Contribution of each leg to the control of unperturbed bipedal stance in lower limb amputees: new insights using entropy

Resting state neurophysiology of agonist-antagonist myoneural interface in persons with transtibial amputation

The agonist-antagonist myoneural interface (AMI) is an amputation surgery that preserves sensorimotor signaling mechanisms of the central-peripheral nervous systems. Our first neuroimaging study investigating AMI subjects conducted by Srinivasan et al. (2020) focused on task-based neural signatures, and showed evidence of proprioceptive feedback to the central nervous system. The study of resting state neural activity helps non-invasively characterize the neural patterns that prime task response. In this study on resting state functional magnetic resonance imaging in AMI subjects, we compared functional connectivity in patients with transtibial AMI (n = 12) and traditional (n = 7) amputations (TA). To test our hypothesis that we would find significant neurophysiological differences between AMI and TA subjects, we performed a whole-brain exploratory analysis to identify a seed region; namely, we conducted ANOVA, followed by t-test statistics to locate a seed in the salience network. Then, we implemented a seed-based connectivity analysis to gather cluster-level inferences contrasting our subject groups. We show evidence supporting our hypothesis that the AMI surgery induces functional network reorganization resulting in a neural configuration that significantly differs from the neural configuration after TA surgery. AMI subjects show significantly less coupling with regions functionally dedicated to selecting where to focus attention when it comes to salient stimuli. Our findings provide researchers and clinicians with a critical mechanistic understanding of the effect of AMI amputation on brain networks at rest, which has promising implications for improved neurorehabilitation and prosthetic control.

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

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

Resting state neurophysiology of agonist-antagonist myoneural interface in persons with transtibial amputation

The agonist-antagonist myoneural interface (AMI) is a novel amputation surgery that preserves sensorimotor signaling mechanisms of the central-peripheral nervous systems. Our first neuroimaging study investigating AMI subjects (Srinivasan et al., Sci. Transl. Med. 2020) focused on task-based neural signatures, and showed evidence of proprioceptive feedback to the central nervous system. The study of resting state neural activity helps non-invasively characterize the neural patterns that prime task response. In this first study on resting state fMRI in AMI subjects, we compared resting state functional connectivity in patients with transtibial AMI (n=12) and traditional (n=7) amputations, as well as biologically intact control subjects (n=10). We hypothesized that the AMI surgery will induce functional network reorganization that significantly differs from the traditional amputation surgery and also more closely resembles the neural configuration of controls. We found AMI subjects to have lower connectivity with salience and motor seed regions compared to traditional amputees. Additionally, with connections affected in traditional amputees, AMI subjects exhibited a connectivity pattern more closely resembling controls. Lastly, sensorimotor connectivity in amputee cohorts was significantly associated with phantom sensation (R2=0.7, p=0.0008). These findings provide researchers and clinicians with a critical mechanistic understanding of the effects of the AMI surgery on the brain at rest, spearheading future research towards improved prosthetic control and embodiment.

Clinical measures of balance and gait cannot differentiate somatosensory impairments in people with lower-limb amputation

BACKGROUND

In addition to a range of functional impairments seen in individuals with a lower-limb amputation, this population is at a substantially elevated risk of falls. Studies postulate that the lack of sensory feedback from the prosthetic limb contributes heavily to these impairments, but the extent to which sensation affects functional measures remains unclear.

RESEARCH QUESTION

The purpose of this study is to determine how sensory impairments in the lower extremities relate to performance with common clinical functional measures of balance and gait in individuals with a lower-limb amputation. Here we evaluate the effects of somatosensory integrity to clinical and lab measures of static, reactive and dynamic balance, and gait stability.

METHODS

In 20 individuals with lower-limb amputation (AMP) and 20 age and gender-matched able-bodied controls (CON), we evaluated the effects of sensory integrity (pressure, proprioception, and vibration) on measures of balance and gait. Static, reactive, and dynamic balance were assessed using the Sensory Organization Test (SOT), Motor Control Test (MCT), and Functional Gait Assessment (FGA), respectively. Gait stability was assessed through measures of step length asymmetry and step width variability. Sensation was categorized into intact or impaired sensation by pressure thresholds and differences across groups were analyzed.

RESULTS

There were significant differences between AMP and CON groups for reliance on vision for static balance in the SOT, MCT, and FGA (p < 0.01). Despite differences across groups, there were no significant differences within the AMP group based on intact or impaired sensation across all functional measures.

