Hip impingement, also called FAI (femoroacetabular impingement), occurs when there is a mismatch between the shape of the ball (femoral head) and socket (acetabulum) of the hip joint. In a normal hip joint, the ball is perfectly round (spherical) and the socket covers the ball adequately (not too much or too little), and impingement rarely if ever occurs. Some people are born with or develop abnormalities of these bones, including a socket with too much coverage, a ball that is not perfectly round, or a combination of both. When this occurs, the bones contact each other abnormally, leading to damage of the hip joint, and resulting pain. A hip socket with too much coverage is called a pincer deformity, and a ball that is not perfectly round is called a cam deformity. These bony abnormalities, which require X-ray for diagnosis, lead to pincer, cam or combined hip impingement, altogether known as FAI. Both cam and pincer deformities cause tears of the labrum. The labrum is a ring of specialized cartilage that goes all the way around the rim of the socket and provides essential function to the hip joint. The labrum contains many nerve fibers and typically causes pain in the groin when it is torn. The cartilage layer of the hip socket is frequently injured where it meets the labrum at the rim of the socket.
Patients with FAI are typically 15-50 years old, generally active and have gradual onset of increasing pain. The majority of patients experience pain in the groin (front of the hip joint), but many often feel pain over the outside of the hip, in the buttocks, or near the low back. Many even describe feeling as if pain goes through the hip joint from front to back or vice-versa. Patients also describe feeling an arc of pain in the shape of a “C” from the front, wrapping around the side and back of the hip. Pain is typically worse with deep bending (flexion) and/or rotation of the hip. Pivoting, cutting, and jumping are often painful, but simple daily activities such as sitting for a long period of time, getting out of low seat or car or putting on socks and shoes can be painful as well.
The combination of labral tears and cartilage damage can result in arthritis over time if left untreated. Physical therapy, activity modification, rest, anti-inflammatory medications, and injections are the first line of treatment for FAI. Non-surgical treatment can improve the symptoms of FAI, but they cannot repair or heal the labrum. Also, they cannot change the structural cause of FAI (the cam or pincer bony abnormalities). If these non-surgical treatments do not alleviate symptoms, surgery is a reliable option for treatment of hip impingement. Surgical options include hip arthroscopy and surgical hip dislocation (SDH), both of which allow for adequate treatment of the labrum (labral repair) as well as resection or trimming of the bony problem (cam resection or pincer resection).
- Labral Tear
- The hip labrum is a ring of specialized cartilage that goes around the rim of the hip socket. The labrum is an important structure for hip function, stability and health, as it creates a suction-seal, increases the depth of the joint, improves joint mechanics and modulates fluid movement inside the joint. When the hip labrum is torn, it frequently causes pain in the groin or about the hip. Not only does it cause pain, but labral tears also compromise the normal function of the hip joint, potentially leading to additional damage of the cartilage and hip joint. The labrum can be repaired surgically using special anchors with attached sutures that are used to secure the torn labrum back to the rim of the socket. Importantly, the cause of the labral tear must be addressed during the same surgery. The most common causes of a torn labrum include bony abnormalities of the ball and socket parts of the hip joint, called cam and pincer deformities. The cam and pincer bony deformities can be removed using a motorized burr. Once the abnormal bone is removed, the ball and socket no longer contact each other abnormally, eliminating hip impingement. This allows the labrum to heal, reduces its chance at re-tearing and allows for a return to function without pain.
- Cam impingement
- Cam impingement is the most common type of hip impingement. It occurs on the ball (femoral head) side of the hip joint, and is characterized by a ball that is not perfectly round (aspherical). The femoral head is frequently aspherical in the same location in most patients, and it can be identified as a bump or a lack of roundness (flat) in the front, top portion of the ball. The cam deformity is thought to have several different causes, including genetics, acute injury to the growth plate as a child, an adaptive change of the growth plate in response to prolonged, high-impact activity (sports) while the growth plates are open, among others. This bump is responsible for causing the damage to the labrum and cartilage. As the hip is flexed (bent) up, the bump pushes into the socket, like a square peg in a round hole, and lifts the labrum off of the rim, separating it from its connection to the rim and cartilage. Over time, this results in irreversible cartilage damage.
- Pincer impingement
- Pincer impingement is less common by itself but is seen relatively frequently with cam impingement. Pincer impingement occurs when the socket (acetabulum) covers too much of ball (femoral head), which leads to early contact of the bones during range of motion. When the hip is flexed up (bent), the edge of the ball contacts the overhanging rim and damages and tears the labrum. Repetitive contact causes progressive damage to the labrum and cartilage and can eventually result in arthritis.