JBJS | Current Concepts Review - Suprascapular Nerve Entrapment*

The Journal of Bone & Joint Surgery, Volume 82, Issue 3

Current Concepts Review | March 01, 2000

Current Concepts Review - Suprascapular Nerve Entrapment*

CRAIG A. CUMMINS, M.D.†; TERRY M. MESSER, M.D.†; GORDON W. NUBER, M.D.†, CHICAGO, ILLINOIS

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Investigation performed at the Department of Orthopaedic Surgery, Northwestern University Medical School, Chicago

The Journal of Bone & Joint Surgery. 2000; 82:415-24

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Introduction

Suprascapular nerve injuries have become increasingly recognized as a cause of shoulder pain and dysfunction. Since Kopell and Thompson⁵⁵ first described these injuries in 1959, more than 100 articles addressing this topic have been written, mostly in the last decade. The purpose of this Current Concepts Review is to critically review the rapidly enlarging body of literature on this subject.

*No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. No funds were received in support of this study.

†Department of Orthopaedic Surgery, Northwestern University Medical School, 645 North Michigan Avenue, Room 1058-B, Chicago, Illinois 60611. 60611. Please address requests for reprints to G. W. Nuber.

*No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. No funds were received in support of this study.

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FIG1-A:: Figs. 1-A and 1-B: Drawings of the anterior (Fig. 1-A) and posterior (Fig. 1-B) aspects of the right shoulder, illustrating the suprascapular nerve (arrow). Fig. 1-A: The trapezius and part of the pectoralis major muscle have been removed. The suprascapular nerve is shown originating from the superior trunk of the brachial plexus.

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FIG1-B:: Fig. 1-B The supraspinatus and infraspinatus muscles have been partially removed. The suprascapular artery and vein are passing over the superior transverse scapular ligament, and the suprascapular nerve is passing beneath this ligament. As the suprascapular nerve and vessels travel distally, they are shown passing through a narrow fibro-osseous tunnel formed by the spine of the scapula and the spinoglenoid ligament.

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FIG2:: Fig. 2 Photograph of the posterior aspect of the left shoulder of a patient with marked atrophy of the infraspinatus muscle.

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FIG3-A:: Figs. 3-A and 3-B: Coronal and axial T2-weighted magnetic resonance images of the right shoulder, demonstrating a ganglion cyst (arrow) in the region of the spinoglenoid notch. The cyst appears to be originating from the posterosuperior aspect of the glenohumeral joint.

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FIG3-B:: Figs. 3-A and 3-B: Coronal and axial T2-weighted magnetic resonance images of the right shoulder, demonstrating a ganglion cyst (arrow) in the region of the spinoglenoid notch. The cyst appears to be originating from the posterosuperior aspect of the glenohumeral joint.

Anatomy

The suprascapular nerve is a mixed motor and sensory peripheral nerve arising from the superior trunk (fifth and sixth cervical nerves) of the brachial plexus with a variable contribution from the fourth cervical nerve root (Figs. 1-A and 1-B). A contribution from the fourth cervical nerve root was identified by Lee et al.⁶¹ in 22 percent of 152 brachial plexus dissections and was identified by Ajmani³ in five of thirty-four cadavera. The suprascapular nerve supplies motor innervation to the supraspinatus and infraspinatus muscles and sends sensory branches to the coracohumeral and coracoacromial ligaments, subacromial bursa, and acromioclavicular and glenohumeral joints. While most anatomical studies have not identified any cutaneous innervation, Ajmani found a cutaneous branch of the suprascapular nerve supplying the proximal-lateral one-third of the arm in five of thirty-four adult cadavera, all of which were studied bilaterally. Horiguchi⁴⁷ reported on an additional five cadavera in which a cutaneous branch of the suprascapular nerve was identified.

From its origin at the brachial plexus, the suprascapular nerve courses through the posterior triangle of the neck and then laterally, deep to the trapezius muscle, toward the suprascapular notch. At the level of the suprascapular notch, the artery and vein enter the suprascapular fossa by passing over the superior transverse scapular ligament, whereas the suprascapular nerve passes beneath this ligament. Within one centimeter of traversing the suprascapular notch, the suprascapular nerve releases a motor branch that typically innervates the supraspinatus muscle by means of two branches^10,67,75,105. The superior articular branch of the suprascapular nerve sends sensory fibers to the coracoclavicular and coracohumeral ligaments, the acromioclavicular joint, and the subacromial bursa^3,50,67. This branch typically leaves the main trunk at or just proximal to the superior transverse scapular ligament and continues with the main branch passing beneath this ligament. After passing through the notch, the main portion of the nerve continues inferiorly toward the spinoglenoid notch, giving off a sensory branch to the posterior aspect of the glenohumeral joint capsule. The suprascapular nerve then courses sharply around the scapular spine, passing through a fibro-osseous tunnel formed by the spinoglenoid ligament and the spine of the scapula and terminating in two, three, or four motor branches that supply the infraspinatus muscle^10,67,75,105.

