Andreas H. Gomoll and Anthony A. Romeo
DEFINITION
Suprascapular nerve (SSN) entrapment is an uncommon cause for shoulder pain and weakness. It was initially described by Koppel and Thompson.11
SSN entrapment typically occurs at the suprascapular or spinoglenoid notch and presents with symptoms ranging from diffuse shoulder pain to weakness and atrophy of the supraspinatus and infraspinatus muscles.
ANATOMY
The SSN arises from the upper trunk of the brachial plexus, with contributions from C5 and C6 (rarely also C4), and provides branches to the supraspinatus and infraspinatus muscles. It also carries afferent fibers from the glenohumeral joint and rarely also cutaneous fibers from the lateral aspect of the shoulder.
The nerve traverses two potential compression points, at the suprascapular notch and spinoglenoid notch (FIG 1), and is accompanied by the suprascapular artery and vein.
At the suprascapular notch, the nerve runs in a fibroosseous canal formed by the scapular notch and the transverse scapular ligament. Generally, the nerve runs under the ligament, but it is occasionally accompanied by a branch of the main vessels, which course over the ligament.
The suprascapular notch is approximately 4.5 cm medial to the posterolateral corner of the acromion and 3 cm medial to the glenoid rim (supraglenoid tubercle). The spinoglenoid notch is approximately 1.8 cm medial to the glenoid rim and 2.5 cm inferomedial to the supraglenoid tubercle.3
Several anatomic studies have described the presence of a spinoglenoid ligament (inferior transverse scapular ligament) at the spinoglenoid notch in 3% to 60% of specimens,5,6 but its role in nerve entrapment at this level is controversial.
PATHOGENESIS
The most common site of entrapment is at the suprascapular notch, where it can be compressed by a thickened or ossified transverse scapular ligament.
The relative confinement of the nerve at the suprascapular notch also places it at risk for injury due to traction, such as seen either in acute trauma or repetitive overhead activities such as volleyball, tennis, or weightlifting.
Compression from labral ganglions can also occur, typically at the spinoglenoid notch.1 These cysts can develop as the result of labral tears that allow fluid extravasation but block backflow, similar to a one-way valve.
More recently, traction injury to the nerve has been described as the result of massive, retracted tears of the posterosuperior cuff.2
Direct or indirect trauma leading to SSN neuropathy has been described as the result of shoulder dislocation, proximal humerus fracture, or scapular fracture.
Iatrogenic injury to the SSN can occur during distal clavicle resection, positioning during spine surgery, transglenoid drilling for instability repair, shoulder arthrodesis, or the posterior approach to the glenohumeral joint.
NATURAL HISTORY
The natural history depends on the presence or absence of a space-occupying lesion as the cause of SSN neuropathy.
Without compression by a mass, most patients will improve with time and supervised physical therapy.8
Conversely, the presence of a mass, such as a cyst or ganglion, usually results in failure of conservative management and will require decompressive surgery.
The natural history of periarticular ganglion cysts in the shoulder is controversial, but they are thought to persist and enlarge with time.9 In rare instances, spontaneous resolution of ganglion cysts has been documented.
PATIENT HISTORY AND PHYSICAL FINDINGS
SSN neuropathy secondary to compression at the suprascapular notch typically presents as a dull pain in the posterior and lateral shoulder, but the pain can also be referred to the anterior chest wall, lateral arm, and ipsilateral neck. Compression at the spinoglenoid notch is often comparatively pain-free and presents with isolated infraspinatus atrophy (FIG 2).
FIG 1 • Anatomy of the suprascapular nerve (SSN). The SSN is accompanied by the suprascapular artery and vein, which course over the transverse scapular ligament (TSL), while the nerve passes underneath. All three then traverse the spinoglenoid notch.
FIG 2 • Posterior photograph of a patient with right infraspinatus muscle wasting secondary to suprascapular nerve entrapment at the spinoglenoid notch.
The patient often provides a history of acute or repetitive trauma to the shoulder, such as a fall on the outstretched hand, or activities such as volleyball, tennis, or weightlifting.
