The Potential for Error With Use of Inverse Dynamic Calculations in Gait Analysis of Individuals With Lower Limb Loss: A Review of Model Selection and Assumptions

Low-cost prosthetic feet for underserved populations: A comparison of gait analysis and mechanical stiffness

BACKGROUND

Lower-limb loss is an ongoing cause of disability throughout the world. Despite advancements in prosthetic technologies, there are numerous underserved populations in need of effective low-cost prosthetic foot options.

OBJECTIVE

To evaluate the biomechanical performance of several low-cost prosthetic feet, using a combination of instrumented gait analysis and mechanical stiffness testing.

STUDY DESIGN

Randomized crossover with additional case study.

METHODS

We compared the solid-ankle-cushioned-heel (SACH), Jaipur, and Niagara feet with carbon fiber feet. Mechanical stiffness was evaluated using a cantilever-style bending test at 2 angles that was designed to mimic late stance gait loading. Eight below-knee amputees participated in the gait analysis, which focused on foot and ankle motion and energetics.

RESULTS

Metric analysis showed significant differences among feet in ankle motion and power as well as distal-to-shank power, with SACH showing reduced ankle motion and positive work compared with the other feet. Waveform analysis additionally revealed a compensatory knee flexion moment in SACH and a knee extension moment in Niagara and Jaipur during midstance. In mechanical stiffness testing, SACH had the highest stiffness, with Niagara and carbon fiber roughly similar, and Jaipur the most compliant with the greatest hysteresis.

CONCLUSIONS

There may be an optimal stiffness range for future prosthesis designs that maximizes propulsive energy. This may be achieved by combining some characteristics of Jaipur and Niagara feet in new designs. Ultimately, optimizing stiffness and energetics for gait biomimicry while maintaining cost, availability, and versatility across cultures will alleviate the effects of limb loss among underserved populations.

Equivalent system based inverse dynamics analysis of transfemoral prosthetic legs: Validation and application

Inverse dynamics analysis of prosthetic legs with polycentric knees is complex due to increased number of links. The present work proposes a simple and general method called equivalent system (ES) analysis. The ES analysis provides forces and moment at hip joint as well as at the functional knee centre (FKC), the instant centre of the polycentric knee. The input to the ES analysis is the motion data. For validation of the proposed method, synthetic motion data for the swing phase of walking with prosthetic legs having different knees are generated by simulations using ADAMS. The hip kinetics evaluated by the proposed method is compared with that from ADAMS. The root mean square errors of the ES analysis are lower than 17 (10^-6) N for hip reaction forces and 2.6 (10^-6) Nm for the hip moments, thereby validating the proposed method. In order to demonstrate the application of the proposed methodology, the motion data of two transfemoral amputees using single-axis and four-bar knee prostheses are obtained during gait trials. The hip kinetics as well as kinetics at FKC are computed using ES analysis. Hip power during the swing phase is also evaluated and compared. The results are presented in this paper and discussed. The ES analysis is shown to be a versatile tool to provide insights into the human-mechanism interaction.

A pilot case series for concurrent validation of inertial measurement units to motion capture in individuals who use unilateral lower-limb prostheses

Introduction

Inertial measurement units (IMUs) may be viable options to collect gait data in clinics. This study compared IMU to motion capture data in individuals who use unilateral lower-limb prostheses.

Methods

Participants walked with lower-body IMUs and reflective markers in a motion analysis space. Sagittal plane hip, knee, and ankle waveforms were extracted for the entire gait cycle. Discrete points of peak flexion, peak extension, and range of motion were extracted from the waveforms. Stance times were also extracted to assess the IMU software's accuracy at detecting gait events. IMU and motion capture-derived data were compared using absolute differences and root mean square error (RMSE).

Results

Five individuals (n = 3 transtibial; n = 2 transfemoral) participated. IMU prosthetic limb data was similar to motion capture (RMSE: waveform ≤4.65°; discrete point ≤9.04°; stance ≤0.03s). However, one transfemoral participant had larger differences at the microprocessor knee joint (RMSE: waveform ≤15.64°; discrete ≤29.21°) from IMU magnetometer interference. Intact limbs tended to have minimal differences between IMU and motion capture data (RMSE: waveform ≤6.33°; discrete ≤9.87°; stance ≤0.04s).

