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M01.03.025 Axillary Nerve
The axillary nerve is a vital peripheral nerve of the upper limb. It arises from the posterior cord of the brachial plexus and plays a significant role in motor and sensory innervation of the shoulder region.
Key Features
| Feature | Details |
|---|---|
| Spinal Roots | C5 and C6 |
| Motor Functions | Innervates the teres minor and deltoid muscles |
| Sensory Functions | Provides sensation to the lower deltoid region (regimental badge area) via the upper lateral cutaneous nerve |
Anatomical Course
- Formation
- Originates from the posterior cord of the brachial plexus.
- Located posterior to the axillary artery and anterior to the subscapularis muscle.
- Pathway
- Exits the axilla through the quadrangular space, accompanied by the posterior circumflex humeral artery and vein.
- Travels medially to the surgical neck of the humerus.
- Branches
- Posterior Terminal Branch: Motor innervation to the posterior deltoid and teres minor, and sensory innervation to the regimental badge area.
- Anterior Terminal Branch: Motor innervation to the anterior deltoid and sensory branches to the shoulder.
- Articular Branch: Supplies the glenohumeral joint.
Quadrangular Space
The quadrangular space acts as a passageway for the axillary nerve and associated vascular structures.
| Boundary | Structure |
|---|---|
| Superior | Inferior aspect of teres minor |
| Inferior | Superior aspect of teres major |
| Lateral | Surgical neck of the humerus |
| Medial | Long head of triceps brachii |
| Anterior | Subscapularis |
Clinical Relevance
Compression or trauma in this area can lead to:
- Weakness in deltoid and teres minor muscles.
- Sensory loss in the regimental badge area.
Motor Functions
The axillary nerve supplies the following muscles:
| Muscle | Function | Branch |
|---|---|---|
| Deltoid | Abduction of the upper limb (15°–90°) | Anterior terminal branch |
| Teres Minor | External rotation of the shoulder | Posterior terminal branch |
Sensory Functions
| Branch | Innervated Area |
|---|---|
| Upper Lateral Cutaneous Nerve | Skin over the inferior deltoid region (regimental badge area). |
Clinical Signs of Sensory Damage
- Loss of sensation in the regimental badge area.
- Paraesthesia (pins and needles) in the same region.
Clinical Relevance
Injury to the Axillary Nerve
| Mechanisms of Injury | Clinical Effects |
|---|---|
| Fracture of the humeral surgical neck | Motor loss: Weakness in abduction and external rotation. |
| Shoulder dislocation | Sensory loss: Numbness over the regimental badge area. |
| Iatrogenic injury during surgery | Chronic complications: Muscle atrophy and neuropathic pain. |
Erb’s Palsy
- Cause: Damage to C5 and C6 nerve roots, stretching the axillary nerve.
- Symptoms:
- Impaired shoulder abduction and external rotation.
- Severity ranges from mild neuropraxia to complete nerve avulsion.
Points to Remember
- The axillary nerve is derived from the C5 and C6 nerve roots of the brachial plexus.
- It provides motor innervation to the deltoid and teres minor muscles and sensory innervation to the regimental badge area.
- The quadrangular space is a key anatomical landmark for its passage.
- Common injuries include fractures, dislocations, and surgical trauma.
- Clinical examination focuses on motor and sensory deficits.
Bibliography
- TeachMeSeries Ltd (2024). Axillary Nerve Anatomy.
- Gray’s Anatomy: The Anatomical Basis of Clinical Practice.
- Moore KL, Dalley AF. Clinically Oriented Anatomy.