Hip dislocation - nerve injury question

[Phloston]

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Attached is a question from Kaplan QBank.

Before you give input, please take a look at p.411 in FA2012.

I answered choice B for this question specifically because FA says for superior gluteal nerve: POSTERIOR HIP DISLOCATION --> deficit in THIGH ABDUCTION.

I mean, what should I make of this question? You can even see in the explanation on the Kaplan question that they say the superior gluteal nerve wouldn't be injured in a posterior hip dislocation.

 

[Myxedema]

Sciatic nerve is more likely to be injured than superior gluteal nerve in a posterior dislocation. This is a classical presentation of dislocation of hip. FA should've mentioned this.

 

[Phloston]

Sciatic nerve is more likely to be injured than superior gluteal nerve in a posterior dislocation. This is a classical presentation of dislocation of hip. FA should've mentioned this.

How sure are you of that?

Are you saying it should always be sciatic over SGN for posterior hip dislocation?

 

[Myxedema]

Always? No. But sciatic n. injury due to hip dislocation is a classic presentation.

 

[RedSoxSuck]

Since we are on MSK topic, do you guys know common MSK injuries or herniations which have been asked on nbme's via images or important to know? I can think of conus medullaris syndrome, cauda equina, sciatica. Thanks!

 

[Myxedema]

I think anything in FA is fair game and should be very well known.

 

[RedSoxSuck]

I think anything in FA is fair game and should be very well known.

I meant anything that is commonly asked or could be asked but isnt in fa.

 

[berry15]

P.411 FA 2012 says both Superior Gluteal and Inferior Gluteal result from posterior hip dislocation. In the entry for Inferior gluteal the motor deficit says "Can't jump, climb stairs, or rise from seated position; can't push inferiorly (downward)" and I have written in from UW "weak hip extension" for the inferior gluteal. This adds a third nerve into this debate, not sure how to go about picking the BEST answer if presented with that question.

 

[Phloston]

P.411 FA 2012 says both Superior Gluteal and Inferior Gluteal result from posterior hip dislocation. In the entry for Inferior gluteal the motor deficit says "Can't jump, climb stairs, or rise from seated position; can't push inferiorly (downward)" and I have written in from UW "weak hip extension" for the inferior gluteal. This adds a third nerve into this debate, not sure how to go about picking the BEST answer if presented with that question.

Notice the vignette in Kaplan just mentioned the posterior hip fracture and asked for the most likely deficit. In this case, as Myxoedema has pointed out, sciatic would be injured > SGN or IGN.

So on the actual USMLE, if a similar question pops up --> sciatic nerve = best anaswer. However if they actually give "loss of abduction" or "can't jump" in the vignette, for example, then we'd know we had SGN or IGN injury, respectively.

 

[thehundredthone]

Isn't extension of the thigh at the hip a function of the gluteus maximus, i.e. IGN?

 

[Fuzuli]

Isn't extension of the thigh at the hip a function of the gluteus maximus, i.e. IGN?

Yes it is. It's also a function of (most) hamstring muscles.

 

[Fuzuli]

Always? No. But sciatic n. injury due to hip dislocation is a classic presentation.

That's due to posterior dislocation of the hip, not all.

 

[thehundredthone]

Yes it is. It's also a function of (most) hamstring muscles.

Did not even occur to me at first. Thanks.