Several anatomical points merit further discussion as they relate to potential sites of injury to the suprascapular nerve. Because of its proximity to the middle and distal thirds of the clavicle, the suprascapular nerve can be injured following a clavicular fracture in this region^8,108. A common proximal site of injury to the suprascapular nerve is at the suprascapular notch as the nerve courses beneath the superior transverse scapular ligament. Rengachary et al.⁸³ examined 211 adult cadaveric scapulae and categorized the notch shape into six different types. A u-shaped notch was the most common type and was identified in 48 percent of the cadavera. A small v-shaped notch was identified in only 3 percent. Although it has been hypothesized that suprascapular nerve entrapment is more likely to be associated with a narrow v-shaped notch, no direct correlation between notch type and suprascapular nerve injury has been demonstrated, to our knowledge. In contrast, variations in the morphology of the superior transverse scapular ligament have been identified and associated with suprascapular nerve injury in several case reports^4,19,34,98. These variations include calcification of the ligament, bifid and trifid ligaments, hypertrophy of the superior transverse scapular ligament, and other congenital malformations.

Distally, the suprascapular nerve courses through a fibro-osseous tunnel formed by the spine of the scapula and the spinoglenoid ligament. The prevalence of the spinoglenoid ligament has varied widely in the literature^{20,23,24,52,67,98}. Ticker et al.⁹⁸ identified the spinoglenoid ligament in only eleven (14 percent) of seventy-nine shoulders. In contrast, Cummins et al.²⁰ found the spinoglenoid ligament to be present in ninety (80 percent) of 112 dissections. The ligament was characterized as a thick band of tissue in 20 percent of the cadavera and as a thin band of tissue in another 60 percent. Cummins et al. noted that the spinoglenoid ligament originated from the spine of the scapula and inserted into the superior aspect of the glenoid neck. However, Demirhan et al.²⁴ reported that the spinoglenoid ligament inserted into the posterior aspect of the glenohumeral joint capsule. In addition, those authors observed that, with adduction and internal rotation of the shoulder, the spinoglenoid ligament became taut and the suprascapular nerve was stretched.

Pathophysiology

Peripheral nerves are highly susceptible to injury from stretch and compression. Both of these mechanisms result in nerve ischemia, edema, microenvironmental changes, and conduction impairment. These changes are proportional to the magnitude and duration of the insult and eventually lead to irreversible damage^59,63,64. Kwan et al.⁵⁹ examined the viscoelastic properties of rabbit tibial nerves and found that a stretch that increased the in situ length by as little as 6 percent led to conduction abnormalities. A stretch of 15 percent resulted in an irreversible functional deficit. Lundborg and Rydevik⁶³ found that the intraneural vascular supply to a rabbit tibial nerve was compromised when the nerve was elongated by 8 percent and that there was total occlusion at 15 percent. Similar changes in the structure and vascularity of the nerve have been noted to occur with compression.

The suprascapular nerve may be injured as a result of trauma, repetitive overuse, a mass lesion, or iatrogenic causes. Traumatic causes of suprascapular nerve injury include scapular fractures^27,92, clavicular fractures^8,108, shoulder dislocations^100,107,111, and penetrating trauma¹⁰⁶. Iatrogenic injury to the suprascapular nerve may occur during operative procedures^25,65,109. Warner et al.¹⁰⁵ dissected thirty-one cadaveric shoulders and demonstrated that the suprascapular nerve is at risk for injury when the supraspinatus and infraspinatus tendons are mobilized more than three centimeters. This concern, however, has not been substantiated in the clinical literature^40,85,109. Ha'Eri and Wiley⁴⁰ found no suprascapular nerve injuries following repair of massive rotator cuff defects with use of the supraspinatus slide procedure²² in thirty-seven patients. Zanotti et al.¹⁰⁹ evaluated ten patients who had undergone repair of a massive rotator cuff tear. Only one patient was found to have an injury to the suprascapular nerve. Mallon et al.⁶⁵ reported two cases of suprascapular neuropathy following excision of the distal aspect of the clavicle. The cause of the injury was attributed to the proximity of the suprascapular nerve and greater than 1.5 centimeters of distal clavicular excision. The suprascapular nerve may also be injured during any operative procedure that violates the region of the posterior aspect of the glenoid neck^10,88,105. Bigliani et al.¹⁰ dissected ninety cadaveric shoulders and concluded that the so-called safe zone of the posterior aspect of the glenoid neck is within two centimeters of the glenoid rim at the level of the supraglenoid tubercle and within one centimeter of the glenoid rim at the scapular spine. We were unable to identify any reports of injury to the suprascapular nerve during posterior operative approaches to the shoulder. Despite this, a thorough understanding of the anatomy of the suprascapular nerve is essential to avoid iatrogenic injury.

