Axillary Nerve Injury - Causes, Symptoms, Treatment

Introduction:

Axillary nerve injury commonly affects the shoulders. The nerve is vulnerable during the surgery of the inferior aspect of the shoulders, and the iatrogenic causes remain the most important complications of shoulder surgery.

What Is the Anatomy of an Axillary Nerve?

The axillary nerve is a peripheral nerve of the brachial plexus derived from its posterior cord. It has both motor and sensory functions. It travels through the quadrangular space and innervates important muscles of the upper limb and skin within the axillary region. It also innervates the glenohumeral joint. Due to its close relationship with the joint, the nerve is injured whenever the joint is damaged.

What Causes an Axillary Nerve Injury?

Stressing the limb beyond its normal range of motion can cause axillary nerve dysfunction. The following causes axillary nerve neuropathy:

• Blunt trauma.

• Other body structures pressure on the axillary nerve.

• Penetrating injuries such as knife or gunshot wounds.

• Hyperextension injury to the shoulder.

• Dislocation of the shoulder joint.

• Iatrogenic causes.

• Proximal humerus fracture.

• Quadrilateral space syndrome.

• Brachial neuritis (nerves belonging to the brachial plexus become damaged or irritated).

What Are the Signs and Symptoms?

1. Feeling numbness or tingling sensation in the shoulder region.

2. Weakness of the shoulder muscles.

3. Difficulty performing routine tasks like lifting the arms above your head or lifting an object. In patients with dislocation or fracture, signs of trauma will be evident on physical examination. During external rotation and abduction, muscle weakness is observed.

4. In brachial neuritis, localized pain and atraumatic neuropathy are observed.

5. In quadrilateral space syndrome, symptoms such as cyanosis (bluish discoloration of the skin) and pallor (pale color) of the hands and fingers, and splinter hemorrhage (tiny blood spots underneath the nail are observed along with neurologic symptoms.

What Is Erb’s Palsy?

Erb’s palsy can happen in infants and adults. It occurs due to an injury of the bundle of nerves in the brachial plexus (includes axillary nerve) at birth when the child is unusually large, or labor goes on for a long time. There is paralysis and muscle weakness in one arm. For most children, recovery occurs from three to six months. But, there are possibilities for a permanent disability in some cases.

What Is a Quadrangular Space Syndrome?

Quadrangular space syndrome is a rare disorder in which compression of the axillary nerve and posterior humeral circumflex artery (part of an axillary artery) is observed. It is mainly due to trauma, fibrous bands, or hypertrophy of one muscular border. The diagnosis becomes complicated when it is associated with other injuries of similar presentation, and it is often excluded. Conservative therapy is first given, and when the patient is not relieved of the symptoms, surgical decompression of the quadrilateral space may be indicated.

How to Diagnose an Axillary Nerve Dysfunction?

Eliciting a good history is essential in arriving at a proper diagnosis. It should include the onset of symptoms, duration, the severity of pain, radiation to other regions, aggravating and relieving factors. While evaluating for axillary nerve injury, we should consider pain, trauma, focal weakness, numbness, tingling sensation, cyanosis, and limitations in the range of motion.

Evaluation for axillary nerve injury should begin with a visual examination to inspect the presence or absence of trauma. Then the tenderness and muscle tone during palpation of the neck and arm on the same side is noted. This is followed by evaluating passive and active ranges of motion. Followed by that, a neurologic examination is done.

Swallowtail, deltoid extension lag, and Bertelli tests are used to examine deltoid muscle weakness. The tests which are used to evaluate the function of teres minor muscle (shoulder muscle) are external rotation lag, drop arm, and patte tests.

Radiography can help identify fractures involving the shoulder region. In case of suspicion of compressive neuropathy or inflammatory processes, a shoulder MRI (magnetic resonance imaging) would help. The gold standard for confirmation of the diagnosis is EMG (electromyograph). However, EMG or nerve conduction tests are not done immediately after the injury. Instead, they should be executed weeks after the initial injury or onset of the symptoms.

What Is the Treatment?

During the acute phase of the injury, the shoulder should be rested, and later, when advised, the patient should undergo extensive physiotherapy and rehabilitation. In many cases, there is spontaneous recovery without any need for treatment. Medications can be prescribed to reduce pain and inflammation. This is followed by physiotherapy to regain the muscle strength and mobility of the shoulders.

• For atraumatic injuries, a baseline EMG should occur within one month, and in the case of traumatic injury, most patients recover without surgery. In many cases, the shoulder is reduced and immobilized for four to six months in the case of young patients and 7 to 10 days in the case of elderly patients.

• Surgery is indicated only if no axillary nerve recovery is observed three to six months after injury. It includes nerve grafting, neurolysis, or nerve reconstruction.

• In the case of neuropraxia, in which there is only focal segmental demyelination (incomplete breakdown of myelin sheath) at the injury site, there is complete recovery in over six to twelve months.

• In the case of axonotmesis, the axons and the myelin sheath (the insulating layer around the nerves of the brain and spinal cord) are damaged, but the neural sheath (insulating layer of nerves and connective tissue around the peripheral nerves) is intact. The recovery may take months, and serial EMG studies are used to assess the prognosis. If there are no signs of recovery, surgical intervention is considered.

• In the case of neurotmesis, where both the nerve and nerve sheath is disrupted, there is no recovery without surgical intervention.

Prognosis is better for younger patients and nerve grafts less than six centimeters. For nerve grafting, a branch of the radial nerve which is not affected by the injury is taken from the triceps muscle and transferred to the axillary muscle, where it eventually grows into the deltoid muscle.

Conclusion:

Axillary nerve injury is an isolated nerve dysfunction, and complications result in permanent numbness to the lateral shoulder region. Athletes are at a higher risk for axillary nerve injury. The management involves a multidisciplinary approach in caring for the affected patients. An early diagnosis helps speedy recovery as the time taken for the healing is reduced. Nerve regeneration takes place at a rate of 1 mm per day, and therefore the long duration taken to heal can be discouraging to patients. Hence the clinician should help manage the expectations in this kind of injury.