PNS 3 - The Axillary Nerve

Question 1

Muscles Innervated

Answer 1

Deltoid and Tm

Question 2

Motor Function

Answer 2

Abduction of arm at shoulder beyond first 15 degrees

Question 3

Sensory

Answer 3

Skin over the shoulder

Question 4

Axillary nerve branches off the large radial nerve and exits axilla through the

Answer 4

Quadrilateral Space (Quadrangular space)

Question 5

Posterior aspect of the scapula showing the 4 boundaries of the quadrangular space: Superior?

Answer 5

Teres minor (Tm) and subscapularis

Question 6

Posterior aspect of the scapula showing the 4 boundaries of the quadrangular space: Inferior?

Answer 6

Teres major muscle (TM)

Question 7

Posterior aspect of the scapula showing the 4 boundaries of the quadrangular space: Lateral?

Answer 7

the surgical neck of the humerus

Question 8

Posterior aspect of the scapula showing the 4 boundaries of the quadrangular space: Medial?

Answer 8

Long head of Triceps muscle (TrM).

Question 9

MOTOR

Answer 9

Deltoids
Teres minor
(Long head of triceps brachii)

Question 10

SENSORY

Answer 10

Sensation to superolateral shoulder over deltoid

Question 11

Causes of axillary nerve injury: 9 causes from notes

Answer 11

• Proximal humeral head/neck fractures
• Anterior shoulder dislocation resulting in traction and compression
• Fibrous bands (post traumatic)
• Soft tissue and osseous tumors
• Deep IM injection
• Compression: sleeping prone with arms over head
• Penetrating injury
• Rotator cuff surgery
• Teres syndrome (Quadrilateral Space Syndrome) compression of axillary nerve in quadrilateral space.

Question 12

Injury to the axillary nerve may lead to:

Answer 12

Deltoid weakness - shoulder abduction (15-90 degrees). Atrophy of the deltoid (flat shoulder deformity).