A common location for injury to the suprascapular nerve is the suprascapular notch. The mechanism by which injury occurs at the suprascapular notch has been termed the sling effect by Rengachary et al.⁸³. They evaluated motion of the suprascapular nerve relative to the suprascapular notch with various movements of the arm and shoulder. They noted that the nerve was often apposed to the sharp inferior margin of the superior transverse scapular ligament and that the contact was accentuated with depression and retraction, or hyperabduction, of the shoulder. Several case reports have identified this so-called sling effect as an etiology of suprascapular nerve injury^{1,13,69,89,110}. The cause of injury to the nerve in most situations is acute or chronic trauma in association with the unique anatomy of the suprascapular notch.

The spinoglenoid notch is another site where the suprascapular nerve is frequently injured. Several hypotheses have been proposed regarding the etiology of this injury. One theory is that the nerve is compressed in the fibro-osseous tunnel formed by the spine of the scapula and a hypertrophied spinoglenoid ligament^2,21. Most authors have expressed the belief that the nerve is injured as a result of the anatomy of the spinoglenoid notch and stress that is placed on the nerve by repetitive overhead activities. This theory is supported by clinical data that show that the majority of these injuries occur in athletes who repetitively stress their shoulder^{21,30,31,37,38,46,70,84,112}. A large percentage of the cases that have been reported were in professional volleyball players^{18,30,31,42,46,70,86,96,104}. Ferretti et al.³⁰ identified asymptomatic atrophy of the infraspinatus muscle in twelve of ninety-six top-level volleyball players. A similar prevalence of suprascapular nerve injury in professional volleyball players has been noted by other authors^42,46. Most of the remaining cases of distal suprascapular nerve injury have also occurred in athletes who use the upper extremities in an overhead fashion. These include baseball players, weight lifters, tennis players, football players, fencers, hunters who use bows, dancers, and figure skaters^{2,11,12,21,37,38,51,57,58,62,84}.

Another hypothesis is that the nerve is compressed between the spine of the scapula and the medial tendinous margin of the infraspinatus and supraspinatus muscles during extreme abduction of the shoulder with full external rotation⁸⁶. Ringel et al.⁸⁴ proposed that stretching of the suprascapular artery during pitching results in intimal damage to the suprascapular artery. Microthrombi form and embolize to the vasa nervorum of the suprascapular nerve with resultant ischemic damage. However, to our knowledge, there are no scientific data to support this theory.

Another mechanism by which the suprascapular nerve may be injured is compression by a mass, most commonly a ganglion cyst. Other masses that have been described include synovial sarcoma, Ewing sarcoma, chondrosarcoma, metastatic renal-cell carcinoma, and a bone cyst^32,90. The exact cause of ganglion cysts has not yet been clearly defined. The proximity of many of these cysts to neighboring joints has led some authors to theorize that trauma to the capsular tissues about the joint may contribute to the formation of a ganglion cyst. This theory has been identified as a probable explanation of ganglion cysts in other joints^29,36,68,78. Also in support of this theory are imaging and arthroscopic findings of posterior capsulolabral tears adjacent to and communicating with ganglion cysts^16,28,48,99.

