Question
A 37-year-old man is brought to the emergency department after being attacked with a knife. Physical examination shows a 4-cm laceration in the midline of the right forearm. An MRI of the right arm shows damage to a nerve that runs between the superficial and deep flexor digitorum muscles. Loss of sensation over which of the following areas is most likely in this patient?
| A. |
Dorsal aspect of the forearm
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| B. |
Lateral aspect of the forearm
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| C. |
Fingertip of the index finger
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| D. |
Dorsum of the thumb
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Show Answer
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Correct Answer � C
Explanation
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Answer C) Fingertip of the index finger
Explanation:
The median nerve, which originates from the lateral and medial cords of the brachial plexus, passes down the arm into the cubital fossa and runs in the midline of the ventral compartment of the forearm between the flexor digitorum superficialis and flexor digitorum profundus.
Dorsal aspect of the forearm
The dorsal aspect of the forearm is innervated by a branch of the radial nerve called the posterior antebrachial cutaneous nerve, which lies in the extensor compartment of the forearm. A different nerve lies between the flexor digitorum superficialis and flexor digitorum profundus.
Palmar surface of the little finger
The palmar surface of the little finger is innervated by palmar branches of the ulnar nerve, which enters the anterior compartment of the forearm between the two heads of flexor carpi ulnaris and lies between the flexor digitorum superficialis and flexor digitorum profundus. However, the ulnar nerve is located medially; it is less likely to be affected by a laceration in the midline of the forearm.
Fingertip of the index finger
The median nerve passes through the carpal tunnel into the hand. Within the hand, the median nerve motor branch innervates the thenar muscles and the lateral two lumbricals. The median nerve also provides sensory innervation to the thenar eminence as well as the dorsal and palmar aspect of the lateral 3½ fingers including the fingertips. Note that the lateral border of the thenar eminence is innervated by the radial nerve.
Dorsum of the thumb
The dorsum of the thumb is innervated by the superficial branch of the radial nerve, which travels through the forearm under the brachioradialis. A different nerve lies between the flexor digitorum superficialis and flexor digitorum profundus.
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