Young, Active Patients With Hip PainPain in the groin or buttocks with a loss of hip motion requires special attention. Early diagnosis and treatment is imperative to avoid degenerative changes in the hip joint later in life. There are many possible causes of this type of hip pain. In this article, surgeons from the Rochester, Minnesota Mayo Clinic focus on femoroacetabular impingement (FAI) as a cause of hip pain leading to hip osteoarthritis.
Femoroacetabular impingement (FAI) describes a condition where the top of the femur (thigh bone) pinches the rim of the hip socket. The area that gets compressed is referred to as the acetabular rim. This type of impingement occurs most often when the hip is flexed and internally rotated.
For a long time, it was believed that FAI only occurred in people with some kind of abnormal anatomy of the hip. There was either a backward tilted angle of the hip socket called retroversion, a larger socket than the ball (head of the femur) inside the socket, or flattening of the femoral head. One type of abnormal shape of the hip was labeled a pistol grip because of the resemblance to the grip of a handgun.
More recent studies have shown it's possible to develop FAI even when the hip structure and anatomy are essentially normal. But, in general, more people with acetabular retroversion end up with hip replacements because of osteoarthritis than any other anatomical abnormality.
To get to the bottom of the cause of hip pain, a thorough history and examination are required. The surgeon looks at foot position, leg angles, leg length differences from one side to the other, hip motion, and muscle strength. Gait (walking) patterns are evaluated. Special tests such as the impingement test are done to identify the presence of an underlying FAI as the cause of the painful symptoms and restricted motion.
In the impingement test, the patient is lying on his or her back. The examiner flexes the involved hip and internally rotates the leg while at the same time moving the foot away from the body. This last motion is called hip abduction.
Limited joint motion and/or painful motion are signs of FAI. The further the hip is flexed, the more it hurts. Comparing hip motion from side to side may be helpful, but only if the patient doesn't have the same anatomical changes on both sides.
A second test for posterior impingement can also be done as part of the exam. This test is used to identify pinching of the cartilage along the back side of the acetabulum (hip socket). It is performed by quickly moving the leg into extension and external rotation while the patient is lying on his or her back. The leg to be tested starts in a position dangling off the end of the table. The patient holds the other leg up against the chest in a flexed position. A positive test is indicated by pain in the groin during the test movement.
X-rays, CT scans and/or MRIs may be used to confirm the diagnosis. A special type of MRI called magnetic resonance arthrography (MRA) is becoming very popular. A contrast dye is injected into the hip joint. The dye is absorbed by any areas of damage or degeneration of the cartilage. The surgeon can see if the femoral head has shifted position and/or is stable. Sometimes, a defect in the cartilage is large enough that the femoral head falls into the hole created by the lesion. An MRA would show this type of change.
Another newer type of MRI technique allows the surgeon to see the femoral head and neck and the position of each in relation to the acetabulum. The MRI takes pictures in a 360-degree rotation from above the femoral head. The surgeon can use this information to decide how to reshape the bone during surgery.
X-rays are particularly helpful in seeing structural abnormalities of the bones that can contribute to FAI. Any signs of osteoarthritis (e.g., bone spurs, loss of joint space, cystic changes) are used to classify the condition as grade zero, one, two, or three (no evidence of osteoarthritis to severe osteoarthritis).
Shape and angle of the femoral head and acetabulum can also be visualized on X-ray. The type of impingement can be identified. For example, a comparison of the size of the femoral head to the size of the socket can be made on imaging. Too-large of a socket for the size of the femoral head causes overcoverage. When the leg is flexed past 90 degrees, the femoral head and neck bump up against the pelvic rim (labrum. This is called pincer impingement. Left untreated, the patient can end up with a damaged (torn or degenerated) labrum and even more pain.
A second type of FAI occurs when the pistol grip-shaped femoral head jams into the acetabulum. This is called cam FAI. Many patients have both types of impingement. Women are more likely to have pincer impingement.
The results of all of these tests are important pieces of information when deciding on the best treatment approach. Surgery is often recommended. The surgeon uses all of this information when choosing the best surgical option. The choices include surgical hip dislocation, periacetabular osteotomy, and hip arthroscopy.
Surgical dislocation refers to taking the femoral head out of the socket and making adjustments and repairs as necessary and then putting the head back in place. The operation can be done without cutting through the muscles and with the least amount of trauma possible. Any damage to the labrum can be repaired. Any problems with femoral head and neck mismatch with the acetabulum can be taken care of. This type of surgery allows for preservation of the joint, which is important in young, active adults.
Periacetabular osteotomy corrects the retroversion (determined by a positive test for anterior impingement). The capsule surrounding the hip joint is cut open. The femoral head and neck are reshaped by shaving or cutting off portions of the bone. The goal is to correct the placement of the femoral head in the hip socket.
The third surgical option (hip arthroscopy) to treat FAI allows the surgeon to gain access to the inside of the joint without cutting it open. This avoids pulling the femoral head away from the socket. Arthroscopic surgery also makes it possible to reattach (rather than remove) a torn labrum.
Studies reporting on the results of these three surgical options have helped determine when each procedure is the best choice. For example, surgical hip dislocation works very well for patients with early disease (grades 1 and 2). But this method cannot be used when the femoral head has shifted into the cartilage defect.
Hip arthroscopy works well for some, but not all, patients. Reaching areas in the posterior or back portion of the joint isn't easy. Open surgery works much better for that. Reattaching the labrum on the back side of the acetabulum is especially difficult with arthroscopy. Certain types of abnormal hip anatomy make it technically difficult to make necessary labral repairs. And entering the hip joint can be very challenging if the patient is obese.
One distinct advantage to all three of these treatment techniques is that conversion is still possible if the procedure fails. Conversion refers to having a second surgery to give the patient a total hip replacement.
Hopefully, with early diagnosis and treatment of young, active patients with FAI, conversion won't be needed. Managing the problem by restoring as normal hip anatomy as possible is the first step. In the future, the arthroscopic approach may become the gold standard. But for now, surgical hip dislocation is still the most commonly used surgical approach for FAI. It is used with good success for patients with mild to moderate (but not severe) degeneration of the joint cartilage, surface, and surrounding capsule.
Rafael J. Sierra, MD, et al. Hip Disease in the Young, Active Patient: Evaluation and Nonarthroplasty Surgical Options. In Journal of the American Academy of Orthopaedic Surgeons. December 2008. Vol. 16. No. 12. Pp. 689-703.
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