Winging of the Scapula

Etiology

Scapular winging describes dysfunction in at least 1 of the scapulothoracic stabilizers, which causes a muscular imbalance in scapular alignment.

Serratus Anterior Palsy

The most common cause of scapular winging is serratus anterior paralysis after an insult to the long thoracic nerve. Injuries to the long thoracic nerve include compression, traction, laceration, and, most commonly, neuropraxia after blunt or stretch injury.[1] The long thoracic nerve is at risk of compression due to its superficial course along the lateral chest wall.[6] Falls from a height, motor vehicles, and sporting accidents are all cited causes.[7] Twisting of the neck and sudden depression of the shoulder are causes of stretch injuries reported in patients with serratus anterior palsy.[8]

Contact sport athletes are at risk of long thoracic nerve injury secondary to blunt trauma.[9] Throwing athletes performing repetitive activities with the head tilted and arms overhead may place the long thoracic nerve during the stretching action. Serratus anterior palsy has also been reported in industrial laborers performing repetitive activities overhead.[8] Iatrogenic causes range from long thoracic nerve compression injury with positioning under anesthesia to accidental surgical disruption.[10]

Potential long thoracic nerve sites of compression include the middle scalene muscle, the first rib, between the clavicle and the second rib, and the inferior angle of the scapula. A fascial sling around the long thoracic nerve at the first intercostal space could cause compression neuropathy with upper extremity abduction and external rotation.[11] Nontraumatic long thoracic nerve lesions have also been reported. Serratus anterior paralysis has been associated with C7 radiculopathy. Arnold-Chiari malformation, Guillain-Barre syndrome, transient brachial neuritis, systemic lupus erythematosus, Lyme disease, and viral illness have all been implicated in serratus anterior palsy.[12]

Trapezius Palsy

Trapezius muscle paralysis is primarily neurogenic due to spinal accessory nerve injury. The superficial course of the spinal accessory nerve in the posterior triangle of the neck places this nerve at risk. Automobile accidents and falls from a height have been implicated in traction injury. Blunt trauma in contact sports may be associated with spinal accessory nerve palsy.[13] Gunshot wounds, bite injuries, and stab injuries have been described as causes of spinal accessory nerve palsy.[7]

Iatrogenic injury to the spinal accessory nerve during cervical lymph node biopsy or excision is the most common cause of trapezius palsy.[14] Previous literature analyzing 83 patients with trapezius palsy reported that 71% of injuries were iatrogenic.[15] Spinal accessory nerve injury during neck surgery is the second most common iatrogenic nerve injury.[16]

Rhomboid Palsy

Dorsal scapular nerve injury results in rhomboid muscle paralysis and may cause scapular winging. A hypertrophic middle scalene muscle entrapping the dorsal scapular nerve is the most common cause of rhomboid palsy. Motor vehicle accidents or heavy lifting can cause a traction or avulsion injury of the C5 nerve root, resulting in rhomboid palsy.[17] Medial scapular winging can also be caused by cervical radiculopathy involving the C5 nerve root.

Facioscapulohumeral Dystrophy

Facioscapulohumeral dystrophy is a genetic neuromuscular dystrophy linked to chromosome 4q35. This autosomal dominant disorder predominantly affects the shoulder girdle, upper extremity muscles, and face. Severe scapular winging results from weakness in the trapezius, rhomboids, and levator scapulae relative to maintained strength in the deltoid and rotator cuff muscles.[18] Patients present with scapular instability, shoulder girdle pain, and weakness during shoulder abduction and flexion; diagnosis is confirmed with genetic testing.

Secondary Scapular Winging

Secondary scapular winging is abnormal scapulothoracic motion due to glenohumeral joint pathology. Painful glenohumeral joint intraarticular conditions cause patients to compensate for the loss of shoulder motion with the scapulothoracic articulation. The scapulothoracic stabilizing muscles quickly fatigue with increased demands, resulting in scapular winging. Glenohumeral instability, rotator cuff tears, adhesive capsulitis, and subacromial bursitis are common causes.[19]

Epidemiology

Winging of the scapula secondary to serratus anterior palsy is rare. A reported 15 out of 7000 cases have been observed in an electromyography lab.[20] After 12,000 neurological examinations, 3 cases of serratus anterior paralysis were diagnosed.[3] Ten instances of serratus anterior paralysis were observed over 3 years among 20 orthopedic surgeons in the University of Pennsylvania hospital system.[3] The incidence of scapular winging secondary to trapezius paralysis is rare and difficult to determine. Rhomboid paralysis is also rare, and its associated functional impairments are even less common.

