Abstract
Osseointegration trans-femoral implants are a novel orthopaedic anchoring method for connecting the stump and prosthesis after an above-knee amputation operation. The implant’s long-term stability is considered to be the essential condition of the osseointegration operation and rehabilitation. However, the stability could be diminished by the bone remodelling that occurs over. No such bone remodelling has been investigated in patients with osseointegrated trans-femoral implants. A bone remodelling algorithm has been developed with computer aided simulation by applying the Finite Element Method (FEM) for patients with osseointegrated trans-femoral implant. These bone remodelling algorithms predict the change of bone geometry that occurs in these patients. Various mechanical factors have been considered as the stimulus that governs the bone growth and bone loss. To achieve the objective of deducing the bone remodelling algorithm, the feasibility and the reliability of the modelling method for Finite Element (FE) femur models were first investigated. A technique was developed for creating FE models of the non-implanted and implanted femur. This has enabled the effect of using different size implants, where clinically representative incomplete contact between femur and implant are modelled, to be assessed. Subsequent FE modelling was undertaken on implanted femurs where bone remodelling has occurred over a 5 year period using long term X-ray data to update the original femur models. This part of study led to the conclusion that the non-adapted and the adapted femur models can be accurately reconstructed using the per-surgery computer tomography (CT) scans and long-term X-ray images. The results of the Finite Element Analysis (FEA) from the femur models showed the bone remodelling rate was regulated by a double control mechanism and a bone remodelling equation with two mechanical variables was deduced. A comparison of the experimental (measured from X-ray images) and the predicted (calculated by bone remodelling equation) bone growth data showed good correlation. Overall, the results of this study indicated that significant bone remodelling occurred in the patient with osseointegrated trans-femoral implants. Further, this was could be described well by the bone remodelling equation. Optimisation of the femur modelling method and osseointegration patient gait measurement should contribute more accurate femur models. If such future works can be achieved, further work should be directed towards enhancing the bone remodelling equation and implementing it within an iterative FE framework.