A combined computational and clinical approach to investigating bone health in lower-limb amputees
File(s)
Author(s)
Kaufmann, Joshua J.
Type
Thesis
Abstract
A disproportionate number of lower-limb amputees are diagnosed with osteopenia and osteoporosis of the hip each year. The issue effects amputees of all ages, increasing their lifetime risk of hip fracture dramatically. Hip fracture compromises short and long-term prosthetic use and therefore has serious implications on mobility, physical dependency and morbidity. Through both clinical evaluation and computational modelling, this research aimed to determine the effect of lower-limb amputation on long-term bone remodelling in the hip and to understand the potential underpinning mechanisms for bone degradation in the younger amputee population.
The issue was investigated clinically with the aim of determining whether bone loss in amputees is systemic through the whole body or localised to the amputated limb. This was done by comparing bone-mineral density (BMD) in both hips and the lumbar spine of a young military population of 86 amputees and 82 control subjects. BMD in the femoral neck of amputee subjects was found to be significantly lower than in controls while BMD at the spine in each population was similar. In unilateral amputees, there was an additional degree of localisation between amputated and intact limbs where bone loss in the amputated limb was not reflected in the intact limb.
Patient specific musculoskelatal (MSK) and finite element (FE) models were developed for one unilateral, below-knee amputee, one bilateral, above-knee/through-knee amputee and one body-matched control subject. MSK modelling enabled comparison of muscle and joint reaction-forces throughout daily loading activities and provided the loading scenario implemented in FE. A strain driven bone adaptation algorithm applied in FE demonstrated the effect of loading on the femur structure of each subject.
Load placed on the femur and hip joint is lower in both amputee subjects than in the able-bodied control. In the unilateral below-knee amputee this is predominantly driven by functional compensation of the contralateral limb. In the bilateral, above-knee amputee the prosthetic appears to shield the amputated femur from the direct forces generated during weight-bearing. As a result of both, large areas of the bone no longer receive the stimulation they would have pre-amputation.
Overall, both clinical and computational findings suggest that changes in bone health could be predominantly mechanically driven where altered joint and muscle loading causes altered mechanical stimulus in the femur; or unloading osteopenia. Then, over many cycles of remodelling, a net bone loss occurs. Importantly, this suggests the issue could be preventable, or even reversible, with the implementation of targeted loading regimes or changes to the design of the prosthetic socket. Moreover, there could be a benefit to distinguishing between bone loss in the young amputee population and systemic osteoporosis secondary to aging and endocrine changes.
The issue was investigated clinically with the aim of determining whether bone loss in amputees is systemic through the whole body or localised to the amputated limb. This was done by comparing bone-mineral density (BMD) in both hips and the lumbar spine of a young military population of 86 amputees and 82 control subjects. BMD in the femoral neck of amputee subjects was found to be significantly lower than in controls while BMD at the spine in each population was similar. In unilateral amputees, there was an additional degree of localisation between amputated and intact limbs where bone loss in the amputated limb was not reflected in the intact limb.
Patient specific musculoskelatal (MSK) and finite element (FE) models were developed for one unilateral, below-knee amputee, one bilateral, above-knee/through-knee amputee and one body-matched control subject. MSK modelling enabled comparison of muscle and joint reaction-forces throughout daily loading activities and provided the loading scenario implemented in FE. A strain driven bone adaptation algorithm applied in FE demonstrated the effect of loading on the femur structure of each subject.
Load placed on the femur and hip joint is lower in both amputee subjects than in the able-bodied control. In the unilateral below-knee amputee this is predominantly driven by functional compensation of the contralateral limb. In the bilateral, above-knee amputee the prosthetic appears to shield the amputated femur from the direct forces generated during weight-bearing. As a result of both, large areas of the bone no longer receive the stimulation they would have pre-amputation.
Overall, both clinical and computational findings suggest that changes in bone health could be predominantly mechanically driven where altered joint and muscle loading causes altered mechanical stimulus in the femur; or unloading osteopenia. Then, over many cycles of remodelling, a net bone loss occurs. Importantly, this suggests the issue could be preventable, or even reversible, with the implementation of targeted loading regimes or changes to the design of the prosthetic socket. Moreover, there could be a benefit to distinguishing between bone loss in the young amputee population and systemic osteoporosis secondary to aging and endocrine changes.
Version
Open Access
Date Issued
2021-01
Date Awarded
2021-07
Copyright Statement
Creative Commons Attribution NonCommercial Licence
License URL
Advisor
Phillips, Andrew
McGregor, Alison
Sponsor
Imperial College London
Publisher Department
Civil and Environmental Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)