Clinical Evaluation

History

Despite the wide range of etiologies of suprascapular nerve injury, most patients present with a similar history. The typical patient is between the ages of twenty and fifty years with involvement of the dominant upper extremity. The patient may recall an acute event that triggered the symptoms, but more often the onset is insidious. The most common presenting symptom is pain, which is typically located in the posterior aspect of the shoulder, characterized as a dull ache, and exacerbated by overhead activities. Proximal lesions of the suprascapular nerve are more likely to be associated with pain when compared with more distal injuries. This finding is in accordance with the anatomical origin of the nerve's sensory fibers. Patients may also have weakness of the affected shoulder. A substantial number of patients may present with weakness as the chief symptom, with little or no pain^{8,30,41,93,96}. Certain patients may be completely asymptomatic, and the atrophy may be detected as an incidental finding³⁰.

Physical Examination

Physical examination should consist of a thorough shoulder, cervical spine, and neurological evaluation to rule out other causes of the symptoms. The differential diagnosis includes cervical spine disease, brachial plexopathy, and rotator cuff and intra-articular glenohumeral pathology. A common finding associated with suprascapular nerve injury is atrophy of the scapular muscles (Fig. 2). Atrophy of the supraspinatus muscle may be difficult to appreciate because of the overlying trapezius muscle. With a proximal lesion of the nerve, patients may have tenderness on palpation of the triangle between the clavicle and the scapular spine. With a more distal lesion, the tenderness is elicited at the spinoglenoid notch. Weakness may be demonstrated on abduction or external rotation, depending on the location of the nerve injury. External rotation strength is a result of both the infraspinatus and the teres minor muscle; therefore, loss of function of the infraspinatus contribution may be difficult to identify⁴³. Several tests for the evaluation of suprascapular nerve injury have been described. The cross-adduction test involves adducting the arm across the chest. This maneuver tenses the nerve on the superior transverse scapular ligament and may result in increased pain¹³. Injection of a local anesthetic into the suprascapular notch has been found by some authors to be helpful in diagnosing suprascapular nerve entrapment^79,82. The specificity of this test is unclear, as the local anesthetic may produce pain relief in patients with another type of shoulder pathology.

Diagnostic Studies

Electrodiagnostic Studies

The diagnosis of a suprascapular nerve injury is often one of exclusion. When the history and physical examination suggest this diagnosis, the patient should be evaluated with electrodiagnostic studies to confirm and localize the lesion. When an injury to the suprascapular nerve occurs at the suprascapular notch, these studies demonstrate changes in both the supraspinatus and the infraspinatus muscle; in contrast, a more distal lesion of the nerve results in changes only in the infraspinatus muscle. Electrodiagnostic studies include both nerve-conduction-velocity studies and electromyography. An increased latency during a nerve-conduction-velocity study represents a nerve-conduction impairment. Kraft⁵⁶ studied the latency from Erb's point to fixed locations in the supraspinatus and infraspinatus muscles and found that the mean times were 2.7 ± 0.5 and 3.3 ± 0.5 milliseconds, respectively. Electromyography is also a useful method for evaluating a suprascapular nerve injury. The study demonstrates increased spontaneous activity, fibrillations, and positive sharp waves in denervated muscles. Additional changes may include polyphasic activity and a reduction in the amplitude of evoked potentials. These changes tend to occur two to three weeks after the injury^15,53,58,76. Disadvantages of the electrodiagnostic studies are that they are invasive and technique-dependent.

Imaging Studies

Imaging studies are an important part of the evaluation of a suprascapular neuropathy. The studies that often are performed initially are plain radiography of the shoulder and the cervical spine, which usually do not demonstrate pathology. Ultrasonography is an excellent and inexpensive method to identify ganglion cysts or other mass lesions about the shoulder^44,73,91,94. Ultrasonography demonstrates a ganglion cyst as a well defined, homogeneous, hypoechoic mass. In addition, it is an effective method with which to evaluate denervation of the scapular muscles. Kullmer et al.⁵⁸ found that sonography could consistently detect denervation changes by fourteen days after the injury. It should be emphasized, however, that the sensitivity and specificity of an ultrasound examination are highly dependent on the individual performing the study. Computed tomography may also be used to evaluate soft-tissue masses about the shoulder. Ganglion cysts typically show low or medium attenuation when compared with the surrounding muscle.

