Scapulohumerale

Scapulohumeral rhythm, sometimes referred to as scapulohumerale in some languages, describes the coordinated movement of the scapula and the humerus during arm elevation. It arises from the interaction between the glenohumeral joint and the scapulothoracic articulation, allowing smooth overhead motion and maintaining clearance for soft tissues around the shoulder.

Normally, during raising the arm to about 180 degrees, roughly 120 degrees of humeral (glenohumeral) elevation occur alongside about 60 degrees of scapular motion, a rough 2:1 ratio of humeral to scapular movement. The initial portion (about the first 30 degrees) is predominantly glenohumeral, with progressively greater contribution from the scapula as elevation continues. The scapula rotates upward, tilts posteriorly, and externally rotates slightly to optimize the subacromial space and allow full range.

Muscles involved in scapulohumeral rhythm include the serratus anterior and the trapezius (especially the upper and lower fibers), which drive upward rotation of the scapula. Supporting roles are played by the rhomboids, levator scapulae, and other scapulothoracic stabilizers, which help position the scapula during movement and synchronize with humeral action.

Clinical relevance: Alterations in this rhythm, or scapular dyskinesis, are associated with shoulder pain and dysfunction, including impingement, rotator cuff pathology, and adhesive capsulitis. Nerve injuries (such as to the long thoracic nerve or spinal accessory nerve) can disrupt rhythm. Assessment and rehabilitation aim to restore balanced, coordinated scapulohumeral movement to improve function and reduce symptoms.