COMPUTER-SIMULATIONS OF STRESS-RELATED BONE REMODELING AROUND NONCEMENTED ACETABULAR COMPONENTS

The authors have used computer modeling techniques to examine stress-r elated bone changes in the acetabular region. Using a previously devel oped theory for bone development and adaptation, the authors simulated the distribution of bone density in the natural pelvis as well as cha nges in bone density following total hip arthroplasty. The geometry of the finite element model was based on a two-dimensional slice through the pelvis. Starting from a solid, homogeneous structure, the compute r simulations predicted the distribution of bone density throughout th e natural pelvis. The predicted bone density distribution in this firs t simulation agreed well with the actual bone density distribution onl y when loads representing multiple activities were incorporated. Using the predicted density distribution as a starting point the authors mo dified the finite element models to study two designs of noncemented, metal-backed acetabular cups. The simulations with fully fixed bone-im plant interfaces predicted extensive loss of bone density medial and i nferior to the prosthetic components. The simulations with loose inter faces led to more moderate losses of bone density, indicating a load t ransfer more similar to that which occurs in the natural joint. The di fferences in simulated bone remodeling between the two component desig ns were quite minimal. These results indicate that acetabular componen ts with full bony ingrowth may induce significant stress-related bone remodeling due to a nonphysiologic transfer of load.