Scapular Dyskinesis

The normal scapulohumeral rhythm, the coordinated movement of the scapula and humerus to achieve shoulder motion, is the key to efficient shoulder function.

Scapular position and motion are closely integrated with arm motion to accomplish most shoulder functions. Scapular movement is a composite of three motions upward/downward rotation around a horizontal axis perpendicular to the plane of the scapula, internal/external rotation around a vertical axis through the plane of the scapula and anterior/posterior tilt around a horizontal axis in the plane of the scapula.

The scapula plays several roles in normal shoulder function. Control of static position and control of the motions and translations allow the scapula to fulfil these roles. In addition to upward rotation, the scapula must also posteriorly tilt and externally rotate to clear the acromion from the moving arm in forward elevation or abduction. Also, the scapula must synchronously internally/externally rotate and posteriorly tilt to maintain the glenoid as a congruent socket for the moving arm and maximise concavity compression and ball and socket kinematics.

The scapula must be dynamically stabilised in a position of relative retraction during arm use to maximise activation of all the muscles that originate on the scapula. Finally, it is a link in the kinetic chain of integrated segment motions that starts from the ground and ends at the hand.

Abnormal scapular motion and/or position have been collectively called ‘scapular winging’, ‘scapular dyskinesia’ and more appropriately ‘scapular dyskinesis’. Scapular winging refers to prominence of the medial border of the scapula, which is most often associated with long thoracic nerve palsy, and in some cases, overt scapular muscle weakness. ‘Winging’ describes a visual abnormality but it fails to indicate whether the abnormality is static, dynamic or both.Scapular dyskinesia by strict definition implies that a loss of voluntary motion has occurred.

Scapular dyskinesis has been identified as: (1) abnormal static scapular position and/or dynamic scapular motion characterised by medial border prominence; or (2) inferior angle prominence and/or early scapular elevation or shrugging on arm elevation; and/or (3) rapid downward rotation during arm lowering. Scapular dyskinesis is a non-specific response to a painful condition in the shoulder rather than a specific response to certain glenohumeral pathology. Scapular dyskinesis has multiple causative factors, both proximally (muscle weakness/ imbalance, nerve injury) and distally (acromioclavicular joint injury, superior labral tears, rotator cuff injury) based. This dyskinesis can alter the roles of the scapula in the scapula– humeral rhythm. It can be due to alterations in the bony stabilisers, alterations in muscle activation patterns or strength in the dynamic muscle stabilisers.

Snapping scapula

Periscapular pain is a relatively common cause of shoulder disability. It often occurs in combination with cervical disc disease or as a secondary phenomenon with other types of shoulder disorders, such as adhesive capsulitis, glenohumeral instability, glenohumeral arthritis, and thoracic outlet syndrome. In some patients the pain is localized to the superomedial angle of the scapula and is exacerbated by scapulothoracic motion.

The term snapping scapula has been used to describe the clinical scenario of tenderness at the superomedial angle of the scapula, painful scapulothoracic motion, and scapulothoracic crepit. Infrequently, an underlying cause for scapulothoracic incongruence is identified. These uncommon etiologies of snapping scapula include scapular exostoses, malunited scapular or rib fractures, and Sprengel’s deformity. Moreoften, pain at the superomedial angle of the scapula, with or without scapulothoracic crepitus, is not associated with osseous abnormalities of the scapula or the thorax.

Treatment

Nonoperative treatment of patients with painful conditions affecting the superomedial angle of the scapula often is successful and is comprised of activity modification, physiotherapy, systemic antiinflammatory medications, and corticosteroid injection into the scapulothoracic bursa. Surgical treatment for patients who have no response to nonoperative management includes scapulothoracic bursectomy, excision of the superomedial angle of the scapula, and combined bursectomy and superomedial angle resection.