The deltoid atrophies when the axillary nerve (C5 and C6) is severely damaged.

Because it passes inferior to the humeral head and winds around the surgical neck of the humerus, the axillary nerve is usually injured during fracture of this part of the humerus.

It may also be damaged during dislocation of the glenohumeral joint and by compression from the incorrect use of crutches.

In addition to atrophy of the deltoid, a loss of sensation may occur over the lateral side of the proximal part of the arm, the area supplied by the superior lateral cutaneous nerve of the arm

Injury to the Dorsal Scapular Nerve

Injury to the dorsal scapular nerve, the nerve to the rhomboids, affects the actions of these muscles. If the rhomboids on one side are paralyzed, the scapula on the affected side is located farther from the midline than that on the normal side.

Surgery in the inferior part of the axilla puts the thoracodorsal nerve supplying the latissimus dorsi at risk of injury.

This nerve passes inferiorly along the posterior wall of the axilla and enters the medial surface of the latissimus dorsi close to where it becomes tendinous

With paralysis of the latissimus dorsi, the person is unable to raise the trunk with the upper limbs, as occurs during climbing.

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