The axillary nerve is a crucial nerve in the shoulder that controls the deltoid muscle
Introduction
The axillary nerve is a crucial nerve in the shoulder that controls the deltoid muscle (responsible for lifting the arm away from the body and rotating it) and the teres minor muscle (involved in external rotation). It also carries sensory information from a small patch of skin on the outer part of the upper arm.
Causes of Axillary Nerve Injury
Damage to the axillary nerve can occur due to several reasons:
- Trauma
- Shoulder dislocation: The axillary nerve is particularly vulnerable during anterior shoulder dislocations, occurring in about 5% of cases as the nerve can be stretched or compressed as the head of the humerus (upper arm bone) moves out of its socket.
- Fracture of the humerus: Breaks in the upper part of the arm bone (surgical neck of the humerus) can damage the nerve.
- Direct blow to the shoulder: A forceful impact on the shoulder area can injure the nerve.
- Improper use of crutches: Pressure from crutches pressing into the armpit can compress the nerve.
- Compression: Quadrilateral space syndrome: In rare cases, the nerve can be compressed as it passes through a space in the back of the shoulder called the quadrilateral space, often due to muscle hypertrophy or fibrous bands.
- Pressure from casts or splints: If casts or splints are too tight, they can put pressure on the nerve.
- Stretching: Sudden or forceful movements of the arm can stretch the nerve beyond its limit.
- Latrogenic injury: The nerve can be accidentally damaged during shoulder surgery.
- Other conditions: In some instances, nerve dysfunction can be associated with body-wide disorders causing nerve inflammation or infections, although these are less common for isolated axillary nerve injury.
Symptoms of Axillary Nerve Injury
Symptoms can vary depending on the severity of the injury but commonly include:-
- Shoulder weakness: Difficulty lifting the arm away from the body (abduction) and rotating it outwards (external rotation). Patients may be unable to lift their arm beyond the first 15 degrees without the help of other muscles.
- Numbness or decreased sensation: Over a small area on the outer part of the upper arm (sometimes described as the “regimental badge area”).
- Pain: Shoulder pain, which may worsen with movement.
- Tingling or “pins and needles” sensation (paresthesia): In the affected area.
- Muscle atrophy: Over time, the deltoid muscle may shrink due to lack of nerve stimulation.
Diagnosis of Axillary Nerve Injury
A Physiotherapist will diagnose an axillary nerve injury through:
- Physical examination: Assessing shoulder strength, range of motion, and sensation. They may note weakness in the deltoid and teres minor muscles.
- Neurological evaluation: Checking reflexes and looking for any signs of nerve damage.
- Imaging studies: X-rays may be taken to identify fractures. MRI can help visualize soft tissues and identify nerve compression or other issues.
- Electrodiagnostic studies (EMG and nerve conduction studies): These tests can help confirm nerve damage, assess its severity, and rule out other nerve problems. These are often done a few weeks after the injury.
Treatment & Recovery
The treatment approach depends on the cause and severity of the nerve injury:
- Conservative treatment: Most axillary nerve injuries improve with non-surgical management, which may include:
- Rest: Avoiding activities that aggravate the shoulder. A sling may be used for comfort and immobilization initially.
- Pain management: Over-the-counter or prescription pain relievers and anti-inflammatory medications (NSAIDs or steroids) to reduce pain and swelling.
- Physical therapy: Exercises to maintain shoulder flexibility, prevent stiffness, and gradually strengthen the shoulder muscles as the nerve recovers. This is crucial for regaining full function.
