“Wrist drop” due to an inability to extend the wrist due to weak / paralyzed extensors can be a result of an injury to __________________________.

Question

“Wrist drop” due to an inability to extend the wrist due to weak / paralyzed extensors can be a result of an injury to __________________________.

BlackTom AI · Accepted Answer

The question asks about a condition described as 'wrist drop' due to inability to extend the wrist, resulting from weakness or paralysis of the extensor muscles. To analyze the options, we consider which nerve supplies the wrist extensor group.
Option 1: Median Nerve. The median nerve mainly innervates many of the forearm flexors and some intrinsic hand muscles; it does not primarily supply the wrist extensors. Injury to the median nerve would more likely cause weakness in flexion and thenar muscles rather than pure loss of wrist extension, so this option is unlikely to produce classic wrist drop.
Option 2: Ulnar Nerve. The ulnar nerve mainly supplies intrinsic hand muscles and some forearm flexors; its injury leads to motor deficits in the intrinsic hand and flexor carpi ulnaris or medial flexor digitorum profundus in some branches, but it is not the principal nerve for wrist extension. Wrist drop is not a typical presentation of an isolated ulnar nerve injury, making this option incorrect for this symptom.
Option 3: Musculocutaneous Nerve. This nerve supplies the forearm flexors (biceps brachii, brachialis, coracobrachialis) and sensory input from the lateral forearm. It does not innervate the wrist extensors, so injury here would not produce wrist drop. Therefore, this choice does not fit the described clinical picture.
Option 4: Posterior Interosseous Nerve (Deep Branch of the radial nerve). The posterior interosseous nerve is the motor continuation of the radial nerve after it passes through the supinator and supplies the extensor compartment of the forearm. Damage to this nerve specifically compromises the wrist and finger extensors, leading to the classic wrist drop with inability to extend the wrist. This aligns directly with the symptom described in the question.
In summary, the wrist extensors are innervated by branches of the radial nerve, particularly the posterior interosseous nerve. The other nerves listed either do not supply the extensor muscles responsible for wrist extension or do so only indirectly, which would not produce the characteristic wrist drop. Therefore, the option that best matches the described clinical scenario is the posterior interosseous nerve injury.

2261 REHSCI 1200 SEC1010 Lecture Exam 2 - Requires Respondus LockDown Browser

“Wrist drop” due to an inability to extend the wrist due to weak / paralyzed extensors can be a result of an injury to __________________________.

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