Conclusion

Findings from this pilot study suggest IMUs have the potential to collect data similar to motion capture systems in sagittal plane kinematics and stance time.

Calculated functional joint center positions are highly variable in individuals with unilateral transtibial amputation walking with identical prosthetic ankle-foot devices

BACKGROUND

Biomechanical modeling of the lower limbs, including prosthetic componentry, makes a number of assumptions that influence the data obtained and their subsequent interpretation. Calculated prosthetic ankle functional joint center (FJC) positions vary between devices and have been suggested as a possible method of comparing device function.

OBJECTIVES

The study aimed to assess the variability of joint center position estimates, calculated using an FJC methodology, in all three planes. This was assessed in participants with unilateral transtibial amputation using an identical prosthetic ankle-foot device during walking on a flat surface.

STUDY DESIGN

Case series.

TECHNIQUE

Three-dimensional motion capture recorded the position of markers placed on the shank and ankle-foot device of five individuals with unilateral transtibial amputation, as they completed 10 trials of level walking using the same ankle-foot device. The FJC between the prosthetic foot and shank segments were calculated for each trial.

RESULTS

The calculated FJC positions were highly variable across individual participants and within each individual. This variability was observed across all three planes of movement and resulted in calculated joint center positions created beyond the physical boundaries of the prosthetic device.

CONCLUSIONS

Biomechanical data are affected by lower limb and prosthetic device modeling assumptions. Definition of a prosthetic "ankle" joint using an FJC method results in highly variable "ankle" joint center positions when applied to a prosthetic ankle-foot device. Their use should be discouraged to avoid misleading interpretations of data.

A kinematic and kinetic dataset of 18 above-knee amputees walking at various speeds

Motion capture is necessary to quantify gait deviations in individuals with lower-limb amputations. However, access to the patient population and the necessary equipment is limited. Here we present the first open biomechanics dataset for 18 individuals with unilateral above-knee amputations walking at different speeds. Based on their ability to comfortably walk at 0.8 m/s, subjects were divided into two groups, namely K2 and K3. The K2 group walked at [0.4, 0.5, 0.6, 0.7, 0.8] m/s; the K3 group walked at [0.6, 0.8, 1.0, 1.2, 1.4] m/s. Full-body biomechanics was collected using a 10-camera motion capture system and a fully instrumented treadmill. The presented open dataset will enable (i) clinicians to understand the biomechanical demand required to walk with a knee and ankle prosthesis at various speeds, (ii) researchers in biomechanics to gain new insights into the gait deviations of individuals with above-knee amputations, and (iii) engineers to improve prosthesis design and function.

Load exposure of osseointegrated implants for transfemoral limb prosthesis during running

Direct skeletal attachment of lower limb prostheses ensures direct load transfer between the prosthetic leg and the skeleton. Knowledge of the load characteristics at the boneimplant interface during high-loading activities is needed to understand the limitations of current implant systems, as well as to inform their future development. The present study estimates the load scenario at the bone-implant interface of a transfemoral amputee while running with kinematic symmetry between the prosthetic and the intact limbs corresponding to that of an ablebodied subject. Kinematic symmetry was used as this represents the ultimate aim of advanced bionic legs. Kinematic data and ground reaction forces from a running trial of an able-bodied subject were matched to a musculoskeletal model of a transfemoral amputee. The joint reaction forces at the boneimplant interface were calculated using inverse dynamics. The normalized peak forces and moments during a single gait cycle were calculated to 153 % BW (body weight) / -14.8 % BWm, 186 % BW / 16.2 % BWm and 56.8 % BW / -18.7 % BWm for the x- (anterior), y- (longitudinal), and z-axis (lateral-medial), respectively. These findings can potentially be used as design input for future implant systems and external safety devices.

Benefits of an increased prosthetic ankle range of motion for individuals with a trans-tibial amputation walking with a new prosthetic foot

BACKGROUND

Individuals with trans-tibial amputation show a greater peak prosthetic ankle power (push- off) when using energy storing and returning (ESAR) prosthetic feet as compared to solid-ankle cushion-heel feet. ESAR feet further contribute to the users' body support and thus limit prosthetic ankle motion. To improve ankle motion, articulating prosthetic feet have been introduced. However, articulating feet may diminish push-off.