SIGNIFICANCE

Despite being able to detect differences between able-bodied individuals and individuals with an amputation, these functional measures cannot distinguish between levels of impairment within participants with an amputation. These findings suggest that more challenging and robust metrics are needed to evaluate the effects of sensation and function in individuals with an amputation.

Subthreshold Vibration Influences Standing Balance but Has Unclear Impact on Somatosensation in Persons With Transtibial Amputations

Stochastic resonance has been successfully used to improve human movement when using subthreshold vibration. Recent work has shown promise in improving mobility in individuals with unilateral lower limb amputations. Furthering this work, we present an investigation of two different signal structures in the use of stochastic resonance to improve mobility in individuals with unilateral lower limb amputations. Cutaneous somatosensation and standing balance measures using spatial and temporal analysis were assessed. There were no differences in the somatosensation measures, but differences in the temporal characteristics of the standing measures were seen with the various vibration structures when compared to no vibration, one of which suggesting mass may play an important role in determining who may or may not benefit from this intervention. Stochastic resonance employed with subthreshold vibration influences mobility in individuals with unilateral amputations, but the full direction and extent of influence is yet to be understood.

Influence of Augmented Visual Feedback on Balance Control in Unilateral Transfemoral Amputees

Patients with a lower limb amputation rely more on visual feedback to maintain balance than able-bodied individuals. Altering this sensory modality in amputees thus results in a disrupted postural control. However, little is known about how lower limb amputees cope with augmented visual information during balance tasks. In this study, we investigated how unilateral transfemoral amputees incorporate visual feedback of their center of pressure (CoP) position during quiet standing. Ten transfemoral amputees and ten age-matched able-bodied participants were provided with real-time visual feedback of the position of their CoP while standing on a pressure platform. Their task was to keep their CoP within a small circle in the center of a computer screen placed at eye level, which could be achieved by minimizing their postural sway. The visual feedback was then delayed by 250 and 500 ms and was combined with a two- and five-fold amplification of the CoP displacements. Trials with eyes open without augmented visual feedback as well as with eyes closed were further performed. The overall performance was measured by computing the sway area. We further quantified the dynamics of the CoP adjustments using the entropic half-life (EnHL) to study possible physiological mechanisms behind postural control. Amputees showed an increased sway area compared to the control group. The EnHL values of the amputated leg were significantly higher than those of the intact leg and the dominant and non-dominant leg of controls. This indicates lower dynamics in the CoP adjustments of the amputated leg, which was compensated by increasing the dynamics of the CoP adjustments of the intact leg. Receiving real-time visual feedback of the CoP position did not significantly reduce the sway area neither in amputees nor in controls when comparing with the eyes open condition without visual feedback of the CoP position. Further, with increasing delay and amplification, both groups were able to compensate for small visual perturbations, yet their dynamics were significantly lower when additional information was not received in a physiologically relevant time frame. These findings may be used for future design of neurorehabilitation programs to restore sensory feedback in lower limb amputees.

Lower limb joint-specific contributions to standing postural sway in persons with unilateral lower limb loss

BACKGROUND

Individuals with lower limb loss are at an increased risk for falls, likely due to impaired balance control. Standing balance is typically explained by double- or single-inverted pendulum models of the hip and/or ankle, neglecting the knee joint. However, recent work suggests knee joint motion contributes toward stabilizing center-of-mass kinematics during standing balance.

RESEARCH QUESTION

To what extent do hip, knee, and ankle joint motions contribute to postural sway in standing among individuals with lower limb loss?

METHODS

Forty-two individuals (25 m/17f) with unilateral lower limb loss (30 transtibial, 12 transfemoral) stood quietly with eyes open and eyes closed, for 30 s each, while wearing accelerometers on the pelvis, thigh, shank, and foot. Triaxial inertial measurement units were transformed to inertial anterior-posterior components and sway parameters were computed: ellipse area, root-mean-square, and jerk. A state-space model with a Kalman filter calculated hip, knee, and ankle joint flexion-extension angles and ranges of motion. Multiple linear regression predicted postural sway parameters from intact limb joint ranges of motion, with BMI as a covariate (p < 0.05).

RESULTS

With eyes open, intact limb hip flexion predicted larger sway ellipse area, whereas hip flexion and knee extension predicted larger sway root-mean-square, and hip flexion, knee extension, and ankle plantarflexion predicted larger sway jerk. With eyes closed, intact limb hip flexion remained the predictor of sway ellipse area; no other joint motions influenced sway parameters in this condition.

