Scapular muscle imbalance: implications for shoulder pain and pathology

Background: The scapula is important for normal shoulder function. The correct length, strength, and sequence of recruitment of the scapulothoracic muscles are important in controlling the movement of the scapula which must maintain an optimal position in relation to the elevating humerus. Changes in the action of scapulothoracic muscles may potentially affect alignment and forces and may contribute to glenohumeral joint pathology.Objective: The purpose of this paper is to review the literature that associates abnormal scapulothoracic muscle function with shoulder joint pain and pathology.Major findings: Shoulder impingement syndrome, superior labrum anterior to posterior (SLAP) lesions and multidirectional instability have all been associated with dysfunctional movement patterns of the scapula. It is not clear if the observed changes in scapular movements and muscular control are the result of or are the cause of these various pathologies at the shoulder joint. Alterations in the force production of the scapulothoracic musculature including all parts of the trapezius and serratus anterior muscles have been reported. Tightness in the pectoralis minor and/or in the posterior glenohumeral joint capsule may also affect movement due to a general anterior tilting of the scapula which impairs its ability to attain a normally upwardly rotated position.Conclusions: The results of the investigations reviewed imply that appropriate assessment of the length, strength, and activation of all parts of the upper trapezius, serratus anterior, and pectoralis minor are important in the rehabilitation of patients with glenohumeral joint pathology.