Abstract: The suprascapular nerve arises from the upper trunk (Erb’s point) of the brachial plexus in the posterior triangle of the neck..This research was conducted to study the anatomy of the suprascapular nerve in the scapular region and its relation to both suprascapular and spinoglenoid notches. This data is very important in suprascapular nerve block and surgical decompression. Dissection of 20 scapular regions of 10 formalin preserved male cadavers was done. Also thirty three adult patients; 26 males and 7 females suffering from vague shoulder pain subjected to suprascapular nerve surgical decompression. In all cadaveric specimens, careful anatomical study of suprascapular nerve regarding its course, distribution and relations was carried out. Origin of the nerve was demonstrated from upper trunk of brachial plexus. Passage of the nerve through a narrow medial compartment of spinoglenoid canal in all cases has been identified. Measurements of two important diameters relevant to suprascapular notch were also reported. The transverse scapular ligament was identified to be of uniform thickness.
In the clinical study of all cases with suprascapular nerve entrapment regardless its etiology whether idiopathic or not, conservative therapy in means of exercise was of limited value especially for the motor affection. All of the cases were subjected to surgical maneuverer to decompress the nerve.
It is concluded that the anatomical findings allow better choice of the surgical procedure, more precise surgical dissection, better results and fewer complications.
Keywords: Suprascapular nerve, suprascapular notch, Spinoglenoid notch, suprascapular nerve entrapment, suprascapular nerve block
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1. Introduction
The suprascapular nerve arises from the upper trunk (Erb’s point) of the brachial plexus in the posterior triangle of the neck. Its root value is C5&6. The suprascapular nerve and vessels reach suprascapular notch of the upper border of scapula. The suprascapular nerve enters the supraspinous fossa by passing through the foramen formed by the suprascapular notch and the transverse scapular ligament (1).
The suprascapular nerve supplies sensory fibers to about 70% of the shoulder joint, including the superior and posterosuperior regions of the shoulder joint and capsule and the acromioclavicular joint(2).
The suprascapular nerve is liable to compression where it crosses osteofibrous canals at the suprascapular and at the spinoglenoid notches (3). Compression by tumors and ganglion cysts, traction injuries, direct trauma such as fracture of scapula and variations in anatomy along the course of the nerve have been reported as the causes of suprascapular nerve entrapment (4-6).
Suprascapular nerve entrapment is characterized by pain in the posterolateral region of the shoulder, atrophy of the infraspinatus and supraspinatus muscles and weakness of the arm’s external rotation and abduction. 1’2 % of shoulder pain is caused by the entrapment of the suprascapular nerve, and therefore can be easily overlooked in the differential diagnoses of shoulder discomfort (7). The diagnosis of the entrapment syndrome is based on the history, physical findings and the abnormal electromyography findings for the affected muscles (8).
The syndrome is treated via non-operative procedures, such as the avoidance of activities that result in irritation to the nerve and a rehabilitation program (8) or the surgical decompression of the suprascapular nerve (4).
Suprascapular nerve block has shown some promise as an alternative treatment for patients with shoulder pain (7).
Anatomical variations in the course of the suprascapular nerve are important for possible entrapment of the nerve, especially for individuals who are involved in violent overhead activities, such as volleyball players and baseball pitchers. Thorough investigations of suprascapular nerve at these sites are needed.
2. Material & Methods
2.1. Materials and Subjects
Anatomical study: The study were conducted through anatomical dissection of 20 scapular regions of 10 formalin preserved male cadavers obtained from Anatomy Department, Faculty of Medicine, Alexandria University. None of these shoulder specimens showed any evidence of past history of trauma or prior surgical intervention. They were exposed and carefully dissected.
The specimens were placed in a prone position and a standard posterior approach to the shoulder joint was utilized. A linear incision was made from the posterolateral corner of the acromion medially along the length of the scapular spine. The skin, soft tissue, and fascia were removed. The deltoid and trapezius were detached from their attachment from medial to lateral and reflected inferiorly allowing for visualization of the supraspinatus and infraspinatus muscles. Both of them were cut and retracted medially to allow visualization of the supraspinous and infraspinous fossae.
The suprascapular nerve was identified and traced as it passes inferior to the superior transverse ligament, across the supraspinous fossa, the spinoglenoid notch and infraspinous fossa. The suprascapular artery was identified and tagged as it runs over the superior transverse ligament.
Measurements were taken by using Vernier Caliper to describe the anatomical position of suprascapular notch from fixed landmarks (Figs 1and 2).
Figure 1: A photograph of left scapular region showing Vernier caliper used for measuring the horizontal diameter from just above the lower angle of lateral border of acromion (A) till the suprascapular notch (‘). SN: suprascapular nerve, V: suprascapular vessels, C: clavicle, SS: supraspinatus muscle.