Dr. Ebraheim’s educational animated video describes the anatomy of axillary nerve.
The Axillary nerve originates from the posterior cord of the brachial plexus.
The axillary nerve supplies the deltoid muscle and teres minor muscle, giving lateral sensation over the shoulder area.
The teres minor muscle is innervated by the posterior branch of the posterior branch of the axillary nerve.
It gives cutaneous innervation to the lateral part of the shoulder.
The axillary nerve passes over the subscapularis and then curves backwards below it and underneath the shoulder joint capsule to enter the quadrangular space.
The Quadrangular space boundaries:
- Teres minor (superior)
- Teres major (inferior)
- Long head of the triceps (medial)
- Surgical neck of the humerus (lateral)
Within the quadrangular space, the axillary nerve is accompanied by the posterior circumflex humeral artery; they run around the surgical neck of the humerus.
After passing through the quadrangular space, the axillary nerve divides into anterior and posterior divisions.
The anterior division curves anteriorly under the deltoid muscle.
The deltoid muscle is innervated by this anterior division of the axillary nerve.
The posterior branch supplies the teres minor and the remaining portion of the deltoid muscle, it also gives the upper lateral cutaneous nerve of the arm which supplies sensation over the lower half of the deltoid muscle.
This close close relashionship to the shouolder joint makes the nerve prone to injure due to dislocation or fracture of the proximal humerus.
Axillary nerve injury:
- The axillary nerve provides abduction of the arm between 30°-90°.
- Test the deltoid by having the patient abduct the arm against resistance, and by moving the arm posteriorly and superiorly against this resistance.
- Look for deficiency of the sensation around the shoulder area.
- The axillary nerve is fixed at the quadrangular space and it is vulnerable to injury because it is fixed.
- The axillary nerve is the most commonly injured nerve arround the shoulder, usually from trauma such as fracture or dislocation, so if you have a young patient who is unable to abduct the arm after an injury, it is probably ana injury to the axillary nerve, but if it’s an elderly patient: then it’s probably a rotator cuff tear and not necessarily an axillary nerve injury.
- The diagnosis of axillary nerve palsy may be very difficult due to the fact that the descending cervical plexus may supply sensation to the involved area.
- Other muscles may also aid in abduction of the arm mimicking the deltoid function even if the deltoid is paralyzed.
- The initial 30 degrees of abduction is controlled by the supraspinatus muscle.
- A powerful supraspinatus muscle can alone abduct the arm to 90° (exam is misleading).
- Abduction above 90° has some control by the trapezius muscle.
- The serratus anterior can assist the anterior deltoid during flexion of the arm above 60°.
- When doing shoulder surgery, it is important to avoid injury to the axillary nerve.
Lateral shoulder approach:
- Incision from the tip of the acromion extended distally.
- The incision and deltoid deltoid is split and the incision should not be more than 5cm distal to the acromion to protect the axillary nerve.
- The axillary nerve runs transversely from posterior to anterior about 7cm distal to the acromion.
- If the incision needs to be extended distally, as in fixation of the proximal humerus, an anterolateral incision over the humeral shaft may be used.
Become a friend on facebook:
Follow me on twitter:
Donate to the University of Toledo Foundation Department of Orthopaedic Surgery Endowed Chair Fund: