The Effects of Femoral Component Malalignment and Femoral Head Necrosis on the Biomechanical Performance in Resurfacing Hip Arthroplasty

Hip resurfacing arthroplasty, with its bone-conserving nature and improvement in bearing surface designs, has recently seen a resurgence of interest. From our previous clinical experience, we had performed hip resurfacing arthroplasty in thirty-eight consecutive patients in our hospital. The results with use of serial radiographs indicated good clinical outcome. To the best of our knowledge, however, lack study has been performed to address the concerns of malalignment of femoral component and osteonecrosis of femoral head on the biomechanical performance following resurfacing arthroplasty. We hypothesize that the improper placement of femoral component and the existence of femoral head necrosis might alter femoral neck loading and that the cortical strain pattern reflecting this loading is directly related to the spatial orientation of the femoral component and the femoral head necrotic lesion size. An additional hypothesis is that these alterations in femoral neck loading resulted in changes of the resistance to neck fracture under axial loading. A systematic exploration combining in vitro mechanical experiment and finite element analysis is thus designed to investigate the biomechanical performance of the postoperative femur on circumstances that the femoral components are in improper placement as well as the existence of femoral head necrosis. The contents of current third-year study are summarized as follows: A. The first-year study (Experiment for evaluation of femoral component malalignment) Thirty-six (36) synthetic femora will be used and divided into six groups based on different placement of femoral components: (A) Varus, (B) Valgus, (C) Neutral, (D) Anteversion, (E) Retroversion and (F) Intact without implantation (six in each). Mechanical experiments including: (1) Surface strain measurement; (2) Static compressive failure test and (3) Dynamic cyclic tests until failure, will be performed using MTS testing machine. The biomechanical performance of the postoperative femora, including the strain alteration, failure load and the longevity of the postoperative femora under cyclic loading among groups will be compared accordingly. B. The second-year study (Experiment for evaluation of femoral head necrosis) Mechanical performance following resurfacing replacement for femora with various femoral head necrotic lesion sizes will be compared by in vitro experiment. To create the necrotic lesion, a conical drill is used to drill the synthetic femora, starting from the most superior part of the femoral head to femoral head center. Twenty-four (24) synthetic femora will be used and divided into four different levels of simulated necrotic lesion sizes: 15%, 25%, 33%, and 50% of the femoral head (six in each). Mechanical experiments identical to the first-year study will be repeated. The biomechanical performance for femora with different levels of necrotic lesion size will be examined. C. The third-year study (Finite element analysis) By using the finite element analysis, the biomechanical performance affected by malalignment of femoral component and femoral head necrosis will be evaluated based on identical conditions as described in the former two years. The results will be compared with those of biomechanical experiments, and the roles of malalignment of femoral component and femoral head necrosis on resurfacing replacement is expected to achieve.

Project ID:PB9808-2370
External Project ID:NSC98-2221-E182-009-MY2