There appears to be an increased incidence of isolated infraspinatus atrophy in asymptomatic volleyball players. This typically responds well to conservative measures.
Depending on the chronicity and degree of compression, varying amounts of weakness in abduction and external rotation can be detected on physical examination.
In longstanding compression, atrophy of the supraspinatus and infraspinatus can be observed.
Atrophy, if present, may assist in differentiating compression at the suprascapular notch from that at the spinoglenoid level, since supraspinatus atrophy occurs only with the former.
Palpation of the spinoglenoid notch and cross-body adduction may reproduce the patient’s symptoms.
It is important to exclude other potential sources of pain, such as the cervical spine, acromioclavicular joint, or rotator cuff.
IMAGING AND OTHER DIAGNOSTIC STUDIES
An anesthetic injection into the suprascapular notch can be diagnostic if it results in complete but transient pain relief.
Stryker notch views, or anteroposterior radiographs of the scapula, with a 15to 30-degrees caudally directed beam, provide visualization of the suprascapular notch. Alternatively, a CT scan can provide good osseous detail in cases of posttraumatic deformity or ossification of the transverse scapular ligament.
MRI can reveal a superior or posterior labral tear and the presence of a ganglion in the area of the suprascapular or spinoglenoid notch (FIG 3). Ganglion cysts present as homogeneous masses with low signal intensity on T1-weighted images and high signal intensity on T2-weighted images.
Electromyography and nerve conduction studies can often provide a conclusive diagnosis by showing denervation potentials, fibrillations, spontaneous activity, and prolonged motor latencies in the supraspinatus or infraspinatus, depending on the level of entrapment.
DIFFERENTIAL DIAGNOSIS
Cervical radiculopathy
Glenohumeral instability
Rotator cuff pathology
Acromioclavicular joint arthrosis
NONOPERATIVE MANAGEMENT
Initial treatment for SSN neuropathy in the absence of a space-occupying lesion is conservative and will lead to nearcomplete resolution of symptoms in most cases.
Complete resolution of pain and weakness can take more than 1 year.
Supervised physical therapy, followed by a self-directed home exercise program, should consist of range-of-motion exercises, as well as strengthening of the rotator cuff muscles, the deltoid, and the periscapular musculature, including the trapezius, rhomboids, and serratus musculature. Restoring proper scapular function is beneficial in recovery and may prevent recurrence of the injury.
Image-guided cyst aspiration has shown success in about half of patients, with persistence or recurrence in the other half.9,12
FIG 3 • T2-weighted MR images depicting axial (A) and oblique (B) sagittal views showing a cyst in the area of the spinoglenoid notch.
SURGICAL MANAGEMENT
Surgical treatment is indicated in patients who have failed to respond to 6 to 12 months of nonoperative measures and continue to have significant pain and dysfunction. SSN neuropathy secondary to a mass is best treated with decompression, and evaluation and potential repair of the glenoid labrum.
Other sources for shoulder pain and dysfunction should be ruled out if the mass is smaller than 1 cm in diameter or is not directly compressing the neurovascular bundle.
Preoperative Planning
Oblique sagittal MR imaging allows visualization of the SSN in the supraspinatus fossa, the spinoglenoid notch, and the infraspinatus fossa.
If a space-occupying lesion is present, this imaging will assist in preoperative planning by delineating the exact position of the mass and determining whether it is confined to the supraspinatus or the infraspinatus fossa or involves both areas.
A paralabral ganglion or cyst that is confined to one area, especially when associated with a labral tear or other intraarticular pathology, is often amenable to arthroscopic decompression.
We have found it useful first to perform a diagnostic shoulder arthroscopy and potential treatment of intra-articular pathology, followed by arthroscopic or open decompression of the SSN.
Arthroscopic decompression has the potential advantages of treating associated intra-articular lesions, such as labral tears and avoiding the morbidity associated with open procedures.
Positioning
Either the beach chair or the lateral decubitus position can be used.
TECHNIQUES
OPEN DECOMPRESSION
Approach to the Suprascapular Notch
Decompression of the suprascapular nerve at the suprascapular notch is best achieved through a trapeziussplitting approach.
