Axillary Nerve

Axillary nerve injury is most commonly seen following trauma to shoulder.

If no axillary nerve recovery is observed by 3 to 6 months after injury, surgical exploration may be indicated, especially if the mechanism of injury is consistent with nerve rupture.

Anatomy

Terminal branch of the posterior cord. (roots C5 &C6)

Course

Crosses the antero-inferior aspect of the subscapularis muscle, passing behind the arm, through the quadrilateral space, winding round surgical neck of humerus ending in two major trunks.

Posterior trunk - Teres minor and posterior deltoid muscle before terminating as the superior lateral brachial cutaneous nerve
Anterior trunk - Middle and anterior deltoid muscle

Motor

Deltoid
Teres Minor

Sensory

Regimental badge area over deltoid

Anatomy in relation to fixation

Deltoid splitting approach extend no more than 5 cm inferior to the acromion edge, the nerve is thought to cross the humerus posteriorly approximately 7 cm distal to the acromion. The acromion may be difficult to asses on radiographs as such the proximal humeral articular surface may be a more reliable landmark. Current data suggests the axillary nerve is located an average of 6 cm from the most superior aspect of the humeral head, with its shortest distance measuring 4.5 cm.

In posterior approaches to the proximal humerus, the nerve must be identified clearly because it lies within 0.7 to 4 cm from the surgical neck.

During external fixation and intramedullary nailing, the axillary nerve may be at risk with penetration of the posterior cortex during proximal AP locking. The nerve lies posteriorly about 1.7 cm distal to the surgical neck, with the shortest distance measuring 0.7 cm.

Mode of injury

Susceptible to injury at several sites:

Origin from the posterior cord
Anteroinferior aspect of the subscapularis muscle and shoulder capsule
Quadrilateral space
Subfascial surface of the deltoid muscle.

Mechanism of injury:

Glenohumeral Dislocation - incidence following dislocation 5% to 54% (depends on age, older more common and work up)
Blunt Trauma - Direct blow to the anterolateral deltoid
Quadrilateral Space Syndrome - rare, compression of axillary n. and posterior humeral circumflex a.
Iatrogenic

Clinical

Presentation variable

Sensory - Regimental badge area
Motor - Deltoid and Teres minor

Exclude C spine as source of symptoms.

Examine and document passive and active ROM.

Electrophysiologic testing (EMG and nerve conduction studies) should be performed 3 weeks after injury as it usually takes several weeks for muscles to show electrical evidence of acute denervation after nerve damage.

EMG and nerve conduction studies provide important information for diagnosis, prognosis and treatment indications. Electrophysiologic testing may help delineate pure axillary nerve injury from injury to the brachial plexus.

Repeat electrophysiologic studies are indicated if no clinical improvement is seen at 3 months post injury, as one may see electrical signs of nerve recovery despite a lack of clinical improvement.

Prognosis

Variable prognosis for nerve and deltoid muscle recovery although functional shoulder recovery may be good to excellent.
The prognosis for recovery is better following shoulder dislocation than following blunt trauma to nerve and Deltoid muscle.

Treatment

Depends

Mechanism of injury
Severity of the injury
Age of patient
Preinjury level of activity.

Physiotherapy

Maintain active and passive ROM, awaiting nerve recovery
Strengthen rotator cuff, deltoid, and periscapular musculature.

Surgical Indications

Axillary nerve exploration is indicated if there is no clinical or electrophysiologic recovery by 3 to 6 months after injury, especially if the mechanism of injury was consistent with a nerve rupture (glenohumeral dislocation).
Such an interval is sufficient for neurapraxic and axonotmetic injuries to resolve and not too long to jeopardize the results of subsequent surgical repair of the axillary nerve.
The axillary nerve primarily motor and travels only a short distance from its origin to its muscle insertion, thus has a good prognosis for recovery after surgical repair and grafting

Alnot et al reported a 57% good to excellent result after surgery.

Many patients with isolated axillary nerve injuries have excellent functional shoulder recovery despite complete paralysis of the deltoid muscle.

References

Christopher M., Grossman, MG, Hochwald N, Tornetta P; Radial and Axillary Nerves: Anatomic Considerations for Humeral Fixation. Clinical Orthopaedics & Related Research. (373):259-264, April 2000.

Perlmutter, Gary S. MD. Axillary Nerve Injury. Clinical Orthopaedics & Related Research. (368):28-36, November 1999

Visser, C. P. J.. Coene, L. N. J. E. M.. Brand, R.. Tavy, D. L. J.. The incidence of nerve injury in anterior dislocation of the shoulder and its influence on functional recovery: A PROSPECTIVE CLINICAL AND EMG STUDY. Journal of Bone & Joint Surgery - British Volume. 81-B(4):679-685, July 1999.