the innate ankle [dorsiflexion (WA: 31.6°, predicate: 27.5°); plantarflexion (WA: 20.7°, predicate: 20.5°)]. Furthermore, the WA facilitated a faster walking speed, suggesting a greater functional capacity with the WA prosthesis. Although further design enhancements are needed, this case study demonstrated feasibility of a proof-of-concept, ruggedized powered ankle-foot prosthesis with electromyographic control.

Free-Living User Perspectives on Musculoskeletal Pain and Patient-Reported Mobility With Passive and Powered Prosthetic Ankle-Foot Components: A Pragmatic, Exploratory Cross-Sectional Study

Introduction

Studies with a powered prosthetic ankle-foot (PwrAF) found a reduction in sound knee loading compared to passive feet. Therefore, the aim of the present study was to determine whether anecdotal reports on reduced musculoskeletal pain and improved patient-reported mobility were isolated occurrences or reflect a common experience in PwrAF users.

Methods

Two hundred and fifty individuals with transtibial amputation (TTA) who had been fitted a PwrAF in the past were invited to an online survey on average sound knee, amputated side knee, and low-back pain assessed with numerical pain rating scales (NPRS), the PROMIS Pain Interference scale, and the PLUS-M for patient-reported mobility in the free-living environment. Subjects rated their current foot and recalled the ratings for their previous foot. Recalled scores were adjusted for recall bias by clinically meaningful amounts following published recommendations. Statistical comparisons were performed using Wilcoxon's signed rank test.

Results

Forty-six subjects, all male, with unilateral TTA provided data suitable for analysis. Eighteen individuals (39%) were current PwrAF users, whereas 28 subjects (61%) had reverted to a passive foot. After adjustment for recall bias, current PwrAF users reported significantly less sound knee pain than they recalled for use of a passive foot (−0.5 NPRS, p = 0.036). Current PwrAF users who recalled sound knee pain ≥4 NPRS with a passive foot reported significant and clinically meaningful improvements in sound knee pain (−2.5 NPRS, p = 0.038) and amputated side knee pain (−3 NPRS, p = 0.042). Current PwrAF users also reported significant and clinically meaningful improvements in patient-reported mobility (+4.6 points PLUS-M, p = 0.016). Individuals who had abandoned the PwrAF did not recall any differences between the feet.

Discussion

Current PwrAF users reported significant and clinically meaningful improvements in patient-reported prosthetic mobility as well as sound knee and amputated side knee pain compared to recalled mobility and pain with passive feet used previously. However, a substantial proportion of individuals who had been fitted such a foot in the past did not recall improvements and had reverted to passive feet. The identification of individuals with unilateral TTA who are likely to benefit from a PwrAF remains a clinical challenge and requires further research.

Evaluation of a quasi-passive biarticular prosthesis to replicate gastrocnemius function in transtibial amputee gait

Lower limb amputees experience gait impairments, in part due to limitations of prosthetic limbs and the lack of a functioning biarticular gastrocnemius (GAS) muscle. Energy storing prosthetic feet restore the function of the soleus, but not GAS. We propose a transtibial prosthesis that implements a spring mechanism to replicate the GAS. A prototype Biarticular Prosthesis (BP) was tested on seven participants with unilateral transtibial amputation. Participants walked on an instrumented treadmill with motion capture, first using their prescribed prosthesis, then with the BP in four different spring stiffness conditions. A custom OpenSim musculoskeletal model, including the BP, was used to estimate kinematics, joint torques, and muscle forces. Kinematic symmetry was evaluated by comparing the amputated and intact angles of the ankle, knee, and hip. The BP knee and ankle torques were compared to the intact GAS. Finally, work done by the BP spring was calculated at the ankle and knee. There were no significant differences between conditions in kinematic symmetry, indicating that the BP performs similarly to prescribed prostheses. When comparing the BP torques to intact GAS, higher spring stiffness better approximated peak GAS torques, but those peaks occurred earlier in the gait cycle. The BP spring did positive work on the knee joint and negative work on the ankle joint, and this work increased as BP spring stiffness increased. The BP has the potential to improve amputee gait compensations associated with the lack of biarticular GAS function, which may reduce their walking effort and improve quality of life.

Taking Both Sides: Seeking Symbiosis Between Intelligent Prostheses and Human Motor Control during Locomotion

Robotic lower-limb prostheses aim to replicate the power-generating capability of biological joints during locomotion to empower individuals with lower-limb loss. However, recent clinical trials have not demonstrated clear advantages of these devices over traditional passive devices. We believe this is partly because the current designs of robotic prothesis controllers and clinical methods for fitting and training individuals to use them do not ensure good coordination between the prosthesis and user. Accordingly, we advocate for new holistic approaches in which human motor control and intelligent prosthesis control function as one system (defined as human-prosthesis symbiosis). We hope engineers and clinicians will work closely to achieve this symbiosis, thereby improving the functionality and acceptance of robotic prostheses and users' quality of life.

