Axillary nerve dysfunction refers to any condition causing the axillary nerve to malfunction. The axillary nerve stems from the C5 and C6 nerve roots and follows a specific anatomical course. It carries motor innervation to the teres minor and deltoid muscles and sensory innervation to the skin over the lateral deltoid.

Epidemiology

While the exact prevalence of axillary nerve dysfunction is not well-documented, it is more commonly observed in individuals involved in overhead sports or activities such as weightlifting and tennis.

Aetiology

The primary cause of axillary nerve dysfunction is compression of the nerve within the quadrangular space. This compression can occur due to:

• Trauma: including dislocation of the shoulder or fractures of the humerus.
• Muscle hypertrophy: particularly in athletes who perform repetitive overhead activities.
• Space-occupying lesions: such as tumors or cysts.

Anatomy of the Axillary Nerve

The axillary nerve originates from the posterior cord of the brachial plexus. It navigates through the axilla, posterior to the axillary artery, and exits the axilla via the quadrangular space alongside the posterior circumflex artery and vein. It runs medial to the surgical neck of the humerus, branching into three divisions:

• Posterior terminal branch: Provides motor innervation to the posterior deltoid and teres minor, then becomes the upper lateral cutaneous nerve supplying the skin over the inferior deltoid.
• Anterior terminal branch: Delivers motor innervation to the anterior deltoid, and subsequently becomes cutaneous branches supplying the anterior and anterolateral shoulder.
• Articular branch: Innervates the glenohumeral joint.

PC

• Weakness of the deltoid and teres minor muscles.
• Diminished or absent sensation over the lateral deltoid skin ('regimental badge').