The best imaging modality for the assessment of soft-tissue masses about the shoulder is magnetic resonance imaging. Magnetic resonance imaging has been demonstrated to be very useful in the diagnosis of a ganglion cyst^{32,35,46,48,99,102}, which appears as a well defined, smoothly marginated mass with low signal intensity on T1-weighted images and with high signal intensity on T2-weighted images (Figs. 3-A and 3-B). Increased signal intensity of the cyst's outer rim may be seen following the administration of gadopentetate dimeglumine. Magnetic resonance imaging is also able to identify changes in the supraspinatus and infraspinatus muscles secondary to denervation. These changes include decreased muscle bulk, fatty infiltration, and homogeneous high signal intensity on T2-weighted images^32,49,58. Kullmer et al.⁵⁸ performed experimental denervation of the supraspinatus and infraspinatus muscles in rats by segmental excision of the suprascapular nerve. They found that the changes of muscle atrophy on magnetic resonance imaging scans and increased signal intensity on T2-weighted images appeared by three weeks after the injury. Magnetic resonance imaging has the added advantage, compared with other imaging modalities, of permitting the detection of intra-articular lesions^16,28,48,71. Labral tears are frequently associated with ganglion cysts of the shoulder. Tirman et al.⁹⁹ retrospectively analyzed the magnetic resonance imaging scans and the clinical and intraoperative findings of twenty patients. They noted that all twenty patients had an area of abnormal signal intensity in the labrum in contact with or connected to a portion of the ganglion cyst. The labral tear was confirmed arthroscopically in all eight patients for whom that procedure was performed. It should be noted, however, that in several case reports magnetic resonance imaging failed to demonstrate a labral tear that was later identified with arthroscopy^16,48,71. Magnetic resonance arthrography has been discussed as a technique with which to better identify labral tears. Palmer et al.⁷⁷ evaluated forty-eight shoulders with magnetic resonance arthrography and found that the test had a sensitivity of 91 percent, a specificity of 93 percent, and an accuracy of 92 percent for the diagnosis of labral lesions.

Treatment

Nonoperative Treatment

Nonoperative treatment should be considered for all patients with a suprascapular nerve injury. The initial treatment includes avoidance of activities that result in trauma and irritation to the nerve. These activities vary from patient to patient but typically involve repetitive overhead motions. This treatment should be combined with a rehabilitation program to enhance flexibility of the surrounding muscles of the glenohumeral joint and a gradual strengthening program of the scapular stabilizing muscles. Later, the rotator cuff should be strengthened and advancement in the rehabilitation program should be monitored closely to avoid reinjury to the nerve while it is healing⁵¹. The results of nonoperative treatment depend on the etiology and location of the nerve lesion.

Although some patients improve with nonoperative management, the overall rate of success is not known^{6,17,26,51,66,82}. Drez²⁶ recommended a period of six to eight months of nonoperative treatment, stating that these injuries represent a traction neurapraxia or axonotmesis and should improve. Callahan et al.¹³ reported on twenty-three patients who had been initially managed with nonoperative measures, and all of them went on to require an operation. Martin et al.⁶⁶ retrospectively reviewed the cases of fifteen patients with a diagnosis of a proximal lesion of the suprascapular nerve. The result was excellent for five patients and good for seven. Three patients went on to require an operation because of persistent symptoms. With nonoperative treatment of a distal injury to the suprascapular nerve, the majority of patients have resolution of pain and improvement in muscle bulk and strength over six months to one year^{11,12,18,38,51,57,62,93,105}. However, failure to follow a proper rehabilitation program and continued participation in athletic activities may cause persistence or worsening of symptoms^18,96.

When a suprascapular nerve injury is secondary to a ganglion cyst, the results of nonoperative treatment are not as good as those reported for nerve injury from other causes. Only twenty-one patients with a suprascapular nerve injury secondary to a ganglion cyst were identified in our review of the literature^{28,35,44,45,71,72,95,97,101,104}. Five of these patients demonstrated marked improvement, one had partial improvement, and fifteen had an unsuccessful result. Of the fifteen patients for whom nonoperative treatment failed, nine later required operative excision of the cyst. All nine patients had complete relief of pain and subjective improvement in strength, with residual muscle atrophy demonstrated in three. These results suggest that it is not detrimental to delay an operation in order to try nonoperative treatment.

Operative Treatment

The operative procedure used in the treatment of a suprascapular nerve injury, and the results, vary depending on the etiology and location of the nerve lesion. When suprascapular nerve entrapment is localized to the suprascapular notch, with no evidence of a mass lesion, the operative treatment has usually consisted of release of the superior transverse scapular ligament through a posterior approach, as described by Post and Mayer⁷⁹. The patient is placed in a semi-prone or lateral position with the arm draped free. The skin incision is made in line with the spine of the scapula, and the trapezius muscle is sharply elevated off the scapular spine and retracted superiorly. The supraspinatus muscle is then carefully reflected inferiorly to expose the suprascapular notch. The superior transverse scapular ligament is identified and divided under direct vision, with care taken to protect the suprascapular neurovascular structures.

