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NBME 22 Answers

nbme22/Block 3/Question#1 (reveal difficulty score)
A 35-year-old man comes to the physician ...
C7 nerve root πŸ” / πŸ“Ί / 🌳

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submitted by βˆ—sympathetikey(1532),
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I sjtu ritde to ikthn of hw'ats eredaesl yb eth ealdArn lleduMa n.)peieip(Ehrn MNTP si eht lyno ohciec tath aedm nsese.

submitted by paulm(9),
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erP WdlroU I(D 3)1555

ehT C7 orto si eht omts tnfeureqly tecfeadf vener orto ni tantpies ihtw ccerilav dhot,upraiyacl nglirestu ni fdiceits oascrs eth demnia nad raaldi reevn sutiidont.isrb

nngiigt"l sinastone fo regnis"f β†’ dmniea erevn

iertcs"p lecusm exlfre si "raecdedes β†’ aaildr eevnr

carmustine  Another important indication that this involves the median nerve is the weakness in pronation. Pronation of the forearm is performed by the pronator teres and the pronator quadratus, both of which are innervated by the median nerve. +4  

submitted by βˆ—mcl(645),
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tranoroP steer nda auqurdtsa era hbto lspuedip by daenmi enrve C1/768(///C5,CCT os sa'htt otn epurs .fh)lplue ixsoetnnE of het rfermoa is dliraa revne sol(a C15,T- sloa ont h)pef.ull isTh edso llet su si ti c'nat be diltaose eniadm ro aid.lar iesTprc edntno xelref si CC7,8/ chhwi wasrnor ti nodw to seeth wto.

naC ayonne ainlxpe yhw it's 7C oerv C8?

joha961  Same question. How could you determine between the specific nerve roots (C7 vs. C8)? +2  
mcl  Someone I was talking to (and post below) was saying that first aid mentions triceps is C7, so that's what should've been the big thing for us. +4  
joanmadd  you might see some ulnar nerve involvement if C8 was involved her +1  
passplease  but he has generalized tingling which is in both ulnar and median regions? +  
chaosawaits  Also, C7 is the most common affected nerve root. If it's a choice between C7 and something else, go with C7 always unless you can definitively prove it's not. +  

submitted by oslerweberrendu(4),
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ncAcoigdr ot ,Udlrwo :IQD 91177C7 memyoot si vdevilno ni ebowl kn.inste oseooxL klei ti tsestel!

submitted by obliviondo (2),
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cAcrdgoin ot AF 2190 rceiTp xefRel is etedimad yb 6,C yse C6 NTO C8, dna C7 In[ D,OLB ilgimpny it si rmeo pnat.rit]mo

peridot  This is on p.498 of FA 2019 for anyone curious +  

submitted by βˆ—welpdedelp(258),
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So I ihntk atht eusis of witrs oieetnnsx n/raod grnfei dpro ulwdo be more dairla enre.v ,eevowHr etrhe saw mreo lioamrxp e,ssankwe so ti dluow be 7.C

8-"7 lay hmet s"thgi,rat eth pt 'cuotndl ya"l mhet "hrttasig so it wdlou eb 7C orot

welpdedelp  *As an addition, median nerve involvement would have leaned more toward C8 than C7. +11  
meningitis  Do you have anymore useful mnemonics for brachial plexus? +  
henoch280  FA pg 494 for mnemonics +  
winelover777  Doesn't look like there are many in FA 2019. S1/S2 - Buckle my shoe. L3/L4 - Shut the door. C5/C6 - Pick up sticks. +  
drzed  S2-S4 keeps the penis off the floor :) (cremaster reflex) +  
peridot  What's crazy @drzed is that in FA 2019 it says L1-L2 ("testicles move") on p.498 so I wonder if that changed +  

submitted by delamj(3),
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yM tgtohuh rsesopc no htis ntsqi:uoe

  • enkssewa fo amr xinnotees and oonparint = odssun eikl nsuauteoclouusmc vener 7)CC5-(

