Compressive neuropathies of the upper extremity are a common cause of pain, dysfunction, and disability. Suprascapular nerve entrapment is one of the less common upper extremity neuropathies, but its presence can cause significant complaints about the shoulder.
KopeII and Thompson1 described suprascapular entrapment neuropathy in 1959. Ganglion cysts commonly occur in periarticular regions, and in the shoulder they can be one of the causes of suprascapular neuropathy. There have been numerous case reports of suprascapular neuropathy, with or without an associated ganglion cyst; however, most of the reports describe only a small number of patients. This article reviews the literature.
The suprascapular nerve originates from the upper trunk of the brachial plexus containing fibers from the ventral divisions of the C5 and C6 spinal nerves; the C4 spinal nerve contributes fibers in up to 50% of cases.2 The nerve courses laterally with the suprascapular artery and vein beneath the inferior belly of the omohyoid muscle and the anterior border of the trapezius muscle, crossing the posterior triangle of the neck.
At the superior border of the scapula, the nerve passes through the suprascapular notch below the transverse scapular ligament while the artery and vein pass superior to the ligament (Fig 1). The nerve is relatively fixed in this location.3 Rengachary et al4 demonstrated that the nerve is closely opposed to the inferior surface of the transverse scapular ligament; the ligament creates a "sling" effect on the nerve because both the nerve's origin and termination into the supraspinatus muscle are above the plane of the suprascapular notch.4
Having entered the supraspinatus fossa, the nerve dives deep to the supraspinatus muscle and supplies motor branches to the muscle and sensory branches to the glenohumeral and acromioclavicular joints. It then travels around the lateral border of the spine of the scapula, the spinoglenoid notch, to supply the infraspinatus muscle with motor branches. The nerve often must pass through an aponeurotic band separating the supraspinatus and infraspinatus muscles in the spinoglenoid notch.
Suprascapular nerve injury may be from trauma, repetitive overuse, mass lesions, or anomalies of the suprascapular notch and transverse ligament anatomy. Neuropathy can present after a scapular fracture from extrinsic pressure by fracture callus or malunited fragments.
Suprascapular nerve injury is the second most common isolated nerve injury after glenohumeral dislocation, axillary nerve injury being the most common.5 Direct blow injuries and forcible shoulder depression also may lead to suprascapular neuropathy.5 Less common is traction neuropathy from clavicle fractures or acromioclavicular joint dislocations when shoulder ptosis is present. The nerve is also susceptible to a traction injury during excessive supraspinatus advancement in rotator cuff repairs.3
Repetitive overuse is hypothesized as a common cause of neuropathy. With abnormal or repetitive movement of the scapula and glenohumeral joint, the suprascapular nerve could become inflamed where it is "slung" underneath the transverse scapular ligament in the suprascapular notch. This could then lead to edema, fibrosis, and ultimately nerve compression and neuropathy.5 Volleyball players are particularly susceptible to this type of injury.6,7
Mass lesions in either the suprascapular notch or at the spinoglenoid notch can cause compression of the nerve as it passes through these right spaces. The most common masses in these locations are ganglion cysts and lipomas (Fig 2). Because they are usually anatomically related to the posterior shoulder capsule, ganglion cysts are most likely to cause compression at the spinoglenoid notch, thereby affecting the infraspinatus nerve branch only.8 Other masses include abscess, hematoma, and benign or malignant neoplasms.9
The pathogenesis of ganglion cysts deserves some consideration as it could affect the treatment of a suprascapular neuropathy caused by compression from a ganglion cyst. The development of a ganglion cyst near a joint has been described for several anatomic areas including the wrist, knee, hip, ankle, and shoulder.1011
Fig 1 : Diagram showing the anatomy of the suprascapular nerve (SN=suprascapular nerve, SSN=suprascapular notch, SGN=spinoglenoid notch, SM=supraspinatus muscle, and IM=infraspinatus muscle).
Some authors contend that these cysts are the result of a primary myxoid degeneration of connective tissue near a joint and not necessarily related to any physical disruption of the joint capsule.1112 Angelides and Wallace10 concluded that wrist ganglia are caused by joint fluid leaking through a weak area in the wrist capsule via a one-way valve mechanism.
Haller et al13 linked hip juxta-acetabular cysts to tears in the labrum; they postulated that the cysts were the result of synovial fluid and tissue leaking through the labral tear.13 Other authors have described an association between shoulder ganglion cysts and glenohumeral intra-articular pathology, namely a posterior capsulolabral tear.814"16
There are causes of entrapment neuropathy that relate to specific anatomic abnormalities of the suprascapular notch. The transverse ligament can become calcified or ossified, resulting in the nerve being kinked under and rubbing against an inflexible tissue.17 The notch can be congenitally small predisposing to entrapment. Rengachary et al4 described six different types of suprascapular notches, from a wide "C"shaped notch to a small, narrow "V" shape.
Fig 2: Axial MRI of the right shoulder demonstrating a ganglion cyst in the spinoglenoid notch (arrowhead) and a posterior labral tear (arrow).
