Lesions of Branches of the Brachial Plexus

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MudPhud20XX

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From Kaplan:

A 43 year old woman suffers a lesion of the radial nerve. She has altered sensation in the skin of the first dorsal web space, wrist drop, and an inability to extend her forearm at the elbow. Which of the following most likely caused the lesion?

A. Dislocation of the humerus
B. Laceration in the axilla
C. Midshaft humeral fracture
D. Subluxation of the radius
E. Wrist laceration

I chose C, but the answer is B.

I went after C (midshaft humeral fracture) since wrist drop is a sign of radial nerve injury and midshaft humeral fracture is one of the most frequent injury that damages radial nerve.

Won't laceration in the axilla cause axillary nerve injury?

Can anyone explain what makes B a better answer choice over C?

Many thanks in advance.

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You ignored that there's weakness in forearm extension which is due to weakness in triceps muscle. Radial nerve supplies triceps before reaching midshaft. So injury must be before reaching midshaft like laceration in axilla.
Axillary nerve damage is more classically associated with surgical neck fracture or anterior dislocation of humerus
Radial nerve damage can be due to midshaft fracture or compression/laceration in the axilla (remember Saturday night palsy or using crutches)
 
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