Evaluation and Management of Suprascapular Nerve Palsy

The Problem

Suprascapular nerve palsy is a relatively uncommon cause of shoulder pain and dysfunction, but can lead to significant disability. Injury to the suprascapular nerve generally occurs either through a traction injury or a compressive mechanism. Suprascapular nerve injury most frequently occurs at the suprascapular and spinoglenoid notches. The suprascapular nerve gives motor branches to the supraspinatus distal to the suprascapular notch and proximal to the spinoglenoid notch. Therefore, impingement at the suprascapular notch will affect both the supraspinatus and infraspinatus muscles, whereas impingement at the spinoglenoid notch will only affect the infraspinatus.

Clinical Presentation

The classic history of a chronic, traction type injury is that of an athlete or laborer who performs repeated overhead activities. However, suprascapular nerve palsy can present in an older population with retracted rotator cuff tears. Additionally, patients with compressive lesions such as paralabral or supraglenoid cysts may also demonstrate a suprascapular neuropathy. Most patients present with a progressive dull, burning, and/or aching type pain in the posterolateral shoulder. Pain is frequently worsened with cross-body adduction and internal rotation. Subjective weakness in external rotation and/or abduction may be present. Patients can often recall a specific traumatic event with progressive worsening of symptoms.

Diagnostic Workup

Depending on the site of suprascapular nerve injury, physical examination will be significant for weakness to resisted external rotation and/or abduction/forward elevation with possible infraspinatus and/or supraspinatus atrophy present. The acromioclavicular joint and supraspinatus fossa may be tender to palpation with injuries localized to the suprascapular notch. Tenderness to palpation at the posterosuperior joint line is typically associated with spinoglenoid notch pathology. Patients may have a sensory disturbance along the posterior and lateral aspects of the shoulder. Patients may also have findings suggestive of other concomitant shoulder pathology such as a rotator cuff tear or a labral tear.

Standard radiographs should be obtained to assess for bony causes of nerve compression. They can also be used to evaluate for other underlying shoulder pathology such as scapular fracture, glenohumeral subluxation, osteoarthritis, and location of humeral head as a marker for rotator cuff tear. A Stryker notch view may also be obtained to better visualize the suprascapular notch for patency. Magnetic Resonance Imaging (MRI) can be particularly helpful in assessing amount of supraspinatus and infraspinatus atrophy, tracing the course of the suprascapular nerve, determining soft-tissue causes of nerve compression, and evaluating for other underlying pathology such as rotator cuff tears or labral tears. Compressive mass lesions such as paralabral ganglion cysts preferentially cause compression at the spinoglenoid notch, and can easily be detected by MRI.

If there is suspicion for suprascapular nerve palsy, but imaging does not localize the pathology, additional diagnostic tests can be considered. A suprascapular nerve block may be performed by injecting local anesthetic into suprascapular or spinoglenoid notch to assess for pain relief. Additionally, electromyography (EMG) and nerve conduction velocity (NCV) studies may also be used to assess the suprascapular nerve and localize pathology. Conduction delays are manifested as increased latency, and signs of denervation include fibrillations and diminished motor potentials.

Non–Operative Management

Non-operative management of suprascapular nerve palsy is the initial treatment. Patients should discontinue repetitive or aggravating overhead shoulder activity and begin a physical therapy program consisting of rotator cuff and deltoid stretching and strengthening with scapular stabilization exercises. Non-surgical treatment may be attempted for up to 12 months, depending on the etiology of nerve injury and duration of symptoms. Patients with an overuse or traction type suprascapular nerve injury without a compressive lesion will generally benefit from non-operative management. Patients with a cyst causing neuropathy may undergo a CT or ultrasound-guided cyst aspiration, although the recurrence rate is high following this treatment.

Indications for Surgery

Surgical indications include failed non-operative management, evidence of a mass lesion compressing the suprascapular nerve, significant muscle atrophy, associated massive rotator cuff tears, and/or accompanying shoulder pathology that requires surgical treatment. Patients that have an overuse or traction type injury do not benefit as significantly from surgery as those with compressive type lesions.

Surgical Technique

Arthroscopic decompression of the suprascapular nerve is preferred over the open technique. The arthroscopic technique allows for decreased post-operative pain and faster rehabilitation. Visualization is also improved with an arthroscope. Furthermore, arthroscopy allows for diagnosis and treatment of concomitant shoulder pathology.

The patient may be placed in the beach-chair or the lateral decubitus position depending on surgeon preference. After standard prepping and draping, bony landmarks and the course of the suprascapular nerve should be marked on the skin. A standard posterior portal is created 2cm inferior from the posterolateral acromial edge and 1cm medial from the posterolateral corner of the acromion. A diagnostic arthroscopy is performed at this time to rule out any concomitant shoulder pathology. Next, an anterior portal is made through the rotator interval using an 18-gauge spinal needle for localization. Adequate hemostasis allows for improved visualization.

