The shoulder labrum is a ring of fibrocartilage attached to the rim of the shoulder socket (glenoid). This structure deepens the otherwise shallow socket, enhancing the overall stability of the shoulder joint. The labrum also serves as an attachment point for ligaments and the biceps tendon. A tear occurs when forces applied to the joint exceed the tensile strength of this cartilage ring, compromising its ability to hold the upper arm bone securely.
Acute Traumatic Injuries
Acute traumatic injuries involve a single, forceful event that immediately tears the labrum. The most common mechanism is a fall onto an outstretched hand (FOOSH), which transmits a sudden force up the arm to the shoulder joint. This impact compresses the head of the upper arm bone (humerus) against the glenoid socket, causing a pinching or grinding action that can rip the labrum.
Another frequent cause is a direct, forceful blow to the shoulder, which can occur during contact sports or a motor vehicle collision. This direct impact can drive the humeral head against the labrum, causing a tear. Sudden, violent traction or pulling on the arm, such as when attempting to catch a heavy object or bracing for a fall, also generates a disruptive force on the labrum.
Shoulder dislocation is a primary high-energy event that almost always results in labral damage. When the head of the humerus slips out of the socket, it forcibly pulls or shears the labrum away from the bone. This mechanism can strip the labrum off the bone, leading to significant instability and a high likelihood of recurrent dislocations.
Repetitive Stress and Overuse
Repetitive stress and overuse cause labral tears through chronic micro-trauma and fatigue failure over time. This mechanism is most frequently observed in “overhead athletes” and workers whose activities involve repeated, high-velocity movements of the shoulder above the head. Sports such as baseball pitching, swimming, tennis, and volleyball place strain on the shoulder joint’s stabilizing structures.
During the throwing motion, the rapid acceleration and subsequent deceleration of the arm generate intense forces that repeatedly stress the labrum and the attachment point of the biceps tendon. This persistent strain leads to accumulating micro-tears within the labral tissue. The constant tugging of the biceps tendon on the superior portion of the labrum can lead to a “peel-back” mechanism, where the tissue is gradually pulled away from the bone.
This continual mechanical loading eventually exceeds the labrum’s capacity to repair itself, leading to a breakdown of the collagen fibers and a structural tear. The repetitive motion also causes subtle, cumulative instability in the joint, which increases the friction and shear forces on the labrum with every movement. Occupational activities like painting, construction work, or other jobs requiring frequent overhead reaching can similarly lead to this type of gradual labral failure.
Age-Related Degeneration
Labral tears can also develop as a result of the natural aging process, independent of any specific injury or intense activity. This mechanism is characterized by a slow, progressive deterioration of the labral tissue, often referred to as degenerative fraying or wear-and-tear. As an individual ages, the fibrocartilage of the labrum loses its elasticity and becomes less resilient.
The diminishing blood supply to the joint structures over time contributes to the labrum’s reduced ability to heal and maintain its structural integrity. This makes the tissue more brittle and susceptible to tearing even during minimal, everyday movements. Microscopic changes and fraying in the superior labrum are commonly observed in asymptomatic individuals beginning around the age of 40, suggesting a normal part of the aging shoulder.
These degenerative changes often manifest as fraying at the free edge of the labrum, which can eventually progress into a full tear. The presence of other age-related joint conditions, such as osteoarthritis, can further accelerate the stress and deterioration of the labral structure.