Shoulders

The shoulders are the region where the upper limbs attach to the trunk, forming the shoulder girdle and the joints that enable a wide range of motion. The key component is the glenohumeral joint, a ball-and-socket articulation between the humeral head and the glenoid cavity of the scapula. The shoulder complex also includes the sternoclavicular and acromioclavicular joints, and the scapulothoracic articulation, which together allow movements of the arm while maintaining stability.

Muscles coordinate these movements. The rotator cuff—comprising the supraspinatus, infraspinatus, teres minor, and subscapularis—stabilizes the joint during arm motion. The deltoid elevates and abducts the arm, while larger muscles such as the pectoralis major and latissimus dorsi control power and rotation. The trapezius, serratus anterior, and other scapular stabilizers position the shoulder blade to optimize function.

Stability is provided by a soft tissue envelope, a fibrocartilaginous labrum that deepens the glenoid, the joint capsule, and ligaments. The subacromial space, bursa, and the acromion contribute to movement and protection from impingement. The scapulohumeral rhythm normally achieves two degrees of arm elevation for every one degree of upward scapular rotation, coordinating glenohumeral and scapular motion.

Common clinical issues include shoulder dislocations, rotator cuff tears and impingement, adhesive capsulitis (frozen shoulder), osteoarthritis, and instability from repetitive overhead activity. Diagnosis relies on history, physical examination, and imaging. Treatments emphasize physical therapy to restore range of motion and strength; many injuries respond to nonoperative care, while some require surgical intervention such as arthroscopic repair or, in end-stage cases, shoulder arthroplasty.