Femoro-acetabular impingement or FAI occurs when the ball of the head of the femur does not have its full range of motion within the socket of the acetabulum of the pelvis.

Impingement itself is the premature and improper collision or impact between the head and/or neck of the femur and the acetabulum. This causes a decreased range of hip joint motion, in addition to pain. Most commonly, FAI is a result of excess bone that has formed around the head and/or neck of the femur, otherwise known as “cam”-type impingement. FAI also commonly occurs due to overgrowth of the acetabular (socket) rim, otherwise known as “pincer”-type impingement, or when the socket is angled in such a way that abnormal impact occurs between the femur and the rim of the acetabulum.

A)	Normal Hip
B)	Cam impingement
C)	Pincer impingement
D)	Combination of cam and pincer impingement

When the extra bone on the femoral head and/or neck hits the rim of the acetabulum, the cartilage and labrum that line the acetabulum can be damaged.

The extra bone can appear on x-rays as a seemingly very small “bump.” However, when the bump repeatedly rubs against the cartilage and labrum (which serve to cushion the impact between the ball and socket), the cartilage and labrum can fray or tear, resulting in pain. As more cartilage and labrum is lost, the bone of the femur will impact with the bone of the pelvis. This “bone on bone” notion is most commonly known as arthritis.

Tears of the labrum can also fold into the joint space, further restricting motion of the hip and causing additional pain. This is similar to what occurs in the knee of someone with a torn meniscus.

The extra bone that leads to impingement is often the result of normal bone growth and development. Cam-type impingement is when such development leads to the bump of bone on the femoral head and/or neck.

Normal development can also result in the overgrowth of the acetabular rim, or pincer-type impingement. Hip trauma (falling on one’s hip) can also lead to impingement. The tears of the labrum and/or cartilage are often the result of athletic activities that involve repetitive pivoting movements or repetitive hip flexion.

MRI of a hip with a torn labrum

Impingement can present at any time between the teenage years and middle age. Many people first realize a pain in the front of their hip or groin after prolonged sitting or walking. Walking uphill is also found to be difficult.

The pain can be a consistent dull ache or a catching and/or sharp, popping sensation. Pain can also be felt along the side of the thigh and in the buttocks.

While the cause is not well understood, patients with FAI often complain of low back pain. This pain is often localized to the sacroiliac joint on back of pelvis, the buttock, or greater trochanter on the side of hip. FAI pain typically does not go beyond the level of the knee.

Hip labral tears are also associated with FAI. If you have had your labral tear treated and are still having pain, you may have unrecognized FAI. This FAI may accelerate the loss of hip cartilage leading to further degeneration. Labral debridement is not the same as labral repair.

Non-Surgical Treatment for Femoro-acetabular Impingement

Non-surgical treatment should always be considered first when treating FAI. FAI can often be resolved with rest, modifying one’s behavior, and a physical therapy and/or anti-inflammatory regimen. Such conservative treatments have been successful in reducing the pain and swelling in the joint.

If pain persists, it is sometimes necessary to differentiate between pain radiating from the hip joint and pain radiating from the lower back or abdomen. A proven method for differentiating between the two is by injecting the hip with a steroid and analgesic.

The injection accomplishes two things: First, if the pain is indeed coming from the hip joint the injection provides the patient with pain relief. Secondly, the injection serves to confirm the diagnosis. If the pain is a result of FAI, a hip injection that relieves pain confirms that the pain is from the hip and not from the back.

Hip Arthroscopy in Treating Femoro-acetabular Impingement

Hip arthroscopy, or a "hip scope," is a minimally-invasive procedure. The use of an arthroscope means that the procedure is done using 2-3 small incisions approximately 1/4-1/2 inch long, rather than a more invasive "open" surgery that would require a much larger incision. These small incisions are used to insert the surgical instruments into the joint.

The flow of saline through the joint during the procedure provides the surgeon with excellent visualization. The surgeon is also aided by fluoroscopy, a portable x-ray apparatus that is used during the surgery to ensure that the instruments and arthroscope are inserted properly.

 

The location of the incisions and instruments for the procedure

The instruments include an arthroscope, which is a long thin camera that allows the surgeon to view the inside of the joint, and a variety of "shavers" that allow the surgeon to cut away or debride the frayed cartilage or labrum that is causing the pain. The shaver is also used to shave away the bumps of bone that are responsible for the cartilage or labral damage.

In addition to removing frayed tissue and loose bodies within the joint, occasionally holes may be drilled into patches of bare bone where the cartilage has been lost. This technique is called "microfracture" and promotes the formation of new cartilage where it has been lost.

The procedure is normally done as an "outpatient" surgery. Normally, the patient is under regional anesthesia.

Patients are normally given crutches to use for the first 1-2 weeks to minimize weight-bearing. A post-operative appointment is normally held a week after the surgery to remove sutures. Following this appointment, the patient normally begins a physical therapy regimen that improves strength and flexibility in the hip. After six weeks of physical therapy, many patients can resume normal activities, but it may take 3-6 months for one to experience no soreness or pain following physical activity.

Following a combination of physical and diagnostic exams, patients are deemed suitable for hip arthroscopy on a case-by-case basis. Patients who respond best to hip arthroscopy are active individuals with hip pain, where there exists an opportunity to preserve the amount of cartilage they still have. Patients who have already suffered significant cartilage loss in the joint may be better suited to have a hip replacement.

Studies have shown that 85-90% of hip arthroscopy patients return to sports and other physical activities at the level they were at before their onset of hip pain and impingement. The majority of patients clearly get better, but it is not yet clear to what extent the procedure stops the course of arthritis. Patients who have underlying skeletal deformities or degenerative conditions may not experience as much relief from the procedure as would a patient with simple impingement.

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