Labrum

The shoulder and hip are ball-and-socket joints, where the rounded end of a bone (the joint head) fits into a concave socket. The shoulder socket (glenoid) is shallow like a plate and small, making it much narrower than the head of the humerus. A firm, elastic ring of tissue surrounds its edge: this is the labrum.

The labrum deepens the socket, increasing the area of contact between the bones. It also maintains pressure within the joint, helping the joint head stay in the socket as though held by gentle suction. The acetabular labrum in the hip plays a similar role, supporting joint centration to hold the femoral head securely within the socket.

The labrum attaches to the edge of the bone and is continuous with the joint capsule and ligament tissue. The long head tendon of the biceps brachii attaches to the upper labrum, so this area is also pulled when you use your arm.

It is difficult to be consciously aware of sensations from the labrum itself in everyday life. However, it works hard during activities involving large overhead arm movements, such as throwing, swimming, and badminton, or wide leg movements and rotation, such as ballet, soccer, and golf. People who frequently take part in these activities sometimes describe a deep ache or a catching sensation in the shoulder or hip.

The labrum may naturally wear down or change shape with age. Many people whose imaging shows changes in the labrum go about daily life without any particular discomfort. For this reason, imaging findings and how the body actually feels are often considered separately.

The outer part of the labrum, near the joint capsule, has a relatively rich blood supply, while the blood supply decreases toward the inner part. Just as the outer and inner parts of the knee's meniscus heal differently, the extent of healing in the labrum varies by location. This makes it important to adjust rest periods and activity levels when stress on the joint builds up.

The glenoid labrum is the labrum located around the edge of the shoulder socket. It raises the rim of the glenoid, which is smaller than the humeral head, increasing the surface in contact with the humeral head and adding stability.

The glenoid labrum attaches to the bony edge of the glenoid and is continuous with the attachment sites of the joint capsule and the glenohumeral ligament complex. The long head tendon of the biceps brachii connects to the upper glenoid labrum. However, the glenoid labrum is not the only structure that stabilizes the shoulder. The bony structure, joint capsule, ligaments, rotator cuff, and the nervous system that controls the muscles all work together to keep the shoulder stable.

To clarify the terminology, labrum is the general term for the fibrocartilaginous rims in both the shoulder and hip, while glenoid labrum refers specifically to the shoulder labrum. The hip labrum is called the acetabular labrum. You can read more about changes in the shoulder's glenoid labrum under Glenoid labral tear, and about the hip region under Femoroacetabular impingement.

• Strengthen the muscles around the joint. In the shoulder, the rotator cuff and muscles around the shoulder blade help hold the joint head securely in the socket; in the hip, the gluteal muscles and deep muscles do this. Training these muscles in a balanced way can reduce the load concentrated on the labrum.
• Take breaks between repetitive movements. When repeating the same movement, as in throwing or swimming, take breaks along the way and increase your exercise volume gradually.
• Warm up thoroughly. Before exercise, slowly circle your shoulder and hip joints, starting with small movements.
• Keep a record of uncomfortable movements. Noting which movements cause a catching sensation can help when discussing it with a professional.

• A catching or pinching sensation repeatedly occurs during a particular movement
• Your shoulder or hip feels unstable, as though it might slip out of place
• You feel discomfort deep in the joint whenever you change position at night

These signs can have various causes, not just the labrum, so consult a professional who can also assess your movement.