RESEARCH QUESTION

Does a novel prosthetic foot, with a serial layout of carbon fibre leaf springs, connected by a multi-centre joint construction, have advantages in kinematics and kinetics over a conventional ESAR prosthetic foot?> METHODS: Eleven individuals with unilateral trans-tibial amputation were fitted with the novel foot (NF) and a conventional ESAR Foot (CF) and underwent 3D gait analysis. As an additional power estimate of the prosthetic ankle, a unified, deformable, segment model approach was applied. Eleven matched individuals without impairments served as a reference.

RESULTS

The NF shows an effective prosthetic ankle range of motion that is closer to a physiologic ankle range of motion, at 31.6° as compared to 15.2° with CF (CF vs. NF p = 0.003/NF vs. Reference p = 0.171) without reducing the maximum prosthetic ankle joint moment. Furthermore, the NF showed a great increase in prosthetic ankle power (NF 2.89 W/kg vs. CF 1.48 W/kg CF vs. NF p = <0.001) and a reduction of 19% in the peak knee varus moment and 13% in vertical ground reaction forces on the sound side for NF in comparison to CF.

SIGNIFICANCE

The NF shows that serial carbon fibre leaf springs, connected by a multi-centre joint construction gives a larger ankle joint range of motion and higher ankle power than a conventional carbon fibre structure alone. Consequently load is taken off the contralateral limb, as measured by the decrease in vertical ground reaction forces and peak knee varus moment.

A prosthesis-specific multi-link segment model of lower-limb amputee sprinting

Lower-limb amputees commonly utilize non-articulating energy storage and return (ESAR) prostheses for high impact activities such as sprinting. Despite these prostheses lacking an articulating ankle joint, amputee gait analysis conventionally features a two-link segment model of the prosthetic foot. This paper investigated the effects of the selected link segment model׳s marker-set and geometry on a unilateral amputee sprinter׳s calculated lower-limb kinematics, kinetics and energetics. A total of five lower-limb models of the Ottobock^® 1E90 Sprinter were developed, including two conventional shank-foot models that each used a different version of the Plug-in-Gait (PiG) marker-set to test the effect of prosthesis ankle marker location. Two Hybrid prosthesis-specific models were then developed, also using the PiG marker-sets, with the anatomical shank and foot replaced by prosthesis-specific geometry separated into two segments. Finally, a Multi-link segment (MLS) model was developed, consisting of six segments for the prosthesis as defined by a custom marker-set. All full-body musculoskeletal models were tested using four trials of experimental marker trajectories within OpenSim 3.2 (Stanford, California, USA) to find the affected and unaffected hip, knee and ankle kinematics, kinetics and energetics. The geometry of the selected lower-limb prosthesis model was found to significantly affect all variables on the affected leg (p < 0.05), and the marker-set also significantly affected all variables on the affected leg, and none of the unaffected leg variables. The results indicate that the omission of prosthesis-specific spatial, inertial and elastic properties from full-body models significantly affects the calculated amputee gait characteristics, and we therefore recommend the implementation of a MLS model.

Gait Analysis of Transfemoral Amputees: Errors in Inverse Dynamics Are Substantial and Depend on Prosthetic Design

Quantitative assessments of prostheses performances rely more and more frequently on gait analysis focusing on prosthetic knee joint forces and moments computed by inverse dynamics. However, this method is prone to errors, as demonstrated in comparison with direct measurements of these forces and moments. The magnitude of errors reported in the literature seems to vary depending on prosthetic components. Therefore, the purposes of this study were (A) to quantify and compare the magnitude of errors in knee joint forces and moments obtained with inverse dynamics and direct measurements on ten participants with transfemoral amputation during walking and (B) to investigate if these errors can be characterised for different prosthetic knees. Knee joint forces and moments computed by inverse dynamics presented substantial errors, especially during the swing phase of gait. Indeed, the median errors in percentage of the moment magnitude were 4% and 26% in extension/flexion, 6% and 19% in adduction/abduction as well as 14% and 27% in internal/external rotation during stance and swing phase, respectively. Moreover, errors varied depending on the prosthetic limb fitted with mechanical or microprocessor-controlled knees. This study confirmed that inverse dynamics should be used cautiously while performing gait analysis of amputees. Alternatively, direct measurements of joint forces and moments could be relevant for mechanical characterising of components and alignments of prosthetic limbs.