The suprascapular notch can be decompressed through the subacromial space. A lateral portal is created 3cm lateral to the border of the acromion using an 18-gauge spinal needle for localization. The arthroscope is placed through this portal, and a shaver is placed through the anterior portal. The subacromial bursa is resected until there is adequate visualization between the acromioclavicular joint and coracoid anteriorly to the scapular spine posteriorly. The coracoclavicular ligaments are identified, and a space between the posterior aspect of the conoid ligament and the anterior aspect of the supraspinatus muscle is identified. Next, an accessory portal is created 2cm medial to the standard Neviaser portal along a line that bisects the angle formed between the scapular spine and the clavicle. A spinal needle is used help obtain the correct position. A blunt trocar is advanced to the anterior supraspinatus. Blunt dissection using the trocar is used to sweep away soft tissue and posteriorly retract the supraspinatus.

The transverse scapular ligament can be identified by its glistening, white fibers and by the position of its lateral fibers, which insert at the medial base of the conoid ligament. The suprascapular artery generally courses superior to the transverse scapular ligament. If needed, needle localization can be used to create another superior portal at the standard Neviaser portal position (junction of scapular spine and posterior aspect of acromioclavicular joint). An elevator can be inserted through this portal to better define the transverse scapular ligament. With the suprascapular nerve protected with a probe or blunt trocar, the transverse scapular ligament is cut as far laterally as possible using arthroscopic scissors. The suprascapular nerve is probed to ensure adequate decompression. An arthroscopic burr may be used to remove any bony structures causing residual compression.

The spinoglenoid notch may be decompressed either through the glenohumeral joint or the subacromial space. Patients with superior labrum anterior-posterior (SLAP) lesions requiring repair should undergo repair prior to suprascapular nerve decompression. After repair is complete, the arthroscope is placed in the anterior portal to visualize the posterior superior capsule. The posterior superior capsule is incised from the 9-o’clock to the 12-o’clock positions by placing a shaver through the posterior portal. The posterior band of the inferior glenohumeral ligament should be identified prior to capsular release so that it is not inadvertently damaged. Next, identifying the fibrous raphe between the supraspinatus and infraspinatus provides a useful landmark. It is seen lateral to the spinoglenoid notch and can be followed medially until the cyst can be visualized on the scapula. The cyst is then decompressed using a shaver. Synovial fluid should be seen, and all visible portions of the cystic wall are removed to reduce recurrence risk.

If no labral tear is noted on diagnostic arthroscopy, a spinoglenoid notch cyst can be decompressed from the subacromial space. A lateral portal is established and serves as the viewing portal. A shaver is introduced from the posterior portal and a subacromial debridement is performed. Dissection is performed from the scapular spine (medial border) to the posterior glenoid (anterior border). The cyst is often found posterior to the suprascapular nerve within this space and can be localized using MRI and arthroscopic dissection. The shaver can be used to further debride any remaining soft tissue to allow for exposure of the spinoglenoid notch cyst. The cyst may be palpable with the tip of the shaver. If it is not, once the cyst is appropriately localized, the shaver can be advanced until synovial fluid is visible. The subsequent debridement can then be performed with caution to avoid injury to the suprascapular nerve. The shaver should not be used along the scapular spine as the suprascapular nerve lies directly on the scapula at the spinoglenoid notch. The suprascapular vessels are located lateral to the nerve and closer to the glenoid.

Pearls and Pitfalls of Technique

Pearls

• Hemostasis is crucial to visualization. The fluid pressure can be increased to 50-55 mmHg and an electrothermal device can be used to cauterize bleeding vessels. The patient’s blood pressure can also be lowered to a systolic pressure of 100-110 mmHg.

• Visualization through the subacromial space is best from the lateral portal while the anterior, posterior, and/or medial portals are best used as working portals. A 70 degree arthroscope may be useful.

• The transverse scapular ligament may be partially or completely ossified. In this case, an osteotome or Kerrison rongeur can be used to resect the ligament.

Pitfalls

• In contrast to other reports, it is preferable to repair SLAP lesions prior to suprascapular nerve decompression. Decompression of a cyst through a disrupted labrum may not allow for adequate visualization of the medial neck of the glenoid and overlying suprascapular nerve. This could lead to iatrogenic suprascapular nerve injury.

• Adequate decompression must be obtained. The suprascapular notch may have variable morphology. Resecting the transverse scapular ligament alone may not provide full decompression. The nerve should be probed to ensure there is no bony impingement. An arthroscopic burr may be used for purpose.

• In the case of a spinoglenoid cyst, all cyst wall contents must be resected to minimize risk of recurrence.

