The loss of joints at the knee and the ankle leads to changes in movement biomechanics. As the amputee returns to ambulation using a prosthesis, different muscle recruitment strategies are required to compensate for the loss of the force producing elements that spanned the amputated joints. In the unilateral amputee, this compensation usually presents itself as a reliance on the intact limb. In the bilateral amputee, a different compensation strategy is required. Balance is maintained through a new compensation strategy governed by the neuromusculoskeletal control of muscles spanning the hip and the sacro-iliac joint. Highly rehabilitated military amputees, including bilateral through and above knee amputees, are capable of walking at speeds much closer to that of a control group than previously seen. These amputees can ascend and descend stairs and slopes and run at speeds exceeding those of their able-bodied counter parts. However, in consideration of the reduction in available biological elements for the production of internal joint moments, it must be expected that the remaining muscle, and hence joint, elements are experiencing biomechanical overloading in order to achieve the walking speeds and styles displayed. So, there exists an apparent dichotomy: the bilateral transfemoral amputee desires more functionality and the ability to explore more of the world, and yet their body is already experiencing an overload that is likely to be detrimental to the health of the hip and sacro-iliac joints due to an increase in joint contact forces caused by increased muscular recruitment for movement.
The objectives of this research, therefore, are to develop an in depth understanding of the musculoskeletal function of bilateral transfemoral amputees; understand the restrictions on walking in this population; understand the implications of the current functional levels as concerns overall neuromusculoskeletal health; and to propose methods by which functional improvements can be made whilst being mindful of the often conflicting ambition of reducing long-term health implications.
An anatomical study (Chapter 2) was conducted based on high-resolution magnetic resonance imaging from fourteen amputees (twenty-four amputated limbs) and six control subjects. Under an assumption of a similar level of daily activity within each amputee and amputee group, this chapter examined the relationships between muscle volume and amputation level, and explores the muscle recruitment strategies being employed by the amputee in order to regain movement function. This showed that the unilateral amputees developed a compensation strategy based on their contralateral limb, whilst bilateral amputees developed a compensation strategy based on increased capacity in hip abductors, hip adductors, and hip flexors. Scaling methods were presented to allow for the rapid approximation of amputee anatomy based on readily measurable anatomical parameters.
A transfemoral amputee musculoskeletal model was developed and validated (Chapter 3) that fully quantifies the biomechanical loading conditions of the hip muscle and joint architectures in bilateral transfemoral amputees, and incorporates the subject specific anatomical datasets and a cost-function that is tuned to the unique muscle performance characteristics of the transfemoral amputee that were derived in the anatomical study. This study had key assumptions that a static optimisation procedure based on the minimisation of muscle expenditure remains valid for the transfemoral amputee population, and the prosthetic socket to residual limb interface was modelled as a single segment. The model predictions displayed a similarity to subject-measured EMG envelopes that was rated as “Good” or better as determined by the Sprague and Geers’ metrics. The model was found to have an average coefficient of concordance for the whole gait cycle of 58%.
Using the results from the transfemoral amputee musculoskeletal model and the anatomical study, hip joint biomechanical loading conditions were quantified (Chapter 4) with a view to understanding the conflicting ambitions of the reduction of joint overload and the improvement in neuromusculoskeletal capacity for the enhancement of functional capability. It was found that hip joint forces are nearly double that of a control population in the transfemoral amputee when walking at similar speeds, due to the sole reliance on muscles that span the hip for the generation of propulsive force. As a result, the larger muscles of the hip are operating much closer to their capacity thresholds leading to the early onset of fatigue in low-level tasks, such as level-ground walking.
Chapter 5 identified the biomechanics of movement in the bilateral transfemoral amputee and highlighted why the hip joint mechanical loading conditions in this population exacerbate long-term musculoskeletal health risk. Chapter 6 used a case study approach to highlight methods by which these mechanics can be optimised through the implementation of kinematic optimisation techniques, such as the development and use of novel wearable technology to provide real-time information to the subject concerning instantaneous hip joint loading.
The work presented in this thesis shows that the neuromusculoskeletal capacity in the amputee is severely compromised, and the return to walking with a prosthesis requires deep-learning of a new compensation strategy based on the residual capacity, and artificial capacity afforded to the amputee by the prosthetic systems. The biomechanical burden of walking was determined and the elevated risk of the development of mechanically driven osteoarthritis in this population was described alongside the causal biomechanics of this burden. Whilst these risk factors are presented, these analyses of bilateral transfemoral biomechanics are presented in a setting that emphasises the achievement of optimality as opposed to a demonstration of functional deficit. The thesis concludes with a case study that highlights the effect of kinematic optimisation on the loading profile, and the effect that this has on musculoskeletal risk. Continuous rehabilitation is key for long-term, successful functional performance in this amputee group; rehabilitation for this subject group cannot have a defined ‘end-date’. Rehabilitation programmes and resources must be made available to ensure long-term functionality is achieved and maintained.