Felix H. Savoie, III, and Larry D. Field
DEFINITION
Suprascapular nerve entrapment may result from constriction within the suprascapular notch, pressure from a ganglion cyst in the floor of the supraspinatus fossa, or a constriction at the spinoglenoid notch.
The nerve is readily accessible via arthroscopic techniques developed by Thomas Samson and Laurent Lafosse.
ANATOMY
The suprascapular nerve receives contributions primarily from the C5 root, with additional minor contributions from C4 and C6 nerve roots.
It exits from the upper trunk of the brachial plexus through the supraclavicular fossa and comes through the suprascapular notch beneath the transverse scapular ligament, dividing into two branches.
One branch exits medially to the supraspinatus muscle.
The second continues across the floor of the supraspinatus fossa of the scapula toward the junction of the scapular spine and the posterosuperior neck of the glenoid.
The nerve makes a short turn around the bone junction under the inconsistently present spinoglenoid ligament and travels medially across the superior aspect of the infraspinatus fossa of the scapula, sending branches into this muscle until terminating into the medial aspect of this muscle.3
PATHOGENESIS
Nerve entrapment usually occurs at the suprascapular notch.
Trauma, repetitive overhead use requiring hyperretraction and protraction of the scapula (ie, volleyball), and chronic rotator cuff injuries may produce swelling in this area, resulting in pressure on the nerve.
Congenital V-shaped suprascapular notch orientation has been implicated as a cause of this entrapment.
Less common areas of entrapment may occur owing to ganglion cyst compression in the middle or posterior aspect of the fossa, and at the spinoglenoid notch.
A thickened spinoglenoid ligament may cause entrapment at the spinoglenoid notch as well.
Unusual sources of nerve entrapment include vascular expansion (aneurysm or varices) and tumors.2
NATURAL HISTORY
The natural history of suprascapular nerve entrapment depends on the cause and pathologic changes in the anatomy.
Spontaneous recovery after rehabilitation treatment has been reported.
However, if electromyographic nerve conduction studies show evidence of compression, surgical treatment is usually indicated.
Compression at the suprascapular notch or spinoglenoid area is often the primary problem and is not associated with intra-articular pathology.6 Compression by ganglion cyst in the supraspinatus fossa is often associated with labral tears that require fixation along with débridement of the cyst. All of these may be managed arthroscopically if nonoperative treatment is ineffective.
PATIENT HISTORY AND PHYSICAL FINDINGS
The patient often presents with signs and symptoms of impingement and rotator cuff tearing, overhead weakness, pain on forced flexion, and subacromial crepitation.
Careful inspection may reveal atrophy in the supraspinatus and infraspinatus fossa compared to the opposite side.
Weakness to supraspinatus isolation, infraspinatus isolation, and Whipple testing is usually present.
Palpation of the rotator cuff reveals no defect. However, there is usually no, or only minimal, palpable swelling on the distal supraspinatus tendon.
IMAGING AND OTHER DIAGNOSTIC STUDIES
Most patients will have to undergo magnetic resonance imaging.
The test should reveal an intact rotator cuff with atrophy of the supraspinatus and infraspinatus musculature.
Occasionally, there will be tearing of the rotator cuff with atrophy that is not in proportion to the size or duration of the tear.
Electromyographic nerve conduction studies by a neurologist specializing in proximal entrapment lesions of the upper extremity will be definitive in cases of entrapment at the suprascapular or spinoglenoid notch.
DIFFERENTIAL DIAGNOSIS
The main confusion in this area is with primary impingement and rotator cuff tears.
The history and physical examination are often similar, but a careful evaluation and physical examination will reveal the differences as delineated in the prior discussion under physical findings.
NONOPERATIVE MANAGEMENT
There is a limited role for nonoperative treatment of true entrapment neuropathy.
Pressure from a cyst may be alleviated by aspiration of the cyst.
Compression at either the suprascapular or spinoglenoid notch, however, will require release if the nerve conduction study reveals pressure to the nerve in these areas.
SURGICAL MANAGEMENT
Several approaches to open release have been described (Nicholson, Vastamake, and Post4,7,8).
Recently, Samson and Lafosse have each focused interest on techniques of arthroscopic release.1–6
Positioning
The patient is positioned in the lateral decubitus (preferred) or beach-chair position.
TECHNIQUES
ARTHROSCOPIC RELEASE OF NERVE ENTRAPMENT
A diagnostic glenohumeral arthroscopy is performed to rule out intra-articular pathology.
The arthroscope is then positioned in the lateral portal of the subacromial bursa in line with the anterior acromion, providing a picture of the supraspinatus muscle and tendon (TECH FIG 1A).
It is advanced along the anterior edge of the supraspinatus until the base of the coracoid is visualized (TECH FIG 1B).
A switching stick is placed in the lateral Neviaser portal and used to palpate along the anterior edge of the supraspinatus fossa medial to the medial aspect of the base of the coracoid (TECH FIG 1C).
