Root Origin
- Spinal nerve roots: C5, C6
- Plexus: Brachial plexus — branches from the upper trunk (Erb's point), before the trunk divides into anterior and posterior divisions
- Type: Mixed (motor and sensory — carries sensory branches to the acromioclavicular and glenohumeral joints, but no cutaneous sensory function)
Course
- Upper trunk. The nerve branches from the upper trunk at Erb's point — where C5 and C6 merge. This is a clinically important landmark: trauma here (Erb's palsy, stingers) affects the suprascapular nerve along with the musculocutaneous and axillary nerves.
- Posterior triangle of the neck. The nerve travels laterally and posteriorly across the posterior triangle, deep to the trapezius and omohyoid.
- Suprascapular notch. The nerve passes through the suprascapular notch on the superior border of the scapula, beneath the superior transverse scapular ligament (also called the suprascapular ligament). The suprascapular artery passes OVER the ligament while the nerve passes UNDER it — the military mnemonic is "army over the bridge, navy under the bridge" (artery over, nerve under). This notch is the primary entrapment site.
- Supraspinous fossa. After passing through the notch, the nerve enters the supraspinous fossa and supplies the supraspinatus. It also gives off articular branches to the acromioclavicular joint and the posterior glenohumeral capsule.
- Spinoglenoid notch. The nerve curves around the lateral edge of the scapular spine through the spinoglenoid notch, passing beneath the inferior transverse scapular ligament (spinoglenoid ligament). This is the second entrapment site.
- Infraspinous fossa. After the spinoglenoid notch, the nerve enters the infraspinous fossa and supplies the infraspinatus.
Motor Distribution
| Muscle | Action | Notes |
|---|---|---|
| anatomy/muscles/supraspinatus | Initiates shoulder abduction (first 15 degrees), stabilizes humeral head in glenoid | Compressed at the suprascapular notch — entrapment here weakens BOTH supraspinatus and infraspinatus |
| anatomy/muscles/infraspinatus | External rotation (primary), stabilizes humeral head posteriorly | Compressed at the spinoglenoid notch — isolated infraspinatus weakness without supraspinatus involvement indicates this more distal site |
Sensory Distribution
- No cutaneous sensory branches. The suprascapular nerve does not supply any skin. It carries afferent (sensory) fibers from the acromioclavicular joint and the posterior glenohumeral joint capsule, contributing to deep joint proprioception and pain perception — but there is no surface numbness with injury.
- Clinical significance: Suprascapular nerve entrapment produces pain and weakness without any area of skin numbness. This distinguishes it from brachial plexus lesions (which produce cutaneous sensory loss) and from C5-C6 radiculopathy (which produces lateral arm dermatomal numbness).
Entrapment Sites
1. Suprascapular Notch
- Location: Superior border of the scapula, beneath the superior transverse scapular ligament
- Structure: The notch shape varies — some people have a deep V-shaped notch, others a shallow U-shape, and approximately 4% have complete bony ossification of the ligament, converting the notch into a foramen. Deeper and narrower notches predispose to entrapment. The nerve can be compressed by the ligament itself (thickened or calcified), ganglion cysts from the AC joint, or traction during repetitive overhead activity.
- Condition: Suprascapular nerve entrapment (suprascapular neuropathy)
- Presentation: Deep, dull, aching posterior shoulder pain localized to the supraspinous and infraspinous fossae. Weakness of both abduction initiation (supraspinatus) and external rotation (infraspinatus). Pain worsens with cross-body adduction (which stretches the nerve through the notch). Onset is usually insidious in overhead athletes.
- MT relevance: This is an underdiagnosed cause of shoulder pain that mimics rotator cuff tendinopathy. If a patient has posterior shoulder pain with weakness of both abduction initiation and external rotation, and standard rotator cuff treatment is not working, consider suprascapular nerve compression. Cross-body adduction (horizontal adduction with the arm at 90 degrees) reproducing the deep posterior pain is suggestive.
2. Spinoglenoid Notch
- Location: Where the nerve curves around the lateral edge of the scapular spine to enter the infraspinous fossa
- Structure: Compression at this site is typically caused by a paralabral cyst — a ganglion arising from a posterior labral tear that tracks along the capsule and compresses the nerve against the scapular spine. Also seen with hypertrophy of the spinoglenoid ligament.
- Presentation: Isolated infraspinatus weakness and atrophy with preserved supraspinatus function — because the supraspinatus branch exits before the spinoglenoid notch. External rotation weakness without abduction initiation weakness. Posterior shoulder pain may be less prominent than with notch-level compression.
- MT relevance: Isolated infraspinatus atrophy in an overhead athlete (especially volleyball players) raises the possibility of a labral tear with secondary nerve compression. This presentation requires imaging referral — the labral pathology is the root cause, and treating the muscle atrophy alone will not resolve it.
