Page "Shoulder problem" Paragraph 3

The shoulder joint is composed of three bones: the clavicle ( collarbone ), the scapula ( shoulder blade ), and the humerus ( upper arm bone ) ( see diagram ).

Two joints facilitate shoulder movement.

The acromioclavicular ( AC ) joint is located between the acromion ( part of the scapula that forms the highest point of the shoulder ) and the clavicle.

The glenohumeral joint, to which the term " shoulder joint " commonly refers, is a ball-and-socket joint that allows the arm to rotate in a circular fashion or to hinge out and up away from the body.

The " ball " is the top, rounded portion of the upper arm bone or humerus ; the " socket ," or glenoid, is a dish-shaped part of the outer edge of the scapula into which the ball fits.

Arm movement is further facilitated by the ability of the scapula itself to slide along the rib cage.

The capsule is a soft tissue envelope that encircles the glenohumeral joint.

It is lined by a thin, smooth synovial membrane.