The diagnosis of suprascapular entrapment neuropathy is based on clinical history and physical examination supplemented with electrophysiologic testing (Table 1). Deep, diffuse shoulder pain, particularly posterolateral, is the most common presenting complaint.18·19 The pain is often characterized as burning, aching, or crushing.19 This sensation of pain is probably referred from the sensory articular branches to the glenohumeral and acromioclavicular joints.
The patient may describe an injury or a pattern of repetitive overuse.7 As the condition progresses, the patient may detect weakness in the shoulder and difficulty with overhead use of the arm.6,20
Physical examination is important for ruling out other conditions of the cervical spine and shoulder, and also for specifically looking for signs of suprascapular neuropathy. Inspection may reveal atrophy of the supraspinatus, infraspinatus, or both.6 If the atrophy is localized to the infraspinatus, it becomes more likely that the entrapment is distal to the suprapinatus branch, possibly at the spinoglenoid notch. Point tenderness over the suprascapular notch is commonly elicited if the entrapment occurs at this location.19
Suprascapular neuropathy can result in weakness of shoulder external rotation and abduction, especially during the initial 20°-30° of abduction.5 Cross arm adduction may be used as a provocative maneuver by putting the nerve under tension and causing pain.19 An injection of lidocaine into the area of entrapment that provides pain relief can be used as a confirmatory diagnostic test.6
Diagnosis of suprascapular neuropathy
Radiographic evaluation should begin with plain radiographs to include the cervical spine if clinically indicated. Radiographs can help rule out other causes of shoulder pain such as osteoarthrosis and may identify an abnormality of the scapula causing the nerve entrapment such as an old scapular fracture.21
Neurophysiologic evaluation should be performed to confirm the diagnosis of entrapment neuropathy of the suprascapular nerve.19·22-3 Electromyography and evaluation Of the distal motor latency are used to diagnose and localize the lesion. The range of normal values for the latency to the supraspinatus is 1 .7 to 3.7 milliseconds and 1.7 to 4 milliseconds to the infraspinatus. Padua et al22 were able to differentiate between entrapment at the suprascapular notch and entrapment at the spinoglenoid notch using these values.
Also noted as abnormal are the presence of fibrillation, insertional activity, decreased amplitude of evoked potentials, and sharp positive waves. The clinician must be specific in ordering the test so mat the electromyographer knows to examine the suprascapular nerve, and the results should be compared to values for the patient's contralateral asymptomatic shoulder.
Magnetic resonance imaging (MRI) also should be performed in most cases to identify possible mass lesions that may be causing the neuropathy, most commonly a ganglion cyst.9 Magnetic resonance imaging also has been used for diagnosis in cases without a mass lesion by demonstrating that the muscular atrophy was isolated to the spinatii muscles.24 Ultrasound can be used for both diagnosis of a cystic lesion and aspiration of the lesion, but no long-term follow-up studies have been reported.25
Rotator cuff disease and other nerve conditions of the upper extremity are the most likely diagnoses to be confused with suprascapular nerve entrapment. Since the suprascapular nerve supplies the two rotator cuff muscles that are typically involved in rotator cuff impingement and tears, entrapment neuropathy and tendon pathology can present with similar history and physical findings.26 Physical examination with selective diagnostic lidocaine injection (into the subacromial space) should be able to differentiate the two conditions.
Glenohumeral and acromioclavicular arthrosis usually will be detected by physical examination and routine radiographs. Suspicion of cervical disk disease should be investigated with examination of the neck and cervical nerve root function and radiographic imaging of the cervical spine to include MRI if indicated. Brachial plexopathy, brachial neuritis, adhesive capsulitis, and Pancoast's tumor should all be kept in mind when evaluating a patient with shoulder pain (Table 2).
The first line of treatment, as with most nonemergent musculoskeletal conditions, is nonoperative based on activity modification with avoidance of provocative positions and an organized program of physical therapy emphasizing rotator cuff strengthening and stabilization of the scapula.27 Nonsteroidal anti-inflammatory medication and analgesics are also helpful.
Martin et al27 reported on 15 patients treated nonoperatively with physical tiierapy. Three patients eventually underwent operative decompression of the nerve. Of the 12 patients treated nonoperatively, 5 had an excellent result and 7 were rated as good. A good result meant mat the patient had only one of the following: persistent pain, objective muscle weakness, or decreased shoulder function. An excellent result had none of those conditions listed. Several authors recommend at least 6 months of conservative therapy for cases without a mass lesion.26-28
When nonoperative treatment fails after a minimum 6-month trial or if there is a mass lesion compressing the nerve, operative decompression should be considered. The more proximal compression requires decompression of the nerve in the suprascapular notch.