Serratus anterior muscle paralysis is well-documented among amateur and professional athletes. The sports involved in serratus anterior paralysis include archery, baseball, basketball, bodybuilding, bowling, football, golf, gymnastics, hockey, soccer, tennis, and wrestling.[21] Sports injuries have also been associated with trapezius and rhomboid paralysis.[22][23] Serratus anterior muscle paralysis secondary to occupational injuries has also been reported.[24]

Pathophysiology

Medial Scapular Winging

Medial scapular winging results from a deficit in serratus anterior muscle function secondary to injury to the muscle directly or injury to the long thoracic nerve. Mechanical injuries to the serratus anterior include traumatic avulsion injuries and displaced fractures of the inferior pole of the scapula. A traction injury is one type of neurologic insult to the long thoracic nerve. A repetitive stretch injury most commonly presents with a gradual onset of weakness and scapular winging. The risk of a traction injury to the long thoracic nerve increases with the head tilted away during overhead arm activity, repetitive throwing, and prolonged shoulder abduction. Therefore, traction nerve injury is commonly observed in weightlifters and volleyball players.[25] High-energy trauma causing traction injury to the long thoracic nerve can result in immediate scapular winging.

A compressive injury is another type of neurologic insult to the long thoracic nerve. Acute compressive injuries can result from blunt trauma during motor vehicle accidents or contact sports. They can also result from a fall from a height, with sudden depression of the shoulder girdle. Potential chronic long thoracic nerve compression sites include the scalene muscles, anterior inferior scapular border, and subcoracoid between the coracoid and first or second rib.

Direct long thoracic nerve injury can also result from iatrogenic or penetrating chest wall injuries. Iatrogenic injury can occur after chest tube placement, axillary lymph node dissection, radical mastectomy, and thoracic surgery. Brachial neuritis can present with isolated unilateral long thoracic nerve palsy. Brachial neuritis should be considered in patients without an apparent traumatic onset and with prior immunological insult or inflammatory response.[26]

Lateral Scapular Winging

Lateral scapular winging results from a deficit in trapezius muscle function secondary to injury to the spinal accessory nerve. Spinal accessory nerve injury can be iatrogenic or traumatic. Iatrogenic injury is most common as the spinal accessory nerve is vulnerable in the posterior triangle of the neck; this type of injury can occur with cervical lymph node biopsy and radical neck dissection. Traumatic injuries can result from blunt trauma, penetrating injury to the neck, or sudden lateral flexion of the neck, causing a traction injury. Lateral scapular winging can also result from a deficit in rhomboid muscle function secondary to injury to the dorsal scapular nerve. Rhomboid paralysis is less common than trapezius paralysis.[27]

History and Physical

History

Patients with scapular winging commonly have shoulder or upper back pain. They also report muscle weakness, especially when elevating the upper extremity above shoulder level. Patients elicit difficulty with activities of daily living or overhead tasks, and athletes who commonly use overhead movements may report limitations. Patients with a prominent scapula might describe discomfort when sitting against hard surfaces or during long periods of driving. Weakness in the serratus anterior or trapezius muscle palsy may elicit muscle cramping and periscapular pain.

Physical

Physical examination for a patient with scapular winging begins with visualization of the entire back for any obvious deformity. Assessing scapular alignment is most easily performed while viewing the patient from behind. Visualization can also assess periscapular muscle atrophy and shoulder asymmetry.

Scapular stabilizing muscle weakness presents in predictable patterns. Long thoracic nerve injury results in serratus anterior muscle paralysis and causes medial scapular winging. The scapula translates superiorly, and the inferior angle rotates medially. Spinal accessory nerve injury results in trapezius muscle paralysis and causes lateral scapular winging. The scapula translates inferiorly, and the inferior angle rotates laterally.

