Three-dimensional hip anatomy in osteoarthritis. Analysis of the femoral offset.

Two hundred twenty-three patients with osteoarthritic hips were analyzed using computed tomography and a specific image processing software (HIP-PLAN) to determine 3-dimensional morphological data of the hip focusing on femoral offset (FO). Mean FO was found to be 42.2 +/- 5.1 mm, 2.2 mm greater than the 2-dimensional FO values reported in the literature. The FO was found to be above 45 mm in 31% of patients and greater than 50 mm in 12%. The error associated with the use of conventional plane x-rays to measure FO was found to be 3.5 +/- 2.5 mm, the x-ray technique generally underestimating the measure of FO. The sum of acetabular and femoral anteversion was found to be out of the safe zone regarding dislocation risk in 47% of patients.