A full-radius shaver can be used from the anterior portal to remove soft tissue as long as it remains lateral to the switching stick, which is functioning as a retractor in addition to a diagnostic tool (TECH FIG 1D).
On encountering the suprascapular artery, a second medial Neviaser portal is created and the retracting switching stick is removed to this portal and used to pull the artery medially and protect it (TECH FIG 1E).
Sliding this retractor along the top of the ligament will also protect any aberrant branches of the nerve that pass superior to the ligament.
TECH FIG 1 • A. When positioning the arthroscope in the lateral portal of the subacromial bursa in line with the anterior acromion, the supraspinatus muscle and tendon can be seen. B. Advancing the arthroscope along the anterior edge of supraspinatus allows the surgeon to visualize the coracoid. C. Placing a switching stick in the lateral Neviaser portal allows the surgeon to palpate the anterior edge of the supraspinatus fossa medial to the medial aspect of the base of the coracoid. D. A shaver can be used from the anterior portal to remove soft tissue; the surgeon must always remain lateral to the switching stick. E. A second Neviaser portal is established so that the switching stick can be used to pull the artery medially and protect it. F. A blunt probe enters to identify the ligament and protect the underlying nerve. G,H. A side biter or shaver can be used to release the ligament. I. The exposed nerve. J. The suprascapular nerve, artery, and vein are allowed to fall back into a relaxed position.
A blunt probe is used to identify the ligament and protect the underlying suprascapular nerve (TECH FIG 1F).
A side biter (TECH FIG 1G) or shaver (TECH FIG 1H) is then used to release the ligament overlying the notch, exposing the nerve (TECH FIG 1I).
The nerve is retracted medially along with the artery and vein and the ligament resection is completed.
The suprascapular notch may also be débrided and beveled at this time to resect any sharp edges. An arthroscopic rasp may then be used to complete this process.
The retractors are removed and the suprascapular nerve, artery, and vein are allowed to fall back into a relaxed position (TECH FIG 1J).
The nerve can be tracked across the floor of the supraspinatus fossa toward the spinoglenoid notch.
The supraspinatus muscle can be evaluated and then retracted anteriorly, exposing the scapular spine, which can then be followed to the spinoglenoid notch if assessment for a constricting spinoglenoid ligament is necessary.
This ligament can then be released using a similar retraction technique on the nerve.
POSTOPERATIVE CARE
The patient is started on immediate therapy, along with a home neuromuscular stimulator, for the infraspinatus. Correct scapular position is essential to recovery and will facilitate recovering normal strength.
Although most patients see an immediate decrease in pain and increase in strength, it usually takes 6 to 12 months to regain normal strength in the infraspinatus and supraspinatus musculature.
Therapy and electrical stimulation are continued until the patient can resume normal activities.
OUTCOMES
Lafosse has reported more than 90% successful releases using his technique.9
His results are equal to, or better than, most open series reported by other authors.
No substantial reports of arthroscopic spinoglenoid ligament release were found during our literature search.
Nicholson has reported satisfactory results with open release of the spinoglenoid ligament in a series of patients.7
COMPLICATIONS
Few complications have been reported with this technique.
The primary complication would be inadvertent nerve resection, but this has not been reported to our knowledge.
REFERENCES
1. Bencardino JT, Rosenbert ZS. Entrapment neuropathies of the shoulder and elbow in the athlete. Clin Sports Med 2006;25:1–19.
2. Fabre TH, Piton C, Leclouerec G, et al. Entrapment of the suprascapular nerve: upper limb. J Bone Joint Surg Br 1999;81B:414–419.
3. Goslin KL, Krivickas LS. Proximal neuropathies of the upper extremity. Neurol Clin 1999;17:525–547.
4. Post M. Diagnosis and treatment of suprascapular nerve entrapment. Clin Orthop Relat Res 1999;368:92–100.
5. Sanders TG, Tirman PFJ. Paralabral cyst: an unusual cause of quadrilateral space syndrome. Arthroscopy 1999;15:632–637.
6. Westerheide KJ, Dopirak RM, Karzel RP, et al. Suprascapular nerve palsy secondary to spinoglenoid cysts: results of arthroscopic treatment. Arthroscopy 2006;22:721–727.
7. Nicholson GP, McCarty LP, Wysolcki R: Suprascapular Nerve Entrapment Isolated to the Spinoglenoid Notch. Results of Open Decompression. Presented at 73rd American Academy of Orthopaedic Surgeons Meeting. Chicago Il, March 2006, and at the American Orthopaedic Society for Sports Medicine Specialty Day. Chicago, IL, March 25, 2006.
8. Vastamaki M, Goransson H. Suprascapular nerve entrapment. Clin Orthop Relat Pres 1993;(297):135–143.
9. Lafosse L, Tomasi A, Corbett S, et al. Arthroscopic release of suprascapular nerve entrapment at the suprascapular notch: technique and preliminary results. Arthroscopy 2007;23(1):34–42.