Nerve


Origin


A direct branch of the upper trunk of the brachial plexus (C4–6)


General route


Crosses the posterior neck, under the trapezius, travels under the transverse scapular ligament through the suprascapular foramen across the spine of the scapula and then through the spinoglenoid notch


Sensory distribution


Glenohumeral joint


Acromioclavicular joint


Subacromial bursa


Cutaneous innervation of the lateral superior shoulder


Motor innervation


Supraspinatus: Abducts the humerus; especially the initial 20–30 degrees


Infraspinatus: Externally rotates the humerus



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Fig. 4.1

Schematic drawing of the course of the suprascapular nerve. Ultrasound probe needle placement is defined for an ultrasound-guided block along the spine of the scapula. (Reprinted with permission from Pain Diagnostics and Interventional Care. Artwork by Zachary Pellis)



The suprascapular artery most commonly passes superficial to the ligament. The SN (stemming from the ventral rami of spinal nerves C4, C5, and C6 and emerging from the upper trunk of the brachial plexus) provides 70% of sensory innervation to the shoulder joint.


Pathophysiology and Clinical Presentation


Shoulder pain can originate from structures (rotator cuff, glenohumeral joint, etc.) innervated by the SN (Table 4.2). In addition, suprascapular neuropathy (SSN) may be considered as a cause of shoulder pain and is seen in individuals who participate in repetitive overhead activities. In particular, these are movements that place substantial load on the shoulder in an overhead or abducted and externally rotated position. The SN may also become entrapped at common sites including the suprascapular notch and spinoglenoid notch (Fig. 4.1). Multiple diagnostic tests can be used to assist in diagnosing suprascapular nerve damage and entrapment (Table 4.3).


Table 4.2

Differential diagnosis for suprascapular nerve-related shoulder pain


























Innervated structures


Differential diagnosis


Supraspinatus


Ganglion cyst at the suprascapular notch


Direct compression


 Trauma


 Fracture callus


Infraspinatus


Ganglion cyst at the spinoglenoid notch


Direct compression


 Trauma


 Fracture callus


Superior labrum


SLAP lesion (Superior labrum anterior-posterior tear)


Labral cyst


Glenohumeral joint


Adhesive capsulitis and osteoarthritis


Poststroke shoulder pain


Acromioclavicular joint


Dislocation


Osteoarthritis




Table 4.3

Diagnostic criteria for suprascapular nerve neuropathy



















Physical exam


Atrophy of supraspinatus and infraspinatus muscles


Weakness with abduction/external rotation.


Ultrasound


Possible edema of the corresponding muscle or direct compression of nerve by a cyst


Electrodiagnostic studies


EMG showing axonal loss limited to SN distribution


Motor NCVs showing reduced amplitude


MRI


Edema, atrophy, or fatty infiltration of supraspinatus or infraspinatus muscles



NCV Nerve conduction velocity, EMG electromyography


Patient Selection


A suprascapular nerve block (SNB) is used for perioperative and postoperative pain control after surgery. The block can also be utilized for chronic pain management and diagnostic purposes for shoulder pain. Pulsed radiofrequency of the suprascapular nerve in conjunction with physical therapy has been shown to accelerate the recovery from adhesive capsulitis.


Ultrasound Scanning


Two approaches exist for targeting the suprascapular nerve: posterior (distal) technique and the anterior (proximal) technique. The posterior approach targets the suprascapular nerve as it courses in the suprascapular fossa over the scapular spine (Figs. 4.1, 4.2, 4.3, 4.4, and 4.5). The less commonly used technique targets the nerve anteriorly at its proximal origin. The nerve is blocked in the supraclavicular region, where it passes underneath the omohyoid muscle. Only the posterior approach is described here.

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Oct 20, 2020 | Posted by in ANESTHESIA | Comments Off on Nerve
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