Effect of stem fixing methods on stress and bone mineral density in the proximal femur following hip resurfacing arthroplasty

Abstract

To construct different 3-D finite element resurfacing arthroplasty of hip models and to explore the biomechanics influences of cement mantle varying in thickness on stress distribution and stressshielding in the proximal femur following hip resurfacing arthroplasty (RSAH), and evaluate the changes of bone mineral density in femur after RSAH , in order to find the adaptive methods to stem fixing. A comparative study was carrie out in patients who underwent RSAH. The bone mineral Density of the proximal femur was measured through dual energy X-ray absorptiomenty of the four zone at post-operation and unoperation 6 months. Changes of bone mineral density ratio in proximal femur between post-operation and unoperation were compared and analyzed.the finite element models of RSAH with different thickness of cement mantle and normal femur were developed and stress analysis was performed under the load of body weight. The mean ration of bone mineral density of proximal femur in zone 1, 2 , 3 increased which was no significantly different from other areas (P > 0.05), the mean ration of bone mineral density of proximal femur in zone 4 and 5 increased which was significantly different from other areas (P < 0.05). Comparing with the 0 mm cement mantle model, the ratio of stress shielding of the cancellous bone around the stem in 1 mm cement mantle model has slightly increased, but also was less than 17%. The ratio of stress shielding was increased obviously in the 2 and 3 mm cement mantle mode and more than 17% in 1, 2 and 5 zone. The cement around stem not thicker than 1 mm produced slightly effect to the stress decreasing and did not result in marked stress shielding in the proximal femur following RSAH, and the bone stock of proximal femur can be well perserves and recovered.