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NBME 20 Answers

nbme20/Block 1/Question#14

A 28-year-old man who is a migrant worker comes to ...

Psoas major

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The major motion of Psoas major is flexion of hip. This patient is held in "rigid extension", hence he does not want to flex. Psoas is the only muscle on this list that connects the lumbars to lower extremity "holds his right lower extremity"

myoclonictonicbionic  The qstem said "lower extremity in rigid extension" which made it sound like extension at the knee joint rather than at the hip. Confusing wording +  

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submitted by aj32803(1),

Uworld specifically says that Psoas abscess means the patient will prefer flexion to avoid stretching the muscle. That's why Psoas did not make sense to me since the patient preferred extension, which would be stretching out the muscle.

On the other hand it's right on the vertebra and it's associated with TB.

adong  it's confusing but i think b/c psoas acts to flex at the hip, staying completely flat would keep the muscle from being contracted. uworld is talking about the psoas test which would end up hyperextending the psoas muscle which would elicit pain (psoas test can also be done with active flexion against pressure which would explain the not wanting to flex). +  
kamilia20  First ideal to my mind is that:patient is a TB, TB prefer psoas +  

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submitted by hayayah(525),

Of all the options, psoas major is the only one that is really associated with the lumbar vertebrae.

Q. Lumborum involves the transverse process of L1 but Psoas Major originates from L1-L5

imnotarobotbut  QL is connected to L1-L5 vertebrae as well (https://en.wikipedia.org/wiki/Quadratus_lumborum_muscle) +