Loads on the prosthesis-socket interface of above-knee amputees during normal gait: validation of a multi-body simulation

Unilateral transfemoral osseointegrated prostheses improve joint loading during walking

People with unilateral transfemoral amputation using socket prostheses are at increased risk for developing osteoarthritis in both the residual hip and intact lower-limb joints. Osseointegrated prostheses are a surgical alternative to socket prostheses that directly attach to the residual femur via a bone-anchored implant, however their multi-joint loading effect is largely unknown. Our objective was to establish how osseointegrated prostheses influence joint loading during walking. Motion capture data (kinematics, ground reaction forces) were collected from 12 participants at baseline, with socket prostheses, and 12-months after prosthesis osseointegration during overground walking at self-selected speeds. Subject-specific musculoskeletal models were developed at each timepoint relative to osseointegration. Internal joint moments were calculated using inverse dynamics, muscle and joint reaction forces (JRFs) were estimated with static optimization. Changes in internal joint moments, JRFs, and joint loading-symmetry were compared using statistical parametric mapping (p≤ 0.05) before and after osseointegration. Amputated limb hip flexion moments and anterior JRFs decreased during terminal stance (p = 0.002, <0.001; respectively), while amputated limb hip abduction moments increased during mid-stance (p < 0.001), amputated hip rotation moment changed from internal to external throughout early stance (p < 0.001). Intact limb hip extension and knee flexion moments (p = 0.028, 0.032; respectively), superior and resultant knee JRFs (p = 0.046, 0.049; respectively) decreased during the loading response following prosthesis osseointegration. These results may indicate that the direct loading transmission of these novel prostheses create a more typical mechanical environment in bilateral joints, which is comparable with loading observed in able-bodied individuals and could decrease the risk of development or progression of osteoarthritis.

Newly compiled Tai Chi (Bafa Wubu) promotes lower extremity exercise: a preliminary cross sectional study

Background

Tai Chi (Bafa Wubu) is a new type of simplified Tai Chi widely practiced by Tai Chi enthusiasts that has developed and perfected simplified Tai Chi movement and enriched Tai Chi practice methods. When practicing, Tai Chi athletes and enthusiasts can choose the Bafa Wubu movements to practice according to their physical conditions. The purpose of this article is to discuss the mechanism by which Bafa Wubu promotes lower extremity exercise from the perspective of exercise biomechanics.

Objectives

This article aims to explore the scientific training methods and technical characteristics of Bafa Wubu, and its contribution to comprehensive exercise of the lower extremities, by analyzing the biomechanical characteristics of the lower extremities of participants who practice Bafa Wubu at different levels and by comparing their ground reaction force, lower limb joints, and muscles during Bafa Wubu.

Methods

A total of 16 male participants were recruited and divided into an amateur group (N = 8) and a professional group (N = 8). The data were collected by a BTS 3D infrared-based motion capture system, and Kistler 3D force plate. The lower extremity joint forces and muscle strength were calculated by anybody simulation software with inverse dynamics.

Results

During elbowing and leaning sideways with steps sideways (ELS), the ground reaction force of the professional group was significantly higher than that of the amateur group in the sagittal, vertical, and frontal axes (P < 0.01). While stepping forward, backward, and sideways, the professional group's joints loading at the hip, knee, and ankle was always higher in the vertical direction (P < 0.01). Furthermore, during warding off with steps forward (WOF), laying with steps forward (LF), and rolling back with steps backward (RBB), hip joint loading increased in the med-lat direction. During actions with steps backward and sideways, the professional group's ankle flexion/extension torque and hip abduction/rotation torque were significantly larger than those of the amateur group (P < 0.01). Different actions in Bafa Wubu activate muscles to different degrees, whereas the iliacus is mainly responsible for stabilizing postures when practitioners perform standing knee lifting motions.

Conclusions

Professional groups who have been practicing Tai Chi (Bafa Wubu) for a long time have higher ground reaction force, and the force on the three joints of the lower extremities is different for various movements, which has positive significance for exercising the joints of the lower extremities. In addition, various motions activate muscles of different types at different levels. For amateurs to practice different movements to stimulate the muscles, targeted areas of practice promote the lower extremity muscles' synergistic force. In summary, the muscles and joints of the lower extremity can obtain comprehensive and balanced exercise through Bafa Wubu.

