Femoroacetabular Impingement (FAI) in the Hip

What Is FAI?

Femoroacetabular impingement (FAI) is a condition in which the bones of the hip have developed abnormally. Because the ball and socket of the hip do not fit together perfectly, the “out of round” conflict of the hip can cause damage to the hip joint. The hip is a ball-and-socket joint. The acetabulum (socket) is formed from all three of the bones that make up the pelvis. The femoral head (ball) fits within the acetabulum. This normally round on round joint allows for movement forwards and back, side to side, and internal/external rotation. A slippery tissue (articular cartilage) covers the surface of the ball and the socket. It creates a smooth, low friction surface that helps the bones glide easily across each other. The acetabulum is rimmed by strong fibrocartilage, called the labrum. The labrum forms a gasket around the socket, creating a tight seal and helping to provide stability to the joint. The labrum also helps protect the articular cartilage. In a healthy hip, the femoral head fits perfectly into the acetabulum.

In FAI, there is an abnormal amount of bone off the acetabulum or femoral head or both. The resultant conflict can cause labral tears of the hip. The labral tear event is usually when patients start experiencing symptoms from their FAI. Once the labrum is torn, the protective effect of the labrum to the articular cartilage is decreased, and articular cartilage damage may occur. Over time, this breakdown of articular cartilage can lead to hip arthritis.

What Are the Types of FAI?

There are three types of FAI: pincer, cam, and combined cam & pincer impingement.

  • Pincer impingement occurs because extra bone extends out over the normal rim of the acetabulum. The labrum can be crushed between the prominent rim of the acetabulum and the neck of the femur.
  • Cam impingement occurs because the femoral head is out of round and cannot rotate smoothly inside the acetabulum. The abnormal “cam bump” causes increased tension force on the labrum, eventually tearing the labrum off the bone of the acetabulum.
  • Combined impingement (a combination of cam and pincer impingement) is the most common form of FAI (86% of cases).

What Are the Symptoms of FAI?

It is not known how many people may have FAI. Some people may live long, active lives with FAI and never have problems. When symptoms develop, however, it usually indicates that there is damage to the cartilage or labrum and the disease is likely to progress.

Symptoms may include:

  • Pain or aching (usually located in the inner hip or groin area)
  • A locking, clicking or “catching” sensation within the joint
  • Pain sitting for long periods of time, such as when riding in a car or plane
  • Pain when rising from a seated position
  • Difficulty putting on socks and/or shoes
  • Difficulty walking uphill/downhill
  • Stiffness
  • Limping

FAI usually presents as groin pain with activities or with hip motion. Sometimes, patients with FAI can recall a single traumatic event that they note as the cause of their symptoms, but often the onset is more insidious. FAI is associated with articular cartilage damage, labral tears, early hip arthritis, hyper-laxity, sports hernias, and low back pain. FAI can become symptomatic in patients from all walks of life, from high-level athletes to weekend warriors to more sedentary individuals. Because the hip bones developed abnormally, the only steps that can be taken to prevent symptoms from FAI are to decrease the long-term pressure on the hips by keeping the patient’s weight optimal (increasing body weight increases pressure on the hip joint). Because athletically active people may work the hip joint more vigorously, they may begin to experience pain earlier than those who are less active. However, exercise itself does not cause FAI.

The most common finding among patients with FAI-related pain is reproduced when they are positions of flexion, adduction and internal rotation (anterior impingement test). The symptoms can be chronic and achy, or sharp and mechanical with certain motions. In some cases, the patients may also have referred pain to the buttocks or down the thigh.

What Other Diagnoses Might Be Confused With FAI?

  • Hip dysplasia (adult form)
  • Lumbar spine pain (low back pain)
  • Lumbar radiculopathy (low back pinched nerve, low back facet disease)
  • Sacroiliitis (SI pain/dysfunction, back of pelvis)
  • Trochanteric bursitis (outer/lateral hip pain)
  • Piriformis syndrome (back of hip pain)
  • Psychosomatic pain disorder (stress-related illness)
  • Iliopsoas tendinitis/tendinosis (hip flexor inflammation)
  • Groin pull (adductor strain)
  • Sports hernia (core muscle injury (CMI), abdominal muscle strain)
  • Iliac apophysitis (front of pelvis pain)
  • Quadriceps hernia/strain (thigh muscle pull)
  • Endometriosis
  • Deep gluteal syndrome (DGS)
  • Hamstring tendinitis/tendinosis
  • Chronic pain syndromes

Can Back Pain Be a Sign of FAI?

