Wrist drop is caused by all except?

NHM UP Staff Nurse - 2016

Medical Surgical Nursing

Easy

Appeared in: NHM UP Staff Nurse - 2016

Explanation

Ulnar nerve palsy does not cause wrist drop; it affects a different set of muscles than those responsible for wrist extension.
The ulnar nerve primarily supplies intrinsic hand muscles (like the interossei and medial two lumbricals) and the flexor carpi ulnaris.
Injury to the ulnar nerve results in a characteristic 'claw hand' deformity, where the metacarpophalangeal (MCP) joints of the 4th and 5th digits are hyperextended, and the interphalangeal (IP) joints are flexed.
Wrist drop is specifically caused by weakness in the wrist and finger extensor muscles, which are innervated by the radial nerve.

Option A: This is a known cause of wrist drop. Lead is a neurotoxin that can cause a motor peripheral neuropathy, with a classic predilection for the radial nerve.
Option B: This is the most direct and classic cause of wrist drop. The radial nerve innervates the posterior compartment of the forearm, which contains the muscles responsible for extending the wrist and fingers.
Option D: This option is incorrect because it groups two actual causes of wrist drop. The question asks for the exception, meaning the one option that does not cause the condition.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Peripheral Nerve Injuries and Associated Deformities as background academic context rather than a clinical decision trigger.
Nurses must be able to perform a basic neurological assessment of the hand to differentiate nerve injuries, which is crucial for timely reporting and appropriate patient care.
A quick screening includes asking the patient to: extend the wrist against resistance (tests radial nerve), spread fingers apart against resistance (tests ulnar nerve), and make an 'OK' sign or oppose the thumb to the little finger (tests median nerve).
What if? If a patient with a mid-shaft humerus fracture suddenly develops wrist drop, the nurse must suspect radial nerve entrapment or injury. The immediate actions are to immobilize the limb, assess neurovascular status, and urgently notify the physician, as this could be a surgical emergency.

How to Approach the Question

First, identify the keyword 'except' in the question. This means you are looking for the option that is NOT a cause of wrist drop.
Next, define the central term: 'Wrist drop'. This is the inability to extend the wrist, pointing to a problem with the extensor muscles.
Recall the innervation of the forearm muscles. The extensor muscles are supplied by the radial nerve.
Evaluate each option based on this knowledge:
Radial nerve palsy: Directly affects the nerve for extension, so it's a cause.
Lead poisoning: A known cause of radial neuropathy, so it's also a cause.

Concept Tested & Keywords

Concept Tested: Peripheral Nerve Injuries and Associated Deformities
Stem keywords: Wrist drop
Lead-in keywords: except
Negative lead-in flag: The question uses negative framing ('except'), asking to identify the option that is NOT a cause of wrist drop.

QClNXo_emvOXEJ7So2l50H

E6 Anatomy BDChaurasia V1 10e p. 100-102

E6 Anatomy MindMaps BDChaurasia V1 10e p. 7-9

E6 Anatomy Workbook HumanAnatomy Vol 1 p. 76-78