SIGNIFICANCE

Hip, knee, and ankle motions influence postural sway during standing balance among individuals with lower limb loss. Specifically, increasing intact-side hip flexion, knee extension, and ankle plantarflexion motion increased postural sway. With vision removed, a re-weighting of lower limb joint sensory mechanisms may control postural sway, such that increasing sway may be regulated by proximal coordination strategies and vestibular responses, with implications for fall risk.

Standing posture and balance modalities in unilateral transfemoral and transtibial amputees

INTRODUCTION

Lower limb amputation impairs postural performance that could be characterized by biomechanical parameters. This study is to investigate postural performance of persons with transfemoral and transtibial amputation compared to controls without amputation.

METHODS

Eight transtibial, nine transfemoral and twelve able-bodied males participated in this study. Lower limb joints, pelvis and trunk angles were obtained from an optoelectronic motion analysis system to evaluate body posture parameters. The mean, range and speed of the center of pressure (CoP) in both antero-posterior and medio-lateral axes as well as the ellipse area covered by 90% of CoP and free moment were calculated using a single force-plate.

RESULTS AND DISCUSSION

Differences in body posture were only noted between the non-amputee and the transtibial groups. Transtibial amputees leaned more forwardly their trunk by 3.5° compared to able-bodied (p = 0.028). The mean CoP position in transfemoral amputees was closer to the non-amputated side than transtibial amputees (p = 0.034) and as compared to the dominant side in non-amputees (p = 0.042). Factor analysis revealed three postural performance modalities. Non-amputees postural performance was characterized solely by body posture parameters. Transfemoral amputees exclusively favored a modality associated with standing balance parameters, whereas transtibial amputees exhibited a mixed modality comprising a combination of postural and balance parameters.

CONCLUSION

These findings support that the level of amputation is characterized by postural performance modalities different from non-amputees. Clinicians could apply this knowledge as part of their routine rehabilitation program to enhance postural and standing balance assessments in unilateral transfemoral and transtibial amputees.

Inter-limb coupling in individuals with transtibial amputation during bilateral stance is direction dependent

We investigated the control of upright standing in individuals with unilateral transtibial amputation (TTA) by assessing the inter-limb coupling and the coupling between the center of pressure beneath both limbs combined (COP_NET) and the center of pressure (COP) beneath the prosthetic limb and the intact limb. Twenty-one adults with TTA and eighteen unimpaired adults completed 90 s of standing on two parallel force plates. The inter-limb coupling and the coupling between the COP beneath each limb and the COP_NET were assessed by quantifying the synchronization of the COP signals. This included the number of epochs with synchronized signals, the total duration of signal synchronization and the relative phase and deviation phase between the signals. Additionally, magnitude and temporal characteristics of the COP displacements were quantified. Individuals with TTA exhibited looser inter-limb coupling in the anterior-posterior direction, characterized by more shifts between epochs with synchronized signals, shorter total duration of signal synchronization, less in-phase coordination patterns and a higher deviation phase between the two limbs, compared to unimpaired individuals. This coincided with a larger and more irregular postural sway in the TTA group. No group difference was observed in the mediolateral direction. The coupling between the COP_NET and the COP beneath the individual limbs was similarly direction dependent, and tighter for the intact side, suggesting that an intact limb-driven strategy was utilized.

Bodyweight distribution between limbs, muscle strength, and proprioception in traumatic transtibial amputees: a cross-sectional study

OBJECTIVES

To evaluate how transtibial amputation (TT) affects bodyweight distribution, voluntary knee joint position sense (JPS), and quadriceps (QUA) and hamstrings (HAM) strength in prosthetized patients.

METHODS

Only TT patients who had been prosthetized for more than one year were included, and an age-paired able-bodied group was used as control. The participants stood on force plates with their eyes open to measure bodyweight distribution between the limbs. Knee voluntary JPS was assessed by actively reproducing a set of given arbitrary joint angles using a video analysis approach, and QUA and HAM strength were assessed isometrically with a hand-held dynamometer.

RESULTS

Sixteen TT subjects (age: 39.4±4.8 years) and sixteen age-paired control subjects (age: 38.4±4.3 years) participated in the study. The amputees supported their bodyweight majorly on the sound limb (54.8±8.3%, p<0.001). The proprioceptive performance was similar between the amputated (absolute error (AE): 2.2±1.6°, variable error (VE): 1.9±1.6°, constant error (CE): -0.7±2.0°) and non-amputated limbs (AE: 2.6±0.9°, VE: 2.1±0.9°, CE: 0.02±2.3°), and was not different from that of control subjects (AE: 2.0±0.9°, VE: 1.4±0.4°, CE: -1.1±1.7°). There was a considerable weakness of the QUA and HAM in the amputated limb compared with the sound limb and control subjects (p<0.001 both).

