| The knee is one of the most important joints in the human body. Degenerative damage in this joint sometimes results in function loss, and leads to total knee replacements (TKR). However, mild wear of ultra-high-molecular-weight-polyethylene (UHMWPE) tibial inserts greatly affects the longevity of TKRs. To understand the dynamics of the natural knee and to improve TKR implant designs, it is essential to develop proper tools to study the contact and wear mechanism of the knee. This dissertation provides the conceptual and computational details of a methodology for investigating contact and wear in the knee during human movements. It includes four steps: articular geometry preparation, efficient surface-surface distance evaluation, three-dimensional contact model development, and dynamic contact model construction. The geometry of the articular surfaces is obtained from CT and MRI images for the natural knee or from CAD models for the implant designs. The contact model is incorporated into the dynamic simulation system. The dynamic simulation is driven by in vivo fluoroscopy data of gait or stair. Wear is predicted by a computational wear model using the dynamic contact solutions. Sample analyses compare well to experiment results and TKR insert retrievals with reliable accuracy within reasonable CPU time.; This methodology is applied to the study of wear sensitivity of TKR polyethylene to insert thickness and patient body mass. The simulations of twenty five combinations of insert thickness (6, 8, 10, 12 and 14 mm) and body mass (50, 75, 100, 125 and 150 kg) are performed in the neighborhood of a nominal simulation that predicts in vivo damage well both quantitatively and qualitatively. Each simulation predicts maximum wear, creep, and damage depth, along with damage area and volume lost. When the polyethylene thickness increases, maximum wear depth, creep depth, damage depth, and volume lost decrease while wear area increases. The regression equations are fit to the results and can be used to estimate the wear benefit achieved by using a thicker insert given the patient's body mass or by losing weight, given the insert thickness. |
