Axillary nerve injury

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. ;

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.

Axillary nerve injury may be caused by:Shoulder dislocation (anterior and inferior)Blunt trauma to the shoulder/upper armHumerus fracturePersisting nerve pressure (entrapment) with cast/splintWrong positioning of crutches in the arm pitOngoing pressure on the axillary nerve from surrounding tissues

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 activityIncreased predisposition to neuropathy

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 armNumbness and tingling to the posterior shoulder and the lateral side of the armWeakening of shoulder flexion, abduction and external rotationDeltoid muscle weakness or atrophySubluxation of the humerus head

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 lacerationsShoulder and neck to identify the area of nerve compression based on symptoms arising from movementPresence of atrophy of deltoid and teres minor musclesRestriction of shoulder movement in flexion, abduction and external rotationChanges in the sensation of shoulder and upper armUse of special tests: sulcus sign, apprehension test, anterior release test, deltoid extension lagElectrodiagnostic testElectromyography testX-rays to rule out shoulder dislocation and fracturesBlood tests to exclude the existence of other medical conditions (diabetes, hypothyroidism)

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 dislocationApplication of ice padsAdministration of NSAIDsLocal steroid injections with more severe symptomsPain medications/anaestheticsPhysical therapy to strengthen the tone of the deltoid muscle

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 graftingNeurotisation (nerve transfer)

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 slingTreatment with analgesics and NSAIDsIce padsShoulder joint exercises (pendulum movement)Isometric strengthening of the deltoid, rotator cuff and postural musclesComplicationsIf injury to the axillary nerve is not treated rapidly it may lead to the following complications:Arm deformityShoulder contracture or frozen shoulderShoulder dysfunctionPartial loss of sensation in the arm (specific skin areal over the deltoid muscle)

Simple recommendations to prevent axillary nerve dysfunction and injury include:Avoid prolonged pressure on the axillary pitReduce the risk of shoulder dislocation (falls)Proper education for the use of crutchesEnsure adequate cast or splint fit