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Nerve Injuries Affecting the Upper Extremity

Topic: Pharmacology

Created on Wednesday, December 27 2006 by jdmiles

Last modified on Wednesday, December 27 2006.

A Greek female deity was gouged in the axilla by a Narwhal yesterday. She presents to your clinic today complaining of numbness in the area shaded in green in the image above. She also, as pictured, is unable to extend her arm at the elbow, or abduct at the shoulder.
Which of the following is the most likely site of the lesion?

 
        A) Posterior cord
 
        B) Posterior interosseous nerve
 
        C) Axillary nerve
 
        D) Radial nerve
 
        E) Median nerve
 

 


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This question was created on December 27, 2006 by jdmiles.
This question was last modified on December 27, 2006.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

ANSWERS AND EXPLANATIONS




A) posterior cord

This answer is correct.


The sensory and motor deficits this patient complains of are consistent with a posterior cord injury. The triceps is one of the muscles innervated by the radial nerve, which is a branch of the posterior cord. This explains the inability to extend the arm at the elbow. Impaired abduction at the shoulder results from weakness of the deltoid muscle. The deltoid is innervated by the axial nerve, which is also a branch of the posterior cord. The distribution of numbness resembles a radial nerve lesion, as the axillary nerve provides sensation to only a small area of skin on the lateral aspect of the upper arm.   (See References)

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B) posterior interosseous nerve

This answer is incorrect.


The posterior interosseous nerve is a distal motor branch of the radial nerve. It branches off the radial nerve distal to the elbow, and does not affect arm extension. It does affect finger flexion. A lesion of this nerve would not cause numbness.   (See References)

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C) axillary nerve

This answer is incorrect.


A lesion of the axillary nerve would result in weakness of the deltoid, but not in weakness of the triceps. The distribution of the sensory component of the axillary nerve is limited to a small patch on the lateral surface of the upper arm. An axillary nerve lesion could not explain the motor or sensory symptoms this patient has.   (See References)

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D) radial nerve

This answer is incorrect.


The sensory deficit in this lesion could be consistent with a radial nerve injury, and triceps weakness (impaired extension at the elbow) would also be seen in such a lesion. However, the radial nerve does not innervate the deltoid, so impaired abduction at the shoulder is not consistent with a radial nerve injury. A posterior cord lesion would produce similar symptoms as a radial nerve injury, but would also produce deficits consistent with axillary nerve dysfunction, such as deltoid weakness.   (See References)

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E) median nerve

This answer is incorrect.


The distribution of the sensory deficit is not consistent with a median nerve lesion, and the median nerve does not affect extension of the arm at the elbow.   (See References)

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References:

1. Preston, D.C., and Shapiro, B.E. (2005). Electromyography and Neuromuscular Disorders: Clinical-Electrophysiologic Correlations, 2nd Edition. Elsevier, Philadelphia. Pp. 663-666.
2. Bickley, L.S., and Hoekelman, R.A. (1999). Bates' Guide to Physical Examination and History taking, 7th Edition. Lippincott, Philadelphia. Pp. 163-244.
3. Leigh, R.J., and Zee, D.S. (2006). The Neurology of Eye Movements, 4th Edition. Oxford University Press, Oxford.
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pharmacology
Nerve Injuries Affecting the Upper Extremity
Question ID: 12270601
Question written by J. Douglas Miles, (C) 2006-2009, all rights reserved.
Created: 12/27/2006
Modified: 12/27/2006
Estimated Permutations: 362880

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