CONCLUSIONS

The asymmetric bodyweight distribution in the transtibial amputees was not accompanied by a reduction in knee proprioception. There was significant weakness in the amputated limb, which could be a potential issue when designing rehabilitation programs.

Development of a theoretical model for upright postural control in lower limb prosthesis users

Methods used to assess quiet standing in unilateral prosthesis users often assume validity of an inverted pendulum model despite this being shown as invalid in some instances. The aim of the current study was to evaluate the validity of a proposed unilaterally-constrained pin-controller model in explaining postural control in unilateral prosthesis users. Prosthesis users were contrasted against the theoretical model as were able-bodied controls that stood on a platform which unilaterally constrained movement of the CoP. All participants completed bouts of quiet standing with eyes open, eyes closed and with feedback on inter-limb weight bearing asymmetry. Correlation coefficients were used to infer inverted pendulum behavior in both the anteroposterior and mediolateral directions and were derived from both kinematic (body attached markers) and kinetic (centre of pressure) experimental data. Larger, negative correlation coefficients reflected better model adherence, whilst low or no correlation reflected poorer model adherence. Inverted pendulum behavior derived from kinematic data, indicated coefficients of high magnitude in both mediolateral (all cases range 0.71–0.78) and anteroposterior (0.88–0.91) directions, irrespective of groups. Inverted pendulum behavior derived from kinetic data in the anteroposterior direction indicated validity of the model with large negative coefficients associated with the unconstrained/intact limbs (prosthesis users: − 0.45 to − 0.65, control group: − 0.43 to − 0.72), small coefficients in constrained/prosthetic limbs (prosthesis users: − 0.02 to 0.07, control group: 0.13–0.26) and large negative coefficients in combined conditions (prosthesis users: − 0.36 to − 0.56, control group: − 0.71 to − 0.82). For the mediolateral direction, coefficients were negligible for individual limbs (0.03–0.17) and moderate to large negative correlations, irrespective of group (− 0.31 to − 0.73). Data suggested both prosthesis users’ and able-bodied individuals’ postural control conforms well to that predicted by a unilaterally-constrained pin-controller model, which has implications for the fundamental control of posture in transtibial prosthesis users.

A block randomised controlled trial investigating changes in postural control following a personalised 12-week exercise programme for individuals with lower limb amputation

BACKGROUND

Individuals with a lower limb amputation (LLA) have an increased risk of falls and often report lower balance confidence. They must compensate for altered mechanics and prosthetic limitations in order to execute appropriate motor responses to postural perturbations. Personalised exercise could be an effective strategy to enhance balance and reduce falls.

RESEARCH QUESTION

In this study, we investigated whether a personalised exercise programme could improve postural control and self-reported balance confidence in individuals with an LLA.

METHODS

Participants were block randomised into two groups (exercise, n = 7; control, n = 7) based on age and level of amputation. The exercise group completed a 12-week personalised exercise programme, including home-based exercise sessions, consisting of balance, endurance, strength, and flexibility training. The control group continued with their normal daily activities. All participants performed the Sensory Organization Test (SOT) and Motor Control Test (MCT) on the NeuroCom SMART Equitest, and completed the Activities-specific Balance Confidence-UK (ABC) self-report questionnaire, at baseline and post-intervention.

RESULTS AND SIGNIFICANCE

Exercise group equilibrium scores improved significantly when standing on an unstable support surface with no visual input and inaccurate somatosensory feedback (SOT condition 5, P < 0.012, d = 1.45). There were significant group*time interactions for medium (P = 0.029) and large (P = 0.048) support surface forward translations, which were associated with a trend towards increased weight-bearing on the intact limb in the control group (medium: P = 0.055; large: P = 0.087). No significant changes in ABC score were observed. These results indicate reduced reliance on visual input, and/or enhanced interpretation of somatosensory input, following an exercise programme. However, objective improvements in aspects of postural control were not associated with subjective improvements in self-reported balance confidence. More weight-bearing asymmetry in the control group suggests that a lack of targeted exercise training may have detrimental effects, with potential adverse long-term musculoskeletal consequences, that were quantifiable within a short timeframe.

