Biomechanical models for the analysis of partial foot amputee gait

Partial foot amputation is becoming a more viable and common surgical intervention for the treatment of advanced diabetes, vascular insufficiency and trauma. Statistics describing the incidence of partial foot amputation are scarce. In Australia, it is not known how many people undergo partial foot amputation annually however in the United States upwards of 10,000 partial foot amputations are performed each year. Many of these procedures are likely to be in preference to below-knee amputation under the pretext of improved function associated with preserving the ankle joint and foot length despite common failings including ulceration and equinus contracture which can lead to more proximal amputation. There is a substantial body of literature, which lends support to the contention that much of clinical practice has not been based on experimental evidence describing the gait of partial foot amputees or the influence of prosthetic and orthotic intervention. This limited scientific underpinning of practice may contribute to the common failures and allow misconceptions, such that preserving foot length and the ankle joint improves function, to perpetuate. The aim of this investigation was to develop accurate mechanical models to analyse the effects of amputation and prosthetic/orthotic intervention on the gait of partial foot amputees. Anthropometric and linked-segment inverse dynamic models were developed to accurately depict the affected lower limb and account for prosthetic/orthotic intervention and footwear. These novel techniques enhance the accuracy of kinetic descriptions, affecting the results obtained for terminal swing phase. These models more accurately portray the requirements of the hamstring and gluteus maximus muscles to decelerate the swinging limb in response to the net increase in mass and inertia of the limb segments due to prosthetic fitting. With an appreciation of the influence these models have on the estimation of kinetic parameters, the gait of partial foot amputees was investigated. Kinematic abnormalities were primarily limited to the ankle and were characterised by poor control of tibial rotation during the mid-stance phase consistent with reduced eccentric work by the triceps surae muscles. The centre of pressure excursion and anterior progression of the trunk outside the reduced base of support was limited until contralateral initial contact; which could reflect triceps surae weakness and an inability to substantially load the prosthetic forefoot. Reductions in power generation across the affected ankle were the result of reductions in the angular excursion of the ankle and reductions in the ankle moment. Reductions in the ankle moment were consistent with the limited excursion of the centre of pressure commensurate with peak ground reaction forces. During early stance, concentric activity of the hip extensor musculature was observed, bilaterally, to advance the body forward. Results from these investigations focus on restoring power generation across the ankle given that the primary reason for preserving the ankle joint and calf musculature would seem to be the ability to use it functionally. Improvements in triceps surae strength may allow individuals to capitalise on improvements in below ankle prosthetic design and affect significant improvements in ankle power generation. In conjunction with improvements in muscle strength, below ankle prosthetic design needs to incorporate a socket and toe lever capable of comfortably distributing forces caused by loading the prosthetic forefoot. In conjunction with improvements in muscle strength, above ankle prosthetic design needs to incorporate an ankle joint. The development of a suitable joint poses significant design challenges for the engineer and prosthetist. This thesis provides new insights into the gait of partial foot amputees and the influence of prosthetic/orthotic design, which challenge common misconceptions underpinning clinical practice, prosthetic prescription and surgery. Aside from advancing the understanding of partial foot amputee gait and the influence of prosthetic/orthotic fitting, these investigations challenge and aim to improve current prosthetic and rehabilitation practice. Thus reducing the incidence of complications, such as ulceration which have been associated with the need for more proximal below knee amputation and allow partial foot amputees to utilise the intact ankle joint complex.