Computer graphic analysis of endosteal expansion after total hip arthroplasty.

Femoral endosteal expansion is known to occur naturally with aging and may contribute to femoral component loosening after cemented total hip arthroplasty (THA). Previous roentgenographic models used to quantify femoral expansion have used a limited number of measurements at arbitrary axial sites in one roentgenographic view. A computer graphic model is introduced, which uses standard anteroposterior (AP) and lateral roentgenograms to reconstruct a three-dimensional model of the femur between the lesser trochanter and the distal end of a cemented prosthesis. The model was used retrospectively to calculate endosteal and periosteal surface area and volume at the time of surgery and at follow-up examination for 22 patients who had been treated with hip arthroplasty (average, 9.3-year follow-up observation). Endosteal surface area and volume were found to increase an average of 3.1 cm2 and 1.7 cm3, respectively. Periosteal dimensions did not change significantly. Overall endosteal expansion occurs in the vicinity of the implanted prosthesis. The extremely low interobserver variability indicates that this model provides a reliable method of following surface area and volume changes around a cemented hip prosthesis.