Patient-reported Outcome Measures following Traumatic Lower Extremity Amputation: A Systematic Review and Meta-analysis

BACKGROUND

Outcomes after traumatic major lower extremity amputation (MLEA) have focused on surgical complications, despite the life-altering impact on patients. With advances in the surgical management of MLEA, a heightened need for consistent reporting of patient-centered outcomes (PCO) remains. This meta-analysis assesses articles for the prevalence and methods of PCO reporting among traumatic MLEA studies.

METHODS

An electronic database search was completed using Ovid MEDLINE for studies published between 2000 and 2020. Studies were included that reported any outcome of traumatic MLEA. Weighted means of outcomes were calculated when data were available. The prevalence of PCO was assessed in the categories of physical function, quality of life (QOL), psychosocial, and pain. Trends in PCO reporting were analyzed using Pearson's chi-squared test and analysis of variance when appropriate.

RESULTS

In total, 7001 studies were screened, yielding 156 articles for inclusion. PCO were evaluated in 94 (60.3%) studies; 83 (53.2%) reported physical function and mobility outcomes, 33 (21.2%) reported QOL and satisfaction measures, 38 (24.4%) reported psychosocial data, and 43 (27.6%) reported pain outcomes. There was no change in prevalence of PCO reporting when comparing 5-year intervals between 2000 and 2020 (P = 0.557).

CONCLUSIONS

Optimization of function and QOL following traumatic MLEA has become a cornerstone of surgical success; however, only 60% of studies report PCO, with no trend over the last two decades suggesting improvement. As healthcare progresses toward patient-centered care, this inconsistent means of reporting PCO calls for improved inclusion and standardization of instruments to assess function, QOL, and other patient-focused measures.

The effect of powered ankle prostheses on muscle activity during walking

Individuals with transtibial amputation (TTA) walk with greater muscle activity and metabolic costs than non-amputees. Powered prostheses aim to address these deficits by replicating the active function of the biological ankle. The purpose of this study was to determine if people with TTA alter muscle activity when walking with a powered prosthesis, and if this change relates to changes in metabolic costs. Ten individuals with TTA and 10 non-amputees walked on a treadmill while we measured metabolic cost and muscle activity from 16 lower limb muscles. Participants with TTA walked with their prescribed unpowered prosthesis and a commercial powered prosthesis (BiOM T2, Bedford, MA, USA), in random order. The integrated EMG across the gait cycle was greater with the powered prosthesis for the intact limb gluteus medius (p = 0.002) and residual limb vastus medialis (p = 0.013). There were several non-significant, moderate-to-strong correlations between changes in muscle activity and changes in metabolic cost between prostheses (p > 0.0504). Decreased muscle activity in the residual limb gluteus medius correlated with lower metabolic cost (r = 0.543). In contrast, lower metabolic cost was correlated with increased residual limb rectus femoris activity (r = -0.627) and increased co-contractions in the residual limb thigh muscles in terminal stance (r = -0.585) and late swing (r = -0.754). Overall, there were no consistent changes in muscle activity in response to the powered prosthesis. The correlations suggest that individuals who can effectively stabilize their residual limb during stance are more likely to benefit metabolically.

Functional performance differences between carbon fiber and fiberglass prosthetic feet

BACKGROUND

Persons with lower limb amputation require increased functionality. The largest category of feet for active individuals with a transtibial amputation is energy storage and return (ESR) feet. These feet are typically constructed of carbon fiber composite materials. Recently, a prosthetic foot composed of a fiberglass composite has emerged in the market. However, there are no comparative studies of these devices.

OBJECTIVES

Compare the biomechanical performance and prosthesis-related quality of life when using a fiberglass prosthetic foot design compared with traditional carbon fiber ESR designs.

STUDY DESIGN

This is a repeated-measures randomized cross-over trial.

METHODS

Gait analysis was performed on 10 experienced male subjects with unilateral transtibial amputations (K-level III) while walking on level ground and a ramp. Patient-reported outcomes were collected using the Prosthesis Evaluation Questionnaire.

RESULTS

Gait data demonstrated increased ankle dorsiflexion (P < .01), similar ankle moments (P = .07), and increased ankle power generation (P = .01) when using the fiberglass foot. The increased power generation occurred at the correct time in the gait cycle such that the timing and magnitude of peak knee flexion was unaffected (P > .19). The fiberglass foot had greater energy absorption during gait (P = .01) with no difference in energy return (P = .37). The subjects expressed improved prosthesis-related quality of life with the fiberglass foot (P = .01).

CONCLUSIONS

The findings of this study demonstrate that the new ESR foot comprising a fiberglass material had better performance than traditional designs using a carbon fiber material.

