The influence of the mechanical properties of trans-tibial prostheses on amputee performance
, PhD thesis, Salford : University of Salford.
Achieving the required functionality of a trans-tibial prosthesis during the stance phase of
gait (e.g., shock absorption, close to normal roll-over characteristics, and smooth transition
into swing) depends on the "Amputee Independent Prosthesis Properties" (AIPP), defined
here as the mechanical properties of the prosthetic components distal to the socket that
directly influence the performance of the amputee. Accordingly, if research studies are to
inform the design of better prostheses, AIPP must be a primary consideration. Therefore, the
objectives of this PhD study were: 1) develop a standardised method of AIPP
characterisation, and 2) investigate the effects of AIPP on amputee performance through
human performance testing.
For the first objective, a modified version of the roll-over shape model, referred to as the
Salford AIPP model, was developed in order to characterise the mechanical properties of a
trans-tibial prosthesis (i.e., foot and pylon). A custom-built test-rig was built in order to
measure the parameters of this model.
For the second objective, a series of human performance studies were conducted which
measured the biomechanical, physiological, and subjective performance of five amputees
during four walking conditions: self-selected walking speed (SSWS) on the level, fast walking
speed on the level, SSWS on a 5% grade incline, and SSWS on a 5% grade decline. A custombuilt
foot-ankle mechanism allowed for independent modulation of the prosthetic plantar
and dorsiflexion stiffness. Four combinations of plantar and dorsiflexion stiffness were
tested during each of the four walking conditions.
Results indicated that dorsiflexion stiffness is a dominant factor in trans-tibial amputee gait
performance and decreased stiffness improved performance (e.g., increased gait symmetry
and reduced metabolic energy expenditure). However, future work on identifying effective
AIPP for improved gait performance must involve amputee gait simulation, in which results
from this study may serve as a means of validation.
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