The shoulder is responsible for approximately 16% of all primary care musculoskeletal visits. (1) Many of these patients exhibit an often overlooked, altered scapular position and motion pattern called, “Scapular dyskinesis” (i.e. “winging”) (2,3) In order for clinicians to properly manage shoulder pain, including rotator cuff problems, they must first be able to recognize and treat scapular dyskinesis.
Normal scapulohumeral motion maintains the humeral center of rotation directly above the concave scapular glenoid throughout the shoulders range of motion. This integrated motion between the scapula and humerus provides efficient function and joint stability. (5) When this rhythm is disrupted by abnormal scapular motion, the resulting disproportionate humeral shift creates increased stress on the shoulder capsule and rotator cuff. (5)
Causes of Scapular Dyskinesis
Muscular imbalance, neurologic injury, or joint pathology are potential causes of scapular dyskinesis. The most common origin of scapular dyskinesis is muscular imbalance resulting from a combination of weakness, tightness, fatigue or altered activation. (6) Tightness in the pectoralis minor or short-head of the biceps leads to dyskinesis by placing excessive pull on the corcoid process. (7) It is not completely clear whether pec minor tightness is a causative factor or an adaptive response to scapular malposition. (8) Weakness or fatigue in the lower trapezius or serratus anterior triggers dyskinesis from inadequate acromial elevation. (5,9,10) Dyskinesis can occur from dysfunction in the distal kinetic chain, including hip abductor or core weakness. (52) Hyperkyphosis or “slouched” postures are known contributors. (11-13)
Scapular dyskinesis may be secondary to various shoulder pathology, including AC separation, A/C instability, A/C arthrosis, labral injury, glenohumeral internal derangement, glenohumeral instability, biceps tendinitis, and prior clavicle or scapula fracture. (7,10,14) Neurologic origins of scapular dyskinesis include cervical radiculopathy or peripheral neuropathy. (7,15) Injury to the spinal accessory nerve, long thoracic nerve, or suprascapular nerve is the cause of scapular dyskinesis in approximately 5% of cases. (16)
Scapular dyskinesis diminishes subacromial space and leads to decreased rotator cuff strength, impingement symptoms, and eventual rotator cuff damage. (17-22) One hundred percent of patients with shoulder impingement demonstrate scapular dyskinesis. (3) Uncoordinated movement of the scapula and humerus leads to a loss of dynamic stability in the glenohumeral joint via excessive strain on the anterior glenohumeral ligaments, with concurrent diminished rotator cuff strength. (3,23-25) Sixty-four percent of patients with glenohumeral instability demonstrate scapular dyskinesis. (3)
Although scapular dyskinesis is linked to a variety of shoulder problems, it may be asymptomatic initially. Up to 76% of healthy college athletes demonstrate some form of asymptomatic scapular asymmetry. (26) The dominant shoulder is affected more frequently. (4) When symptomatic, early complaints can include pain in the anterior or posterosuperior aspect of the shoulder. Discomfort may radiate inferiorly toward the lateral deltoid or superiorly into the trapezius region. Pec minor tightness may generate pain over the corcoid. (27) The consequences of long-standing altered mechanics lead to more well-recognized pain syndromes.
The goal of clinical evaluation is to recognize altered scapular mechanics and identify the underlying causative factors. (9) The acronym “SICK” scapular syndrome has been used to identify the components of scapular dyskinesis, including Scapular malposition, Inferior angle prominence, Coracoid tenderness/malposition, and dysKinesis. (16) Assessment begins with observation for winging (prominence of the inferior angle or medial border of the scapular) or asymmetry. (3) The lateral scapular slide test compares side-to-side measurements of the distance between the inferior angle of the scapula to the adjacent spinous process. The validity of this type of static measurement is open to discussion. (28-30)
Scapular dyskinesis becomes more apparent with dynamic testing, particularly during the lowering phase of arm movement. (3-28) Literature defines several tests for the dynamic assessment of scapular dyskinesis including the Scapulohumeral rhythm test and Scapular dyskinesis test. (27,32,33) The Scapular dyskinesis test involves a visual assessment of a patient performing weighted shoulder flexion and abduction. The clinician observes for the presence of winging or dysrhythmia (early, excessive, or discoordinated motion).
A range of motion deficit is possible. Posterior shoulder tightness may limit internal rotation, which leads to scapular protraction and dyskinesis- particularly in overhead athletes. Assessment of posterior capsule tightness is performed by measuring internal rotation at 90 degrees of abduction, by having the patient reached behind their back to the highest spinal level, or by assessing horizontal adduction. (34) Internal rotation should be measured while stabilizing the scapula. (35) Palpation may demonstrate tenderness over the coracoid or subacromial region. Trigger points are possible in the pectoral, biceps, upper trapezius, and rotator cuff muscles. Scapular dyskinesis is often part of a larger biomechanical problem- “Upper crossed syndrome”. Clinicians should assess for even more distant origins of instability, including hip abductor weakness.
Conservative management is capable of producing significant improvements in pain and function, despite the fact that research shows static and dynamic measurements of scapular dyskinesis remain relatively unchanged after three months of care. (38) The successful management of scapular dyskinesis requires identifying and addressing all of the causative components. Treatment should begin by restoring the flexibility of tightened and hypertonic tissues. Myofascial release and stretching may be necessary for the pec minor, biceps, and upper trapezius. (39-40) Strengthening exercises should be directed at the serratus anterior, lower trapezius, and middle trapezius. (41-43)
The middle and lower trapezius may be strengthened in side-lying forward flexion, external rotation, prone extension, and/or pure horizontal abduction. (44,45) The serratus anterior is activated in various quadruped and push-up positions. (41) Rehab of scapular dyskinesis is most effective when muscles are activated in functional patterns versus isolated strengthening. (46) Functional exercises useful for rehabbing scapular dyskinesis include inferior glide and low row. (47) Strengthening exercises should be performed with the patient focusing on scapular retraction, thereby, increasing serratus anterior and lower trapezius activation. Patients should avoid “shrugging” their shoulders or otherwise activating the upper trapezius. Patients demonstrating weakness in the hip abductors or core musculature may require proximal stabilization prior to implementing more specific scapular stabilization. (48,49) Scapular mobilization may help assist in restoring scapular thoracic mobility. The use of manipulative therapy is a “preferred” treatment that may accelerate recovery. (50,51)
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