Suprascapular Nerve Entrapment

Suprascapular nerve entrapment is an under-recognised cause of shoulder pain and weakness, and it is frequently misdiagnosed as rotator cuff pathology or cervical radiculopathy. Early recognition is what prevents irreversible muscle atrophy, and surgical decompression yields good outcomes when it is performed before advanced fatty infiltration.

Who. Overhead athletes, weightlifters, swimmers and manual labourers. The disability is significant in athletes and manual workers alike.

Two sites. The nerve can be caught at the suprascapular notch or, more distally, at the spinoglenoid notch. The two sites produce distinct clinical pictures, and paralabral ganglion cysts are the most common compressive lesion at the spinoglenoid notch.

The course. The suprascapular nerve (C5-C6, occasionally C4) arises from the upper trunk of the brachial plexus. It travels posteriorly through the suprascapular notch at the superior border of the scapula, beneath the transverse scapular ligament, and gives motor branches to supraspinatus. It then continues around the scapular spine through the spinoglenoid notch at the base of the spine, under the spinoglenoid ligament, to innervate infraspinatus.

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Why the level matters. Compression at the suprascapular notch denervates both supraspinatus and infraspinatus. Compression at the spinoglenoid notch spares supraspinatus and isolates infraspinatus, so a preserved supraspinatus is the key sign pointing to distal compression. The nerve is relatively fixed at both notches, which makes it vulnerable to traction and mass effect.

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Not purely motor. The nerve is predominantly motor, but it carries articular (sensory) branches to the acromioclavicular joint, the subacromial bursa and the posterosuperior glenohumeral joint capsule. Together these supply roughly 70 percent of the sensory innervation of the shoulder joint. That is the anatomical basis of the suprascapular nerve block, infiltrated at the suprascapular notch or the floor of the supraspinatus fossa, and used for analgesia in:

• Adhesive capsulitis
• Rheumatoid and osteoarthritic shoulder pain
• Post-operative pain
• Palliation of malignant shoulder pain

The paralabral ganglion. A superior or posterosuperior labral tear allows synovial fluid to track into the spinoglenoid region. The fluid accumulates into an expanding cyst that compresses the nerve against the notch, and infraspinatus denervation and wasting follow. Recurrence is high if the labral tear is not addressed, which is why cyst decompression alone is not enough and the operation includes labral repair.

Traction from a massive cuff tear. A distinct, examinable mechanism beyond the two compressive notches: a massive, medially retracted supraspinatus/infraspinatus tear tethers and tractions the suprascapular nerve. As the musculotendinous junction retracts medially, the nerve is drawn medially and its angle at the suprascapular notch increases, producing a traction neuropathy that compounds the wasting of the torn cuff.

This is the likely reason EMG abnormalities are commoner with massive cuff tears (as in the Boykin series), and it is the rationale for nerve assessment in that setting. Restoring the musculotendinous unit by repairing the retracted tear can relieve the traction, and is generally preferred to an isolated nerve release. Distinguish this traction mechanism from true notch entrapment by a discrete compressive lesion.

What happens to the muscle. Chronic compression leads to muscle atrophy followed by fatty infiltration (Goutallier stages). Irreversible changes begin after 6-12 months of untreated compression.

Distinguishing the notch level is the single most important step in planning surgery.

By aetiology. Repetitive traction in overhead athletes, weightlifters and swimmers is one mechanism. The nerve can also be compressed by a thickened or ossified transverse scapular ligament, a ganglion, fracture callus, or a space-occupying lesion such as a tumour or varix. Entrapment can also be iatrogenic, after distal clavicle excision or shoulder surgery. Ganglion cysts account for the majority of surgically treated spinoglenoid notch cases.

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History. The pain is deep, aching and posterior, related to activity and worse at night. Weakness shows as difficulty with external rotation, overhead lifting and throwing. Onset is insidious in ganglion cases and acute after trauma or repetitive stress. Ask about previous treatment: failed physiotherapy, injections or rotator cuff repairs.

Inspection. Compare the two sides. Infraspinatus fossa wasting is the hallmark, and supraspinatus wastes as well if the lesion is proximal.

Pain without numbness. Expect no cutaneous numbness at either site, because the suprascapular nerve supplies no skin. Its articular branches produce a deep, poorly localised posterosuperior ache instead, so the discriminating pattern is pain without numbness. Demonstrable dermatomal or patch numbness points elsewhere: C5 radiculopathy, or the axillary nerve for the regimental badge area.

Examination tests. External rotation is weak at the side and in 90 degrees of abduction.

• Infraspinatus strength. Seated, arm at the side, elbow flexed 90 degrees, resist external rotation. Weakness against the contralateral side indicates infraspinatus dysfunction.
• External rotation lag sign. Passively externally rotate to maximum and release. A lag greater than 10 degrees indicates significant infraspinatus weakness.
• Hornblower sign. The patient brings the hand to the mouth with the elbow elevated. It is positive if the arm drops into internal rotation (infraspinatus failure).
• Jobe test. Positive if supraspinatus is involved.
• Notch palpation. Tenderness 2 cm medial to the posterolateral acromion (suprascapular notch) or at the base of the scapular spine (spinoglenoid notch).

