Radiographic analysis of a low-modulus titanium-alloy femoral total hip component. Two to six-year follow-up.

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Abstract
We performed a detailed serial radiographic analysis of the femoral component of 323 cemented low-modulus titanium-alloy total hip prostheses. There was a low incidence of femoral component loosening as manifested by radiolucent zones at the stem-cement interface or cement fractures. There was also a low incidence of resorption of the calcar and cortical hypertrophy. Comparison of our data with those of others indicated that the incidence of loosening, calcar resorption, and cortical hypertrophy was usually lower than with similarly designed conventional high-modulus Charnley stems. These findings appear to support computer-modeling studies that have predicted a more even distribution of stresses along the entire length of the stem of the titanium-alloy prosthesis. Of the two configurations of femoral components used, the straight stems demonstrated a significantly lower incidence of radiographic evidence of loosening, calcar resorption, and cortical hypertrophy than the curved stems did. These findings have provided sufficient biomechanical rationale for the evolutionary development of the second-generation femoral components, which incorporate many features of the straight stem.