Step I NBME 6 -Anatomy q

[determined1.]

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A 37-year-old man comes to the physician because of severe back pain for 2 days. The pain radiates down the buttock, posterior thigh, and posterolateral leg. He also has numbness on the side of his left foot. On physical examination, sensation to pain is decreased over the lateral side of the left foot. Deep tendon reflexes are absent at the left ankle, and there is weakness of dorsiflexion of the left foot. Compression of which of the following nerve roots is the most likely cause of these findings?
A ) T12
B ) L2
C ) L4
D ) S1
E ) S3

Dx-Common Peroneal injury = L4-S2

So I chose C, but answer is D= S1.... ?

 

[dfib slim]

A 37-year-old man comes to the physician because of severe back pain for 2 days. The pain radiates down the buttock, posterior thigh, and posterolateral leg. He also has numbness on the side of his left foot. On physical examination, sensation to pain is decreased over the lateral side of the left foot. Deep tendon reflexes are absent at the left ankle, and there is weakness of dorsiflexion of the left foot. Compression of which of the following nerve roots is the most likely cause of these findings?
A ) T12
B ) L2
C ) L4
D ) S1
E ) S3

Dx-Common Peroneal injury = L4-S2

So I chose C, but answer is D= S1.... ?

Numbness over the S1 dermatome with absent Achilles reflex (S1-S2)

 

[determined1.]

So, it's not common peroneal nerve injury?

 

[addy]

So, it's not common peroneal nerve injury?

This is a radiculopathy, not a nerve lesion.

 

[dfib slim]

So, it's not common peroneal nerve injury?

Nope. The question asks for a compressed nerve root. The common peroneal nerve doesn't directly come off the spinal cord, it's a branch of the sciatic nerve (L4-S3). A common peroneal nerve injury would occur with a fibular neck fracture and wouldn't present with back pain radiating down the leg.

I'd think it was an L5-S1 disc herniation causing compression of the S1 nerve root.

 

[determined1.]

Thank you guys. I understand now. Someone posted wrong answer in another forum.

Here's another anatomy question:

A 17-year-old boy is stabbed in the anterior axilla. He has loss of sensation on the anterolateral surface of the forearm and loss of the biceps reflex. Which of the following nerves is most likely to be damaged?

A ) Axillary
I ) Musculocutaneous

I chose axillary since they mentioned he was stabbed in axilla and lost biceps reflex so I was thinking biceps are innervated by axillary nerve and not musculocutaneous.

 

[addy]

You need to review first aid and the relevant Anatomy section.

p. 414 in 2014 FA. Better diagrams in UWorld, though.

 

[determined1.]

Thanks addy, I will. My anatomy sucks so I have to review the whole thing..