Axillary nerve injury
The axillary nerve is part of the brachial plexus originating from the cervical spine

Definition

Axillary nerve injury manifests through motor and sensory dysfunction in the regions innervated by this nerve, the deltoid muscle, part of the skin of the shoulder and the upper arm. 

Example of axillary nerve injury following a shoulder dislocation

Pathology

The axillary nerve is a long nerve and therefore susceptible to injury at several sites, including the cervical spine, the anterior inferior aspect of the subscapularis muscle and shoulder capsule, the quadrilateral space and the deltoid muscle. 

Anterior and inferior shoulder dislocations are the most common causes of axillary nerve injury mostly occurring in patients over 50 years of age. The frequency of axillary nerve dysfunction increases dramatically when shoulder dislocation is associated with a proximal humerus fracture or when the dislocation of the humerus remains untreated for over 12 hours. With a shoulder dislocation, the damage to the axillary nerve is produced through stretching and/or compression of the nerve when the humerus head is displaced out of the socket. Compression of the axillary nerve on the posterior side of the shoulder affects the function of the quadrilateral space, which is formed by three muscles (teres minor, teres major and triceps) and the humerus. This may lead to the quadrilateral space syndrome, a painful condition of this region, which also arises independently from trauma.

Classification

Fractures of the humerus shaft can display various patterns: transverse, oblique, spiral, and comminuted. In addition they are differentiated depending on whether the fracture is displaced or undisplaced, relative to the loss of bone alignment and closed or open fracture. The AO (Arbeitsgemeinschaft für Osteosynthesefragen) Foundation, an international organisation founded in Switzerland, focussing on research and education for the management of orthopaedic injuries), is one of most used systems available to characterise humerus shaft fractures. According to the AO humerus shaft fractures are divided into their level of comminution:

Type A - No comminution

Type B - Presence of butterfly fragment (wedge-shaped fragment of bone

Type C - Comminution

Proximal humerus fracture can cause an injury to the axillary nerve

Causes

Axillary nerve injury may be caused by:

Shoulder dislocation (anterior and inferior)

Blunt trauma to the shoulder/upper arm

Humerus fracture

Persisting nerve pressure (entrapment) with cast/splint

Wrong positioning of crutches in the arm pit

Ongoing pressure on the axillary nerve from surrounding tissues

The pressure of crutches on the armpits can lead to axillary nerve damage 

Risk factors

There are various risk factors thought to contribute to axillary nerve injury and dysfunction:

Chronic disorders causing systemic neuropathy (diabetes)

Postures involving prolonged pressure in the axillary pit (crutches, cast, splint and backpacks)

Shoulder overuse, pressure by overhead activity

Increased predisposition to neuropathy

Pain on the upper arm is typical of an axillary nerve injury

Symptoms

The manifestation of axillary nerve dysfunction and injury can be masked by the symptoms caused by an injury to the shoulder and upper arm. The symptoms of axillary nerve injury are:

Pain over the deep and outer shoulder irradiating to the proximal arm

Numbness and tingling to the posterior shoulder and the lateral side of the arm

Weakening of shoulder flexion, abduction and external rotation

Deltoid muscle weakness or atrophy

Subluxation of the humerus head

Sulcus sign is a test used to diagnose axillary nerve injury

Diagnosis

In order to establish an exact diagnosis for axillary nerve injury the doctor will discuss the medical history with the patient. During the clinical examination the following body parts and functions are investigated:

Shoulder joint for possible dislocation or injury, bruises and lacerations

Shoulder and neck to identify the area of nerve compression based on symptoms arising from movement

Presence of atrophy of deltoid and teres minor muscles

Restriction of shoulder movement in flexion, abduction and external rotation

Changes in the sensation of shoulder and upper arm

Use of special tests: sulcus sign, apprehension test, anterior release test, deltoid extension lag

Electrodiagnostic test

Electromyography test

X-rays to rule out shoulder dislocation and fractures

Blood tests to exclude the existence of other medical conditions (diabetes, hypothyroidism)

Treatment

Antiinflammatory medications reduce pain and inflammation after axillary nerve injury

Nonoperative treatment

Dysfunction of the axillary nerve can recover spontaneously but may require several months. Early conservative treatment includes:

Immobilisation of the shoulder especially after reduction in case of dislocation

Application of ice pads

Administration of NSAIDs

Local steroid injections with more severe symptoms

Pain medications/anaesthetics

Physical therapy to strengthen the tone of the deltoid muscle

Left, sequence of nerve graft procedure for axillary nerve tear, right, neurorrhaphy

Surgical treatment

Surgical inspection and surgical reconstruction following axillary nerve dysfunction or injury is rare and only used in severe cases. They include permanent nerve damage, failure of conservative treatment over 3-6 months and lack of recovery of nerve function demonstrated by electromyogram. Surgical approaches take place through the anterior or posterior side of the shoulder with the purpose to release the axillary nerve via:

Neurolysis (release of the nerve compressed by soft tissue adhesions)

Neurorrhaphy (suture of the severed nerve)

Reconstruction of the injured nerve with nerve grafting

Neurotisation (nerve transfer)

Immobilisation of the shoulder is only recommended for a short period

Rehabilitation

If the damage to the axillary nerve occurs simultaneously with shoulder dislocation, physiotherapy management will coincide for both pathologies and includes:

Temporary immobilisation of the shoulder with a sling

Treatment with analgesics and NSAIDs

Ice pads

Shoulder joint exercises (pendulum movement)

Isometric strengthening of the deltoid, rotator cuff and postural muscles

Complications

If injury to the axillary nerve is not treated rapidly it may lead to the following complications:

Arm deformity

Shoulder contracture or frozen shoulder

Shoulder dysfunction

Partial loss of sensation in the arm (specific skin areal over the deltoid muscle)

Avoid falls and impacts on the upper arm prevents damage to the axillary nerve

Prevention

Simple recommendations to prevent axillary nerve dysfunction and injury include:

Avoid prolonged pressure on the axillary pit

Reduce the risk of shoulder dislocation (falls)

Proper education for the use of crutches

Ensure adequate cast or splint fit