RELATIONSHIP BETWEEN FOUR-BAR LINKAGE CONFIGURATION AND ENERGY EXPENDITURE IN TRANSFEMORAL AMPUTEE GAIT
Barnes, L. J 1and Bach, T. M.2
1Royal Darwin Hospital, Darwin, NT, Australia and
2La Trobe University, Bundoora, Victoria, Australia
The purpose of this study was to examine the effect of four-bar linkage (4BL) configurations on energy expenditure in transfemoral amputee gait. An experimental 4BL knee unit was designed and manufactured which enabled adjustment of linkage lengths and linkage centres. A computer simulation was used to choose linkage configurations with certain attributes, specifically, height of the instant centre during stance and the extent of limb shortening during swing. The relationship between these variables and energy expenditure was explored.
Oxygen consumption, freely chosen walking velocity and a number of indices of gait symmetry were measured in eight transfemoral amputee subjects under five knee-configuration conditions. In three conditions, limb shortening remained constant and the stance phase instant knee centre heights were varied (between 200 mm and 300 mm above the anatomical knee axis). In three conditions, the knee instant centre height remained constant and limb shortening during swing was varied (a difference of 16 mm in limb shortening between the configurations). One configuration was common to both conditions.
The results showed that higher instant centres of rotation during stance resulted in significantly reduced oxygen consumption while increased limb shortening during swing resulted in a significant increase in oxygen consumption. Symmetry of gait was not significantly correlated with oxygen consumption for the subjects studied in these trials. Subjects appeared to maintain a constant walking velocity across trials rather than adjusting their velocity to achieve a constant rate of energy expenditure. The results of this study clearly demonstrated that 4BL knee unit configurations which incorporate a high stance phase instant centre provide greater locomotor efficiency for transfemoral amputees.
THE EFFECTS OF ORTHOTICS ON EMG PATTERNS DURING WALKING IN PATIENTS WITH POST-POLIO SYNDROME
Evans, C. E.1,3Adler, R.2, and Bach, T. M.1
1La Trobe University, 2Bethesda Hospital, and 3Orthopaedic Appliances, Melbourne, Australia
Late effects of polio include joint and muscle pain and decreased endurance which may indicate progressive decrease in muscle strength. Although the effects of muscle paralysis on walking patterns have been studied, the effects of muscle weakness have not. In order to provide the best possible outcomes through orthotic management in such patients, it is important to understand the compensatory motor patterns associated with muscle weakness and fatigue and the ways in which orthoses can modify and improve motor patterns. The purpose of this study was to examine EMG profiles in post-polio patients who exhibited instability, muscle pain or joint pain and who experienced relief through orthotic management.
Ten post-polio subjects were examined using a Motion Lab Systems MA100 EMG system. Eight lower extremity muscles (erector spinae, gluteus maximus, gluteus medius, vastus lateralis, biceps femoris, gastrocnemius, soleus, peroneus longus) were examined during walking with and without orthotics. Comparisons between normal and post-polio EMG patterns were made to determine compensatory patterns in post-polio patients and to determine the effects of orthotic treatment.
Comparison of individual EMG patterns in the post-polio group with normative data provided insights into the sources of muscle fatigue and pain during unaided walking and into the improvements in gait and the relief in symptoms experienced by patients using orthoses.
EFFECTS OF INERTIAL LOADING ON ENERGY EXPENDITURE AND GAIT CHARACTERISTICS IN TRANSTIBIAL AMPUTEES
Jans, M. A. and Bach, T. M.
La Trobe University, Bundoora, Victoria, Australia
A number of investigations have demonstrated that, in transfemoral (TF) amputees, energy expenditure can be reduced and gait characteristics can be improved by addition of mass to the prosthesis. Although there have been suggestions that the same applies in transtibial (TT) amputees, there have been no well controlled studies which have examined this issue. The purpose of this study was to examine the effects of inertial loading on TT amputee gait.