Analysis of lower limb prosthetic socket interface based on stress and motion measurements

The study was designed to establish a biomechanical assessment platform for the lower limb residuum/socket interface as a function of duration and speed of movement. The approach exploits an interface sensor which measures multi-directional stresses at the interface. The corresponding interface coupling motion was assessed using a 3D motion capture system. A longitudinal study, involving a trans-femoral amputee, was conducted with nine repeated level walking sessions over a 12-month period. The effect of walking speed on interface biomechanics was also assessed. Interface peak pressures and shear stresses in the range of 55–59 kPa and 12–19 kPa were measured, respectively, over all sessions in the 12 months study period at the posterior-proximal location of the residuum. The peak pressure and longitudinal shear values were found to fluctuate approximately 11% and 40% as against its maximum value, respectively, over 12 months. In addition, up to 12° of angular coupling and up to 28 mm of pistoning were recorded over a gait cycle, which was found to change by 29% and 45% respectively over the study period. The variation in walking speed, by altering self-selected cadence, resulted in changes of pressure and shear stresses at mid-stance of the gait cycle. In particular, as compared with self-selected cadence, for fast speed, peak pressure and peak longitudinal shear stress decreased by 5% and 33%, respectively. For slow speed, peak pressure and peak longitudinal shear stress increased by 7% and 17%, respectively. The corresponding angular and pistoning revealed a variation of up to 29% and 45%, respectively. This biomechanical assessment approach shows promise in the quantitative assessment of interface kinematics and kinetics for lower limb prosthetics, the usage of which could assist the clinical assessment of prosthetic socket fit.

Characterizing loads at transfemoral osseointegrated implants

Establishing normative and outlying loads on transfemoral osseointegrated devices will assist development of preclinical mechanical testing strategies to inform manufacturers and government regulators. Therefore, force and moment data from osseointegrated transfemoral transcutaneous implants were collated to better understand baseline load levels. Load data were also collected from other devices including transfemoral socket prostheses, instrumented hip stems, instrumented knee devices, instrumented limb salvage femoral endoprostheses, as well as estimated loads on transfemoral prostheses using data from able-bodied subjects. These additional data were assessed for their ability to bolster the limited osseointegrated device data. Several activities of daily living were investigated to characterize normative loading. Falling events were investigated to characterize outlying loads. Results revealed that limited loading data exist for osseointegrated devices. The most often reported activity was level walking. While these normative data may inform fatigue testing, they may not fully characterize fatigue loads during all activities of daily living. Socket prosthetics and able-bodied individuals may provide supplementary data, but significance is limited by sample sizes. Falling data are sparse, and insufficient data exist for characterizing adverse loads on osseointegrated devices. Future data collection should include more activities of daily living and adverse events to better define osseointegrated device loading profiles.

Mechanical and Finite Element Analysis of an Innovative Orthopedic Implant Designed to Increase the Weight Carrying Ability of the Femur and Reduce Frictional Forces on an Amputee's Stump

This study was designed to test the hypothesis that: "A properly designed implant that harnesses the principle of the incompressibility of fluids can improve the weight carrying ability of an amputee's residual femur and reduce the frictional forces at the stump external socket interface." The hypothesis was tested both mechanically on an Amputee Simulation Device (ASD) and through Finite Element Analysis (FEA) modeling software. With the implant attached to the femur, the FEA and ASD demonstrated that the femur carried 90% and 93% respectively of the force of walking. Without the implant, the FEA model and ASD femur carried only 35% and 77%, respectively, of the force of walking. Statistical calculations reveal three (3) degrees of separation (99% probability of non-random significant difference) between with and without implant data points. FEA modeling demonstrates that the normal contact forces and shear forces are pushed the distal weight-bearing area of the amputee stump, relieving the lateral stump of frictional forces. The ASD mechanical and FEA modeling data validate each other with both systems supporting the hypotheses with confidence intervals of three degrees of separation between with implant and without implant models.