  • siercTp hertsct rxeefl CC);-7(8

Rltsu:ueo psBcei is C-65C os r/o C.6 C8 dot'ens itf oesuucuaouncltsm smuecl oniacst itoanc os r/o .6C Meadni adn ailRda reesvn vhae teeirfnfd scelum soctian os or/ osthe sa wel,l vgnelai sujt C7 stbe ittingf hte g.ntvteei

delamj  C8 doesn't fit musculocutaneous muscle actions action so r/o C8.** +1  
lsp1992  I think you have the function of the musculocutaneous nerve wrong. Musculocutanous nerve's motor function is flexion (biceps, brachialis and corachobrachialis) and supination. Musculocutaneous dysfunction would cause weakness of flexion and supination. Weakness of extension would be radial nerve. Weakness of pronation would be median +1  

submitted by βˆ—azibird(227),
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eeHr si a tpar of the UodrlW atebl tabou lcrcivae edplthaioai.uscr dAn sye ehyt idd asy htat C7 si hte mtos frletneuqy e.vdnlivo I khtni teh ewansr is htta 6C olwud eonvvil eth ,scepbi C8 wolud vvoneil the fengis,r dna inpooantr is nemadi ere.nv So ti sha ot be C7.


submitted by magrufnis(0),
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Im’ ouecdfsn boaut tish eo.n kseansWe fo nsoeienxt nad pinnoorta of eht thrig mroa,fer iwth a sredecdea eicprts ucelms tsherct x.reelf Teh answer was 7C ervne or,ot tub who aer uyo aebl to zlcailoe to 7C and otn 6C or ?C8 I riedgfu taht sonexenti si irl,ada C-,5T1 dna pntoraion si dna,eim also .C1T5- rTpisce efrlex si C7C8- 2(F901A says C76)C.- oHw wlodu ouy arrown dnow to stuj C7 ?madage

txallymcbeal  My FA2018 has β€œC7” bolded, meaning it is the main nerve root. But I also got this one wrong so I can’t be much help besides that. +1  
mnemonia  Honestly just a guess but I have this vague understanding that intrinsic hand muscles are C8-T1 so we might’ve expected more hand motor findings as well with a C8 lesion. +5  
theecohummer  I narrowed it down to C7 using the fact that the C7 myotome is elbow extension. I also learned that the C7 nerve root was the main contributor to the triceps DTR so I just went with that. +  
mchu21  They also mentioned that the person had weakness pronating the right forearm which is performed by the biceps. Biceps is innervated by the musculocutaneous nerve which is C5-C7 and that's what helped me pick C7 > C8. +4  
mcl  Sorry, I thought the biceps was a supinator of the forearm? +16  
henoch280  yes.. its the supinator not pronator +  

submitted by βˆ—feanor(1),
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Teh 7C evrne otor is ni dbol no e.49P4ag FA 2081 in the cpriTe rxeelf totlesr,o t'sTha onhgeu ofr em l.ol ishT gimth dousn a bti tdlcoaane btu I ermmebre igndrae eowesremh atth nwrvehee C8 or 1T gseo eht niticrsin semslcu of eht adhn era syalwa deetceff.

submitted by βˆ—madamestep(3),

"The flexor group of muscles is involved in pronation of the forearm and flexion of the wrist and fingers, while the extensor group of muscles is involved in the supination of the forearm and extension of the wrist and fingers."

From Amboss

Weakness of extension (Radial n) and pronation (Median n).

C6 damage would give you MC signs. C8 would give you ulnar signs. C7 goes to Median and Radial.

submitted by βˆ—nwinkelmann(349),
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Pre da:iipiWke Teh rptisce ,exerlf a depe otendn rl,fexe si a efrxel sa it icteils vunnlitroay cornaocttin fo teh pscerti iahicbr seulc.m It is eniiitdat by the cveralCi (fo hte ncek )goenir ilpasn enrve 7 rveen toor th(e alslm ngestem of hte eevrn hatt grseeem mrfo het lisnpa c.)rod eTh eelfrx si edstet as arpt of eht loocianleugr ieatnmiaxno ot ssseas eth reonssy adn mtroo swathayp iwntih eht 7C dna C8 npails venesr.

s,lAo rofm a etdffinre weset:bi eTh ptcreis lreefx is medeiatd by eht 6C adn 7C nvere or,ots iyaetndnomlpr by C7. i/p./u/gs.yeelmb/rr/pomodoheatuu.tftxustifdrh.esrl/muern:lssyenmdceune.

this is my way to think(please correct me if it's not correct: a. weakness of triceps muscle reflex --> C6 / C7 / C8 problem (FA P498 2019) b. weakness of extension of the forearm --> radial nerve is involved --> damage of C7 root leads to axillary or RADIAL nerve defect (FA P441 2019)

+/- joyceeepan(6),

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