A 19-year-old man comes to the emergency department after being stabbed in the right arm during a fight. The patient has no chronic medical conditions. Vital signs are within normal limits. Examination of the right upper extremity shows a 4-cm laceration oriented transversely over the volar (flexor) surface of the proximal forearm. The patient is taken to the operating room for surgical repair. While exploring the wound, a nerve that courses between the flexor digitorum superficialis and profundus muscles is found to be transected. Which of the following movements is most likely to be impaired in this patient?

Question

A 19-year-old man comes to the emergency department after being stabbed in the right arm during a fight.  The patient has no chronic medical conditions.  Vital signs are within normal limits.  Examination of the right upper extremity shows a 4-cm laceration oriented transversely over the volar (flexor) surface of the proximal forearm.  The patient is taken to the operating room for surgical repair.  While exploring the wound, a nerve that courses between the flexor digitorum superficialis and profundus muscles is found to be transected.  Which of the following movements is most likely to be impaired in this patient?

Quizplus · Accepted Answer

11ec160b_35bc_ce4f_9249_4304a8e2b8b3_MD0001_00 The median nerve is formed from spinal nerves C5-T1 via the medial and lateral cords of the brachial plexus. It courses with the brachial artery between the biceps brachii and brachialis muscles before entering the forearm. In the anterior (volar) forearm, the median nerve passes between the heads of the pronator teres before coursing between the flexor digitorum superficialis and profundus muscles. It ultimately passes into the hand through the carpal tunnel beneath the flexor retinaculum. The median nerve is most commonly injured by compression within the carpal tunnel (ie, carpal tunnel syndrome), leading to pain and numbness in the first 3 digits and lateral half of the fourth, along with weakness of thumb flexion and opposition. However, the nerve can be injured more proximally by penetrating trauma to the upper forearm, supracondylar fracture, or entrapment between the heads of pronator teres. In addition to the above symptoms, proximal injury causes decreased sensation over the thenar eminence and weakness of flexion in the wrist and second and third digits (ie, preacher or benediction hand). (Choices A and B) The adductor pollicis muscle (adduction of the thumb) and palmar interossei (adduction of the third and fourth digits) are innervated by the deep branch of the ulnar nerve. The ulnar nerve courses between the flexor digitorum profundus and flexor carpi ulnaris in the medial forearm. (Choices C and F) The extensor digitorum (extension of digits at metacarpophalangeal joints) and supinator (supination of forearm) are innervated by the deep branch of the radial nerve (posterior interosseous nerve). This nerve runs in the posterior forearm between the deep and superficial extensor muscles. (Choice D) Extension of the wrist is largely performed by extensor carpi ulnaris and extensor carpi radialis longus and brevis, which are innervated by the radial nerve. The radial nerve courses between the medial and lateral heads of the triceps brachii in the upper arm before splitting into deep and superficial branches. Educational objective: The median nerve is most commonly injured within the carpal tunnel, leading to pain and numbness in the first 3 digits and lateral half of the fourth, as well as weakness of thumb flexion and opposition. More proximal injury (in the forearm) additionally causes decreased sensation over the thenar eminence and weakness of flexion in the wrist and second and third digits. __________ References: High median nerve injuries. (http://www.ncbi.nlm.nih.gov/pubmed/27387077)

A 19-Year-Old Man Comes to the Emergency Department After Being