The anterior approach requires a more complex dissection and therefore carries a higher risk of neurovascular complications. It also offers incomplete visualization of the SSN posterior to the notch and is generally not recommended.
A saber-type skin incision following the Langer lines is performed over the top of the shoulder. The incision begins posteriorly at the distal third of the scapular spine and extends anteriorly to a point 2 cm medially off the acromioclavicular joint (TECH FIG 1A).
A transverse skin incision parallel to the scapular spine can be chosen instead but produces a less cosmetic scar.
The trapezius fascia and muscle is divided in line with its fibers for a distance of 5 cm.
Abduction of the arm decreases tension on the muscle, which if necessary can be elevated off the scapular spine for an extensile exposure.
The supraspinatus muscle is bluntly dissected off the anterior aspect of the suprascapular fossa and retracted posteriorly to provide access to the suprascapular notch (TECH FIG 1B).
TECH FIG 1 • Schematic and intraoperative photograph demonstrating suprascapular nerve release at the suprascapular notch. A. The trapezius muscle is split in line with its fibers. B. The supraspinatus muscle is bluntly dissected off the suprascapular fossa and retracted to expose the suprascapular notch. C. The transverse scapular ligament has been released.
The overlying suprascapular artery and vein are gently retracted to expose the transverse scapular ligament.
A small right-angle clamp can be used to bluntly dissect under the ligament and protect the underlying nerve while the ligament is transected with a scalpel.
Occasionally the nerve is still tethered after release of the transverse ligament, requiring careful resection of the medial aspect of the suprascapular notch. The resected edge of the bone must be smooth at the completion of the procedure.
If the trapezius was detached during the approach, it should be sutured back to the bone of the scapular spine. If the muscle was only split in line with its fibers, it is reapproximated with interrupted, absorbable sutures.
Approach to the Spinoglenoid Notch
The Posterior approach provides direct visualization of the suprascapular nerve at the spinoglenoid notch.
A longigudinal skin inision is centered approximately 4 cm medial to the posterolateral corner of the acromion, approximately 5 cm in length. Following Langer lines provides a cosmetically acceptable scar.
The underlying fascia and deltoid muscle is split in line with its fibers beginning at the level of the scapular spine and extending 5 cm distal from the posterior acromion (TECH FIG 2A). A stay suture placed at the distalmost extent of the incision protects against propagation of the split, which carries a risk of injury to the axillary nerve.
The infraspinatus is identified, dissected off the scapular spine, and retracted inferiorly (TECH FIG 2B).
Commonly, a small area of vascular fibrous tissue is encountered posterior to the site of the spinoglenoid notch, covering the suprascapular neurovascular structures.
If a ganglion is present, the contents of the cyst should be removed along with the wall (TECH FIG 2C).
A spinoglenoid ligament, if present, should be excised.
Decompression is complete when the SSN can be followed along its entire length from the spinoglenoid notch until it arborizes into its infraspinatus branches (TECH FIG 2D).
The infraspinatus muscle is allowed to return to its anatomic position.
The deltoid muscle and fascia is reapproximated with interrupted, absorbable sutures.
TECH FIG 2 • Schematics and intraoperative photographs showing suprascapular nerve release at the spinoglenoid notch. A. The deltoid muscle is split in line with its fibers, beginning about 4 cm medial to the posterolateral corner of the acromion. B. The spinoglenoid notch has been exposed. The retractors displace the infraspinatus muscles posteriorly and inferiorly. C. A multilobulated ganglion cyst. D. The suprascapular nerve is now visible after the soft tissue band has been divided.
ARTHROSCOPIC DECOMPRESSION
Approach to the Suprascapular Notch
Routine glenohumeral arthroscopy is performed to assess concomitant pathology, especially tears of the superiorposterior labrum.
The subacromial bursa is resected, extending more medially than what is usual for subacromial decompression.
The bursectomy should allow adequate visualization from the acromioclavicular (AC) joint and coracoid anteriorly to the scapular spine posteriorly.
The coracoid is palpated with a probe or switching stick, which can also be used to bluntly dissect the surrounding soft tissues to expose the coracoclavicular ligaments.
