The Role of Femoral Head Necrosis on Hip Resurfacing Arthroplasty---Thermal Damage Potential, Component Stability and Stress Distribution (I)

Hip resurfacing arthroplasty, with its bone-conserving nature and improvement in bearing surface designs, has recently seen a resurgence of interest for the treatment of femoral head necrosis. 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 component stability, stress distribution and potential thermal injury in surface replacement for the treatment of osteonecrosis of femoral head. We hypothesize that necrotic lesion size of femoral head might influence the component stability, stress distribution following resurfacing arthroplasty and heat generated by polymerization of bone cement during hip resurfacing for femoral head necrosis are sufficiently high to cause thermal necrosis of the remaining bone. A systematic exploration combining laboratory thermal measurement, in vitro mechanical experiment and finite element analysis is thus designed to investigate the temperature profile at the cement-bone interface and postoperative stability of the prosthesis as well as stress distribution in varying sizes of necrotic lesions following implantation of resurfacing hip prosthesis. The contents of current three-year study are summarized as follows: A.The first-year study (Temperature Profile Evaluation): A laboratory model to analyze the temperature profile at the cement-bone interface in varying sizes of necrotic lesions as well as the effect of pulsed lavage on the reduction of thermal injury will be developed. Peak temperatures and durations of temperatures above 50℃ are measured and compared among four necrotic lesion sizes: 15%, 25%, 33%, and 50% of the femoral head and a control group in which no cystic lesion existed, with the specimens being tested under 37℃ saline bath or with copious pulsed lavage. B. The second-year study (Biomechanical Experiment): Component stability following resurfacing replacement will be compared by in vitro biomechanical experiment. Thirty (30) synthetic femora will be used and divided into five different levels of simulated necrotic lesion size. Mechanical experiments including: (1). Static compressive test with measurements of surface strain of femoral neck and angular motion of component; and (2). Dynamic cyclic tests until failure will be performed using MTS testing machine. The biomechanical performance among groups including component stability and the longevity of the hip joint for femur with different levels of necrotic lesion size will be compared accordingly. C. The third-year study (Finite Element Analysis): By using the finite element analysis, the evaluation of stress distribution following resurfacing replacement in varying sizes of necrotic lesions will be carried out. CT scan images of a standard composite femur will be used to generate the 3-D finite element models, and the stress distributions of the postoperative femora will be determined. The results will be compared with those of biomechanical experiments performed in the 2nd year, and influence of necrotic lesion size on resurfacing replacement is expected to be verified.

Project ID:PB9709-3574
External Project ID:NSC97-2221-E182-001