Arthroscopic Release of Nerve Entrapment

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, with some studies suggesting a third sensory branch exists and travels laterally toward 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 due 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

In athletes, adhesions medial to the spinoglenoid notch may produce neuropathy when the arm is maximally externally rotated as in volleyball and tennis serves.

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 areas 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.

Lafosse et al4,5 has described a test for suprascapular nerve entrapment in which the scapula is protracted while the head and neck are extended away from the affected extremity.

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, whereas in the very early stages (ie, athletes), one may simply see edema in the muscles affected by the nerve compression.

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.

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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. An initial trial of ultrasound or fluoroscopically guided injection into the area of compression followed by therapy and electrical stimulation to the affected muscles may provide relief.

Pressure from a cyst may be alleviated by aspiration of the cyst with injection, but this improvement has been shown to be relatively brief.

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.6,7

Recently, Samson and Lafosse (Samson and Lafosse, personal communication, 2000) have each focused interest on techniques of arthroscopic release.1,2,3,4,5,6

Positioning

The patient is positioned in the lateral decubitus (preferred by the authors) or beach-chair position.

TECHNIQUES

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).

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. The arthroscope is then advanced into a room with walls. F. A second Neviaser portal is established so that the switching stick can be used to pull the artery medially and protect it. One then enters a room with walls with the supraspinatus muscle being one wall, the cc ligaments being the opposite wall, the coracoid base and supraspinatus fossa being the floor, and the clavicle being the roof.

G. A blunt probe enters to identify the ligament and protect the underlying nerve. H-I. A side biter or shaver can be used to release the ligament. J. The exposed nerve. K. The suprascapular nerve, artery, and vein are allowed to fall back into a relaxed position.

TECH FIG 1 (continued)

A full-radius shaver can be used carefully 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).

One then advances the arthroscope into a “room with walls,” with the posterior wall the supraspinatus muscle, the floor the base of the coracoid, the anterior wall of the coracoclavicular (cc) ligaments, and the medial wall of the protective switching stick behind which are the protected suprascapular nerve and artery (TECH FIG 1E).

A second medial Neviaser portal is created and the retracting switching stick is removed to this portal and used to pull the

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artery and nerve medially to protect both structures. It may also be placed directly into the suprascapular notch to further protect the nerve and artery (TECH FIG 1F).

Sliding this retractor along the top of the ligament will also protect any aberrant branches of the nerve that pass superior to the ligament.

A blunt probe placed through the lateral Neviaser portal is used to further identify the ligament and protect the underlying suprascapular nerve (TECH FIG 1G).

A side biter (TECH FIG 1H) or shaver (TECH FIG 1I) is then used to release the ligament overlying the notch, exposing the nerve (TECH FIG 1J).

The nerve is retracted medially along with the artery and vein and the ligament resection is completed. Palpating the nerve anterior and posterior to the notch is important in revision cases where adhesions may have developed.

The lateral 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, removing any sharp edges.

The retractors are removed and the suprascapular nerve, artery, and vein are allowed to fall back into a relaxed position (TECH FIG 1K).

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.

• Spinoglenoid Notch Release

The anatomy near the base of the scapular spine is less consistent than the anterior suprascapular notch. In this area, we favor a dual portal technique similar to the anterior approach (TECH FIG 2A-H).

The arthroscope is maintained in the lateral viewing portal.

The standard posterior portal is used for the shaver, and the scapular spine identified.

An accessory posterior portal in line with the spinoglenoid notch is created and a blunt switching stick or trocar is placed at the base of the spinoglenoid notch to protect the nerve.

An electrocautery or shaver is then used to dissect down the spine until either the spinoglenoid ligament or the retractor is visualized. Once near the base, the nerve can be located using a blunt probe.

In primary cases, we have found there are usually adhesions medial to the notch that must be released for an adequate decompression as the spinoglenoid ligament is an inconsistent anatomic structure.

In revision cases, there is usually scar just lateral to the nerve, seemingly often after placement of a posterior superior anchor and suture passage during superior labral anterior posterior (SLAP) repairs.

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TECH FIG 2 • A. Lateral decubitus position showing portal placement. B. The arthroscope in the lateral portal, the shaver in the standard posterior portal, and the switching stick in the medial posterior portal protecting the nerve. C. The probe is placed through the accessory posterior portal to protect the nerve. D. The dissection is continued to the perineural fat while the retractor continues to protect the nerve. E. The blunt probe is placed on the spine and then used to carefully dissect the nerve under direct visualization. F. The suprascapular nerve is visualized wrapping around the scapular spine. G. The dissection is continued medially, breaking the medial adhesions often seen in athletes. H. Once the medial adhesions are released, one can track the nerve medially and observe the muscle branches into the infraspinatus.

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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 et al5 has reported more than 90% successful releases using his technique. 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.

Mall et al6 has reported satisfactory results with open release of the spinoglenoid ligament in a series of patients.

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;81-B:414-419.

    

    

3. Goslin KL, Krivickas LS. Proximal neuropathies of the upper extremity. Neurol Clin 1999;17:525-547.

    

    

4. Lafosse L, Piper K, Lanz U. Arthroscopic suprascapular nerve release: indications and technique. J Shoulder Elbow Surg 2011;20(2 suppl):S9-S13. doi:10.1016/j.jses.2010.12.003.

    

    

5. 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.

    

    

6. Mall NA, Hammond JE, Lenart BA, et al. Suprascapular nerve entrapment isolated to the spinoglenoid notch: surgical technique and results of open decompression. J Shoulder Elbow Surg 2013;22(11):e1-e8.