Shortcomings of human-in-the-loop optimization of an ankle-foot prosthesis emulator: a case series

Human-in-the-loop optimization allows for individualized device control based on measured human performance. This technique has been used to produce large reductions in energy expenditure during walking with exoskeletons but has not yet been applied to prosthetic devices. In this series of case studies, we applied human-in-the-loop optimization to the control of an active ankle-foot prosthesis used by participants with unilateral transtibial amputation. We optimized the parameters of five control architectures that captured aspects of successful exoskeletons and commercial prostheses, but none resulted in significantly lower metabolic rate than generic control. In one control architecture, we increased the exposure time per condition by a factor of five, but the optimized controller still resulted in higher metabolic rate. Finally, we optimized for self-reported comfort instead of metabolic rate, but the resulting controller was not preferred. There are several reasons why human-in-the-loop optimization may have failed for people with amputation. Control architecture is an unlikely cause given the variety of controllers tested. The lack of effect likely relates to changes in motor adaptation, learning, or objectives in people with amputation. Future work should investigate these potential causes to determine whether human-in-the-loop optimization for prostheses could be successful.

The influence of powered prostheses on user perspectives, metabolics, and activity: a randomized crossover trial

BACKGROUND

Powered prosthetic ankles provide battery-powered mechanical push-off, with the aim of reducing the metabolic demands of walking for people with transtibial amputations. The efficacy of powered ankles has been shown in active, high functioning individuals with transtibial amputation, but is less clear in other populations. Additionally, it is unclear how use of a powered prosthesis influences everyday physical activity and mobility.

METHODS

Individuals with unilateral transtibial amputations participated in a randomized clinical trial comparing their prescribed, unpowered prosthesis and the BiOM powered prosthesis. Participants' metabolic costs and self-selected walking speeds were measured in the laboratory and daily step count, daily steps away from home, and walking speed were measured over two weeks of at-home prosthesis use. Participants also rated their perception of mobility and quality of life and provided free-form feedback. Dependent measures were compared between prostheses and the relationships between metabolic cost, perception of mobility, and characteristics of walking in daily life were explored using Pearson's correlations.

RESULTS

Twelve people were randomly allocated to the powered prosthesis first (n = 7) or unpowered prosthesis first (n = 5) and ten completed the full study. There were no differences in metabolic costs (p = 0.585), daily step count (p = 0.995), walking speed in-lab (p = 0.145) and in daily life (p = 0.226), or perception of mobility between prostheses (p ≥ 0.058). Changes varied across participants, however. There were several medium-sized effects for device comparisons. With the powered prosthesis, participants had increased self-reported ambulation (g = 0.682) and decreased frustration (g = 0.506).

CONCLUSIONS

There were no universal benefits of the powered prosthesis on function in the lab or home environment. However, the effects were subject-specific, with some reporting preference for power and improved mobility, and some increasing their activity and decreasing their metabolic effort. Additionally, self-reported preferences did not often correlate with objective measures of function. This highlights the need for future clinical research to include both perception and objective measures to better inform prosthetic prescription.

TRIAL REGISTRATION

https://clinicaltrials.gov , #NCT02828982. Registered 12 July 2016, https://clinicaltrials.gov/ct2/show/NCT02828982.

Biomechanical Design and Prototyping of a Powered Ankle-Foot Prosthesis

Powered ankle-foot prostheses for walking often have limitations in the range of motion and in push-off power, if compared to a lower limb of a healthy person. A new design of a powered ankle-foot prosthesis is proposed to obtain a wide range of motion and an adequate power for a push-off step. The design methodology for this prosthesis has three points. In the first one, a dimensionless kinematic model of the lower limb in the sagittal plane is built, through an experimental campaign with healthy subjects, to calculate the angles of lower limb during the gait. In the second point a multibody inverse dynamic model of the lower limb is constructed to calculate the foot-ground contact force, its point of application and the ankle torque too, entering as input data the calculated angles of the lower limb in the previous point. The third point requires, as input of the inverse dynamic model, the first dimensioning data of the ankle-foot prosthesis to obtain the load acting on the components of the prosthesis and the angle torque of the actuator during the gait cycle. Finally, an iteration cycle begins with the inverse dynamic model modifying the ankle torque and angle until these quantities during the gait are as close as possible to the physiological quantities. After the mechanical design and the construction of the prototype of the prosthesis, an experimental methodology was used for preliminary validation of the design. The preliminary tests in the laboratory on the prototype alone show that the range of motion of the ankle angle during the gait is close to a healthy person’s: 27.6° vs. 29°. The pushing force of the distal area of the prototype is 1.000 N, instead of 1.600 N, because a budget reduction forced us to choose components for the prototype with lower performance.

Human-prosthesis coordination: A preliminary study exploring coordination with a powered ankle-foot prosthesis

BACKGROUND

Powered ankle-foot prostheses were developed to replicate the mechanics of the biological ankle by providing positive work during the push-off phase of gait. However, the benefits of powered prostheses on improving overall human gait efficiency (usually quantified by metabolic cost) have not been consistently shown. Here, we have focused on the mechanical work produced at the prosthetic ankle and its interaction with the amputee's movement.

