A patient presents with a right wrist drop and an inability to extend the wrist and fingers at the metacarpophalengeal joints. This is most likely the result of an injury to what nerve?

Question

BlackTom AI · Accepted Answer

Question restatement: A patient presents with a right wrist drop and an inability to extend the wrist and fingers at the metacarpophalangeal (MCP) joints. Which nerve injury best explains this presentation?

Option A: Anterior Interosseous Nerve
- The anterior interosseous nerve (AIN) is a branch of the median nerve that primarily innervates deep forearm flexors such as the flexor pollicis longus, flexor digitorum profundus to the index and middle fingers, and pronator quadratus. It does not innervate the extensor muscles responsible for MCP extension. Therefore, AIN injury would produce deficits in flexion and thumb/index flexion actions, not a loss of MCP extension. This option is inconsistent with the observed inability to extend at MCP joints.

Option B: Posterior Interosseous Nerve
- The posterior interosseous nerve (PIN) is the continuation of the deep branch of the radial nerve after it passes through the supinator. It primarily supplies the extensor musculature of the forearm, including the extensors of the wrist and fingers (e.g., extensor digitorum, extensor indicis, extensor digiti minimi, extensor pollicis longus, extensor pollicis brevis, and abductor pollicis longus). Injury to the PIN typically results in weakness or loss of finger extension, particularly at the MCP joints, and often preserves some wrist extension due to intact contributions to wrist extensors supplied proximal to the PIN. In the context of a presentation emphasizing loss of MCP extension (finger extension) with wrist involvement, PIN involvement is a well-recognized explanation for the finger-extension deficit component of the pattern, making this option the most consistent with the described extensors affected.

Option C: Median Nerve
- The median nerve primarily innervates forearm flexors and several intrinsic hand muscles (thenar group and lateral two lumbricals) but does not innervate the primary MCP-extensor muscles. Loss of median nerve function would cause deficits in flexion and thumb/index opposition, not an isolated or predominant loss of MCP extension. This option does not fit the observed extension deficits.

Option D: Ulnar Nerve
- The ulnar nerve supplies many intrinsic hand muscles (interossei, hypothenar muscles, medial two lumbricals) and some wrist extensors (through the flexor carpi ulnaris and, variably, the extensor carpi ulnaris). However, ulcering primary MCP extension through dorsal interossei and extensor digitorum is more directly affected by radial nerve extensor pathways. An isolated ulnar nerve injury would not typically produce a primary failure of MCP extension as described. This option is unlikely given the motor pattern involved.

Synthesis across options: The deficit described involves loss of extension at the MCP joints, which is driven by the extensor compartment of the forearm. Among the listed nerves, the posterior interosseous nerve is the one most closely associated with motor fibers to the finger-extensor muscles. While a proximal radial nerve injury can cause a wrist drop, PIN involvement is classically linked to impaired finger extension at the MCP joints, aligning best with the presented inability to extend the fingers at the MCP joints. The other options do not account for the extensor deficits in the same direct way.

In sum, option B (Posterior Interosseous Nerve) provides the most coherent explanation for the observed pattern of extensor weakness at the MCP joints. The remaining options correspond to nerves whose distributions do not primarily innervate the extensor muscles responsible for MCP extension, making them less compatible with the presentation.

2261 REHSCI 1200 SEC1010 Bonus Graded Quiz 7 (Optional)

A patient presents with a right wrist drop and an inability to extend the wrist and fingers at the metacarpophalengeal joints. This is most likely the result of an injury to what nerve?

View Explanation

Log in for full answers

Similar Questions

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

In a consumer society, many adults channel creativity into buying things

Economic stress and unpredictable times have resulted in a booming industry for self-help products

People born without creativity never can develop it

A product has a selling price of $20, a contribution margin ratio of 40% and fixed cost of $120,000. To make a profit of $30,000. The number of units that must be sold is: Type the number without $ and a comma. Eg: 20000

Which of the following statement regarding cost is correct:

Under the assumptions used in cost-volume-profit analysis, as the activity increases:

The CVP and break-even analysis are supported by a range of important assumptions. Which of the following is not an assumption of the CVP:

More Practical Tools for Students Powered by AI Study Helper

Homework AI Solver

Stylized AI Paper Writer

Plagiarism Checker Assistant

Citation AI Academic Writing Tool

In-Class Translation Assistant

AI Note Generator

AI Quiz Answers

Past Exam Questions from University Test Bank

Smart Practice Assistant

Adaptive Practice

Making Your Study Simpler