Concurrent multibody and Finite Element analysis of the lower-limb during amputee running

Lower-limb amputee athletes use Carbon fiber Energy Storage and Return (ESAR) prostheses during high impact activities such as running. The advantage provided to amputee athletes due to the energy-storing properties of ESAR prostheses is as yet uncertain. Conventional energy analysis methods for prostheses rely upon multibody models with articulating joints. Alternatively, Finite Element (FE) analysis treats bodies as a deforming continuum and can therefore calculate the energy stored without using these rigid-body mechanics assumptions. This paper presents a concurrent multibody and FE model of the femur, tibia, socket and ESAR prosthesis of a transtibial amputee athlete during sprinting. Gait analysis spatial data was used to conduct an offline simulation of the affected leg's stance phase in COMSOL Multiphysics. The calculated peak elastic strain energy of the prosthesis was 80J, with an overall RMSE of simulated marker displacement of 4.19 mm. This concurrent model presents a novel method for analyzing in vivo ESAR prosthesis behavior.

Differentiation between solid-ankle cushioned heel and energy storage and return prosthetic foot based on step-to-step transition cost

Decreased push-off power by the prosthetic foot and inadequate roll-over shape of the foot have been shown to increase the energy dissipated during the step-to-step transition in human walking. The aim of this study was to determine whether energy storage and return (ESAR) feet are able to reduce the mechanical energy dissipated during the step-to-step transition. Fifteen males with a unilateral lower-limb amputation walked with their prescribed ESAR foot (Vari-Flex, Ossur; Reykjavik, Iceland) and with a solid-ankle cushioned heel foot (SACH) (1D10, Ottobock; Duderstadt, Germany), while ground reaction forces and kinematics were recorded. The positive mechanical work on the center of mass performed by the trailing prosthetic limb was larger (33%, p = 0.01) and the negative work performed by the leading intact limb was lower (13%, p = 0.04) when walking with the ESAR foot compared with the SACH foot. The reduced step-to-step transition cost coincided with a higher mechanical push-off power generated by the ESAR foot and an extended forward progression of the center of pressure under the prosthetic ESAR foot. Results can explain the proposed improvement in walking economy with this kind of energy storing and return prosthetic foot.

Comparison of mechanical energy profiles of passive and active below-knee prostheses: a case study

BACKGROUND

With the recent technological advancements of prosthetic lower limbs, there is currently a great desire to objectively evaluate existing prostheses. Using a novel biomechanical analysis, the purpose of this case study was to compare the mechanical energy profiles of anatomical and two disparate prostheses: a passive prosthesis and an active prosthesis.

CASE DESCRIPTION AND METHODS

An individual with a transtibial amputation who customarily wears a passive prosthesis (Elation, Össur) and an active prosthesis (BiOM, iWalk, Inc.) and 11 healthy subjects participated in an instrumented gait analysis. The total mechanical power and work of below-knee structures during stance were quantified using a unified deformable segment power analysis.

FINDINGS AND OUTCOMES

Active prosthesis generated greater peak power and total positive work than passive prosthesis and healthy anatomical limbs.

CONCLUSION

The case study will enhance future efforts to objectively evaluate prosthetic functions during gait in individuals with transtibial amputations.

CLINICAL RELEVANCE

A prosthetic limb should closely replicate the mechanical energy profiles of anatomical limbs. The unified deformable (UD) analysis may be valuable to facilitate future clinical prescription and guide fine adjustments of prosthetic componentry to optimize gait outcomes.

A unified deformable (UD) segment model for quantifying total power of anatomical and prosthetic below-knee structures during stance in gait

Anatomically-relevant (AR) biomechanical models are traditionally used to quantify joint powers and segmental energies of lower extremity structures during gait. While AR models contain a series of rigid body segments linked together via mechanical joints, prosthetic below-knee structures are often deformable objects without a definable ankle joint. Consequently, the application of AR models for the study of prosthetic limbs has been problematic. The purpose of this study was to develop and validate a unified deformable (UD) segment model for quantifying the total power of below-knee structures. Estimates of total below-knee power derived via the UD segment model were compared to those derived via an AR model during stance in gait of eleven healthy subjects. The UD segment model achieved similar results to the AR model. Differences in peak power, total positive work, and total negative work were 1.91±0.31%, 3.97±0.49%, and 1.39±0.33%, relative to the AR model estimates. The main advantage of the UD segment model is that it does not require the definition of an ankle joint or foot structures. Therefore, this technique may be valuable for facilitating direct comparisons between anatomical and disparate prosthetic below-knee structures in future studies.

