The hip joint is a ball-and-socket joint, facilitating a wide range of motion necessary for walking, running, and jumping. The smooth, spherical head of the femur (thigh bone) fits securely into the cup-shaped socket of the pelvis, known as the acetabulum. The joint relies on several soft tissue structures for its strength and function. The acetabular labrum is a ring of specialized tissue that acts as a gasket around the rim of the hip socket, playing a role in maintaining the health and stability of the entire joint. This ring, which is susceptible to tears and damage, is integral to understanding certain types of chronic hip pain.
Anatomy and Stabilizing Function
The acetabular labrum is composed of tough, flexible fibrocartilage attached to the bony edge of the acetabulum. This structure is triangular in cross-section and acts to extend the bony socket, effectively deepening the cup by about 22%. The deepening of the socket helps to embrace the femoral head more firmly, enhancing joint stability and reducing stress on the underlying cartilage.
The labrum also maintains the joint’s internal environment by creating a tight seal around the femoral head, often described as a “suction seal.” This seal helps to maintain a negative pressure within the joint capsule, which is necessary to resist forces that try to pull the ball and socket apart.
The seal also plays a role in joint lubrication by retaining a layer of pressurized synovial fluid. This fluid is distributed evenly across the smooth articular cartilage surfaces, reducing friction and ensuring smooth movement. When the labrum is torn, this suction seal is compromised, leading to a loss of stability and abnormal distribution of the fluid, which can accelerate wear and tear on the joint surfaces.
Factors Contributing to Labral Damage
Damage to the acetabular labrum can occur from acute trauma, such as a severe blow, a fall, or a hip dislocation. However, most labral tears occur gradually due to chronic stress and repetitive microtrauma, often associated with underlying structural issues in the hip joint. The most common structural cause is Femoroacetabular Impingement (FAI), a condition where abnormal bone growth on the femur, the acetabulum, or both, causes premature contact between the bones during hip movement. This abnormal rubbing or “impingement” repeatedly pinches and stresses the labrum, leading to fraying and degeneration. Other contributing factors include hip dysplasia, which causes abnormal joint mechanics and excessive forces on the labrum, and degenerative changes related to aging.
Cam Impingement
Cam impingement involves an extra bone bump on the head-neck junction of the femur, making the femoral head less spherical. As the hip flexes and rotates, this non-spherical area forcefully levers the labrum away from the acetabulum, causing a shearing injury to the labrum and the adjacent cartilage.
Pincer Impingement
Pincer impingement occurs when the acetabulum has excessive bony coverage, causing the rim of the socket to pinch the labrum against the femoral neck. This repeated crushing action leads to labral degeneration and tearing.
Symptoms of a Labral Tear
The primary symptom experienced by individuals with an acetabular labral tear is a deep, aching pain located in the groin area. This groin pain is the most consistent complaint because the anterior-superior portion of the labrum is the most frequently injured area. The discomfort often worsens with activities that require deep hip flexion, such as squatting, or with prolonged periods of sitting or standing.
Patients report mechanical symptoms, which indicate torn tissue interfering with smooth joint movement. These sensations may include clicking, catching, or locking within the hip joint as the torn piece of labrum gets momentarily trapped between the ball and socket. Stiffness and a limited range of motion are also common complaints.
Medical Evaluation and Management
The medical evaluation of a suspected labral tear begins with a detailed physical examination, where a physician will perform specific tests to reproduce the pain. The most common of these is the anterior hip impingement test (FADIR), which involves flexing, adducting, and internally rotating the hip. Provocation of pain during this maneuver suggests the presence of a labral tear or FAI.
Initial imaging usually involves plain X-rays to assess the bony structure of the hip, specifically looking for the tell-tale signs of Cam or Pincer impingement that may have caused the tear. However, the definitive diagnostic tool is Magnetic Resonance Arthrography (MRA), which involves injecting a contrast dye directly into the hip joint before the MRI scan. The dye outlines the labrum and leaks into any tears, providing a much clearer picture of the damage than a standard MRI.
Management typically begins with conservative treatment, especially if symptoms are mild or intermittent. This non-surgical approach includes:
- Rest and modifying activities to avoid painful movements.
- Using Nonsteroidal Anti-Inflammatory Drugs (NSAIDs) to manage pain and swelling.
- Physical therapy is often prescribed to strengthen the muscles surrounding the hip and improve stability, which can help compensate for the damaged labrum.
If conservative measures fail to provide sufficient relief, surgical intervention via hip arthroscopy is considered. Arthroscopy is a minimally invasive procedure that allows the surgeon to visualize the joint and address the damage. The surgeon will either perform a labral repair, where the torn tissue is sutured and reattached to the acetabular rim, or a debridement, where the damaged, frayed portion of the labrum is trimmed away. In cases where FAI is the underlying cause, the surgeon must also simultaneously reshape the abnormal bone growth on the femur (osteoplasty) or acetabulum to prevent the tear from recurring.