Higher Degree Theses
	The Effect of Four Bar Linkage Knee Configurations on Transfemoral Amputee Gait A Computer Simulation of Swing Phase in Human Walking

THE EFFECT OF FOUR BAR LINKAGE KNEE CONFIGURATIONS ON TRANSFEMORAL AMPUTEE GAIT

Leslie James Barnes

Supervisors: T. M. Bach, PhD¹ and W. E. Morrison, PhD^1
1 La Trobe University
² Victoria University of Technology, Melbourne

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.

Timothy Michael Bach

Supervisors: O. M. Evans and I. G. A. Robinson
La Trobe University, Melbourne, Australia

A series of computer simulation and experimental studies were undertaken to estimate the effect on amputee gait of altered inertial characteristics of transfemoral prosthetic limbs.

A ballistic model of swing phase in human walking was developed. Dimensions and inertial parameters of body segments were based on normal anthropometric data. A computer simulation was developed to solve the equations of motion of the model to satisfy cer tain boundary conditions and constraints. Good correspondence between simulation predictions and published observations of human gait characteristics was obtained.

An anthropometric survey was undertaken to describe the inertial characteristics of typical transfemoral prostheses and amputation stumps. A geometric model based on socket and limb measurements was developed to estimate the mass and mass distribution of the stump. Substantial differences from normal limb data were observed for both endoskeletal and exoskeletal prosthetic limbs.

Inertial characteristics of transfemoral prosthetic limbs were used as input data to the swing phase model. Simulation results based on these data were consistent with a number of temporospatial and kinematic alterations which characterize amputee gait. Changes in inertial parameters alone were insufficient to produce good agreement with published observations of amputee gait. Changes in boundary conditions which constrained the simulated performance also had substantial effects.

Finally, the model was used to optimize inertial characteristics of prosthetic limbs by addition of mass to the shank-foot segment of the prosthetic limb. Model predictions were tested in a group of five transfemoral amputees. Results demonstrated that optimizations which maximized swing phase symmetry resulted in combinations of mass and mass location which were preferred by amputees and resulted in lower metabolic energy expenditure than other combinations tested. Performance of unweighted prostheses was significantly worse than weighted conditions. Examination of temporospatial, kinematic, kinetic and energetic patterns provided insights into underlying causes of observed differences.

This study enhanced knowledge of the theoretical basis for normal and amputee locomotion and suggested a means for substantially improving amputee management.

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