Acetabular labrum

The acetabular labrum (glenoidal labrum of the hip joint or cotyloid ligament in older texts) is a fibrocartilaginous ring which surrounds the circumference of the acetabulum of the hip, deepening the acetabulum. The labrum is attached onto the bony rim and transverse acetabular ligament. It is triangular in cross-section (with the apex represented by the free margin). The labrum contributes to the articular surface of the joint (increasing it by almost 10%). It embraces the femoral head, holding it firmly in the joint socket to stabilise the joint. It thus also seals the joint cavity, facilitating even distribution of synovial fluid so that friction is reduced and dissolved nutrients are better distributed. The anterior portion of the labrum is most susceptible to tears. It is estimated that 75% of acetabular labrum tears have an unknown cause. Tears of the labrum have been credited to a variety of causes such as excessive force, hip dislocation, capsular hip hypermobility, hip dysplasia, and hip degeneration. A tight iliopsoas tendon has also been attributed to labrum tears by causing compression or traction injuries that eventually lead to a labrum tear. Most labrum tears are thought to be from gradual tear due to repetitive microtrauma. Incidents of labrum tears increase with age, suggesting that they may also be caused by deterioration through the aging process. Labrum tears in athletes can occur from a single event or recurring trauma. Running can cause labrum tears due to the labrum being used more for weight bearing and taking excessive forces while at the end-range motion of the leg: hyperabduction, hyperextension, hyperflexion, excessive external rotation. Sporting activities are likely causes, specifically those that require frequent lateral rotation or pivoting on a loaded femur as in hockey or ballet. Constant hip rotation places increased stress on the capsular tissue and damage to the iliofemoral ligament. This in turn causes hip rotational instability putting increased pressure on the labrum.