METHODS

Five unilateral transtibial amputees walked on a treadmill using 1) a powered ankle-foot prosthesis and 2) their daily passive device. We determined the net ankle work and ankle work loops on the prosthesis-side to quantify the efficiency of the human-prosthesis physical interaction. We further studied peak propulsion timing and the posture of the amputee's lower limb and prosthesis as indicators of the human-prosthesis coordination. Comparisons were made between the passive and powered prosthesis conditions for each participant.

FINDINGS

The powered prosthesis did not consistently increase net ankle work compared to each participant's passive device. For participants that lacked efficiency in interacting with the powered prosthesis, we observed 1) early prosthesis-side peak propulsion timing (≥ 4% earlier) and 2) a more vertical residual shank at the time of peak propulsion (> 2° more vertical) indicating that the human's limb movement and the prosthesis control during push-off were not well coordinated.

INTERPRETATION

Results from this preliminary study highlight the need for future work to systematically quantify the coordination between the human and powered prosthesis and understand how such coordination at the joint level influences overall gait efficiency.

Movement asymmetry during low and high demand mobility tasks after dysvascular transtibial amputation

BACKGROUND

Movement asymmetries between lower limbs are commonly exhibited by adults after transtibial amputation. However, the degree of movement asymmetry between low- and high-demand functional tasks remains unknown.

METHODS

Kinematic and kinetic data were collected during overground walking (low-demand) and step ascent (high-demand) tasks for two groups: 1) persons with transtibial amputation and 2) healthy matched peers. Analysis of covariance was used to compare sagittal-plane peak knee moment and joint angle (primary) and hip and ankle moments and joint angles, vertical ground reaction force and impulse (secondary).

FINDINGS

Within transtibial amputation group comparisons showed significantly greater between-limb asymmetry in peak knee moment (p < .01), vertical impulse (p < .01), peak vertical ground reaction force (p = .05), peak ankle angle (p < .01) and peak ankle moment (p < .01) with the step ascent task compared to overground walking. The transtibial amputation group had greater between-limb asymmetry during step ascent in peak knee moment (p < .01), vertical impulse (p < .01), peak vertical ground reaction force (p = .04) and peak ankle angle (p < .01) than healthy matched peers. During overground walking, the transtibial amputation group had greater between-limb asymmetry in peak vertical impulse (p = .05) and peak ankle moment (p < .01) than healthy matched peers.

INTERPRETATION

Movement asymmetry is increased during step ascent compared to overground walking for adults with transtibial amputation. While the restoration of overground walking is the focus of post-amputation rehabilitation and prosthetic design, higher demand tasks should also be considered to maximize mobility for adults with transtibial amputation.

Neuromechanical force-based control of a powered prosthetic foot

This article presents a novel neuromechanical force-based control strategy called FMCA (force modulated compliant ankle), to control a powered prosthetic foot. FMCA modulates the torque, based on sensory feedback, similar to neuromuscular control approaches. Instead of using a muscle reflex-based approach, FMCA directly exploits the vertical ground reaction force as sensory feedback to modulate the ankle joint impedance. For evaluation, we first demonstrated how FMCA can predict human-like ankle torque for different walking speeds. Second, we implemented the FMCA in a neuromuscular transtibial amputee walking simulation model to validate if the approach can be used to achieve stable walking and to compare the performance to a neuromuscular reflex-based controller that is already used in a powered ankle. Compared to the neuromuscular model-based approach, the FMCA is a simple solution with a sufficient push-off that can provide stable walking. Third, to assess the ability of the FMCA to generate human-like ankle biomechanics during walking at the preferred speed, we implemented this strategy in a powered prosthetic foot and performed experiments with a non-amputee subject. The results confirm that, for this subject, FMCA can be used to mimic the non-amputee reference ankle torque and the reference ankle angle. The findings of this study support the applicability and advantages of a new bioinspired control approach for assisting amputees. Future experiments should investigate the applicability to other walking speeds and the applicability to the target population.

Prosthetic push-off power in trans-tibial amputee level ground walking: A systematic review

OBJECTIVE

Unilateral trans-tibial amputation signifies a challenge to locomotion. Prosthetic ankle-foot units are developed to mimic the missing biological system which adapts push-off power to walking speed in some new prosthetic ankle-foot designs. The first systematic review including the two factors aims to investigate push-off power differences among Solid Ankle Cushion Heel (SACH), Energy Storage And Return (ESAR) and Powered ankle-foot units (PWR) and their relation to walking speed.

DATA SOURCES

A literature search was undertaken in the Web of Science, PubMed, IEEE xplore, and Google Scholar databases. The search term included: ampu* AND prosth* AND ankle-power AND push-off AND walking.

STUDY APPRAISAL AND SYNTHESIS METHODS

Studies were included if they met the following criteria: unilateral trans-tibial amputees, lower limb prosthesis, reported analysis of ankle power during walking. Data extracted from the included studies were clinical population, type of the prosthetic ankle-foot units (SACH, ESAR, PWR), walking speed, and peak ankle power. Linear regression was used to determine whether the push-off power of different prosthetic ankle-foot units varied regarding walking speed. Push-off power of the different prosthetic ankle-foot units were compared using one-way between subjects' ANOVAs with post hoc analysis, separately for slower and faster walking speeds.

