Date of Award

4-2010

Degree Name

MS in Engineering - Biomedical Engineering

Department

Biomedical and General Engineering

Advisor

Scott Hazelwood

Abstract

Calculating femoral bone density changes after hip arthroplasty is of interest to researchers and clinicians for predicting the longevity of the prosthetic implant and the surrounding bone. Recently clinicians have been administering bisphosphonate drugs in an attempt to reduce the bone resorption due to stress shielding caused by these implants. Current strain-adaptive computational models with bisphosphonate treatment don’t predict the long term effects or look at treatment with hip resurfacing implants. The main goal of this study was to create and validate a computer model of the human femur incorporating a bone remodeling algorithm based on biological remodeling processes and bisphosphonate drug treatment. A secondary objective was to then create various bisphosphonate drug treatment scenarios and evaluate differences in bone density, damage, and activation frequency. Experimental studies were used to validate the model and the effects of bisphosphonates. A finite element model created from a CT scan of a cadaveric femur, a bone remodeling algorithm, and a bisphosphonate algorithm were incorporated into the model with loading conditions representative of walking and stair climbing. The model was allowed to evolve from an initial state of homogenous density to a steady state form with a density similar to that of the femur. Reduced loading representative of decreased muscle forces were applied to the steady state form to simulate preoperative conditions of a patient with hip osteoarthritis. Both a femoral hip resurfacing component and an uncemented, tapered stem were then integrated in the computer model representative of a postoperative state. Bisphosphonate treatment was applied to both the preoperative and postoperative states in several scenarios after untreated simulations. Bone loss was predicted over a six year postoperative period for both implants and varying treatments. Femoral bone loss in bisphosphonate treatment scenarios matched results seen clinically. Bone volume fraction (BVF) showed little change between one year preoperative to one year postoperative Alendronate treatment and one year postoperative Alendronate treatment for a specific implant type. Both treatment scenarios increase the BVF over no treatment. Pretreating with Alendronate appears to help against femoral neck fracture. This study successfully created a three-dimensional finite element model able to simulate long term effects of the remodeling process in bone with Alendronate treatment. The results show an importance of treatment timing for both types of implants especially when potentially requiring a revision surgery.

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