USMLE (United States Medical Licensing Examination) Step 1 Practice Exam

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Which nerves are typically involved in an upper brachial plexus injury?

  1. Musculocutaneous and Suprascapular Nerves

  2. Median and Radial Nerves

  3. Ulnar and Axillary Nerves

  4. Femoral and Sciatic Nerves

The correct answer is: Musculocutaneous and Suprascapular Nerves

An upper brachial plexus injury commonly affects the roots C5 and C6, which are primarily responsible for innervating the muscles of the shoulder and upper arm. The musculocutaneous nerve, originating from this area, innervates the coracobrachialis, biceps brachii, and brachialis muscles, playing a vital role in flexing the elbow. The suprascapular nerve, also from the C5-C6 roots, innervates the supraspinatus and infraspinatus muscles, which are important for shoulder abduction and external rotation. When there is an injury in this region, such as from trauma (e.g., a motorcycle accident, falling onto the shoulder, or obstetric complications), these nerves can become compromised. Symptoms may include weakness in shoulder abduction and flexion as well as decreased sensation in the lateral aspect of the arm. The other listed nerves, such as the median and radial nerves, are more commonly associated with lower brachial plexus injuries, while the ulnar and axillary nerves are also related to more distal injuries. The femoral and sciatic nerves are not involved in brachial plexus injuries, as they primarily innervate the