RESULTS

474 publications were retrieved, 28 of which were eligible for inclusion. Correlations between walking speed and peak push-off power were found for ESAR (r = 0.568, p = 0.006) and PWR (r = 0.820, p = 0.000) but not for SACH (r = 0.267, p = 0.522). ESAR and PWR demonstrated significant differences in push-off power for slower and faster walking speeds (ESAR (p = 0.01) and PWR (p = 0.02)).

CONCLUSION

Push-off power can be used as a selection criterion to differentiate ankle-foot units for prosthetic users and their bandwidth of walking speeds.

Preliminary Analysis Of Positive Knee Energy Injection In A Transfemoral Amputee Walking With A Powered Prosthesis

Individuals with lower limb amputations show higher metabolic costs during ambulation than able-bodied individuals. This high metabolic cost may be explained by the inability of available passive prostheses to replicate the biomechanics of intact legs during walking. Powered prostheses promise to address this issue by imitating the power generation of intact legs. Several studies have investigated the effect of power generation and energy injection at the ankle joint in transtibial amputees. In contrast, no study has directly addressed knee power generation in transfemoral amputees. This study investigates the effect of knee power generation in late stance in one transfemoral amputee subject using a lightweight powered prosthesis. Experimental results suggest that injecting positive energy into the gait cycle at the knee level may improve gait ability by reducing effort.

Motorized Biomechatronic Upper and Lower Limb Prostheses-Clinically Relevant Outcomes

People with major limb amputations are severely impaired when it comes to activity, body structure and function, as well as participation. Demographic statistics predict a dramatic increase of this population and additional challenges with their increasing age and higher levels of amputation. Prosthetic use has been shown to have a positive impact on mobility and depression, thereby affecting the quality of life. Biomechatronic prostheses are at the forefront of prosthetic development. Actively powered designs are now regularly used for upper limb prosthetic fittings, whereas for lower limbs the clinical use of actively powered prostheses has been limited to a very low number of applications. Actively powered prostheses enhance restoration of the lost physical functions of an amputee but are yet to allow intuitive user control. This paper provides a review of the status of biomechatronic developments in upper and lower limb prostheses in the context of the various challenges of amputation and the clinically relevant outcomes. Whereas most of the evidence regarding lower limb prostheses addresses biomechanical issues, the evidence for upper limb prostheses relates to activities of daily living (ADL) and instrumental ADL through diverse outcome measures and tools.

A Model-Based Method for Minimizing Reflected Motor Inertia in Off-board Actuation Systems: Applications in Exoskeleton Design

The research and development of wearable robotic devices has been accelerated by off-board control and actuation systems. While off-board robotic actuation systems provide many benefits, the impedance at the robotic joint is often high. High joint impedance is undesirable for wearable devices like exoskeletons, as the user is unable to move their joint without actively controlled motion from the motors. We propose that the impedance can be reduced substantially in off-board robotic actuation systems by minimizing the reflected inertia from the motor. We have developed a model and optimization-based methodology for selecting a motor and set of mechanical design parameters that minimize reflected inertia. This methodology was implemented in the design of an off-board knee exoskeleton as a case study. A grey-box model was developed that incorporates biomechanical knee trajectories, an experimentally determined human-device interface stiffness model, Bowden cable stiffness and friction, and a motor model. A constrained optimization routine was developed that uses the model and a library of157 candidate servo motors to select the actuator and mechanical design parameters that minimize reflected inertia at the exoskeleton joint. We found that S6 of the motors were able to carry out the necessary torque-velocity trajectories to achieve the prescribed exoskeleton joint torques and limb motions. The optimal motor was the Kollmorgen C133A-one of the largest in the library of candidate servo motors and required a 2.25 cm actuator pulley at the knee joint and a 17.5 cm cable sheave at the motor output. This methodology can be adapted by exoskeleton designers to develop more backdriveable exoskeletons and improve experimental capabilities. All code developed for the case study is open-source and freely available online.

Statistical analysis of timeseries data reveals changes in 3D segmental coordination of balance in response to prosthetic ankle power on ramps

Active ankle-foot prostheses generate mechanical power during the push-off phase of gait, which can offer advantages over passive prostheses. However, these benefits manifest primarily in joint kinetics (e.g., joint work) and energetics (e.g., metabolic cost) rather than balance (whole-body angular momentum, H), and are typically constrained to push-off. The purpose of this study was to analyze differences between active and passive prostheses and non-amputees in coordination of balance throughout gait on ramps. We used Statistical Parametric Mapping (SPM) to analyze time-series contributions of body segments (arms, legs, trunk) to three-dimensional H on uphill, downhill, and level grades. The trunk and prosthetic-side leg contributions to H at toe-off when using the active prosthesis were more similar to non-amputees compared to using a passive prosthesis. However, using either a passive or active prosthesis was different compared to non-amputees in trunk contributions to sagittal-plane H during mid-stance and transverse-plane H at toe-off. The intact side of the body was unaffected by prosthesis type. In contrast to clinical balance assessments (e.g., single-leg standing, functional reach), our analysis identifies significant changes in the mechanics of segmental coordination of balance during specific portions of the gait cycle, providing valuable biofeedback for targeted gait retraining.