Methodological factors affecting joint moments estimation in clinical gait analysis: a systematic review

Quantitative gait analysis can provide a description of joint kinematics and dynamics, and it is recognized as a clinically useful tool for functional assessment, diagnosis and intervention planning. Clinically interpretable parameters are estimated from quantitative measures (i.e. ground reaction forces, skin marker trajectories, etc.) through biomechanical modelling. In particular, the estimation of joint moments during motion is grounded on several modelling assumptions: (1) body segmental and joint kinematics is derived from the trajectories of markers and by modelling the human body as a kinematic chain; (2) joint resultant (net) loads are, usually, derived from force plate measurements through a model of segmental dynamics. Therefore, both measurement errors and modelling assumptions can affect the results, to an extent that also depends on the characteristics of the motor task analysed (i.e. gait speed). Errors affecting the trajectories of joint centres, the orientation of joint functional axes, the joint angular velocities, the accuracy of inertial parameters and force measurements (concurring to the definition of the dynamic model), can weigh differently in the estimation of clinically interpretable joint moments. Numerous studies addressed all these methodological aspects separately, but a critical analysis of how these aspects may affect the clinical interpretation of joint dynamics is still missing. This article aims at filling this gap through a systematic review of the literature, conducted on Web of Science, Scopus and PubMed. The final objective is hence to provide clear take-home messages to guide laboratories in the estimation of joint moments for the clinical practice.

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.

Influence of transfemoral amputation length on resulting loads at the osseointegrated prosthesis fixation during walking and falling

BACKGROUND

Transfemoral amputation is a surgical measure in which the surgeon typically conserves as much tissue and bone as possible. Osseointegrated fixation of prostheses is a promising alternative to conventional socket-based fixation. However, osseointegrated prostheses pose some risk of possible bone fracture under unexpected high-impact loading scenarios, such as a fall, and this should be protected against by a safety element. The aim of the present study was to determine the effect of amputation height on the forces and moments at the bone-prosthesis interface during normal gait and three falling scenarios.

METHODS

Forces and moments at four amputation heights were determined from a multi-body simulation driven by data captured from an able-bodied participant.

FINDINGS

In all three falling scenarios, forces were relatively independent of amputation height, while moments generally displayed considerable increases with shorter residual limb length. Peak moments ranged from 105Nm (SD 75) (most distal amputation height) to 229Nm (SD 99) (most proximal amputation height) for a "falling during gait" scenario.

INTERPRETATION

Our findings reveal the dependence of interface loads on amputation height in normal gait and falling. This information may lead to improved prosthesis safety elements against bending moments.

Effect of prosthetic alignment changes on socket reaction moment impulse during walking in transtibial amputees

The alignment of a lower limb prosthesis affects the way load is transferred to the residual limb through the socket, and this load is critically important for the comfort and function of the prosthesis. Both magnitude and duration of the moment are important factors that may affect the residual limb health. Moment impulse is a well-accepted measurement that incorporates both factors via moment-time integrals. The aim of this study was to investigate the effect of alignment changes on the socket reaction moment impulse in transtibial prostheses. Ten amputees with transtibial prostheses participated in this study. The socket reaction moment impulse was measured at a self-selected walking speed using a Smart Pyramid in 25 alignment conditions, including a nominal alignment (clinically aligned by a prosthetist), as well as angle malalignments of 2°, 4° and 6° (abduction, adduction, extension and flexion) and translation malalignments of 5 mm, 10 mm and 15 mm (lateral, medial, anterior and posterior). The socket reaction moment impulse of the nominal alignment was compared for each condition. The relationship between the alignment and the socket reaction moment impulse was clearly observed in the coronal angle, coronal translation and sagittal translation alignment changes. However, this relationship was not evident in the sagittal angle alignment changes. The results of this study suggested that the socket reaction moment impulse could potentially serve as a valuable parameter to assist the alignment tuning process for transtibial prostheses. Further study is needed to investigate the influence of the socket reaction moment impulse on the residual limb health.