Shoulder

Shoulder refers to the region where the upper limb connects to the trunk and includes bones, joints, muscles, and soft tissues that enable a wide range of motion. The skeletal framework consists of the clavicle, the scapula, and the humerus. The shoulder girdle comprises three true joints—the glenohumeral joint, the acromioclavicular joint, and the sternoclavicular joint—together with the scapulothoracic articulation, which describes the functional relationship between the scapula and the thoracic cage. The glenohumeral joint is a ball-and-socket articulation that allows extensive arm movements but is relatively unstable, relying on soft tissue structures for stability and guidance.

Anatomy and soft tissues: The rotator cuff, formed by tendons of the supraspinatus, infraspinatus, teres minor, and subscapularis, stabilizes the joint and assists in lifting and rotating the arm. The deltoid, pectoralis major, latissimus dorsi, and other muscles power shoulder movements, while the glenoid labrum deepens the socket to improve stability. Ligaments such as the coracoclavicular and acromioclavicular ligaments reinforce the AC joint, and the joint space is cushioned by several bursae, notably the subacromial bursa.

Function and movement: The shoulder enables flexion, extension, abduction, adduction, and rotation, with motion produced by coordinated action of the rotator cuff, deltoid, and scapular stabilizers. Scapulohumeral rhythm describes the integrated movement of the shoulder girdle and the scapula that allows full arm elevation.

Clinical relevance: Shoulder disorders are common and include dislocations, rotator cuff tears and tendinopathies, impingement syndrome, adhesive capsulitis (frozen shoulder), arthritis, and biceps tendon injuries. Evaluation relies on history, examination, and imaging. Treatments range from activity modification, physical therapy, and injections to surgical options such as arthroscopy, ligament reconstruction, or shoulder arthroplasty, depending on pathology and patient needs.