David Rusaw

Effects of an unstable shoe construction on balance in women aged over 50 years.

BACKGROUND Shoes with an unstable sole construction are commonly used as a therapeutic tool by physiotherapists and are widely available from shoe and sporting goods retailers. The aim of this study was to investigate the effects of using an unstable shoe (Masai Barefoot Technology) on standing balance, reactive balance and stability limits. METHODS Thirty-one subjects agreed to participate in the study and underwent balance tests on three different occasions. After test occasion one (baseline) 20 subjects received Masai Barefoot Technology shoes and were requested to wear them as much as possible for the remaining eight weeks of the study. Three specific balance tests were administered on each test occasion using a Pro Balance Master (NeuroCom International Inc., Oregon, USA). Tests included; a modified sensory organization test, reactive balance test and limits of stability test. FINDINGS Subjects in the intervention group significantly improved their performance on elements of all three tests however results on these variables were not demonstrated to be significantly better than the control group. No significant differences were observed across testing occasions in the control group. INTERPRETATION Results from the present study suggest that, for this group of individuals, use of unstable footwear may improve certain aspects of balance.

Effects of an Unstable Shoe Construction on Standing Balance in Children with Developmental Disabilities: A Pilot Study

This study aimed to investigate if prolonged use of shoes incorporating an unstable sole construction could facilitate improvements of balance in a sample of developmentally disabled children. Ten children (six male and four female) aged between 10 and 17 years participated in the study. Children were fitted with shoes incorporating an unstable sole (Masai Barefoot Technology®) and instructed to wear them for a minimum of two hours per day for eight weeks. A within subjects repeated measures design was used. Children were tested prior to receiving the shoes, four weeks after receiving the shoes and eight weeks after receiving the shoes. A force plate capable of rotating about a single axis (NeuroCom International Inc, Oregon) was used to test static balance, reactive balance and directional control. Static balance was not found to be influenced by prolonged use of the footwear; however, significant improvements were noted in childrens reactive balance both with the shoes and barefoot. Results suggest that reactive balance can be improved by prolonged and regular use of shoes incorporating an unstable sole construction.

Can vibratory feedback be used to improve postural stability in persons with transtibial limb loss

The use of vibration as a feedback modality to convey motion of the body has been shown to improve measures of postural stability in some groups of patients. Because individuals using transtibial prostheses lack sensation distal to the amputation, vibratory feedback could possibly be used to improve their postural stability. The current investigation provided transtibial prosthesis users (n = 24, mean age 48 yr) with vibratory feedback proportional to the signal received from force transducers located under the prosthetic foot. Postural stability was evaluated by measuring center of pressure (CoP) movement, limits of stability, and rhythmic weight shift while participants stood on a force platform capable of rotations in the pitch plane (toes up/toes down). The results showed that the vibratory feedback increased the mediolateral displacement amplitude of CoP in standing balance and reduced the response time to rapid voluntary movements of the center of gravity. The results suggest that the use of vibratory feedback in an experimental setting leads to improvements in fast open-loop mechanisms of postural control in transtibial prosthesis users.

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.

Sagittal plane position of the functional joint centre of prosthetic foot/ankle mechanisms

BACKGROUND The use of motion analysis techniques in amputee rehabilitation often utilizes kinematic data from the prosthetic limb. A problem with methods currently used is that the joint positions of the prosthetic ankle are assumed to be in the same position as that of an intact ankle. The aim of this study was to identify both traditional anatomical joint centres as well as functional joint centres in a selection of commonly used prosthetic feet. These coordinates were then compared across feet and compared to the contralateral intact ankle joint. METHODS Six prosthetic feet were fit to a unilateral trans-tibial amputee on two separate occasions. The subjects intact limb was used as a control. Three-dimensional kinematics were collected to determine the sagittal position of the functional joint centre for the feet investigated. FINDINGS None of the prosthetic feet had a functional joint centre that was within the 95% CI for that of an intact ankle (both x- and y-coordinate position), nor any of the other prosthetic feet investigated. The repeatability of the method was found to be adequate, with 95% CI of the difference (test-retest) of the prosthetic feet similar to that for the intact ankle and within clinically accepted levels of variability. INTERPRETATION The motion of the prosthetic feet tested is clearly different from that of an intact ankle. Kinematic methods that assume ankle constraints based on an intact ankle are subject to systematic error as this does not reflect the real motion of the prosthetic foot.

Bilateral Electromyogram Response Latency Following Platform Perturbation in Unilateral Transtibial Prosthesis Users: Influence of Weight Distribution and Limb Position

Appropriate muscular response following an external perturbation is essential in preventing falls. Transtibial prosthesis users lack a foot-ankle complex and associated sensorimotor structures on the side with the prosthesis. The effect of this lack on rapid responses of the lower limb to external surface perturbations is unknown. The aim of the present study was to compare electromyogram (EMG) response latencies of otherwise healthy, unilateral, transtibial prosthesis users (n = 23, mean +/- standard deviation [SD] age = 48 +/- 14 yr) and a matched control group (n = 23, mean +/- SD age = 48 +/- 13 yr) following sudden support-surface rotations in the pitch plane (toes-up and toes-down). Perturbations were elicited in various weight-bearing and limb-perturbed conditions. The results indicated that transtibial prosthesis users have delayed responses of multiple muscles of the lower limb following perturbation, both in the intact and residual limbs. Weight-bearing had no influence on the response latency in the residual limb, but did on the intact limb. Which limb received the perturbation was found to influence the muscular response, with the intact limb showing a significantly delayed response when the perturbation was received only on the side with a prosthesis. These delayed responses may represent an increased risk of falling for individuals who use transtibial prostheses.