While the cause is not well understood, patients with FAI often complain of low back pain. This pain is often localized to the SI (sacroiliac joint on the back of the pelvis), the buttock, or the greater trochanter (side of the hip). The hip joint and the low back frequently “play off each other”, and compensation for a hip issue can frequently cause increased pressure on the low back, causing back symptoms, and vice versa.

What Are Some Common Activities Associated With FAI?

  • Ice hockey
  • Horseback riding
  • Yoga
  • Football (American)
  • Soccer
  • Ballet/dance/acrobatics
  • Golf
  • Tennis
  • Baseball
  • Lacrosse
  • Field hockey
  • Rugby
  • Bike riding/cycling
  • Martial arts and mixed martial arts
  • Deep squatting activities, such as power lifting
  • Surfing
  • Rowing sports (kayaking, sculling/rowing)
  • Riding in a car or plane (in a deep-seated position or bucket-seat position)

What Is the Treatment for FAI?

When symptoms first occur, it is helpful to try and identify an activity or something you may have done that could have caused the pain. Sometimes, you can reduce your activities, let your hip rest, and see if the pain will settle down. Over-the-counter anti-inflammatory medicines (ibuprofen, naproxen) may be helpful.

If the pain continues despite the initial treatment, seeking a physician knowledgeable about painful hip conditions can help. Most patients can be diagnosed with a good history, physical exam, and plain x-ray films. A careful history of the patient (symptoms, current activity level, previous activity level, previous pre-disposing injuries) can key the clinician to possible diagnoses. The physical exam will generally confirm the patient’s history and eliminate other causes of hip pain. The plain x-ray films are used to determine the shape of the ball and socket as well as assess the amount of joint space in the hip. X-rays can also show signs of arthritis and the existence of bony overgrowth. However, many times patients are seen by hip specialists who have X-rays that were previously read as “normal”, when in fact they do have FAI. If the clinician reading the X-ray films is not trained/skilled in looking for FAI, it can easily be missed.

Often, an MRI of the hip is used to confirm a labral tear or damage to the joint surface. The MRI is most helpful in eliminating certain causes of non-FAI hip pain, including avascular necrosis (dead bone) of the hip and tumors. Magnetic resonance imaging (MRI) scans can create better images of soft tissue. They will help your doctor find any damage to the labrum and articular cartilage. Injecting dye into the joint during the MRI may make the damage show up more clearly. Your doctor may also inject a numbing medicine like novocaine or possibly cortisone into the joint as a diagnostic test. If the numbing medicine/cortisone provides temporary pain relief, it confirms that the inside of the hip joint is the source of the pain. MRI is not a perfect test, and an MRI read as “normal” does not necessarily rule out FAI and labral tears as a source of pain.

The most appropriate initial treatment for most patients is physical therapy focusing on hip range of motion and strength, as well as the strengthening of core/gluteal muscles. Physical therapy in combination with intermittent NSAIDs can often help alleviate symptoms for long periods of time. In select patients, the judicious use of a corticosteroid injection into the hip joint can be beneficial as well. The use of these modalities, in concert with activity modification, is sometimes successful in the treatment of FAI.

If conservative treatment is unsuccessful, FAI can be treated with a minimally invasive procedure, hip arthroscopy. The surgeon makes small incisions, which introduces a fiber-optic camera and small instruments inside the hip. The surgeon can address the labral tear as well as re-shape the cam and pincer lesions arthroscopically. In most cases, Dr. Ochiai prefers to repair the labral tear, fixing it with surgical string and anchors back down to the bone, restoring the normal labral function. Patients undergoing this outpatient procedure are usually off crutches between two days and two weeks following the procedure.

If you have hip or groin pain or any orthopedic injury, contact the experts at Nirschl Orthopaedic Center in Arlington, Virginia. Schedule an appointment with our orthopaedists today by calling 703-525-2200.