In our review of the literature, we identified 178 instances in which operative decompression of the suprascapular nerve was performed at the suprascapular notch^{1,4-6,8,13,17,19,26,34,39,41,42,51,60,66,79,81,83,84,87,103}. Most of the patients had complete resolution of pain and a substantial increase in muscle strength. The return of muscle bulk tended to be less predictable and more prolonged. Hagert and Linder⁴¹ operatively released the superior transverse scapular ligament in eleven patients who had a proximal injury to the suprascapular nerve. Ten of the eleven patients reported immediate relief of pain, and the remaining patient noted a decreased level of pain. Muscle strength returned more gradually. Post and Mayer⁷⁹ managed eight patients with an operative release of the superior transverse scapular ligament; all eight patients had a good or excellent result. Recurrence of symptoms and complications following the decompression are uncommon. Some authors have described performing a widening of the suprascapular notch in addition to a release of the superior transverse scapular ligament. These results appear to be equally successful^{1,13,60,66,81}.

With isolated involvement of the infraspinatus muscle, the location of the nerve lesion is typically at the spinoglenoid notch. In this clinical scenario, releasing the superior transverse scapular ligament without addressing the nerve distally is likely to lead to a poor result^84,91. Operative exploration of the distal part of the suprascapular nerve is performed through a posterior approach as already described. Sandow and Ilic⁸⁶ recommended approaching the nerve at the spinoglenoid notch on both sides of the scapular spine. To expose the nerve on the superior side of the spinoglenoid notch, the supraspinatus muscle is reflected superiorly. To expose the inferior side of the spinoglenoid notch, the deltoid muscle may be split in line with its fibers or partially detached from the spine of the scapula. The infraspinatus muscle is then reflected inferiorly, exposing the suprascapular nerve and vessels. When a distal lesion of the suprascapular nerve is treated distally, it is important to assess the anatomy of the spinoglenoid notch for structures that may be compressing the nerve—specifically, the spinoglenoid ligament^2,20,54, scapular spine, or medial tendinous margin of the rotator cuff^84-86. Compression by these structures may be addressed by release of the spinoglenoid ligament and deepening of the lateral margin of the scapular spine^{2,20,31,42,54,86}. The surgeon should avoid excessive deepening of the notch (by more than one centimeter) so as not to compromise the strength of the base of the acromion, which can lead to fracture⁸⁶. The results of operative decompression are good, with almost all case reports demonstrating excellent relief of pain. Return of motor bulk and strength, however, is more variable^{2,14,20,30,31,42,54,86}.

When compression of the suprascapular nerve is secondary to compression by a ganglion cyst, other treatment options are available. Our review of the literature revealed eight cases of ultrasonography or computed tomography-guided aspiration of ganglion cysts about the shoulder^9,32,44,99. These treatment modalities resulted in decreased pain in all eight patients; however, one patient was noted to have a recurrence of the cyst, as documented on magnetic resonance imaging. Both methods appear to be effective for decompression of the cyst and are associated with little morbidity. The disadvantage of these treatment options is that they do not allow evaluation or treatment of intra-articular lesions; therefore, the patient may be at increased risk for recurrence.

Options for the operative treatment of ganglion cysts of the shoulder include open and arthroscopic procedures. Arthroscopy may be performed as the sole method of decompression of the cyst or in combination with aspiration or open excision of the cyst. Historically, ganglion cysts of the shoulder have been treated with open resection through a posterior approach. Our review of the literature identified twenty-eight cases of open excision of the ganglion cyst, with adequate follow-up information, in which the glenohumeral joint was not assessed with arthroscopy^{32,33,45,72-74,80,91,94,95,97}. Open resection of the ganglion cyst resulted in complete resolution of pain in all but one patient. Strength improved in the majority of patients. Atrophy of the scapular muscles was the slowest to improve and the least likely objective measure to show improvement. The symptomatic ganglion cyst recurred in three patients after an initial resolution of symptoms^71,91. In an additional three patients, the cyst could not be identified at the time of the operation^71,91. In two of these patients the cyst was inaccurately localized on preoperative magnetic resonance images, and in the third patient the cyst was believed to have spontaneously decompressed. It is important to carefully evaluate the preoperative electrodiagnostic and imaging studies to accurately identify the location of the cyst. As with the ultrasound and computed tomography-guided aspirations, open excision of the cyst does not allow the surgeon to identify or treat intra-articular lesions that may have contributed to the formation of the cyst.