Six TT amputees were examined during treadmill walking at a comfortable velocity. Oxygen consumption was measured using a metabolic cart. Gait characteristics were determined from motion analysis data obtained using a VICON system. Each subject was examined during overground and treadmill walking wearing a lightweight (1.38 ± .25 kg) prosthesis. Four experimental conditions were examined: no added mass and added masses of 375, 750 and 1125 grams. Added masses were located at a position on the prosthesis which was calculated to substantially reduce the period of oscillation of the stump-prosthesis system.
Subjective preferences were significantly higher for the 375 and 750 gram added mass conditions. All added mass conditions significantly increased walking velocity. The 750 gram added mass condition significantly improved gait symmetry. No significant differences in oxygen consumption were observed although problems with the metabolic cart resulted in loss of data for 3 subjects. The results of this study suggest that inertial characteristics of TT prostheses should be considered as an important aspect of the overall prescription.
A VISUAL FEEDBACK SYSTEM FOR MYOELECTRIC TRAINING
Cooper, R.1,2, Cullis, E.2, Cumbo, J.2, Angliss, V.2, Bach, T. M.1
1La Trobe University, Australia, 2 REHAB Tech, Australia
One of the major disadvantages of myoelectric prostheses is that the user is deprived of the sensory feedack provided by the harness of a body powered design. The amputee using a myoelectric prosthesis relies heavily upon visual feedback to perform the task. In order to enance the information available to the amputee, a visual feedback system was designed at Monash Rehabilitation Technology Research Unit. The feedback mechanism uses L.E.D.s which display information regarding electrode activation, grip and the level of battery power. The purpose of this study was to determine the effects of the enhanced visual feedback provided by this device on learning in novice myoelectric users.
Fourteen able-bodied subjects were fitted with an adjustable myoelectric training arm. Subjects were randomly assigned to two groups: an experimental group which received training with feedback and a control group which trained with the feedback unit turned off. Subjects received five one-hour training sessions and were evaluated on a form board test at the end of each session.
A two-way ANOVA for repeated measures indicated that the effect of training was significant in that both groups improved across training sessions (F=8.38, df=48,4, p<0.001). However, enhanced feedback did not significantly affect learning (F=0.71, df=4,4, p=0.591). Subjects in the experimental group commented that the feedback was useful in the early learning stages but that they relied les and less on the feedback unit as training progressed. Based on the results and the comments of participants, design modifications to the feedback unit were recommended.
OPTIMIZATION OF LOWER LIMB PROSTHESES BY INERTIAL LOADING
Bach, T. M. and Jans, M.
La Trobe University, Bundoora, Victoria, Australia
A number of investigators have suggested that the mass and mass distribution of modern lower limb prostheses are sub-optimal and that substantial improvement could be obtained by adding mass to the prosthesis. Many of these studies have demonstrated improved function with added mass while others have shown little or no effect. In some studies, attempts have been made to identify optimal inertial properties. It appears that the mass and mass distribution of lower limb prostheses are important determinants of functional outcome but developments in this area have been hampered by a lack of a sound theoretical approach to the problem. The purpose of this paper is to review studies of the effects of inertial loading in transtibial (TT) and transfemoral (TF) amputees and to present a theoretical approach developed in our laboratory which provides a framework for the interpretation of these results.
In TF amputees, we have used a computer simulation to predict an added mass and mass location which would provide the greatest swing phase symmetry between the sound and prosthetic limbs. In empirical laboratory tests of these predictions, optimized prostheses provided the best function of a number of combinations of added mass and mass location. Energy expenditure was significantly lower and gait symmetry and subjective ratings of performance were significantly higher for computer optimized prostheses compared to unweighted prostheses. Similar studies of TT amputees are currently in progress and an overview of results will be presented.
It is possible to explain these and other results in terms of a compound pendulum model of the shank-foot segment of the prosthetic limb.
