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.
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.
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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
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.
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
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
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
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)
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 NSAIDsIce 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)
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