Radiographs. AP, axillary and scapular Y views of the shoulder. They are usually normal and serve to rule out other bony pathology; look for ossification at the notch, fracture callus and bony tumours.

EMG. Indicated in every suspected case before surgery; it confirms the diagnosis and localises the level. The findings are fibrillations, positive sharp waves and reduced recruitment in infraspinatus, and in supraspinatus as well if the lesion is proximal. Fibrillations and positive sharp waves appear 3-4 weeks after onset, so study at least 3-4 weeks after symptoms begin. A normal early EMG does not exclude entrapment; repeat it if suspicion is high.

Denervation is the minority finding. In the Boykin referral series, frank denervation was present in only 33% of electrodiagnostically confirmed cases, while the commonest abnormality was far subtler: abnormal motor unit action potentials, in 88%. A study reported without fibrillations therefore does not exclude the diagnosis, and waiting for denervation before imaging will miss most of it. Do not make MRI conditional on finding denervation on EMG.

MRI. The key investigation, indicated in all cases with a positive EMG or high clinical suspicion. Axial and coronal oblique T2 fat-saturated sequences, with an MR arthrogram if a labral tear is suspected. It shows the size and location of a ganglion cyst, the labral tear, muscle atrophy and fatty infiltration, and ligament thickening. Always comment on labral integrity and the Goutallier grade of fatty infiltration.

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Intraosseous cyst. A less common compressive mechanism is a multiloculated intraosseous cyst extending to the spinoglenoid notch. T1, fluid-sensitive and contrast-enhanced sequences distinguish its cystic content, its enhancing margins and its relation to the suprascapular nerve.

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Ultrasound. Ultrasound can demonstrate a cystic lesion at the spinoglenoid notch and guide aspiration or diagnostic injection. MRI better maps the labral communication and muscle denervation.

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CT. Reserved for selected cases: bony notch narrowing, fracture callus or tumour. It gives better bone detail for planning a notchplasty.

Conservative first for most. Non-operative care is first line for most cases and is appropriate for idiopathic or traction-related entrapment without a space-occupying lesion. The aim is to reduce nerve irritation, maintain muscle function and allow spontaneous recovery in traction or idiopathic cases.

Weeks 0-6. Avoid repetitive overhead loading, heavy lifting and contact sports; light daily activities and scapular stabilisation exercises are allowed. Physiotherapy focuses on periscapular strengthening and posture correction.

Weeks 6-12. Repeat the clinical examination for pain, strength and progression of atrophy, and reassess every 6 weeks with objective strength testing. A short course of NSAIDs or analgesia treats a flare. Repeat the EMG, and if there is no improvement at 3 months, consider surgery.

The decision at 3 months. Continue non-operative care when symptoms are mild and stable, compliance is good and there is no mass lesion. Surgery is indicated for:

• Failed conservative care (more than 3 months)
• Progressive weakness or worsening atrophy
• Persistent pain affecting function
• A compressive lesion confirmed on MRI, such as a ganglion
• Acute traumatic entrapment with documented denervation

The ganglion does not wait. A documented ganglion cyst causing progressive infraspinatus atrophy is best managed surgically, because delay risks irreversible fatty infiltration.

Muscle quality sets the ceiling. Assess fatty infiltration before decompression. Advanced fatty change (greater than Goutallier grade 2) predicts poorer functional recovery after decompression, and advanced fatty infiltration (Goutallier greater than 3) is listed as a contraindication to suprascapular notch release in the approach table below.

Choosing the approach. The notch and the pathology decide between an arthroscopic and an open approach.

Suprascapular notch release. Identify the superior transverse scapular ligament, protect the suprascapular artery, and divide the ligament in a controlled way under direct vision, and add a notchplasty if the notch is narrow. Adequate release is confirmed without traction or thermal injury to the nerve.

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Spinoglenoid ganglion, arthroscopic. Beach chair or lateral decubitus with the arm in traction. A posterior viewing portal, an anterior working portal, and an accessory posterolateral portal for access to the cyst.

1. Address the labral tear with suture anchors
2. Decompress the cyst by incising the capsule and draining its contents
3. Release the spinoglenoid ligament if it is thickened
4. Confirm the nerve is free of compression

After surgery. Sling for 4-6 weeks with early passive range of motion, then progressive strengthening after the labrum has healed.

Complications arise both from the untreated entrapment and from surgical decompression.

Of the untreated entrapment.

• Irreversible atrophy of infraspinatus, with or without supraspinatus, with fatty infiltration (Goutallier)
• Permanent external-rotation weakness and loss of overhead and throwing power
• Secondary impingement and scapular dyskinesis, because loss of infraspinatus alters scapular mechanics and force couples
• Chronic posterior shoulder pain and reduced sporting or occupational capacity
• Cyst enlargement with intra-osseous extension, or recurrent effusion, if a labral tear is left untreated

Of surgical decompression.

• Iatrogenic nerve injury to the suprascapular nerve itself, or to the nearby axillary nerve (inferior) during spinoglenoid work
• Suprascapular artery injury causing bleeding; the artery runs over the ligament at the notch
• Incomplete decompression, with the ligament not fully divided or the notch still stenotic, and persistent symptoms
• Persistent weakness despite a technically successful release, when advanced fatty infiltration was present before surgery
• Stiffness or failure of labral healing, and the standard arthroscopic risks of infection and chondral injury