Just the slightest change in the morphology (shape and structure) of the hip joint can cause problems for some people. Athletes are affected most often as they push their bodies past the normal limits of motion repeatedly. Some of those problems such as femoroacetabular impingement (FAI) can lead to early joint osteoarthritis.
As the author of this article points out, early recognition of femoroacetabular impingement (FAI) is important. Early intervention can help prevent painful, debilitating arthritis when the athlete hits his or her 30s to 50s. What is FAI and what can be done about it?
Femoroacetabular impingement occurs in the hip joint. Impingement refers to some portion of the soft tissue around the hip socket getting pinched or compressed. Femoroacetabular tells us the impingement is occurring where the femur (thigh bone) meets the acetabulum (hip socket). There are several different types of impingement. They differ slightly depending on what gets pinched and where the impingement occurs.
The first type of femoroacetabular impingement (FAI) is called pincer impingement. This type occurs when the rim of the acetabulum (hip socket) sticks out farther than normal.
There are several causes of this problem. There can be an overgrowth of cartilage forming the rim or even extra bone that forms in the area. Sometimes the hip socket is tilted backward slightly. In either case, every time the athlete flexes the hip, the rim that’s sticking out too far pinches the labrum against the neck of the femur. The labrum is a fibrous rim of cartilage around the socket to help give it some depth. It is a normal part of the hip biology.
The second type of femoroacetabular impingement is called CAM impingement. Normally, the head of the femur is a smooth, round shape. It is even all around so it can rotate inside the socket evenly. But any change in the shape can cause it to hit one point of the socket more than the others as the head of the femur moves inside the socket.
The asymmetrical rotation of the pistol-shaped femoral head is called the cam effect. Anytime something repeatedly rubs against something unevenly, there is uneven wear, tear, and damage. In this case, when the hip is flexed or bent, the unevenly shaped femoral head doesn’t glide over the labrum as it should. Instead, it bumps up against the edge of the cartilage. Over time, the labrum gets worn down to the bone.
And finally, the third type of femoroacetabular impingement is a combination of the two just described (pincer and cam). Cam impingement is more common in males and brings on symptoms earlier than the pincer type. The combination of both types together causes problems sooner than if only one type was present.
How does the orthopedic surgeon know that the hip and/or groin pain a patient reports is coming from femoroacetabular impingement? And how do they know what type it is? The diagnosis begins with a patient interview and history. Then comes a physical exam. The physician looks at pelvic and hip motion and palpates muscles and tendons for areas of tenderness.
There may be a telltale snapping of the iliopsoas tendon as the patient moves the leg from one position to another (flexion to extension, external rotation to internal rotation). Several other tests can be done to identify what’s going on.
As is often the case, one problem can lead to others. With femoroacetabular impingement, hip bursitis can develop. The gluteal (buttock) muscles may be extra tender or sore from trying to compensate and correct the problem.
The clinical exam is followed up by imaging studies including X-rays, MRIs, and CT scans. X-rays show the presence of any extra bone build up as well as the position and alignment of the bones and joint. Using different X-ray views, the radiologist and orthopedic surgeon can see the shape of the femoral head and look for any asymmetries (i.e., where the head is no longer an even round shape).
MRIs can show any damage to the labrum but not necessarily to the surface of the hip joint. The presence of edema (swelling) under the bone may show up and requires further evaluation to decide if it is from femoroacetabular impingement or some other cause (e.g., cyst, tumor, stress fracture). Using MRI with a dye injected into the joint (called magnetic resonance arthrography or MRA) provides greater detail of the joint surface and may be needed.
CT scans help show the exact shape of the bone and reveal any abnormalities in the bone structure. CT scans might be the most helpful when arthroscopic surgery is planned. It gives the surgeon a better idea of what needs to be done to reshape the bone. If the procedure is going to be done with an open incision, then the CT scan isn’t necessary. The surgeon will see everything once the area is opened up.
More details about planning treatment for femoroacetabular impingement (FAI) will be provided in part 2 of this article series. This first article focused on accurately diagnosing the problem. Since it is known that FAI leads to damage of the hip that can end an athlete’s career, early recognition is important to prevent the severe problems that often develop.