What is the relationship between Femoroacetabular Impingement and Osteoarthritis?
Patients with Femoroacetabular Impingement (FAI) present with groin pain exacerbated by sitting or athletics. Hip flexion is limited to 90 degrees. They have limitation in internal rotation at the 90 degree flexed position with pain at the end point of internal rotation (impingement sign). They may have a click/snap with hip rotation as a result of a labral or chondral lesion. The mechanism underlying FAI is that normal motion such as flexion results in abnormal contact between the femoral head or proximal femur at the head–neck junction, and the anterior rim of the acetabulum. This can lead to labral tears and early OA. Two types of FAI are recognized:
- a. Cam impingement is caused by any deformity of the proximal femur or femoral head resulting in an aspherical femoral head with loss of the normal femoral head–neck offset (pistol grip deformity). Flexion of the hip causes the abnormal femoral head to rotate into the acetabulum causing stress on the labrum and cartilage of the anterosuperior acetabular rim. A cross-table lateral radiograph, computed tomography scan, or magnetic resonance imaging (MRI) may show a cam deformity (so-called because of its resemblance to a camshaft in an engine) at the femoral head–neck junction.
- b. Pincer impingement is caused by local or global overcoverage of the femoral head by the acetabulum. Hip flexion compresses the labrum against the acetabular rim cartilage. Radiographs show a deep acetabular socket
The treatment is surgical removal of bony factors contributing to abutment of the femoral head and/or neck with the acetabular ring.