Effects of vibrotactile feedback on postural sway in trans-femoral amputees: A wavelet analysis

Loss of somatosensory feedback after amputation inflicts a serious challenge to achieve postural stability. Improving motor skills by incorporating sensory feedback in rehabilitation protocols for persons with lower limb amputation has been gaining traction over time. However, the control mechanisms involved in this regarding time-frequency analysis have not been investigated yet. The purpose of this study was to explore the frequencies/time-scales responsible for postural stability in trans-femoral amputees with vibrotactile feedback. Center of Pressure (COP) signals were collected from 5 trans-femoral amputees and 10 healthy subjects during weight shifting balance tasks. A customized foot insole was used to estimate the COP for actuation of vibratory feedback. The evaluation of postural sway fluctuations by means of COP excursions with vibrotactile feedback was computed by wavelet transform method. Vibrotactile feedback was found to be effective in controlling low frequency postural sway in amputees. We found significantly higher energy (p = 0.004, 0.0007) at shorter time-scales (j = 6,7, freq. = 0.6-1.25 Hz) and lower energy (p = 0.0006) at longer time-scale (j = 10, freq. = 0.078 Hz) in amputees with vibrotactile feedback in comparison to healthy subjects using Coif 1 wavelet. We also found significant increase in energy (p = 0.003) during forward weight shifting with vibrotactile feedback in the sound limb of amputees in comparison to no feedback session at frequency/time-scales corresponding to somatosensory acuity (j = 6-8, freq. = 0.3-1.5 Hz) using Haar wavelet. These findings reflect the higher contribution of somatosensory receptors in amputees with vibrotactile feedback and may provide a better understanding of the mechanisms associated with standing balance in terms of time-frequency analysis.

Postural Sway in Lower Extremity Amputees and Older Adults May Suggest Increased Fall Risk in Amputees

BACKGROUND

Falls can be detrimental to overall health and quality of life for lower extremity amputees. Most previous studies of postural steadiness focus on quantification of time series variables extracted from postural sway signals. While it has been suggested that frequency domain variables can provide more valuable information, few current studies have evaluated postural sway in amputees using frequency domain variables.

METHODOLOGY

Participants were assigned to 3 groups: lower extremity amputation (n=6), healthy young adults (n=10), and healthy older adults (n=10). Standing barefoot on a force platform, each individual completed 3 trials of each of 3 standing conditions: eyes open, eyes closed, and standing on a foam balance pad. Time and frequency domain variables of postural sway were computed and analyzed.

RESULTS

Comparison of older adults, younger adults, and amputees on the three conditions of standing eyes open, eyes closed, and on foam revealed significant differences between groups. Mean mediolateral (ML) sway distance from the center of pressure (COP), total excursions and sway velocity was significantly higher for amputees and older adults when compared to young adults (p<0.05). Furthermore, power of sway signal was substantially lower for both amputees and older adults. When compared to that of older adults, postural steadiness of amputees was more affected by the eyes closed condition, whereas older adults' was more affected when sensory and proprioceptive information was perturbed by standing on foam.

CONCLUSION

Our findings showed that fall risk is greater in amputees than in young adults without amputation. Additionally, amputees may rely more heavily on visual information than proprioceptive information for balance, in contrast to older and young adults without amputation.

Intermuscular coupling and postural control in unilateral transfemoral amputees - a pilot study. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2020;2020:3815-3818. [PMID: 33018832 DOI: 10.1109/embc44109.2020.9176850] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

The dynamics of the adjustment of center of pressure (CoP) has been utilized to understand motor control in human pathologies characterized by impairments in postural balance. The control mechanisms that maintain balance can be investigated via the analysis of muscle recruitment using electromyography (EMG) signals. In this work, we combined these two techniques to investigate balance control during upright standing in transfemoral unilateral amputees wearing a prosthesis. The dynamics of the CoP adjustments and EMG-EMG coherence between four muscles of the trunk and lower limb of 5 unilateral transfemoral amputees and 5 age-matched able-bodied participants were quantified during 30 s of quiet standing using the entropic half-life (EnHL) method. Two visual conditions, eyes open and eyes closed, were tested. Overall, the group of amputees presented lower EnHL values (higher dynamics) in their CoP adjustments than controls, especially in their intact limb. The EnHL values of the EMG-EMG coherence time series in the amputee group were lower than the control group for almost all muscle pairs under both visual conditions. Different correlations between the EnHL values of the CoP data and the EMG-EMG coherence data were observed in the amputee and control groups. These preliminary results suggest the onset of distinct neuromuscular adaptations following a unilateral amputation.Clinical Relevance - Understanding neuromuscular adaptation mechanisms after an amputation may serve to design better rehabilitation treatments and novel prosthetic devices with sensory feedback.

