Axillary Nerve Injury – When the Arm Can No Longer Be Lifted to the Side

The axillary nerve is a key nerve in the shoulder area, responsible for both movement and sensation. When this nerve is injured or irritated, it can lead to noticeable impairments – such as weakness when lifting the arm to the side, numbness in the outer shoulder area, or even pain. Causes are varied and may include falls, surgeries, or overstretching. A focused diagnostic work-up – especially using high-resolution nerve ultrasound – can help identify the exact site of injury.

Schematic illustration of the shoulder joint with the course of the axillary nerve. — The axillary nerve runs close to the shoulder joint and may be affected by injuries in this region.

What Does the Axillary Nerve Do?

The axillary nerve is a mixed motor and sensory nerve that originates from the posterior cord of the brachial plexus, a network of nerves arising from the cervical spine. It passes through the armpit (axilla) and curves around the upper arm bone (humerus).

Schematic figure showing abduction movement of the left arm at the shoulder joint. — Abduction refers to lifting the left arm sideways – illustrated here up to 80 degrees at the shoulder joint.

Its main functions:

The axillary nerve innervates the deltoid and teres minor muscles. The deltoid muscle is especially important for abducting the arm at the shoulder joint, particularly between 30 and 90 degrees.
The axillary nerve conveys sensation from the outer shoulder region, primarily via the superior lateral cutaneous nerve of the arm, one of its terminal sensory branches.

Possible Causes of Axillary Nerve Injury

Shoulder dislocation (luxation)
Fractures near the head or neck of the humerus
Shoulder surgery (e.g., prosthetic implants, rotator cuff repair)
Compression or positioning injuries (e.g., during anesthesia)
Sports injuries involving overhead motion
Blunt trauma, hematomas, or unrecognized overstretching

Illustration showing arm paralysis and numbness after a shoulder dislocation and axillary nerve injury. — A shoulder dislocation may lead to injury of the axillary nerve or the brachial plexus.

Symptoms

Weakness when lifting the arm to the side (especially between 30–90 degrees)
Numbness or altered sensation in the lateral shoulder
Pain in the affected area (less common)
Muscle wasting (atrophy) of the deltoid muscle if the condition persists

Why the Diagnosis Can Be Challenging

Symptoms are often attributed to the joint or rotator cuff
Standard nerve conduction studies (NCS) often cannot reliably assess the axillary nerve
Associated injuries (e.g., to tendons or bone) may obscure the neurological findings

Modern Diagnostics – Nerve Ultrasound, Muscle Ultrasound, and Additional Imaging

An experienced specialist can often clarify the situation through clinical examination and advanced imaging techniques. High-resolution nerve ultrasound is particularly helpful:

Direct visualization of the axillary nerve from the posterior cord
Assessment of swelling, scarring, or entrapment
Dynamic evaluation during arm movement
Completely non-invasive and radiation-free

Muscle sonography (muscle ultrasound) allows assessment of the muscle supplied by the axillary nerve – especially the deltoid muscle. High-resolution ultrasound can detect changes in muscle structure and volume early on.

Muscle ultrasound: Ultrasound examination of muscles to diagnose scarring, fatty degeneration, atrophy, and muscle wasting. — Muscle ultrasound can help identify changes such as bleeding, scarring, atrophy, and fatty degeneration in muscles. It can also support follow-up examinations and assessment over time.

Such a finding of muscle atrophy can be a clear indication of functionally relevant axillary nerve damage. Additionally, ultrasound can be used to screen neighboring muscles to determine whether other nerves or parts of the brachial plexus might also be involved.

Cartoon-like illustration of a muscle that has atrophied and become fatty after nerve damage. — Muscle ultrasound can help indirectly locate the site of nerve damage by showing typical patterns of fatty muscle degeneration.

Depending on the clinical findings, MR neurography may also be useful. This specialized form of magnetic resonance imaging provides high-resolution views of the nerves and surrounding tissue – especially in deeper or more complex injuries.

Electrophysiological testing can further support the diagnosis – particularly EMG (electromyography). This measures electrical activity in the deltoid muscle and can reveal whether axillary nerve damage is present and how severe it is.

Nerve conduction studies (NCS) are often of limited value in this area due to the short segment of the nerve that is accessible. However, they may still be useful to evaluate adjacent nerves.

Impact on Daily Life and Prognosis

The degree of functional impairment depends on the extent of the damage. Milder forms may improve over time. In more severe or long-standing cases, persistent weakness or sensory disturbances may remain. Early and accurate diagnosis is essential for proper treatment planning.

No One-Size-Fits-All Approach to Therapy

Which treatment is appropriate depends on the individual findings. Options include physical therapy, activity modification, or in some cases surgical exploration or nerve reconstruction. Reliable diagnosis is the key to making the right decision.

Disclaimer: The information provided on this page is for general informational purposes only and does not constitute medical advice. It is not a substitute for personal consultation, examination, or treatment by a physician or other qualified healthcare professional. No guarantees of healing or cure are made. While we strive for accuracy and completeness, we cannot guarantee that all content is up to date or free from errors, and we accept no liability for any inaccuracies.