Anatomy of the Hip
The hip is a ball-and-socket joint formed by the acetabulum (the socket) and the upper end of the femur, called the femoral head (the ball). Covering the surfaces of both the acetabulum and the femoral head is articular cartilage, which is a slippery tissue that allows the bones to smoothly glide past one another. The labrum is a strong cartilage around the acetabulum that forms a tight seal around the socket to provide stability to the joint.
Types of Femoroacetabular Impingement (FAI)
- Pincer – This occurs because extra bone extends beyond the normal rim of the acetabulum, which crushes the labrum beneath.
- Cam – In this type, the femoral head is not perfectly round and therefore cannot rotate smoothly in the joint. The bump on the femoral head grinds away at the labrum and articular cartilage, causing labral tears and osteoarthritis.
- Combined – both pincer and cam types are present.
A less common type of hip impingement can occur when the iliopsoas tendon impinges on the front of the hip joint (or more commonly a hip arthroplasty) and causes pain.
Femoroacetabular impingement (FAI) occurs because the bones of the hip did not form correctly during childhood growth. There is generally nothing that can be done to prevent FAI. Some athletes with FAI may begin experiencing symptoms earlier than those who are less active because of vigorous hip movement, but athletics and exercise do not actually cause femoroacetabular impingement.
Not everyone with femoroacetabular impingement experiences symptoms. Those who do generally report:
- Pain, in either the groin area or the outside of the hip
- Sharp, stabbing pain when turning, twisting, or squatting
As part of a physical exam, a doctor will conduct an impingement test, in which the knee is brought up toward the chest and then rotated inward toward your opposite shoulder. Pain indicates impingement. X-rays and/or CT scans will show the shapes of the bone abnormalities, and an MRI will often be ordered to assess damage to the labrum and articular cartilage. These tests will also rule out the presence of other conditions, such as osteoarthritis or hip dysplasia, which may need treatment instead of impingement.
Sometimes, simply resting from vigorous activity and taking over-the-counter pain medication for a short period of time is enough to relieve the symptoms. Physical therapy may be suggested to strengthen the muscles around the hip joint, which will relieve some of the stress on injured labrum or cartilage.
There is some risk that if an impingement is not corrected through surgery, future damage, such as osteoarthritis, will occur to the cartilage and/or labrum.
If non-surgical treatment fails, you may consider surgery. Many impingements can be treated arthroscopically. The surgeon will either repair or clean out any damage to the labrum and cartilage, and may also trim down the bony rim in a pincer or shave down the femoral bump in a cam. If the case is very severe, it may not be possible to do with an arthroscope and will instead require an open incision.
With any surgery involving the hip, there is a risk of infection and blood clots. Hip arthroscopy has a slight risk of injury to nerves around the hip joint. Some procedures around the hip carry a small chance of heterotopic ossification, where healing tissue becomes calcified and turn to bone causing stiffness and pain. More rare but more severe complications of FAI surgery include hip instability or dislocation, femoral neck fracture, and osteonecrosis of the femoral head.
After surgery for FAI, there is generally a period of restricted weight bearing if any repairs were performed on the labrum or if any microfracture procedures were performed on the hip joint cartilage. This can be up to 6 weeks depending on the specific procedure. Physical therapy is usually started very early after surgery to ensure motion and strength of the hip are maintained. It may be up to 6 months before return to high-level sports is permitted.
- Does all hip impingement need surgery?
No, it depends on many factors. Age and activity level are very important considerations, as younger athletic people will tend to have more persistent symptoms and are more likely to cause damage to the hip joint without surgery. Patients who already have significant arthritis in the hip are not good surgical candidates because they will likely still have pain after correcting the impingement.
- If I have FAI, does that mean that I also have arthritis?
No, if hip impingement is detected early then it is unlikely any significant cartilage damage (arthritis) has occurred.
- Does all femoroacetabular impingement cause pain?
No, sometimes stiffness of the hip joint is the only presenting symptom.
- Is an acetabular labral tear different than FAI?
Yes, but labral tears commonly occur as a result of FAI. Simply treating a labral tear with debridement may not treat the underlying cause of impingement and may not relieve your symptoms.
If you have more questions, please call my office at 502-394-6341.