CEMENTLESS IMPLANT COMPOSITION AND FEMORAL STRESS - A FINITE-ELEMENT ANALYSIS

Proximal atrophy and thigh pain are recognized problems with some ceme ntless femoral stems in total hip arthroplasty, It is thought that red uced femoral stress from alterations in load transfer caused by an int ramedullary stem contributes to proximal femoral atrophy, An increase in flexural rigidity and bone stress near the stem tip is thought to c ontribute to thigh pain, A three-dimensional finite element analysis s tudy was performed to calculate stresses in the proximal femur and bon e near the stem tip before and after implantation of a collared, proxi mally coated, cementless femoral prosthesis, The influence of prosthet ic material was examined by changing implant composition from cobalt c hrome to titanium alloy and leaving all other parameters constant, Fem oral stress was increased twofold immediately below the collar with th e titanium implant compared with the cobalt chrome, However, the proxi mal femoral stress in the titanium implanted model was still 1/10 that in the corresponding region of the unimplanted femur model, At the st em tip, as much as a 30% reduction in femoral stress was seen with the titanium stem compared with the cobalt chrome, These findings suggest biomechanical evidence of an advantage for titanium as an implant mat erial compared with cobalt chrome for cementless femoral stems.