Multiple femur finite element analysis of the resurfaced femoral head

Abstract

Finite Element Analysis is used extensively to assess the design and variation of surgical parameters in joint prostheses, but the majority of these analyses are undertaken on a single sample. The variation in implant stability has been found to be as large between patients as the variation found between different loading scenarios. Recent investigations have suggested that single sample studies are unable to account for natural inter-patient variation in bone geometry and material property distribution. This thesis investigates two methods which can be implemented to account for the patient variation experienced over the population. The first method involves analysing a group of patients and examining the variation in the results to determine the spread of data over the population. Developments in computer tomography based analyses make multiple sample studies possible; the question remains how many femurs are required to perform a study which accounts for such variations. This work uses computer tomography based finite element analyses on a group of 16 femurs to determine the effect of the resurfacing arthroplasty and variables in the surgical procedure and implant design. Sample sizing techniques are developed in this work and implemented on these case studies to determine whether or not a suitable number of femurs had been analysed in the investigations. The second method utilises probabilistic techniques in the analysis of the implant, these methods are able to account for inter-patient variables along with multiple variables such as surgical parameters and implant design. Two case studies are undertaken on a single femur model; one varying only surgical parameters the second incorporating patient variables such as load and bone density. The thesis determines that probabilistic methods will prove to be invaluable in future implant design analyses, however there will need to be a substantial development of current techniques before this becomes feasible. A more immediate answer to the question of inter-patient variation is the modelling of multiple femurs. This thesis has developed a set of sample sizing calculations that can be implemented in multi-sample studies to determine if a suitable sample sizes have been analysed.

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