Choosing appropriate prosthetic ankle work to reduce the metabolic cost of individuals with transtibial amputation

Powered ankle prostheses have been designed to reduce the energetic burden that individuals with transtibial amputation experience during ambulation. There is an open question regarding how much power the prosthesis should provide, and whether approximating biological ankle kinetics is optimal to reduce the metabolic cost of users. We tested 10 individuals with transtibial amputation walking on a treadmill wearing the BiOM powered ankle prosthesis programmed with 6 different power settings (0-100%), including a prosthetist-chosen setting, chosen to approximate biological ankle kinetics. We measured subjects' metabolic cost of transport (COT) and the BiOM's net ankle work during each condition. Across participants, power settings greater than 50% resulted in lower COT than 0% or 25%. The relationship between power setting, COT, and net ankle work varied considerably between subjects, possibly due to individual adaptation and exploitation of the BiOM's reflexive controller. For all subjects, the best tested power setting was higher than the prosthetist-chosen setting, resulting in a statistically significant and meaningful difference in COT between the best tested and prosthetist-chosen power settings. The results of this study demonstrate that individuals with transtibial amputation may benefit from prescribed prosthetic ankle push-off work that exceeds biological norms.

Effect of toe joint stiffness and toe shape on walking biomechanics

During typical human walking, the metatarsophalangeal joints undergo extension/flexion, which we term toe joint articulation. This toe joint articulation impacts locomotor performance, as evidenced by prior studies on prostheses, footwear, sports and humanoid robots. However, a knowledge gap exists in our understanding of how individual toe properties (e.g. shape, joint stiffness) affect bipedal locomotion. To address this gap, we designed and built a pair of adjustable foot prostheses that enabled us to independently vary different toe properties, across a broad range of physiological and non-physiological values. We then characterized the effects of varying toe joint stiffness across a range of different ankle joint stiffness conditions, and the effects of varying toe shape on walking biomechanics. Ten able-bodied individuals walked on a treadmill with prostheses mounted bilaterally underneath simulator boots (which immobilized their biological ankles). We collected motion capture and ground reaction force data, then computed joint kinematics and kinetics, and center-of-mass (COM) power and work. To our surprise, we found that varying toe joint stiffness affected COM Push-off dynamics during walking as much as, or in some cases even more than, varying ankle joint stiffness. Increasing toe joint stiffness increased COM Push-off work by up to 48% (6 J), and prosthetic anklefoot Push-off work by up to 181% (12 J). In contrast, large changes in toe shape had little effect on gait. This study brings attention to the toes, an aspect of prosthetic and robotic foot design that is often overlooked or overshadowed by design of the ankle. Optimizing toe joint stiffness in assistive and robotic devices (e.g. prostheses, exoskeletons, robot feet) may provide a complementary means of enhancing Push-off or other aspects of locomotor performance, in conjunction with the more conventional approach of augmenting ankle dynamics. Future studies are needed to isolate the effects of additional toe properties (e.g. toe length).

Performance of Optimized Prosthetic Ankle Designs That Are Based on a Hydraulic Variable Displacement Actuator (VDA)

Current energy storage and return prosthetic feet only marginally reduce the cost of amputee locomotion compared with basic solid ankle cushioned heel feet, possibly due to their lack of push-off at the end of stance. To the best of our knowledge, a prosthetic ankle that utilizes a hydraulic variable displacement actuator (VDA) to improve push-off performance has not previously been proposed. Therefore, here we report a design optimization and simulation feasibility study for a VDA-based prosthetic ankle. The proposed device stores the eccentric ankle work done from heel strike to maximum dorsiflexion in a hydraulic accumulator and then returns the stored energy to power push-off. Optimization was used to establish the best spring characteristic and gear ratio between ankle and VDA. The corresponding simulations show that, in level walking, normal push-off is achieved and, per gait cycle, the energy stored in the accumulator increases by 22% of the requirements for normal push-off. Although the results are promising, there are many unanswered questions and, for this approach to be a success, a new miniature, low-losses, and lightweight VDA would be required that is half the size of the smallest commercially available device.