Trajectory of the center of rotation in non-articulated energy storage and return prosthetic feet

Non-articulated energy storage and return prosthetic feet lack any true articulation or obvious point of rotation. This makes it difficult to select a joint center about which to estimate their kinetics. Despite this absence of any clear point of rotation, methods for estimating the kinetic performance of this class of prosthetic feet typically assume that they possess a fixed center of rotation and that its location is well approximated by the position of the contralateral lateral malleolus. To evaluate the validity of this assumption we used a finite helical axis approach to determine the position of the center of rotation in the sagittal plane for a series of non-articulated energy storage and return prosthetic feet. We found that over the course of stance phase, the sagittal finite helical axis position diverged markedly from the typically assumed fixed axis location. These results suggest that researchers may need to review center of rotation assumptions when assessing prosthetic foot kinetics, while clinicians may need to reconsider the criteria by which they prescribe these prosthetic feet.

Biomechanical models in the study of lower limb amputee kinematics: a review

BACKGROUND

Optoelectronic motion capture may provide a platform for the development of objective biomechanical outcome measures applicable to the young, active individual with lower limb loss. In order to create valid and robust tools, the modelling strategy applied must adequately represent both natural and prosthetic segments and joints.

OBJECTIVES

To explore existing usage of optoelectronic motion capture and modelling strategies for the analysis of amputee function.

STUDY DESIGN

Literature review.

METHODS

Systematic search of Medline (OVID) and keyword search of the Journal of Prosthetics and Orthotics.

RESULTS

Over 60% (n = 32) of the 51 studies extracted adopted a conventional three degree-of-freedom modelling approach. Linear segment representation (15%) and six degree-of-freedom techniques (19%) were employed in the remaining papers. Prosthetic modelling strategies were poorly reported. Landmarks were estimated from corresponding positions on the contralateral intact limb, mechanical joint centres and regression equations. No model defined the residuum and socket independently.

CONCLUSIONS

In the absence of a definitive solution, it is essential that the limitations of any model are understood in the development and establishment of reliable outcome measures for this population using motion capture technology. Poor reporting and a lack of consistency make comparison of results between studies and institutions impractical.

CLINICAL RELEVANCE

Standard modelling techniques may not consistently represent the body and prosthesis adequately to produce valid results for the analysis of function of persons with lower limb loss. Variation in modelling techniques limits the utility of findings reported in the literature. Development and application of a uniform, robust modelling strategy would benefit research and clinical practice.

Motion-analysis studies of transtibial prosthesis users: a systematic review

BACKGROUND

Three-dimensional motion analysis has been used since the beginning of the 1980s to evaluate many aspects of physical function of transtibial amputees. Despite its common use for clinical research, there is large variability in methods of capturing three-dimensional data, description of these methods, reporting of joint kinematics and interpretation of research findings.

OBJECTIVES

The aim of the following review is to critically examine the specific methodologies used by researchers when collecting three-dimensional kinematic data on transtibial amputees and to provide an overview of the methods used.

STUDY DESIGN

Systematic review.

METHODS

A systematic review of the literature between January 1984 and June 2009 was conducted. A total of 68 papers were identified for review based on the following criteria: experimental research design, collection of three-dimensional kinematic data of lower-extremity joints, and inclusion of transtibial amputees as experimental subjects.

RESULTS

A number of methodological shortcomings were identified in the papers reviewed.

CONCLUSIONS

The authors recommend that future studies more appropriately address the product name and number of prosthetic components used; how the position of reflective markers on the prosthesis is defined; presentation of data from both sound and affected sides; and definition of the neutral position of the ankle when reporting kinematic data. Where possible, the authors recommend use of a control group.

CLINICAL RELEVANCE

This paper has identified numerous sources of discrepancy and potential error in kinematic data collected on trans-tibial amputees. Clinicians and researchers should make themselves aware of these issues when collecting and interpreting gait data.