-Written by Daniel Weiland, MD
What is Femoroacetabular Impingement (FAI)?
The hip is what is known as a ball and socket joint. The femoral head (or ball) sits in the acetabulum (socket) which is deepened by a cartilage cuff called the labrum. FAI occurs when the ball rubs abnormally on the socket, impinging the labrum. FAI can also damage the articular cartilage, or the smooth cartilage that lines and protects the ends of bones during weight bearing. A majority of time, FAI happens on both sides of the joint.
Types of FAI
CAM Type FAI
CAM FAI occurs when the femoral head and neck are not perfectly round (Figure 1). This causes abnormal contact between the femoral head and the acetabulum. This leads to a shearing force on the articular cartilage which may damage it. CAM FAI usually leaves the labrum intact (Figure 2).
Pincer Type FAI
This is caused by a bony overgrowth of the acetabular rim. It leads to the labrum being crushed between the excess bone of the acetabulum and the femoral head. Pincer type FAI is demonstrated in Figure 3 by what is known as cross over sign. The edge of the anterior wall of the acetabulum (blue line) is medial (inside) to the edge of posterior wall (red line) in the bottom segment of the hip, but in the top segment, this relationship reverses. Cross over sign is an indicator of acetabular retroversion. This basically means the socket sits too far forward, i.e. it over-covers, the head of the femur. The femoral head and neck prematurely contact the acetabulum during flexion and rotation (Figure 4.). This can cause tears, usually in the front portion of the labrum or degeneration of the labrum. In Pincer type FAI the articular cartilage is usually unharmed.
Symptoms of FAI
-Deep pain in the groin
-Continuous dull, aching pain in the hip with occasional sharp, shooting pain
-Increased pain with sitting for prolonged periods of time
-Usually insidious(gradual) onset of pain
-Pain with deep hip flexion and/or internal rotation
Treatment of FAI
In some cases, individuals may overcome FAI with activity modification, medication, and physical therapy. When conservative treatment fails, other options must be considered. A steroid injection with anesthetic can be both diagnostic and therapeutic. The injection is diagnostic in the sense that if there is immediate relief then it verifies the hip joint is the exact structure causing the problem. It is also therapeutic in the sense that it can give relief of symptoms for an indeterminable amount of time. A steroid injection may work for only a few days, or it can last forever. Each patient has a different outcome.
When all other forms of treatment fail, hip arthroscopy must be considered. Surgical intervention addresses repair of the labrum as well as any articular cartilage damage and bony abnormalities. Hip arthroscopies are outpatient surgeries.
No formal incision is made, only portals to allow for the surgical instrumentation. Many patients return to normal activity by six weeks, although full recovery may take up to six months. However, in cases where arthritis is already present in the joint, arthroscopy is no longer of any benefit. These patients ultimately require joint replacement if conservative measures fail and they can no longer tolerate the discomfort.