scapulohumeral

Scapulohumeral refers to the functional relationship between the scapula (shoulder blade) and the humerus (upper arm bone), most notably embodied in the glenohumeral joint and the coordinated movement known as scapulohumeral rhythm. The glenohumeral joint is a ball‑and‑socket articulation formed by the head of the humerus and the glenoid cavity of the scapula, allowing a wide range of motion in flexion, extension, abduction, adduction, internal and external rotation. The scapula moves on the thoracic wall via the serratus anterior, trapezius, levator scapulae and rhomboid muscles, providing a stable base for humeral motion.

Scapulohumeral rhythm describes the proportion of glenohumeral to scapulothoracic movement during arm elevation, typically a 2:1 ratio: for every 2° of humeral elevation, the scapula rotates about 1°. This coordination maximizes the length‑tension relationship of rotator‑cuff muscles, maintains subacromial space, and optimizes joint stability. Disruption of this rhythm can result from rotator‑cuff tears, nerve injuries, or adhesive capsulitis, leading to impaired range of motion, pain, and functional limitation.

Clinically, assessment of scapulohumeral dynamics involves observation of scapular positioning, palpation of rhythmic movement, and measurement of range of motion. Rehabilitation programs target strengthening of periscapular stabilizers, proprioceptive training, and gradual progressive loading to restore normal rhythm and shoulder function.