The hip joint is a ball and socket joint. The ball (also called femoral head) is part of the thigh bone (femur) and the socket (acetabulum) is part of the pelvis. Femoroacetabular Impingement (shortened to FAI) occurs when there are subtle changes in the ball and socket that make up the hip joint.
This results in the ball and socket rubbing abnormally against each other, causing wear and damage to structures that are important to the proper function of the hip, such as:
- cartilage (soft cushioning tissue overyling the bone)
- labral (soft tissue providing stability to the joint)
- ligamentum teres (a ligament inside the joint)
Damage to these structures eventually results in osteoarthritis of the hip.
FAI is a common condition, affecting 25% of people and is one of the most common causes of hip arthritis.
There are 2 types of FAI.
- CAM impingement - The bone abnormality is located on the ball.
- PINCER impingement - The bone abnormality is located on the socket.