Deformities are differentiated by scapular position and shoulder range of motion. Patients with serratus anterior palsy struggle with active forward shoulder flexion beyond 120°. Patients with trapezius palsy have difficulty elevating the scapula and performing shoulder abduction; these patients also have asymmetry of the trapezius with shoulder visualization.[28]

Strength Testing

Isolated strength testing of the shoulder should also be performed. Trapezius muscle strength can be tested with resisted elevation of the scapula. The function of the rhomboid and levator scapulae is evaluated by having the patient place both hands on the hips and pushing the elbows posteriorly against resistance. Serratus anterior strength can be assessed with the forward shoulder flexion to 90° while the patient performs push-ups. Medial scapular winging may occur immediately or present with muscle fatigue after multiple repetitions, consistent with serratus anterior weakness.[27]

Evaluation

The initial diagnostic workup of the scapular winging should include cervical spine, chest, scapula, and shoulder radiographs. Plain radiographs may help identify accessory ribs, cervical spine disease, fracture malunions, osteochondromas, or shoulder disorders. Advanced imaging is recommended for any patient with comorbid conditions. Osteochondromas may be better characterized by computed tomography imaging. Magnetic resonance imaging is reserved for patients with cervical disk disease, rotator cuff tears, and shoulder instability.[7]

Electromyography (EMG) and nerve conduction velocity testing are adjuncts to confirm physical exam findings. These modalities are also helpful in distinguishing neuromuscular causes of scapular winging.[13] EMG and nerve conduction velocity evaluation of the spinal accessory and long thoracic nerves is recommended to avoid an incomplete assessment.[29]

Treatment / Management

Neuropraxic Injury

Neuropraxic injury is the most common cause of scapular winging and will frequently resolve within 6 to 9 months.[8] After the diagnosis of neuropraxia causing scapular winging is made, nonsurgical modalities should be initiated. The primary treatment is physical therapy to maintain shoulder range of motion and prevent shoulder stiffness. A course of nonsurgical treatments to observe nerve recovery for 1 to 2 years is recommended.[30](B2)

The initial treatment for neuropraxic injury consists of nonsurgical modalities, including analgesics, nonsteroidal anti-inflammatories, and physical therapy. Activities should be modified to limit the elevation of the arm above shoulder level and avoid aggravating activities. Physical therapy should focus on the shoulder range of motion and strengthening the cervical muscles, scapular stabilizers, and rotator cuff. Shoulder immobilization with a sling may be beneficial in the acute period for pain control, but should be avoided for prolonged periods, as this may lead to stiffness.[30](B2)

Iatrogenic or Penetrating Nerve Injury 

Iatrogenic or penetrating nerve injury requires surgical exploration with neurolysis or nerve grafting. One technique has been described specifically for trapezius muscle palsy. The authors advocated for exploration and intraoperative spinal accessory nerve stimulation to distinguish between partial and complete lesions. Trapezius muscle contraction with stimulation is an indication for neurolysis. Complete spinal accessory nerve transection can be treated with primary repair, neuroma resection, or sural nerve graft. Good outcomes are possible if surgery is performed within 20 months of injury. Age older than 50 years, radical neck dissections, and delay in treatment beyond 20 months were associated with poor prognosis.[31]

Results of long thoracic nerve neurolysis with nerve transfer for medial scapular winging have been favorable. One study described long thoracic nerve decompression and supraclavicular neurolysis with complete resolution of scapular winging.[27] Procedures involving medial pectoral or thoracodorsal nerve transfers to the long thoracic nerve have resulted in the resolution of scapular winging.[32](B3)

Scapular winging secondary to contusion, traction injury, or neuromuscular palsy that does not resolve within 2 years indicates dynamic muscle transfer. Serratus anterior palsy can be addressed by transferring the pectoralis major sternal head to the inferior angle of the scapula.[8] Eight patients treated with pectoralis major sternal head transfer and fascia lata autograft elicited excellent results at 2 years post-procedure.[33] A separate study assessed 8 patients with serratus anterior palsy treated with pectoralis major transfer augmented with hamstring autograft. Seven patients had complete resolution of scapular winging at 32 months.[27]

Another study reviewed pectoralis major sternal and clavicular head transfer with fascia lata autograft augmentation for medial scapular winging. Full active shoulder elevation with the resolution of winging at 1 year occurred in 88% of patients. Two reconstructions failed secondary to graft stretching and progressed to scapulothoracic arthrodesis.[10]

A more recent study demonstrated successful pectoralis major muscle transfer without augmentation. Three patients were treated with pectoralis major sternal head transfer, and all reported satisfaction. The findings questioned the need for autograft augmentation with increased morbidity at the graft harvest site.[34]

Trapezius muscle palsy that has failed nonsurgical treatment or nerve exploration can be managed with the Eden-Lange dynamic muscle transfer. The procedure involves lateralizing the rhomboid minor, rhomboid major, and levator scapulae insertions on the scapula. These transfers allow for the synergistic activity of the trapezius's 3 components.[5] At 7 years, 59% of patients treated with Eden-Lange transfers regained normal shoulder function.[29]

