Arthroscopic Release of Nerve Entrapment

Felix H. Savoie III

Michael J. O’Brien

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.

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