Understanding Your Diagnosis

The hip joint is a ball and socket joint that is formed from the femur, or thigh bone, and the acetabulum, or the hip socket. In an ideal hip, these parts fit together perfectly like a puzzle. Both the ball and socket are lined in a smooth cartilage that cushions the joint, called articular cartilage. On the rim of the socket, there is a specialized fibrocartilage called the labrum. The labrum helps to suction seal the joint and acts as a gasket to keep the joint fluid in the joint.

In this episode of eOrthopodTV, orthopaedic surgeon, Randale C. Sechrest, MD, narrates an animated tutorial on the anatomy of the hip joint.

Hip Impingement / FAI

In many hips, the head of the femur (ball) and the acetabulum (socket) don't fit together perfectly, causing abnormal contact and friction in the joint. This underlying structural problem of the hip is called hip impingement, or femoroacetabular impingement (FAI). After repetitive contact from repetitive activities, like running or kicking, FAI causes the joint to get inflamed and become painful. If left untreated, it can also cause cartilage damage and progress the development of arthritis in the hip joint.

There are three forms of FAI: CAM impingement, Pincer impingement and Mixed impingement (involving both CAM and pincer type). In CAM impingement, the femur (ball) has boney growth on it that contacts the hip socket during movement. In pincer impingement, the acetabulum, or socket, covers the ball too much causing abnormal contact. The accompanying videos show the anatomy of each type of impingement.

The first sign of FAI is often pain in the groin, on the outside of the hip or in the buttocks. Many patients also feel tightness and a loss in range of motion, and may also have pinching with high flexion or rotation.

Since the hip is a complex joint with many pain referral patterns, it is important that a physician who is experienced in the hip be involved in the diagnosis. Dr. Ellis uses several advanced tests to ensure that the right decision is made. Diagnosis begins with a physical exam that includes a thorough history of the condition, a gait (walking) analysis and range of motion testing. During the physical exam, Dr. Ellis rules out any conditions that can mimic FAI, such as pain coming from the spine, bursitis and muscle strains or tightness. Dr. Ellis also collaborates with experienced radiologists to look for x-ray findings of boney evidence of FAI, and may also order an MRI to look for labral tears and rule out the presence of cysts or cartilage damage. In some cases, Dr. Ellis may also do an injection of a local anesthetic (numbing agent) into the hip joint to ensure that the pain is coming from the joint.

Labral Tears

The acetabulum (hip socket) is lined with a cartilage tissue called the articular cartilage. A specialized piece of cartilage on the rim of the socket called the labrum is essential to hip anatomy (In the videos above, the labrum is the pink/red piece of the hip socket that is pinched).

The labrum helps to stabilize the joint and provides a suction seal to keep the joint stable. In most patients with FAI, the acetabular labrum is torn due to the shape mismatch between the ball and the socket of the hip joint. As the hip flexes, the front of the ball hits the front of the hip socket causing an "impingement". This impingement can damage the labrum and the adjacent cartilage resulting in hip pain. The labral tear also breaks the suction seal of the hip, causing abnormal joint mechanics and placing strain on the surrounding ligaments and muscles.

Cartilage Tears

cartilage tearsTypically seen with FAI, cartilage tears can cause instability of the hip, pain, and can continue to get bigger without treatment. If cartilage damage is too advanced, a joint replacement may the only surgical treatment option.

If cartilage damage is not advanced, Hip Arthroscopy can be used to trim out the unstable cartilage. A microfracture of the bone may be performed to stimulate the growth of new cartilage. Microfracture procedures are also done arthroscopically, and begin with removing loose cartilage and preparing the joint. Next, small holes, or microfractures, are made over the damaged area. These holes produce a rough area of bone for nutrient blood clots to adhere to, and the clot eventually matures into a smooth cartilage surface.

Loose Bodies

loose bodiesSometimes loose bodies, typically from cartilage or bone, can cause instability of the hip joint. This can cause a person to experience a sudden, sharp pain in the hip, sometimes causing them to fall.

These loose bodies can be taken out arthroscopically and allows the patient to resume full activities sometimes within days after the surgery.


Synovitis is an irritation or inflammation of the lining inside the hip joint. It is commonly seen in conjunction with other mechanical problems inside the hip joint, or with arthritis and other inflammatory diseases.

Synovitis is treated arthroscopically with debridement, or removal of damaged tissue, using specialized shavers.

Ligamentum Teres Rupture

This is usually seen after a traumatic dislocation or twisting injury to the hip. The torn ligament can get trapped inside the hip joint causing instability and pain.

This is typically treated with resection on the ligament since it is no longer needed in the adult hip.