The Functional Roles of Muscles, Passive Prostheses, and Powered Prostheses During Sloped Walking in People With a Transtibial Amputation

Sloped walking is challenging for individuals with transtibial amputation (TTA) due to the functional loss of the ankle plantarflexors. Prostheses that actively generate ankle power may help to restore this lost function. The purpose of this study was to use musculoskeletal modeling and simulation to quantify the mechanical power delivered to body segments by passive and powered prostheses and the remaining muscles in the amputated and intact legs during sloped walking. We generated walking simulations from experimental kinematic and kinetic data on slopes of 0, ±3 deg and ±6 deg in eight people with a TTA using powered and passive prostheses and eight nonamputees. Consistent with our hypothesis, the amputated leg hamstrings generated more power to both legs on uphill slopes in comparison with nonamputees, which may have implications for fatigue or overuse injuries. The amputated leg knee extensors delivered less power to the trunk on downhill slopes (effect size (ES) ≥ 1.35, p ≤ 0.02), which may be due to muscle weakness or socket instability. The power delivered to the trunk from the powered and passive prostheses was not significantly different (p > 0.05), However, using the powered prosthesis on uphill slopes reduced the contributions from the amputated leg hamstrings in all segments (ES ≥ 0.46, p ≤ 0.003), suggesting that added ankle power reduces the need for the hamstrings to compensate for lost ankle muscle function. Neither prosthesis replaced gastrocnemius function to absorb power from the trunk and deliver it to the leg on all slopes.

When to biomechanically examine a lower-limb amputee: A systematic review of accommodation times

BACKGROUND

Hundreds of investigations examining biomechanical outcomes of various prostheses have been completed, but one question remains unanswered: how much time should an amputee be given to accommodate to a new prosthesis prior to biomechanical testing?

OBJECTIVE

To examine the literature for accommodation time given during biomechanical investigations to determine whether consensus exists.

STUDY DESIGN

Systematic review.

METHODS

A systematic search was completed on 7 January 2016 using PubMed and Scopus.

RESULTS

The search resulted in 156 investigations. Twenty-eight studies did not provide an accommodation or were unclear (e.g. provided a "break in period"), 5 studies tested their participants more than once, 25 tested only once and on the same day participants received a new prosthesis (median (range): above-knee: 60 (10-300) min; below-knee: 18 (5-300) min), and 98 tested once and gave a minimum of 1 day for accommodation (hip: 77 (60-180) days; above-knee: 42 (1-540) days; below-knee: 21 (1-475) days).

CONCLUSION

The lack of research specifically examining accommodation and the high variability in this review's results indicates that it remains undecided how much accommodation is necessary. There is a need for longitudinal biomechanical investigations to determine how outcomes change as amputees accommodate to a new prosthesis. Clinical relevance The results of this review indicate that little research has been done regarding lower-limb amputees accommodating to a new prosthesis. Improper accommodation could lead to increased variability in results, results that are not reflective of long-term use, and could cause clinicians to make inappropriate decisions regarding a prosthesis.

Feasibility study of transtibial amputee walking using a powered prosthetic foot

Passive prosthetic feet are not able to provide non-amputee kinematics and kinetics for the ankle joint. Persons with amputations show reduced interlimb symmetry, slower walking speeds, and increased walking effort. To improve ankle range of motion and push off, various powered prosthetic feet were introduced. This feasibility study analyzed if predefined motor reference trajectories can be used to achieve non-amputee ankle biomechanics during walking with the powered prosthetic foot, Walk-Run Ankle. Trajectories were calculated using the desired ankle angle and ankle moment based spring deflection at a given spring stiffness. Model assumptions of the motor-spring interaction were well reflected in the experiment. The powered foot was able to improve range of motion, peak ankle power, average positive ankle power, peak ankle moment, and positive moment onset compared to a passive usage of the foot. Furthermore, symmetry improvements were identified for step length and duty factor. Further studies with an increased number of subjects are needed to show if the approach is also valid for other amputees. Using this method as a base, trajectories can be further individualized using human in the loop optimization targeting a reduction of user effort, improved stability, or gait symmetry.

The effect of segmental weight of prosthesis on hemodynamic responses and energy expenditure of lower extremity amputees

[Purpose] The aim of this study was to investigate the effect of segmental weight of the prosthesis on hemodynamic responses and energy expenditure in lower extremity amputees. [Subjects and Methods] Thirteen patients with a mean age of 44 ± 15.84 years and with unilateral transtibial, transfemoral and Syme’s amputation were included to the study. The difference between the lightest and the heaviest prosthesis, 250 g used as the weight. All the patients completed the measurements first without weight and then with 250 g weight on the ankle joint. The blood pressure and heart rate of the patients were recorded before and after Six Minute Walk Test (6MWT) and 10 stairs up & down stairs test. Physiological Cost Index was used to calculate the energy expenditure. [Results] Heart rate and energy expenditure increased significantly when without weight and with weight results compared. [Conclusion] We conclude that the segmental weight of the prosthetic limb has a significant effect on the heart rate and energy expenditure but has no effect on the systolic and diastolic blood pressure of lower limb amputees. In order to generalize our results to lower limb amputees, more patients need to be included in future studies.

Gait biomechanics following lower extremity trauma: Amputation vs. reconstruction

BACKGROUND

Surgical advances have substantially improved outcomes for individuals sustaining traumatic lower extremity injury. Injuries once requiring lower limb amputation are now routinely managed with limb reconstruction surgery. However, comparisons of functional outcomes between the procedures are inconclusive.

PURPOSE

To compare gait biomechanics after lower limb reconstruction and transtibial amputation.

