Acetabular rim profile measurement in femoroacetabular impingement patients - biomed 2011.

Morphological variations in hip joint anatomy are a possible mechanism for femoroacetabular impingement (FAI) which leads to hip osteoarthritis. Significant geometric variations of the acetabular rim exist between patients including variations in depths of the postereosuperior depression (PSD) and psoas valley (PV). Computed tomographic scans of 48 FAI patients were segmented to create three-dimensional bone reconstructions. A pelvic plane was established using bony landmarks at the inferior iliac spines and the pubis. Placing a sphere on the articular surface of each acetabulum, the center of rotation was found. A curve was drawn on the acetabular rim to extract equally spaced points (0.67mm) to maximize output for an accurate representation of the profile. The acetabular plane was fit to the points using the least-squares method and translated to the center of rotation. The rim points were converted to cylindrical coordinates in degrees along the acetabulum and depth with respect to the mean acetabular plane. The mean depth of the PSD and PV were 7.27mm (SD 1.99) and 4.65mm (SD 2.12), respectively. The affected FAI hip was the right hip in 25 patients and the left hip in 23 patients. Comparisons were made on a per-patient basis between the acetabulum with FAI and without, and FAI hips had an increased coverage of the femoral head by the acetabulum. The appearance of cam and/or pincer impingement was also noted. The novel method of quantification of morphometric variations in the acetabular rim will further aid in understanding the development of FAI.