Scapular dyskinesia is a term used to describe poor movement patterns of the shoulder blade. The shoulder blade, or scapula, moves in multiple planes and must be coordinated with the glenohumeral joint in order to allow full range of motion of the shoulder. When the length, strength or timing for firing the scapular stabilizing musculature is not optimal, scapular dyskinesia occurs. One type of scapular dyskinesia is winging of the scapulae.
Scapular winging can result from either weakness or stiffness of multiple muscle groups, including serratus anterior, trapezius, rhomboid major and minor, and/or levator scapulae. Of these muscles, serratus anterior is the most common muscle contributing to winging. It is a flat muscle that originates on the upper eight or nine ribs and inserts on the medial border of the scapula. Its primary action is to stabilize the scapula against the rib cage, then laterally rotate the inferior angle of the scapula during overhead activity. The trapezius muscle may also be involved with scapular winging. This muscle helps retract, elevate and rotate the scapula and is most often injured with surgeries in the cervical area. A third muscle group that may be involved is the rhomboid major and minor, which together retract, elevate and medially retract the inferior angle of the scapula. Injury to these muscles can be a result of entrapment of the C5 nerve under a hypertrophied scalene muscle.
As previously mentioned, the cause of scapular dyskinesia is a muscle imbalance of the scapular stabilizers that can either be neurogenic in nature or inherently muscular. With scapular winging in particular, traction or stretch injuries to the long thoracic nerve can be a primary cause. The long thoracic nerve passes between the anterior and middle scalenes then travels along the chest wall to the serratus anterior. Positions in overhead sports can easily stretch the long thoracic nerve resulting in repetitive or traumatic stretch injuries to the nerve and resulting in neuropraxia that inhibits the serratus anterior. Neuropraxia can occur with increases in nerve length of only ten per cent. Aside from long thoracic nerve injuries, spinal accessory nerve injury can also lead to scapular winging as it inhibits trapezius muscle activity.
Iatrogenic injuries to the long thoracic nerve or spinal accessory nerves can also occur. These may include invasive procedures such as first rib resections, lymph node biopsy, mastectomy, surgical treatment for pneumothorax and infraclavicular plexus anathesia. Atraumatic causes of scapular winging may include Arnold Chiari malformation, Guillian Barre syndrome, lupus, and Lyme disease, all of which can cause shoulder girdle weakness.
The clinical presentation of an individual with scapular winging typically includes report of posterior shoulder pain that may radiate down the arm or up the neck. The pain can either be associated with an event or insidious in nature. The individual may experience loss of range of motion into forward flexion or abduction, weakness and a sensation or clicking or catching of the shoulder joint with movement. A skilled clinician will look at scapular position at rest and identify any scapular dyskinesia present with active range of motion of the shoulder or weight bearing on hands in a push up type position. A patient with serratus anterior palsy with exhibit winging at rest and may have pain at rest in periscapular muscles that are attempting to compensate for the weak serratus. Winging is typically accentuated in a wall push up position. If trapezius palsy is involved, wasting or atrophy of the muscle will be visible at the neckline and shoulder drooping will be present. Weakness will be present in overhead positions and winging will become apparent with resisted abduction or external rotation. Winging associated with rhomboid dysfunction is the most difficult to identify. Patients may report medial scapular pain and demonstrate mild winging at rest that increases as they lower their arms from forward flexion.
With many possible causes and clinical presentations, the incidence and prevalence of scapular winging is unknown as it is often misdiagnosed. Common misdiagnoses include rotator cuff tendinopathy, shoulder instability, cervical radiculopathy, acromioclavicular joint disorders and nerve disorders. EMG testing is the only definitive diagnosis for serratus anterior, trapezius, rhomboid and levator scapulae dysfunction that may contribute to scapular winging, however the extent of nerve damage or recovery potential cannot be identified unless serial EMG tests are performed. Furthermore, it is important to understand that patients presenting with symptomatic winging may not show EMG dysfunction, thus clinical findings are equally as important. Identifying scapular dyskinesias and the muscle length and strength relationships involved is key to proper diagnosis of scapular syndromes. More importantly, early identification of scapular winging as a component of shoulder dysfunction is important for maximizing outcomes and minimizing continued pain or secondary injury to the shoulder.
Nonoperative treatment is the most common for scapular winging, whether the cause be neurogenic, muscular, or both. Physical therapy should focus on range of motion and periscapular strengthening to correct scapular winging associated with serratus anterior, trapezius, rhomboid and/or levator scapulae imbalance . Palsies are also initially treated conservatively with the same physical therapy focus. Traumatic serratus anterior palsies typically resolve in six to nine months, nontraumatic palsies may take up to twenty four months. Chronic palsies that do not resolve with conservative care can be treated with surgical techniques including muscle transfer from the sternal head of the pectoralis major to the inferior scapular pole, facial grafts, slings, and scapular fusion to the rib cage. Trapezius palsy, though initially treated similarly to serratus palsy with conservative physical therapy treatment, does not have the same success rate with recovery. Maximum function is typically gained after just one year of conservative physical therapy, after which surgical techniques are considered. The Eden Lange dynamic muscle transfer procedure involves using rhomboid major and minor and levator scapulae to mimic the trapezius muscle function. Success rates are relatively high for improving function and decreasing pain, ranging from 71 to 92 per cent. Nerve transfer procedures can also be performed for iatrogenic or traumatic spinal accessory nerve injury.