
Femoroacetabular impingement (FAI) of the hip, also known as hip impingement, occurs when extra bone forms along one or both sides of the hip joint.
The hip joint is made up of the ball of the femur bone and the acetabulum (socket) of the pelvis. The extra bone causes the ball and socket to have an irregular shape. This causes a mismatch between the two bones, causing the bones to rub against each other during certain activities. Over time, the rubbing can cause joint damage and pain.
Types of FAI
Extra bone can form on the neck of the femur (CAM Lesion), edge of the socket (Pincer Lesion) or both.
- CAM: In CAM-type impingement, extra bone forms along the connection of the head and neck of the femur. This extra bone causes the ball of the femur to rotate abnormality within the socket during certain movements. The bump of bone can cause irregular wear and damage to the cartilage inside the hip joint.
- Pincer: In Pincer-type impingement, extra bone forms along the outside rim of the acetabulum (socket). There is a rim of thick cartilage tissue called the labrum that sits on the outside rim of the socket. When there is extra bone along the socket the labrum can become crushed and damaged.
- Mixed: In mixed-type impingement, there is extra bone along the edge of the socket and the head/neck of the femur.
Causes of Hip Impingement
The exact cause of hip impingement is not clear, but it is related to the hips not growing properly during childhood and adolescent years. The thought is that the extra bone forms to protect a growth plate on the neck of the femur.
Patients who are athletic or physically active tend to have symptoms earlier than those who are not. It is not clear how many people have FAI. Some people never become symptomatic. When symptoms do develop, it is typically a sign of damage occurring inside the hip joint.
Symptoms of FAI
The most common symptom associated with hip impingement is groin pain that is worse with squatting or hip flexion activities. Studies have shown though that not everyone experiences pain in the same location. Pain coming from inside the hip joint may refer to other areas. Studies have shown that up to 30% of patients with hip pain have symptoms in the gluteal/buttock region.
Pain may also refer to the low back or sacroiliac joint. Isolated low back pain, however, is unlikely to be caused by hip impingement. Some patients may experience tight muscles and trigger points in the gluteal region.
Pain may radiate down the front, side, or back of the thigh. Hip impingement is unlikely to cause numbness or pain that extends below the knee. Symptoms below the knee are typically caused by nerve irritation in the back.
Patients with hip problems can develop muscle dysfunction or a limp, which can in turn cause back problems. Some patients experience clicking or popping in the front of the hip. This can be a sign of a torn labrum or a tight hip flexor muscle.
While the symptoms of FAI may come and go, the impact on the hip joint does not go away.
Diagnosis of Hip Impingement
Hip impingement/FAI is usually diagnosed with special hip X-rays and a physical exam. X-rays will usually show extra bone along the head and neck of the femur and/or acetabulum. The X-rays can also show if the socket is twisted backwards (retroversion). A backwards socket is a risk factor for developing FAI.
An MRI of the hip joint will show whether the labrum has been damaged. Early signs of arthritis may not show up on x-rays, but an MRI will allow your doctor to get a good view of the health of the joint surface.
FAI Treatment
We start with nonsurgical treatment, including:
- Rest and avoiding activities that cause pain
- Over-the-counter pain medication including ibuprofen, acetaminophen or anti-inflammatories
- Physical therapy with a therapist who is experienced in treating hip impingement
- Cortisone injection (usually only recommended when arthritis is present)
If conservative treatment fails, we may recommend surgery. Prior to surgery, we usually recommend an injection of numbing medication inside the hip joint to confirm that the hip impingement is the source of pain. This is especially important in patients who do not have typical symptoms of FAI.
Surgery is done arthroscopically through three small one-inch incisions. The procedure usually lasts two to three hours, and patients go home the same day. During surgery, we inspect the joint and shave off any extra bone. If there is a torn labrum, we will usually fix this as well.
Long-Term Hip Impingement Treatment Outcomes
The goal of hip impingement treatment is to control pain and prevent further joint damage. Treatment cannot correct damage that has already been done, and it cannot guarantee that damage will not continue to occur.
Hip impingement research and treatment continue to change at a rapid rate. Treatments continue to evolve, and we are always looking at new techniques. The long-term outcomes and progression of joint damage is a topic that is currently being heavily studied in orthopedic research.
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