Question

A person sustains a left brachial plexus injury in an auto accident. After initial recovery the following is observed: 1) the diaphragm functions normally, 2) there is no winging of the scapula, 3) abduction cannot be initiated, but if the arm is helped through the first 45 degrees of abduction, the patient can fully abduct the arm. From this amount of information and your knowledge of the formation of the brachial plexus where would you expect the injury to be:

A. axillary nerve
B. posterior cord
C. roots of plexus
D. superior trunk
E. suprascapular nerve

Answer 1

Based on the symptoms described, the most likely injury to the brachial plexus in this scenario is to the suprascapular nerve, which results in the inability to initiate abduction in the shoulder.

Step-by-step explanation:

The student is asking about the specifics of an injury to the brachial plexus and its effects on muscle function following an auto accident. Given the symptoms described in the question: 1) normal diaphragm function, 2) absence of winging of the scapula, and 3) inability to initiate abduction until the arm is assisted past 45 degrees, we can deduce that the most likely location of the injury is the suprascapular nerve. The suprascapular nerve branches from the upper trunk of the brachial plexus and is responsible for innervating muscles that initiate abduction at the shoulder, specifically the supraspinatus muscle. The fact that the diaphragm functions normally rules out a high cervical injury, while the ability to continue abduction after the first 45 degrees indicates function of the deltoid muscle, which is innervated by the axillary nerve, suggesting that the axillary nerve and its associated posterior cord are intact. Therefore, the injury would not be located at the axillary nerve, posterior cord, roots of the plexus, or superior trunk, which leaves us with the suprascapular nerve as the most likely injured part.