Femoroacetabular impingement (FAI), commonly referred to as “Hip Impingement” occurs when there is increased bony friction in the hip joint due to bony irregularities causing pain and decreased motion. The femoral head and acetabulum rub against each other creating cartilage damage and pain to the hip joint. The damage can occur to the articular cartilage (the smooth white surface of the ball or socket) or the labral tissue (the lining of the edge of the socket) during normal movement of the hip. The labral tissue or articular cartilage can fray or tear after repeated friction. Over time, more cartilage and labrum is lost due to repetitive damage until eventually the femur bone and acetabulum bone impact on one another. Bone on bone friction is commonly referred to as osteoarthritis.
FAI impingement generally occurs as two forms – cam and pincer, or a combination of both:
CAM Impingement – The Cam form of impingement results with an aspherical femoral head and neck. This “out of roundness” causes abnormal contact between the femoral head/neck junction and acetabulum resulting in labral tears
PINCER Impingement – The Pincer form of impingement is when the socket or acetabular rim has overgrown and is too deep. It covers too much of the femoral head resulting in the labral cartilage being pinched. The Pincer form of impingement may also be caused when the hip socket is abnormally angled backwards (acetabular retroversion) causing abnormal impact between the femoral head and the rim of the acetabulum
Most FAI diagnoses are a combination of both CAM and Pincer abnormalities