Three dimensional morphological assessment of normal and FAI femoral head geometries

Cam type femoroacetabular impingement (FAI) is characterized by a nonspherical femoral head that shears itself into the hip socket (acetabulum) causing damage to the labrum and adjacent cartilage; a hip with slightly abnormal geometry is prone to develop early osteoarthritis due to increased mechanical demand. FAI diagnosis using plain film radiographs is difficult since the subtlest deformities are often missed. Improved methods incorporating 3D hip morphology to locate deformities could clarify the best surgical approach. This study develops a preoperative 3D modeling protocol for cam FAI patients and statistically compares femoral head morphologies between cam patients and normal controls. The proximal femurs of ten patients with suspected cam FAI and ten cadaver femurs, to serve as controls, were scanned using computed tomography (CT). Computer generated 3D models of each femoral head were then fit to spheres and rotational conchoids using a least squares regression. The results confirm that joints with cam FAI are morphologically abnormal compared to normal hips. However, unlike measurements from radiographs, 3D models allow for visualization of the varying magnitude and location of the deformity. To this end, the approach that was used in this study to quantify FAI pathology may be applied to assist with the diagnosis and pre-operative surgical planning for patients with suspected cam FAI.