Alternatively, the ligaments can be found approximately 15 mm medial to the AC joint and then followed inferiorly to their insertion on the coracoid.
The conoid ligament attaches to the coracoid just laterally to the suprascapular notch. Fibers of the conoid ligament are in continuity with the transverse scapular ligament.
The suprascapular notch is typically covered by the supraspinatus muscle and fat, complicating visualization of the neurovascular bundle (TECH FIG 3A).
An accessory portal is created approximately 2 cm medial to the standard Neviaser portal along a line that bisects the angle formed between the clavicle and spine of the scapula. An 18-gauge spinal needle helps with correct positioning of the portal (TECH FIG 3B).
Use of a switching stick or smooth trocar through this accessory portal allows careful, blunt dissection of the fat to expose the suprascapular vessels coursing over the transverse scapular ligament, which presents as glistening white fibers.
Once adequate visualization has been achieved, the nerve is protected with a probe or small trocar while the overlying ligament is cut with the arthroscopic scissors as far lateral as possible (TECH FIG 3C–E).
The SSN is probed to ensure adequate decompression; any residual compression from the bony structures can be removed with the arthroscopic burr.
TECH FIG 3 • Schematic and arthroscopic images showing arthroscopic suprascapular nerve release at the suprascapular notch. A. After soft tissue removal, the nerve (N) can be visualized underneath the superior transverse scapular ligament (STSL). A blunt trocar is retracting the overlying vessel. B. The arthroscope is positioned in the lateral portal and the instruments are introduced through a superior portal, medial to the standard Neviaser portal. C. Arthroscopic scissors positioned to cut the STSL. D,E. The ligament has been released. A, artery. (A,C,E: Courtesy of Dr Laurence Higgins.)
Approach to the Spinoglenoid Notch
Ganglion cysts associated with labral tears are most commonly located at the spinoglenoid notch. They often extend into the infraspinatus fossa.
With an intact labrum, the joint capsule above the superior-posterior labrum is incised, beginning posterior to the biceps root and extending posteriorly for 2 to 3 cm.
After incision of the capsule, the fibrous raphe between the supraspinatus and infraspinatus seen lateral to the spinoglenoid notch provides a useful landmark.
The spinoglenoid notch can be palpated with an arthroscopic instrument, providing a bony landmark that can be correlated with the cyst position as seen on preoperative MR imaging.
An accessory posterolateral portal is placed after first establishing correct orientation with an 18-gauge spinal needle.
Similar to open decompression, fibrovascular tissue covers the neurovascular bundle and has to be bluntly dissected with a switching stick or similar tool through the accessory portal before the nerve can be visualized.
The SSN is positioned medially, in direct contact with the bone of the spinoglenoid notch; the vascular structures are positioned laterally and closer to the glenoid.
Ganglion cysts are typically located posterior to the nerve and should be removed completely, including the lining.
After cyst removal, the nerve should be inspected for any additional sites of compression.
POSTOPERATIVE CARE
The arm is immobilized in a sling for 2 or 3 days for comfort.
Pendulum exercises commence on postoperative day 1, and active motion is increased as tolerated.
OUTCOMES
Nonoperative treatment is successful in 80% of patients without space-occupying lesions.8
Open decompression with release of the transverse scapular ligament improved pain and weakness in 73% to 87% of patients.4,13
Reports on the outcomes of arthroscopic decompression are rare, but outcomes seem to approach the success rate of open approaches.
COMPLICATIONS
Damage to the suprascapular nerve and vessels
Damage to the spinal accessory nerve if mobilization of the trapezius muscle is carried out far medially
Incomplete decompression, especially in rare cases of compression at both suprascapular and spinoglenoid notch
PEARLS AND PITFALLS
REFERENCES
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· Cummins CA, Anderson K, Bowen M, et al. Anatomy and histological characteristics of the spinoglenoid ligament. J Bone Joint Surg Am 1998;80:1622–1625.
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· Tirman PF, Feller JF, Janzen DL, et al. Association of glenoid labral cysts with labral tears and glenohumeral instability: radiologic findings and clinical significance. Radiology 1994;190:653–658.
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