The hip is a ball and socket joint that connects the thigh bone (femur) to the hip socket in the pelvis (acetabulum) to allow movement of the legs. The hip joint consists of the thigh bone and pelvis that are both covered in a smooth tissue called cartilage and separated by fluid to cushion the joint and allow smooth movement. The bones are held together by ligaments, tendons and muscles.
In a normal hip, the head of the femur moves smoothly within the hip socket enabling movement without pain. With femoro-acetabular impingement or FAI, the femur pinches against the cartilage in the hip socket impeding smooth movement and causing pain.
Femoro-acetabular impingement is a condition in which the femoral head does not perfectly fit into the acetabulum due to the bones of the hip joint growing abnormally. This causes the bones in the hip joint to rub against the other on movement resulting in damage to the joint.
Femoro-acetabular impingement can cause:
- Hip arthritis
- Labral tears – The labrum is a ring of fibrous cartilage that sits along the rim of the hip socket (acetabulum) to ensure the top of the thigh bone (femoral head) is head securely in the socket. Tears to the labrum can result in pain, locking or clicking of your hip joint, and reduced movement.
- Cartilage damage
There are three types of femoro-acetabular impingement:
- CAM impingement deformity – the femoral head is not perfectly round and cannot rotate smoothly in the hip joint. This causes the cartilage to be worn away in places, and the bones to rub against each other on movement.
- Pincer – occurs when the acetabulum grows too far over the femoral head resulting damage to the labral cartilage.
- Combined – occurs when a combination of CAM and Pincer types of femoro-acetabular impingement are present.