Axillary Nerve Injury: Causes, Symptoms, and Treatment

Описание: The axillary nerve is the most commonly injured nerve in shoulder dislocations, occurring in approximately 5% of cases. Following a shoulder dislocation, patients typically experience an inability to abduct the shoulder due to deltoid muscle dysfunction, which results in a lack of muscle tone in the deltoid. The supraspinatus muscle may still function, but there will be decreased or absent sensation over the lateral shoulder.

Clinical Evaluation
After a shoulder dislocation, if a patient cannot abduct the shoulder, it is important to rule out a rotator cuff tear and assess shoulder sensation. In some cases, an intact rotator cuff may allow for some abduction, which can confuse the examiner. However, regardless of whether the rotator cuff is intact or torn, the key diagnostic feature of axillary nerve palsy is loss of sensation over the lateral shoulder.

Axillary nerve injuries can range from neuropraxia (temporary conduction block) to a complete nerve tear.

Anatomy of the Axillary Nerve
The axillary nerve passes through the quadrangular space and divides into:

Anterior division: Travels anteriorly beneath the deltoid and innervates the anterior and middle deltoid fibers.
Posterior division: Innervates the teres minor muscle, the posterior deltoid, and the skin over the shoulder.
The anterior branch of the axillary nerve is located 5 to 7 cm distal to the lateral edge of the acromion. Exceeding a deltoid-splitting approach more than 5 cm below the acromion increases the risk of axillary nerve injury.

Clinical Examination for Axillary Nerve Injury
To assess for axillary nerve dysfunction:

Ask the patient to abduct the arm against resistance to evaluate deltoid muscle strength.
Observe and palpate the anterior and middle fibers of the deltoid during this maneuver.
Management of Axillary Nerve Injury
Initial Treatment

Provide a sling for comfort.
Initiate physical therapy to prevent stiffness and maintain function.
Monitor the patient’s clinical progress.
Electrodiagnostic Studies

EMG and nerve conduction studies should be performed:
Biphasic waves at 3 to 4 weeks suggest nerve recovery.
Fibrillation potentials and positive sharp waves (P waves) indicate poor prognosis.
Surgical Considerations

If there is no shoulder abduction despite 4 to 6 months of physiotherapy, the condition is likely permanent.
If the rotator cuff cannot compensate, then surgical intervention is required:
Nerve exploration, release, repair, or reconstruction using a nerve graft.
Tendon transfer:
Trapezius muscle transfer to the proximal humerus is an option.
However, outcomes of this procedure are generally poor.
Quiz Questions
1) What is the most commonly injured nerve in shoulder dislocation?

Axillary nerve ✅
Suprascapular nerve
Radial nerve
Musculocutaneous nerve
Explanation: The axillary nerve is most frequently injured in anterior shoulder dislocations.
2) What percentage of shoulder dislocations result in axillary nerve injury?

1%
5% ✅
10%
15%
Explanation: Axillary nerve injury occurs in about 5% of shoulder dislocations.
3) Which muscle loses tone in axillary nerve injury?

Supraspinatus
Deltoid ✅
Infraspinatus
Biceps brachii
Explanation: The axillary nerve innervates the deltoid, which loses function when the nerve is damaged.
4) Which muscle remains functional despite axillary nerve injury?

Supraspinatus ✅
Deltoid
Trapezius
Latissimus dorsi
Explanation: The supraspinatus initiates abduction and remains functional if the axillary nerve is injured.
5) What is the key sensory loss in axillary nerve injury?

Medial arm
Lateral shoulder ✅
Posterior forearm
Anterior forearm
Explanation: Sensation loss over the lateral shoulder is a hallmark of axillary nerve injury.
6) What structure should be avoided in a deltoid-splitting approach beyond 5 cm below the acromion?

Axillary nerve ✅
Brachial artery
Suprascapular nerve
Musculocutaneous nerve
Explanation: The anterior branch of the axillary nerve lies 5–7 cm below the acromion.
7) Which nerve exits through the quadrangular space?

Axillary nerve ✅
Radial nerve
Musculocutaneous nerve
Suprascapular nerve
Explanation: The axillary nerve and posterior circumflex humeral artery pass through the quadrangular space.
8) Which division of the axillary nerve innervates the teres minor?

Posterior division ✅
Anterior division
Lateral division
Medial division
Explanation: The posterior division of the axillary nerve innervates the teres minor and posterior deltoid.
9) What is the first-line treatment for axillary nerve injury?

Sling and physical therapy ✅
Immediate surgery
Corticosteroid injection
Plate fixation
Explanation: Conservative management is the first-line approach for axillary nerve injury.
10) Which diagnostic test helps evaluate nerve recovery?

MRI
EMG ✅
CT scan
X-ray
Explanation: EMG studies are used to assess nerve recovery and degeneration.