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 individuals 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.

The validity of forceplate data as a measure of rapid and targeted volitional movements of the centre of mass in transtibial prosthesis users

Abstract Purpose: To validate outcome variables from the limits of stability protocol that are derived from the center of pressure with those same variables derived from the center of mass during rapid, volitional responses in transtibial prosthesis users. Method: Prosthesis users (n = 21) and matched controls (n = 21) executed movements while force and motion data were collected. Correlation coefficients were used to investigate relationships between center of pressure and center of mass for: x/y coordinates positions, limits of stability outcome variables and muscular reaction times. Results: Significant differences were seen in correlation between x/y coordinate positions toward the intact limb (mean effect size of differences: r = .38). Limits of stability variables were positively correlated (reaction time and maximum excursion range rs: .585–.846; directional control and mean velocity range rs: .307–.472). Muscular reaction times correlated weakly with those from center of pressure (mean rs prosthesis users: .186 and controls: .101). Conclusions: Forceplate measures are valid in describing rapid, volitional movements in unilateral transtibial prosthesis users. Limits of stability outcomes extracted from center of pressure and center of mass are highly correlated, but can be sensitive to direction. Muscular reaction time correlates very little with reaction times extracted from the other variables. Implications for rehabilitation Rehabilitation programs utilizing limits of stability are valid measures of postural control in transtibial prosthesis users. Clinicians interpreting the outcomes from limits of stability need to be aware of their varying validity. Muscular reaction times correlate weakly with other measures of reaction time, highlighting the complexity of rapidly coordinating volitional movements in prosthesis users.

Development of a limits of stability protocol for use in transtibial prosthesis users: Learning effects and reliability of outcome variables

The aims of this study were to empirically quantify reliability and learning effects of a Limits of Stability protocol for transtibial prosthesis users. Outcome variables from center of pressure and center of mass were tested on: 1) multiple test repetitions within a single test occasion; and 2) between multiple test occasions. Trantibial prosthesis users (n=7) and matched controls (n=7) executed five trials of the Limits of Stability protocol on two occasions per day, on two consecutive days. Inter-trial learning effects and reliability of outcomes extracted via center of mass and center of pressure were evaluated utilizing standard biomechanics laboratory equipment. Reliability was good to excellent except the reaction time variable which was poor (Pooled 95%CI of ICC=0.248-0.484). An inter-trial learning effect was present in directional control for prosthesis users when the first trial was included in analysis (center of mass: 95%CI of r=0.065-0.239; center of pressure: 95%CI of r=0.076-0.249). The use of standard biomechanics lab equipment can produce reliable results for the Limits of Stability protocol. Researchers should be aware of low reliability of reaction time variable in the protocol assessed and should execute at least one practice trial prior to that which is used in subsequent analysis.

Do predictive relationships exist between postural control and falls efficacy in unilateral transtibial prosthesis users

OBJECTIVE To assess whether variables from a postural control test relate to and predict falls efficacy in prosthesis users. DESIGN Twelve-month within- and between-participants repeated measures design. Participants performed the limits of stability (LOS) test protocol at study baseline and at 6-month follow-up. Participants also completed the Falls Efficacy Scale-International (FES-I) questionnaire, reflecting the fear of falling, and reported the number of falls monthly between study baseline and 6-month follow-up, and additionally at 9- and 12-month follow-ups. SETTING University biomechanics laboratories. PARTICIPANTS Participants (N=24) included a group of active unilateral transtibial prosthesis users of primarily traumatic etiology (n=12) with at least 1 year of prosthetic experience and age- and sex-matched control participants (n=12). INTERVENTIONS Not applicable. MAIN OUTCOME MEASURES Postural control variables derived from center of pressure data obtained during the LOS test, which was performed on and reported by the Neurocom Pro Balance Master, namely reaction time, movement velocity (MVL), endpoint excursion (EPE), maximum excursion (MXE), and directional control (DCL). Number of falls and total FES-I scores. RESULTS During the study period, the prosthesis users group had higher FES-I scores (U=33.5, P=.02), but experienced a similar number of falls, compared to the control group. Increased FES-I scores were associated with decreased EPE (r= -0.73, P=.02), MXE (r= -0.83, P<.01) and MVL (r= -0.7, P=.03) in the prosthesis users group, and DCL (r= -0.82, P<.01) in the control group, all in the backward direction. CONCLUSIONS Study baseline measures of postural control, in the backward direction only, are related to and potentially predictive of subsequent 6-month FES-I scores in relatively mobile and experienced prosthesis users.