Clinical Tests
| Test | Procedure | Positive Finding | What It Tells You |
|---|---|---|---|
| Cross-body adduction test | Patient actively or passively horizontally adducts the arm (arm at 90 degrees flexion, pull across the body). | Deep posterior shoulder pain — not anterior AC joint pain but deep aching in the supraspinous or infraspinous fossa. | Traction on the suprascapular nerve through the notch. Differentiate from AC joint pathology — AC pain is anterior and superficial; suprascapular pain is deep and posterior. |
| Infraspinatus MMT | Patient externally rotates the arm against resistance with elbow at 90 degrees and arm at the side. | Weakness compared to the opposite side. | Infraspinatus motor function. Weakness here localizes to the suprascapular nerve (suprascapular or spinoglenoid notch) or the C5-C6 root. |
| Supraspinatus empty can test | Arm abducted to 90 degrees, 30 degrees of horizontal adduction (scapular plane), thumb pointing down (internal rotation). Apply downward force. | Weakness or pain. | Tests supraspinatus in relative isolation. Weakness points to suprascapular nerve or supraspinatus tear. Pain without weakness is more consistent with tendinopathy. |
| Observation for infraspinatus atrophy | Visually inspect the infraspinous fossa bilaterally from behind with the patient's arms at rest. | Visible depression or flattening in the infraspinous fossa compared to the opposite side. | Chronic infraspinatus denervation atrophy. In lean individuals, subtle atrophy is visible early. In muscular individuals, compare the bulk over the infraspinous fossa side-to-side. |
Clinical Notes
- The great mimicker of rotator cuff tendinopathy. Suprascapular nerve entrapment produces posterior shoulder pain and rotator cuff weakness — exactly the same presentation as supraspinatus or infraspinatus tendinopathy. The key difference: nerve entrapment produces weakness OUT OF PROPORTION to what you would expect from the pain level, and cross-body adduction aggravates the deep posterior pain. If rotator cuff treatment plateaus and weakness persists despite pain reduction, consider nerve entrapment.
- Overhead athletes are the highest-risk population. Volleyball players have the highest incidence of suprascapular neuropathy due to the extreme shoulder positions during serving (traction at the suprascapular notch) and the floater serve technique. Swimmers, baseball pitchers, and tennis players are also at risk. Bilateral infraspinatus atrophy in a volleyball player is almost pathognomonic.
- The labral tear connection. At the spinoglenoid notch, the most common compressive lesion is a paralabral cyst arising from a posterior labral tear. The cyst is the symptom — the labral tear is the cause. Treating the nerve compression without addressing the labral pathology leads to recurrence. Always refer for MRI when isolated infraspinatus atrophy is found.
- No skin numbness — ever. The suprascapular nerve has no cutaneous sensory branches. If a patient with posterior shoulder pain also has skin numbness, the problem is not the suprascapular nerve — consider C5-C6 radiculopathy, axillary nerve injury (regimental badge area), or brachial plexus pathology.
- Cross-body adduction differs from AC joint testing. Both conditions are aggravated by horizontal adduction, but the pain location is different. AC joint pathology produces sharp, localized pain directly over the AC joint (superior/anterior). Suprascapular nerve entrapment produces deep, dull aching in the posterior fossa region. Ask the patient to point with one finger to where it hurts.
Related Nerves
- anatomy/nerves/axillary-nerve — C5-C6, posterior cord. Supplies the remaining external rotator (teres minor) and the deltoid. Together the suprascapular and axillary nerves innervate three of the four rotator cuff muscles. Upper trunk lesions (Erb's palsy) affect both nerves.
- anatomy/nerves/long-thoracic-nerve — C5-C7. Another early brachial plexus branch. Serratus anterior (long thoracic) and supraspinatus/infraspinatus (suprascapular) must all function for normal scapulohumeral rhythm. Dysfunction of either nerve disrupts overhead movement patterns.
- anatomy/nerves/dorsal-scapular-nerve — C5. Shares the C5 root. Supplies rhomboids and levator scapulae. A C5 root lesion would affect all three of these nerves — suprascapular, long thoracic (C5 component), and dorsal scapular.
Key Takeaways
- Supplies supraspinatus and infraspinatus — two of four rotator cuff muscles — without any cutaneous sensory branch, so entrapment produces pain and weakness but never skin numbness.
- Suprascapular notch entrapment weakens both muscles; spinoglenoid notch entrapment isolates infraspinatus — this distinction helps localize the lesion.
- The great mimicker of rotator cuff tendinopathy — consider nerve entrapment when weakness is disproportionate to pain and cross-body adduction reproduces deep posterior shoulder pain.
- Isolated infraspinatus atrophy in an overhead athlete suggests a posterior labral tear with paralabral cyst compressing the nerve at the spinoglenoid notch — refer for imaging.