labrum

Labrum is a term used in anatomy to describe a lip-like structure that rims a cavity or joint, helping to deepen the socket or guide a passage. The word derives from Latin, meaning “lip.” The concept appears in several biological contexts, but its most widely referenced examples are in human joints and in arthropod mouthparts.

In human anatomy, the glenoid labrum and the acetabular labrum are the two best-known variants. The glenoid labrum is a fibrocartilaginous rim attached around the margin of the glenoid cavity of the scapula. It deepens the shoulder socket to improve stability of the glenohumeral joint and distributes forces across the joint surface. Injuries to the labrum, commonly called labral tears, can result from trauma or repetitive overhead motions and may cause pain, instability, and limited range of motion.

The acetabular labrum surrounds the acetabulum of the pelvis, enlarging the hip socket and enhancing joint stability. It helps to seal the joint, aiding in the maintenance of synovial fluid within the capsule and contributing to smooth articulation between the femoral head and pelvis. Labral pathology in the hip can present with groin pain and mechanical symptoms and is often evaluated with MRI or hip arthroscopy.

In arthropods, the labrum refers to the upper lip of the mouthparts. It is a movable or rigid plate that forms part of the feeding apparatus and can vary in size and structure across groups.

Etymology traces back to Latin labrum, “lip.”