Femoro-acetabular impingement (FAI)

Femoro acetabular Impingement (FAI)  is a clinical syndrome in which the anatomic abnormalities of the femoral head and/or the acetabulum result in an abnormal contact between the two during hip motion, especially in positions of hip flexion and rotation, leading to hip pain.

Three types of morphologic abnormalities can occur in FAI:

1. Cam - characterized by an abnormal/aspherical morphology of the proximal femur.
2. Pincer - characterized by focal or general overcoverage of the femoral head by the acetabulum.
3. Mixed- a combination of cam and pincer impingement characteristics.

Abnormal contact between the femoral head and acetabular rim results in supraphysiologic stress that tears the acetabular labrum and delaminates the acetabular articular cartilage from the underlying bone. Over time this repetitive mechanical insult to the articular tissues leads to hip degeneration and development of hip OA.