The last treatment option to be discussed involves arthroscopy, either in conjunction with one of the treatment methods mentioned earlier or as the sole means of performing the decompression. Fehrman et al.²⁸ reported on six patients with a ganglion cyst in the shoulder. After arthroscopic evaluation, all six patients were found to have a posterior capsulolabral tear from which the cyst originated. The labral tears were debrided at the time of the arthroscopy, and the ganglion cysts were excised through an open posterior exposure. Five of the six patients reported complete relief of pain, while one patient reported only partial relief. Several patients subjectively assessed their shoulders as normal; however, on objective evaluation, the shoulders were noted to have persistent muscle atrophy with weakness of external rotation strength. No recurrences were noted, with the duration of follow-up ranging from four months to two years.

Moore et al.⁷¹ reported on twenty-two ganglion cysts in twenty-one patients. Sixteen of the shoulders were treated operatively by three surgeons. Five of these shoulders were treated with open resection alone; six, with a combined arthroscopic and open procedure; and five, with arthroscopic decompression of the cyst alone. The operative technique was chosen according to the preference of the operating surgeon. Fifteen of the sixteen patients had a good or excellent result; however, the results were not separated according to the type of operative treatment. One patient who had been managed with a combined arthroscopic and open procedure had a recurrence of symptoms. A repeat magnetic resonance imaging scan demonstrated recurrence of the cyst. Arthroscopic reevaluation showed a labral tear that was believed to have been missed at the time of the original procedure. Following débridement of the labral tear and decompression of the cyst, the patient was pain-free.

Iannotti and Ramsey⁴⁸ reported on three patients with dysfunction of the suprascapular nerve secondary to a ganglion cyst. They performed arthroscopic decompression of the cyst through the labral tear or a capsulotomy near the junction of the capsule and labrum if no tear was present. The ganglion was drained into the joint with the aid of manual pressure over the cyst. All three patients had complete relief of pain with return of external rotation strength. One of the three patients had residual muscle atrophy. Magnetic resonance imaging was performed postoperatively and demonstrated no recurrences of the cysts. Chochole et al.¹⁶ also reported on a patient who underwent arthroscopy for a ganglion cyst of the shoulder. During the arthroscopy, an anterior-posterior lesion of the superior aspect of the labrum was identified and treated with aggressive débridement. No additional interventions were performed to address the ganglion cyst. Approximately eight weeks postoperatively, a magnetic resonance imaging scan demonstrated no recurrence of the cyst, and at twelve weeks the patient had had full recovery.

In summary, nonoperative management is a treatment option for ganglion cysts but is associated with a high failure rate. Ultrasound and computed tomography-guided aspiration are both effective methods for decompression of a ganglion cyst and are associated with minimal morbidity. The disadvantage of these techniques is that the glenohumeral joint is not directly assessed. Open resection of a ganglion cyst has a high rate of success but does not allow the surgeon to identify and treat associated intra-articular capsulolabral tears and is associated with more morbidity than the other modalities for decompression. Although not clearly demonstrated in the literature, this may place the patient at an increased risk for recurrence of the cyst. Arthroscopy is an excellent method with which to evaluate and treat intra-articular lesions, and it may also be used to decompress the cyst. Arthroscopy may also be used in combination with aspiration or open excision of the cyst. Because of the increased morbidity, consideration should be given to reserving open resection for cases that do not respond to the other treatment options.

Overview

Suprascapular nerve injuries should be considered in the differential diagnosis of shoulder pain and dysfunction. Electrodiagnostic studies are useful for confirming the diagnosis and identifying the site of the nerve injury. Magnetic resonance imaging is an excellent method with which to evaluate shoulder pathology. The test can help to exclude other etiologies of a patient's symptoms, to look for mass lesions, and to identify labral tears in association with ganglion cysts. Treatment is directed toward the cause of the nerve injury. A trial of nonoperative management is warranted for most patients; however, it has a high rate of failure in the treatment of ganglion cysts. If nonoperative management does not result in improvement, an operation may be indicated. Operative decompression of the suprascapular nerve is associated with a high rate of pain relief and functional improvement. However, resolution of muscle atrophy is less predictable.

References

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