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Nerve Injuries/Entrapment

Nerve injuries can occur with both arthroscopic and open shoulder procedures. The axillary nerve courses from anterior to posterior from the posterior cord of the brachial plexus, 3 to 5 mm medial to musculotendinous junction of the inferior lateral border of the subscapularis muscle. It lies in contact with the GH joint capsule until it exits the quadrangular space and then reflects anteriorly, running deep to the surface of the deltoid from posterior to anterior.

Adduction and internal rotation of the arm during an open anterior approach will help to displace the axillary nerve away from the surgical field. In addition, the nerve can be injured during suture placement through the inferior capsule, capsular release for adhesive capsulitis, and retraction of the subscapularis medially and the deltoid laterally . To avoid injury to the posterior branch of the nerve, incisions on the lateral aspect of the shoulder should not extend more than 5 cm below the acromion.

The posterior branch of the anterior circumflex branch of the axillary nerve courses medially along the posterior aspectof the inferior glenoid rim for an average distance of 18 mm before entering the muscle at its inferior border. The motor branch to the teres minor arises from the posterior branch of the axillary nerve, just adjacent to the inferior aspect of the capsule at the level of the glenoid rim.

The superolateral brachial cutaneous branches of the axillary nerve also arise from the posterior branch. Therefore, sensory loss over the deltoid may be associated with dysfunction of the teres minor.

The musculocutaneous nerve enters the coracobrachialis muscle 3.1 to 8.2 cm from the coracoid; therefore, excessive traction of the conjoined tendon should be avoided. The long thoracic nerve is at risk where it is draped over the second rib and can be injured indirectly by positioning the patient improperly.

The suprascapular nerve is a mixed peripheral nerve that supplies motor innervation to the supraspinatus and infraspinatus and sensation to the AC and GH joints. The suprascapular nerve lies within 2 cm of the superior glenoid rim and as close as 1 cm to the posterior middle glenoid. This nerve can be entrapped or injured at the suprascapular notch and the spinoglenoid notch by tumors, cysts, excessive traction in overhead athletes, and direct trauma.

The suprascapular nerve first passes through the suprascapular notch, which is bordered by the transverse scapular ligament; the suprascapular artery passes over this ligament . In addition to entrapment in the notch, hypertrophy of the subscapularis muscle can cover the entire anterior surface of the suprascapular notch and lead to nerve compression .

After innervating the supraspinatus, the nerve passes around the base of the glenoid and scapular spine through the spinoglenoid notch, another site of entrapment. The projected distance from the most medial edge of the acromion to the spinoglenoid notch averages 14.5 mm.

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