Microprocessor prosthetic ankles: comparative biomechanical evaluation of people with transtibial traumatic amputation during standing on level ground and slope

BACKGROUND

The compensations occurrence due to the alteration of the posture and the gait of persons with lower limb amputation is still an issue in prosthetic fitting. Recently, prosthetic feet designed to reproduce the physiological behaviour of the ankle using a microprocessor control have been commercialized to address this issue.

OBJECTIVES

Investigate the relevance of these microprocessor prosthetic ankles (MPAs) in the ability of standing on both level and inclined surfaces.

METHODS

Six persons with transtibial amputation usually fitted with energy storing and returning (ESR) foot tested three MPAs: Elan^® Endolite (MPA1), Meridium^® Ottobock (MPA2), ProprioFoot^® Ossur (MPA3). Each MPA data acquisition was preceded of a 2 weeks adaptation period at home and followed by a 3-weeks wash-out period with their ESR. Lower limb angular position and moment, Centre of Pressure (CoP) position, Ground Reaction Forces (GRF) and functional scores were collected in static, on level ground and 12% inclined slope.

RESULTS

MPAs allowed a better posture and a reduction of residual knee moment on positive and/or negative slope compared to ESR. Results also reflect that the MPA2 allows the best control of the CoP in all situations.

CONCLUSIONS

An increased ankle mobility is associated with a better posture and balance on slope. Gait analysis would complete these outcomes.

CLINICAL RELEVANCE

This study compares three MPAs to ESR analysing static posture. Static analysis on level ground and slope represents the challenging conditions people with amputation have to cope with in their daily life, especially outdoors. Having a better understanding of the three MPAs behaviour could help to adequately fit the prosthesis to each patient. Implications for rehabilitation This is a study comparing three MPAs. The static analysis in standard and constraining conditions (slope) reflects the balance of people with amputation in their daily life, especially outdoors. Having a better understanding of the behaviour of each foot could help to adequately fit the prosthesis to each patient.

Neuromuscular adaptations and sensorimotor integration following a unilateral transfemoral amputation

BACKGROUND

Following an amputation, the human postural control system develops neuromuscular adaptations to regain an effective postural control. We investigated the compensatory mechanisms behind these adaptations and how sensorimotor integration is affected after a lower-limb transfemoral amputation.

METHODS

Center of pressure (CoP) data of 12 unilateral transfemoral amputees and 12 age-matched able-bodied subjects were recorded during quiet standing with eyes open (EO) and closed (EC). CoP adjustments under each leg were recorded to study their contribution to posture control. The spatial structure of the CoP displacements was characterized by measuring the mean distance, the mean velocity of the CoP adjustments, and the sway area. The Entropic Half-Life (EnHL) quantifies the temporal structure of the CoP adjustments and was used to infer disrupted sensory feedback loops in amputees. We expanded the analysis with measures of weight-bearing imbalance and asymmetry, and with two standardized balance assessments, the Berg Balance Scale (BBS) and Timed Up-and-Go (TUG).

RESULTS

There was no difference in the EnHL values of amputees and controls when combining the contributions of both limbs (p = 0.754). However, amputees presented significant differences between the EnHL values of the intact and prosthetic limb (p <  0.001). Suppressing vision reduced the EnHL values of the intact (p = 0.001) and both legs (p = 0.028), but not in controls. Vision feedback in amputees also had a significant effect (increase) on the mean CoP distance (p <  0.001), CoP velocity (p <  0.001) and sway area (p = 0.007). Amputees presented an asymmetrical stance. The EnHL values of the intact limb in amputees were positively correlated to the BBS scores (EO: ρ = 0.43, EC: ρ = 0.44) and negatively correlated to the TUG times (EO: ρ = - 0.59, EC: ρ = - 0.69).

CONCLUSION

These results suggest that besides the asymmetry in load distribution, there exist neuromuscular adaptations after an amputation, possibly related to the loss of sensory feedback and an altered sensorimotor integration. The EnHL values suggest that the somatosensory system predominates in the control of the intact leg. Further, suppressing the visual system caused instability in amputees, but had a minimal impact on the CoP dynamics of controls. These findings points toward the importance of providing somatosensory feedback in lower-limb prosthesis to reestablish a normal postural control.

TRIAL REGISTRATION

DRKS00015254 , registered on September 20th, 2018.

