scapulothoracalrhythmus

Scapulothoracic rhythm, also known as scapulohumeral rhythm, refers to the coordinated movement between the scapula (shoulder blade) and the humerus (upper arm bone) during arm elevation. This synchronized motion is essential for achieving a full range of motion at the shoulder joint and for the efficient function of the shoulder complex.

The rhythm typically begins with the initial 30 degrees of arm abduction or flexion, which is primarily driven by the deltoid muscle and supraspinatus. Beyond this initial phase, the scapula begins to rotate upward and laterally, contributing to the remaining range of motion. For every two degrees of arm elevation, the scapula rotates approximately one degree. This coordinated movement allows the glenoid fossa of the scapula to maintain optimal contact with the humeral head, providing a stable base for movement and preventing impingement of the subacromial structures.

Several muscles contribute to the scapulothoracic rhythm, including the serratus anterior, trapezius, rhomboids, and pectoralis minor. The serratus anterior is particularly important for upward rotation of the scapula, while the trapezius assists in this motion and also contributes to scapular retraction. Dysfunctions in this rhythm can arise from muscle weakness, imbalance, or poor neuromuscular control, leading to a variety of shoulder pathologies such as impingement syndrome, rotator cuff tears, and frozen shoulder. Assessment and rehabilitation of the scapulothoracic rhythm are therefore crucial components in the management of shoulder injuries.