question #15553 in UW explains this one well. Basically, C5 branches innervate Deltoid (abduction) and Infraspinatus(external rotation) and C6 Biceps (forearm flexion), so the right option should be abduction of the upper extremity.
I got it wrong though lol
Axillary = ABCD + A = Axillary nerve + B = aBduction loss + C = C5-6 + D = Deltoid
Decreased sensations over the thumb and anterior forearm indicates a lesion of the c6 dermatome, which is confirmed by the physician's suspicions of c5/6 nerve damage. The MOST SPECIFIC way of confirming this would be to test for deltoid muscle action (abduction of shoulder) since it's innervated by musculocutaneous nerve (c5/c6). Even though other nerves (like radial) also shares roots with c5/c6, testing those nerve functions will not be as specific.
It's like Erb Plays. Axillary, suprascapularis and musculocutaneous nerve damages.
Compression of the C5/C6 spinal nerves would mean the axillary nerve is compressed.
(Use the mnemonic: 5 Muskateers Assassinated 5 Rats 5 Mice, and 2 Unicorns; assassinated would be C5/C6 and axillary sounds like assassinated)
The axillary nerve innervates the deltoid muscle which abducts the upper extremity.
submitted by โmcl(670)
Deltoid is innervated by axillary nerve, which comes from roots C5/C6. Actions of the deltoid include abduction of the upper extremity.