Stress Analysis with Resurfacing Hip Prosthesis

Principal Investigator: Kai-Nan An, Ph.D.
Project Coordinator: Mark E. Zobitz — zobitz.mark@mayo.edu

Figure 1: Von Mises stresses in femoral neck (left) and cross section of femoral head (right) (MPa).

Survival rate of the resurfacing hip prosthesis in the past has been unpredictable. Aseptic loosening due to bone resorption in the femoral head is a major cause of failure. A main complication of resurfacing is femoral neck fractures, possibly caused by bone resorption as well. An important mechanism of bone resorption is wear induced osteolysis. Indeed, low-wear bearing couples (metal-on-metal) dramatically increased short-term survival. Bone resorption can also be caused by stress concentration or stress resorption (shielding). We hypothesized that changes in design of the stem and shell of the prosthesis could reduce bone resorption and thus decrease aseptic loosening and femoral neck fractures. A finite element model of the proximal femur with a resurfacing prosthesis was created. Parametric tests were performed for implant stiffness, stem length and shell size. Our results demonstrated that stress distribution in the femoral head is affected by the implant characteristics (Fig. 1). Stress profiles were similar to patterns of bone resorption.