A pilot study examining measures of balance and mobility in children with unilateral lower-limb amputation

BACKGROUND

Individuals with unilateral lower-limb amputation (LLA) have altered structure and physiology of their lower limbs which impairs their balance, mobility, physical function and participation in physical activities. As part of (re)habilitation, focus is given to improving gait and balance in order to enhance overall mobility, function, self-efficacy, and independence. However, the relationships amongst body impairments and physical activity limitations remain unclear, particularly in the pediatric population.

OBJECTIVE

To provide an examination of the relationships among balance and mobility measures in children with unilateral lower-limb amputation and able-bodied children.

STUDY DESIGN

Cross-sectional prospective comparative pilot study.

METHODS

Spatiotemporal gait parameters and standing postural control were evaluated in children with lower-limb amputation (n = 10) and age-matched able-bodied children (n = 10) in a laboratory-based setting. Clinical tests for mobility and balance consisted of the 10-m walk test, the 6-min walk test, and the Community Balance and Mobility scale. Energy expenditure was estimated during the 6-min walk test using the Physiological Cost Index. Analysis included comparing variables between able-bodied and lower-limb amputation groups, as well as examining the correlations among them.

RESULTS

Walking speed, distance, and functional balance (p < 0.05) were significantly diminished in children with lower-limb amputation compared to able-bodied children. For children with lower-limb amputation, reduced energy expenditure was associated with narrower step width and more symmetrical gait; better postural control and balance were associated with faster walking speeds (p < 0.05).

CONCLUSION

A greater clinical understanding of gait and balance deficits in this population may help to improve rehabilitation outcomes and overall functional mobility.

CLINICAL RELEVANCE

Improved understanding of deficits in children with lower-limb amputation (LLA) may lead to more targeted interventions and facilitate clinical decision-making in rehabilitation settings for this population. The findings contribute to the limited literature and provide a basis to further examine suitable clinical outcome measures to be used in children with LLA.

Validation of the Inverted Pendulum Model in standing for transtibial prosthesis users

BACKGROUND

Often in balance assessment variables associated with the center of pressure are used to draw conclusions about an individual's balance. Validity of these conclusions rests upon assumptions that movement of the center of pressure is inter-dependent on movement of the center of mass. This dependency is mechanical and is referred to as the Inverted Pendulum Model. The following study aimed to validate this model both kinematically and kinetically, in transtibial prosthesis users and a control group.

METHODS

Prosthesis users (n=6) and matched control participants (n=6) stood quietly while force and motion data were collected under three conditions (eyes-open, eyes-closed, and weight-bearing feedback). Correlation coefficients were used to investigate the relationships between height and excursion of markers and center of masses in mediolateral/anteroposterior-directions, difference between center of pressure and center of mass and the center of mass acceleration in mediolateral/anteroposterior directions, magnitude of mediolateral/anteroposterior-component forces and center of mass acceleration, angular position of ankle and excursion in mediolateral/anteroposterior-directions, and integrated force signals.

FINDINGS

Results indicate kinematic validity of similar magnitudes (mean (SD) marker-displacement) between prosthesis users and control group for mediolateral- (r=0.77 (0.17); 0.74 (0.19)) and anteroposterior-directions (r=0.88 (0.18); 0.88 (0.19)). Correlation between difference of center of pressure and center of mass and the center of mass acceleration was negligible on the prosthetic side (r = 0.08 (0.06)) vs. control group (r=-0.51(0.13)).

INTERPRETATION

Results indicate kinematic validity of the Inverted Pendulum Model in transtibial prosthesis users but kinetic validity is questionable, particularly on the side with a prosthesis.

Passive prosthetic ankle-foot mechanism for automatic adaptation to sloped surfaces

This article describes the development of a prototype prosthetic ankle-foot system that passively adapts to surface slopes on each step of walking. Engineering analyses were performed to design the cam clutch and clutch engagement and disengagement mechanism. The prototype was tested by a veteran with a unilateral transtibial amputation. Kinematic and kinetic data were recorded while the subject walked on a treadmill at slopes ranging from -10 degrees to +10 degrees. After each slope condition, the subject rated his level of exertion and socket comfort. The subject reported increased comfort and reduced exertion for downhill slopes when using the prototype compared with his usual prosthesis. The subject also expressed that when walking downhill on the prototype, it was the most comfortable he has ever been in a prosthesis. The prosthetic ankle torque-angle relationship shifted toward dorsiflexion for uphill and toward plantar flexion for downhill slopes when using the prototype, indicating slope adaptation, but this effect did not occur when the subject walked with his usual prosthesis. The prototype also demonstrated late-stance plantar flexion, suggesting the potential for storing and returning more energy than standard lower-limb prostheses.