One study assessed 16 patients after Eden-Lange transfers with a 29-year follow-up. All 16 patients regained shoulder abduction greater than 90°, and 11 were pain-free. Nine patients reported excellent outcomes and returned to work without limitations. The study's results concluded that the outcomes of Eden-Lange transfers are durable at long-term follow-up.[35](B2)

Another study involved scapulothoracic stabilization procedures in patients without pain relief after dynamic muscle transfer and patients with facioscapulohumeral dystrophy. This condition was treated with wire fixation of the scapula to the thoracic ribs without fusion, which resolved scapular winging in all 9 patients; significant improvements in shoulder abduction strength were seen at 1 year.[36](B2)

A separate study reported on 22 patients with facioscapulohumeral dystrophy and refractory winging treated with scapulothoracic arthrodesis using plates and wires. Pulmonary complications developed in 46% of patients, and 29% developed pseudarthrosis. Routine thoracostomy tube placement and iliac crest autograft are recommended to minimize complications in scapulothoracic arthrodesis.[37](B2)

A recent study investigated the long-term functional results of scapulothoracic arthrodesis using cables in patients with facioscapulohumeral dystrophy. At 128 months follow-up, shoulder range of motion and mean QuickDASH score significantly improved in 12 out of 13 patients. There was a complication rate of 33% due to failure of arthrodesis in 4 shoulders and wound complications in 2 shoulders. Scapulothoracic arthrodesis using a cabling method can improve functional and clinical outcomes for most patients with long-term facioscapulohumeral dystrophy.[38] Most cases of scapular winging are resolved with nonsurgical management. When operative management is warranted in chronic cases, good patient outcomes are seen with acute neurolysis and dynamic muscle transfers.

Differential Diagnosis

The signs and symptoms of scapular winging can present similarly to other pathologies of the upper extremities and scapula. The upper extremity's pain, weakness, and discomfort are also seen in different conditions.[39] Some presentations can appear similar to rotator cuff disorders due to limited motion and weakness in the associated arm. Glenohumeral instability is also a differential diagnosis, as the patient may report shoulder instability. However, scapular winging is more likely caused by instability of the scapula rather than the glenohumeral joint. Peripheral nerve disorders and cervical spine disease could also mimic scapular winging and should be ruled out. Thoracic outlet syndrome and acromioclavicular disorders might also be included in the differential, likely because the presentation of associated pain and weakness with the affected anatomy can be similar.

Prognosis

Serratus anterior muscle palsy responds well to nonoperative treatment, with most cases functionally recovering within 1 month to 2 years. After functional resolution of medial scapular winging, mild deficits in shoulder endurance and asymptomatic winging may persist.[40] Serratus anterior paralysis secondary to trauma usually leads to a poorer prognosis.[41]

Medial scapular winging secondary to serratus anterior palsy will persist in approximately 25% of patients after attempted conservative management. Dynamic muscle transfers consistently show positive outcomes with pain relief, resolution of winging, and improved function.[42]

Static stabilization involves a fascial graft to tether the scapula to the ribs or spinous processes. Static stabilization is less frequently performed secondary to the recurrence of winging as the graft stretches out over time.[8] Scapulothoracic arthrodesis using a cabling method improves long-term functional and clinical outcomes for most patients with facioscapulohumeral dystrophy.[38]

Functional recovery of the trapezius due to spinal accessory nerve injury does not consistently benefit from nonsurgical treatment. Nonsurgical treatment failure is primarily due to a lack of appropriately strengthened adjacent muscle groups that are enough to compensate for the trapezius muscle cross-sectional area and direction of pull.[5] Excellent results are reported in approximately two-thirds of patients with lateral scapular winging treated with neurolysis or nerve grafting.[43] The Eden-Lange procedure produces good outcomes with functional overhead motion and adequate pain relief.[35]

Complications

Lack of treatment can lead to complications of undiagnosed scapular winging. These include shoulder range of motion loss and stiffness without initial nonsurgical therapy. There are known complications after scapulothoracic arthrodesis in patients with facioscapulohumeral dystrophy. Pulmonary complications developed in 46% of patients, and 29% developed pseudarthrosis. Routine thoracostomy tube placement and iliac crest autograft are recommended to minimize complications in scapulothoracic arthrodesis.[37] Another study's results reported a complication rate of 33% due to failure of arthrodesis and wound complications after scapulothoracic arthrodesis in patients with facioscapulohumeral dystrophy.[38]