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NBME 21 Answers

nbme21/Block 3/Question#30 (45.3 difficulty score)
A 41-year-old man comes to the physician ...
Abduction of the upper extremityπŸ”

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submitted by mcl(586),
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Ddeoitl si nnevitdrea yb llixarya ev,enr chhwi coems rfom otsor /6CC.5 tinsAco fo eth tldieod elcdnui bunitcoad of teh pprue rtyexeti.m

seagull  I hope everyone memorized every single part of the brachial plexus and all the roots of each, No detail let untouched!!! +26  
mcl  In case anyone else has purged the whole brachial plexus from your memory (like me), this is a great resource linked by another user. +11  
zevvyt  I thought it was radial since he lost sensation in his thumb. If Radial is C5-T1, wouldn't that be included in C5-C6? +1  
alimd  they force us to know brachial plexus like the holy bible +  

submitted by poisonivy(30),

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

submitted by quarantined(4),

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.

kevin  Axillary controls deltoid not musculocutaneous but otherwise yes +  

submitted by misrao(1),

Axillary = ABCD + A = Axillary nerve + B = aBduction loss + C = C5-6 + D = Deltoid

misrao  sorry about formatting, couldn't get it right +  

submitted by burak(52),
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s'It elik rbE lxyi,raAl culpuraaarpssis and onssecmoculuuatu revne a.gsdeam

burak  palsy* +  
nifty95  This is a good way to remember the upper trunk! +