Individuals with transtibial limb loss use interlimb force asymmetries to maintain multi-directional reactive balance control

BACKGROUND

Deficits in balance control are one of the most common and serious mobility challenges facing individuals with lower limb loss. Yet, dynamic postural balance control among individuals with lower limb loss remains poorly understood. Here we examined the kinematics and kinetics of dynamic balance in individuals with unilateral transtibial limb loss.

METHODS

Five individuals with unilateral transtibial limb loss, and five age- and gender-matched controls completed a series of randomly applied multi-directional support surface translations. Whole-body metrics, e.g. peak center-of-mass displacement and net center-of-pressure displacement were compared across cohorts. Stability margin was computed as the difference between peak center-of-pressure and center-of-mass displacement. Additionally, center-of-pressure and ground reaction force magnitude and direction were compared between the prosthetic, intact, and control legs.

FINDINGS

Peak center-of-mass displacement and stability margin did not differ between individuals with transtibial limb loss and controls for all perturbation directions except those loading only the prosthetic leg; in such cases the stability margin was actually larger than controls. Despite similar center-of-mass displacement, greater center-of-pressure displacement was observed in the intact leg during anterior-posterior perturbations, and under the prosthetic leg in medial-lateral perturbations. Further, in the prosthetic leg, ground reaction forces were smaller and spanned fewer directions.

INTERPRETATION

Deficits in balance control among individuals with transtibial limb loss may be due to their inability to use their prosthetic leg to generate forces that are equal in magnitude and direction to those of unimpaired adults. Targeting this force-generating deficit through technological or rehabilitation innovations may improve balance control.

Balance control in lower extremity amputees during quiet standing: a systematic review

Postural control has been widely evaluated for the normal population and different groups over the past 20 years. Numerous studies have investigated postural control in quiet standing posture among amputees. However, a comprehensive analysis is lacking on the possible contributing factors to balance. The present systematic review highlights the current findings on variables that contribute to balance instability for lower extremity amputees. The search strategy was performed on PubMed, Web of Science, Medline, Scopus, and CINAHL and then followed by additional manual searching via reference lists in the reviewed articles. The quality of the articles was evaluated using a methodological quality assessment tool. This review included and evaluated a total of 23 full-text articles. Despite the inconsistencies in the methodological design of the studies, all articles scored above the acceptable level in terms of quality. A majority of the studies revealed that lower extremity amputees have increased postural sway in the standing posture. Asymmetry in body weight, which is mainly distributed in the non-amputated leg, was described. Aside from the centre of pressure in postural control, sensory inputs may be a related topic for investigation in view of evidence on their contribution, particularly visual input. Other balance-related factors, such as stump length and patients' confidence level, were also neglected. Further research requires examination on the potential factors that affect postural control as the information of standing postural is still limited.

Influential factors in stability of lower-limb amputees

OBJECTIVE

Lower-limb amputation is mainly a result of trauma, vascular disease, diabetes, or congenital disorders. Persons with amputation lose their ability to stand and walk on the basis of the level of amputation. Contribution of level of amputation, type of amputation, or cause of amputation to balance impairment has not been clearly defined. Furthermore, it is controversial how much the mentioned parameters influence standing stability. Therefore, the aim of this review article was to find the relationship between the abovementioned factors and balance impairment in the available literature. It was also aimed to find the possibility of improving standing stability by the use of different prosthesis components.

DESIGN

An electronic search was done via the PubMed, EMBASE, and ISI Web of Knowledge databases from 1960 to 2012. Quality of the articles was assessed using the Downs and Black tool.

RESULTS

On the basis of the used key words, 100 articles were found, of which 20 articles were selected in accordance with the selection criteria. The scores of reporting, external validity, internal validity (bias), and internal validity (confounding) varied between 4-9, 1-3, 3-5, and 2-6, respectively.

CONCLUSIONS

The literature review confirmed that standing stability of amputees depends on level of amputation, type of amputation, and cause of amputation. Moreover, prosthetic characteristics such as prosthetic ankle stiffness have influences on dynamic stability, whereas torsional adaptor does not have any positive influence on stability during level walking and on turning stability. Therefore, it can be concluded that the stability of a person with amputation can be improved by the use of appropriate prosthesis components.