Potential Complications

The major potential complication is damage to the suprascapular nerve and/or vessels. This can be avoided by appropriate knowledge of anatomy and careful dissection. Another potential complication is incomplete decompression. The suprascapular nerve can be probed around the notch to ensure that there is no further compression or tethering of the nerve. Some patients may have compression at both the suprascapular and spinoglenoid notches. History, examination, and diagnostic studies should be closely examined to identify the appropriate source(s) of compression. Further, recurrence may occur if a cyst is not fully decompressed and debrided. All portions of the cyst wall should be resected to reduce this risk.

Post–operative Rehabilitation

Post-operatively, the patient’s arm is immobilized in a sling for 2-3 days, primarily for comfort. Patients are encouraged to progress their passive and active range of motion as tolerated. A strengthening program is started when range of motion approaches the contralateral side, which is usually by 2 weeks post-operatively. If a patient had concomitant SLAP repair or rotator cuff repair, patients would follow protocols for those procedures, respectively.

Outcomes/Evidence in the Literature

Shah, AA, Butler, RB, Sung, S-Y. “Clinical outcomes of suprascapular nerve decompression”. J Shoulder Elbow Surg. vol. 20. 2011. pp. 975-982. (In a series of 24 patients available for follow-up who underwent arthroscopic suprascapular nerve decompression, 71% reported significant pain relief based on visual analog scores, and 75% had significant improvement in American Shoulder and Elbow Society (ASES) scores.)

LaFosse, L, Tomasi, A, Corbett, S. “Arthroscopic release of suprascapular nerve entrapment at the suprascapular notch: technique and preliminary results”. Arthroscopy. vol. 23. 2007. pp. 34-42. (A series of 10 patients underwent arthroscopic suprascapular nerve decompression at the suprascapular notch. 9/10 graded their result as excellent, all had at least some decrease in pain and improvement in function, and 7/8 had normalization of EMG findings at a mean of 15 months.)

Leclere, LE, Shi, LL, Lin, A. “Complete Fatty Infiltration of Intact Rotator Cuffs Caused by Suprascapular Neuropathy”. Arthroscopy. vol. 30. 2014. pp. 639-44. (Arthroscopic suprascapular nerve decompression was performed in four patients with complete fatty infiltration of the supraspinatus, infraspinatus, or both in the absence of rotator cuff tear and traction or compression mechanisms. All four patients had immediate improvement in pain and subjective shoulder value scores.)

Oizumi, N, Suenaga, N, Funakoshi, T. “Recovery of sensory disturbance after arthroscopic decompression of the suprascapular nerve”. J Shoulder Elbow Surg. vol. 21. 2012. pp. 759-65. (Twenty-five patients with a sensory disturbance over the posterolateral shoulder underwent arthroscopic release of the suprascapular nerve. All patients fully recovered sensation post-operatively.)

Pillai, G, Baynes, JR, Gladstone, J. “Greater strength increase with cyst decompression and SLAP repair than SLAP repair alone”. Clin Orthop Relat Res. vol. 469. 2011. pp. 1056-60. (Twelve patients with spinoglenoid cysts, SLAP tears, and weakness in external rotation were retrospectively reviewed. Six patients underwent SLAP repair and spinoglenoid cyst decompression, and six underwent SLAP repair alone. A significant increase in external rotation strength was found in patients undergoing both SLAP repair and cyst decompression compared to those undergoing only SLAP repair.)

Martin, SD, Warren, RF, Martin, TL. “Suprascapular neuropathy: results of non-operative treatment”. J Bone Joint Surg Am. vol. 79. 1997. pp. 1159-1165. (Fifteen patients with a diagnosis of suprascapular nerve neuropathy were managed non-operatively. At six months, 80% had good or excellent clinical results with improvement in pain and function. However, many patients had persistent atrophy and mild weakness with persistent EMG deficits.)

Westerheide, KJ, Dopirak, RM, Karzel, RP. “Suprascapular nerve palsy secondary to spinoglenoid cysts: results of arthroscopic treatment”. Arthroscopy. vol. 22. 2006. pp. 721-7. (Fourteen patients underwent arthroscopic decompression of ganglion cysts causing suprascapular nerve palsy. All 14 patients had improvement in external rotation strength, relief of pain, and improvement in Simple Shoulder Test (SST) score. Additionally, no recurrences were identified at an average follow-up of 51 months.)

Summary

Suprascapular nerve palsy typically presents with deep pain to the posterior shoulder, frequently seen in patients that perform repetitive overhead motions. Examination is significant for weakness and/or atrophy of the supraspinatus and/or infraspinatus muscles. Symptoms may be caused be a traction type injury or a compressive lesion. MRI and EMG/NCV studies can assist with diagnosis, and localize and characterize the lesion. Non-operative management with activity modification and a physical therapy program may be attempted. Patients with long-standing symptoms, muscle atrophy, and/or compressive lesions may benefit from surgical intervention. Arthroscopy allows for successful suprascapular nerve decompression at either the suprascapular or spinoglenoid notch, while enabling the surgeon to address concomitant shoulder pathology. Recent studies have demonstrated significant improvement in pain and function when treatment is appropriately individualized.

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