An analysis of collar function and the use of titanium in femoral prostheses.

The quest to avoid or forestall late mechanical failures (loosening, hardware breakage) in total hip arthroplasty has led to numerous femoral component design variations which have included alterations in component geometry and constituent material properties. An understanding of the mechanical effects of these designs is required to make a rational selection of components from among competing designs. The recent advent of titanium femoral components, particularly those incorporating a proximal medial collar, reflects a belief that the proximal medial femoral cortex plays an important role in preventing femoral component loosening. The actual function of the proximal medial femoral cortex in supporting the femoral component and the role of that support in relation to component loosening are, however, subjects of considerable debate. It is clear that the state of stress and strain in the proximal medial femoral cortex is strongly affected by the implantation of femoral component^.^^^^'^^'^''^-'^ It is also clear that this region of the femur commonly (as many as 70% of cases) resorbs