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The glenoid fossa of the scapula or the glenoid cavity is a bone part of the shoulder. The word glenoid is pronounced or (both are common) and is from , "socket", reflecting the shoulder joint's ball-and-socket form. It is a shallow, joint surface, which is located on the lateral angle of the scapula. It is directed laterally and forward and articulates with the Humeral head of the humerus; it is broader below than above and its vertical diameter is the longest.
This cavity forms the glenohumeral joint along with the humerus. This type of joint is classified as a synovial joint, ball and socket joint. The humerus is held in place within the glenoid cavity by means of the long head of the biceps tendon. This tendon originates on the superior margin of the glenoid cavity and loops over the shoulder, bracing humerus against the cavity. The rotator cuff also reinforces this joint more specifically with the supraspinatus tendon to hold the head of the humerus in the glenoid cavity.
The cavity surface is covered with cartilage in the fresh state, and its margins, slightly raised, give attachment to a Fibrocartilage structure, the glenoid labrum, which deepens the cavity. This cartilage is very susceptible to tearing. When torn, it is most commonly known as a SLAP tear which is generally caused by repetitive shoulder movements.
Compared to the acetabulum (at the hip-joint) the glenoid cavity is relatively shallow. This makes the shoulder joint prone to dislocation (luxation). Strong glenohumeral ligaments and prevents dislocation in most cases.
By being so shallow the glenoid cavity allows the shoulder joint to have the greatest mobility of all joints in the body, allowing 120 degrees of unassisted flexion. Additional range of motion in shoulder flexion (typically up to 180 degrees in humans) is also accomplished by the great mobility of the scapula (shoulder blade) through a process known as scapulohumeral rhythm.
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