The shoulder is approached posteriorly through an incision parallel to and just superior to the scapular spine.29 The trapezius is sharply elevated off the scapular spine and retracted superiorly, while the underlying supraspinatus is retracted inferiorly away from the suprascpular notch. Several authors caution against overly aggressive retraction of the supraspinatus as the nerve could be put under tension with this manuever.5,18
The transverse scapular ligament is resected, and any bony impingement is decompressed, taking great care to avoid injuring the nerve or the overlying suprascapular artery and vein. Spinal surgery instruments can be helpful, similar to performing a laminectomy.30
The suprascapular nerve should be traced in its path in the supraspinatus fossa down to the spinoglenoid notch to decompress any other sites of constriction. Some surgeons do not recommend this further dissection of the nerve unless there is electrodiagnostic evidence of a more distal site of compression.5,19 The trapezius should be repaired anatomically with nonabsorbable sutures.
In the case of a mass lesion, the mass itself needs to be removed to achieve decompression of the nerve. Surgical approaches similar to the one described above are typically used. Until recently, open excision also was the approach recommended for removal or decompression of a ganglion cyst. This involves either the approach described above or working more inferiorly by detaching the deltoid and working in the infraspinatus fossa and spinoglenoid notch as determined by the location of the cyst on MRI.
Ganglion cysts are often related to and caused by intra-articular pathology, and it is now recommended that arthroscopic examination of the shoulder be included in the operative treatment of these periarticular cysts.8,14"16 A labral tear is probably present, and arthroscopic examination of the shoulder will allow the surgeon to treat the intraarticular pathology. It has been recommended that the cyst be decompressed through the labral tear and the tear repaired.8,15,16 Iannotti and Ramsey16 described a technique for arthroscopic cyst decompression and reported on successful outcomes of three patients with more than 1 year of follow-up.
If the cyst does not originate from the glenohumeral joint, the subacromial space should be evaluated.31 Occasionally, the typical gelatinous cyst fluid will not be apparent through the labral tear. The tear should be repaired, and the patient monitored clinically for resolution, rather than proceed with open surgery at the same time. If symptoms persist beyond 4 to 6 months and repeat MRI or ultrasound still demonstrate the cyst, open surgery is indicated. Conversely, if a labral tear is not present, Iannotti and Ramsey16 recommend making a small (<1 cm) capsulotomy arthroscopically at the junction Of the labrum and posterior capsule to decompress the cyst.
After open decompression, a sling is used for 10 to 14 days with pendulum range-of-motion exercises, and then active and passive motion are started as tolerated. A program of strengthening similar to the nonoperative protocol is initiated when motion has returned.27 Arthroscopic postoperative rehabilitation would be based on the intra-articular pathology and treatment, ie, labral stabilization.
To simplify the review of a large number of reports, most with a small number of patients, we graded patients as improved if they qualified as either excellent or good as determined by the author. Excellent typically meant that the patient had returned to full activities, had no functional limitation on the shoulder, and had no pain. A good result usually meant that the patient had one of the following: residual pain, objective weakness, or decreased function, but overall the patient was satisfied with the result. Only reports with a minimum of 6 months of follow-up were included.
A total of 176 cases of suprascapular neuropathy were reviewed 6-8·16·1923.2S-29.3M7 Qf ^ ,3g patients who underwent surgery, 106 (77%) had good or excellent results. Of the 38 patients who were treated nonoperatively, 35 (92%) had good or excellent results. One should not draw the conclusion that nonoperative treatment is better because most of the patients who eventually underwent surgery had previously failed an adequate trial of conservative therapy. Moreover, the cases that went on to surgery may have had a more severe case of neuropathy that was refractory to conservative management.
There were 31 ganglion cysts. Seventeen of 20 treated with open surgery improved to good or excellent, 3 treated arthroscopically had complete resolution, 3 treated with ultrasound-guided aspiration improved, and 5 treated nonoperatively improved. There were 2 radiographic or surgical confirmations of ganglion cyst recurrence after open excision, and both patients had recurrent symptoms as well. There were 4 more cases of either open excision or ultrasound-guided aspiration that continued to have some symptoms; 3 of these were graded as a good result.
Almost all patients who were rated as good or excellent returned to full activities including pitching. While most of the cases noted either an excellent or good result with either nonoperative or operative treatment and most patients returned to full activity, residual atrophy was noted in a fairly large number of cases, approximately 50%.6
Suprascapular entrapment neuropathy is an uncommon cause of shoulder pain and functional loss, but should be considered in the assessment of a patient with these shoulder complaints. As with all medical conditions, history and physical examination are the basis of the evaluation, and they are supplemented with radiographs, neurophysiologic tests, and MRI.
The first line of treatment is nonoperative based on physical therapy, activity modification, and nonsteroidal anti-inflammatory medication. If a 6month trial of nonoperative treatment fails, surgical decompression may be considered. Surgery may be considered earlier in the case of a mass lesion.
Surgical treatment consists of open decompression of the suprascapular nerve after localization of the lesion by the neurophysiologic tests, Glenohumeral arthroscopy should be included in the surgical treatment of a ganglion cyst, and the cyst itself may be decompressed arthroscopically, negating the need for open excision. If it is demonstrated that the cyst originates from a labral tear, the tear should be repaired or debrided as indicated.
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Diagnosis of suprascapular neuropathy