METHODS

Twenty-four individuals with unilateral lower limb reconstruction wearing a custom ankle-foot orthosis (Intrepid Dynamic Exoskeletal Orthosis), 24 with unilateral, transtibial amputation, and 24 able-bodied control subjects underwent gait analysis at a standardized Froude speed based on leg length. Lower extremity joint angles, moments, and powers, and ground reaction forces were analyzed on the affected limb of patients and right limb of able-bodied individuals. ANOVA with Tukeys post-hoc tests determined differences among groups and post-hoc paired t-tests with Bonferroni-Holm corrections determined differences between limbs.

RESULTS

The ankle, knee, and hip exhibited significant kinematic differences between amputated, reconstructed and able-bodied limbs. The reconstruction group exhibited less ankle power and range of motion while the amputee group exhibited lower knee flexor and extensor moments and power generation.

CONCLUSION

Gait deficiencies were more pronounced at the ankle following limb reconstruction with orthosis use and at the knee following transtibial amputation with prosthesis use. Although both groups in the cohorts tested can replicate many key aspects of normative gait mechanics, some deficiencies still persist. These results add to the growing body of literature comparing amputation and limb reconstruction and provide information to inform the patient on functional expectations should either procedure be considered.

A powered prosthetic ankle joint for walking and running

BACKGROUND

Current prosthetic ankle joints are designed either for walking or for running. In order to mimic the capabilities of an able-bodied, a powered prosthetic ankle for walking and running was designed. A powered system has the potential to reduce the limitations in range of motion and positive work output of passive walking and running feet.

METHODS

To perform the experiments a controller capable of transitions between standing, walking, and running with speed adaptations was developed. In the first case study the system was mounted on an ankle bypass in parallel with the foot of a non-amputee subject. By this method the functionality of hardware and controller was proven.

RESULTS

The Walk-Run ankle was capable of mimicking desired torque and angle trajectories in walking and running up to 2.6 m/s. At 4 m/s running, ankle angle could be matched while ankle torque could not. Limited ankle output power resulting from a suboptimal spring stiffness value was identified as a main reason.

CONCLUSIONS

Further studies have to show to what extent the findings can be transferred to amputees.

Evaluation of a Powered Ankle-Foot Prosthesis during Slope Ascent Gait

Passive prosthetic feet lack active plantarflexion and push-off power resulting in gait deviations and compensations by individuals with transtibial amputation (TTA) during slope ascent. We sought to determine the effect of active ankle plantarflexion and push-off power provided by a powered prosthetic ankle-foot (PWR) on lower extremity compensations in individuals with unilateral TTA as they walked up a slope. We hypothesized that increased ankle plantarflexion and push-off power would reduce compensations commonly observed with a passive, energy-storing-returning prosthetic ankle-foot (ESR). We compared the temporal spatial, kinematic, and kinetic measures of ten individuals with TTA (age: 30.2 ± 5.3 yrs) to matched abled-bodied (AB) individuals during 5° slope ascent. The TTA group walked with an ESR and separately with a PWR. The PWR produced significantly greater prosthetic ankle plantarflexion and push-off power generation compared to an ESR and more closely matched AB values. The PWR functioned similar to a passive ESR device when transitioning onto the prosthetic limb due to limited prosthetic dorsiflexion, which resulted in similar deviations and compensations. In contrast, when transitioning off the prosthetic limb, increased ankle plantarflexion and push-off power provided by the PWR contributed to decreased intact limb knee extensor power production, lessening demand on the intact limb knee.

Whole-body angular momentum during sloped walking using passive and powered lower-limb prostheses

Sloped walking requires altered strategies for maintaining dynamic balance relative to level-ground walking, as evidenced by changes in sagittal-plane whole-body angular momentum (H) in able-bodied individuals. The ankle plantarflexor muscles are critical for regulating H, and functional loss of these muscles from transtibial amputation affects this regulation. However, it is unclear if a powered prosthesis, which more closely emulates intact ankle function than a passive energy-storage-and-return prosthesis, affects H differently during sloped walking. Therefore, our purpose was to investigate H in individuals with unilateral transtibial amputation when using powered and passive prostheses. Overall, the range of H was greater in people with a transtibial amputation relative to able-bodied individuals. On a -10° decline, individuals with amputation did not decrease H as much as able-bodied individuals, and had reduced prosthetic limb braking ground reaction forces and knee power absorption. On a +10° incline, individuals with amputation had a greater relative increase of H than able-bodied individuals, a more anterior placement of the prosthetic foot, and higher peak hip power generation. The powered prosthesis condition resulted in a smaller range of H during prosthetic stance relative to the passive condition, although it was still larger than able-bodied individuals. Our results suggest that prosthetic ankle power generation may help regulate dynamic balance during prosthetic stance, but alone is not sufficient for restoring H to that of able-bodied individuals on slopes. Contributions of knee extensor muscles and the biarticular gastrocnemius in regulating H on slopes should be further investigated.