"Foot drop" is caused by damage to which of the following nerves?

ISRO 2024

Applied Anatomy

Easy

Appeared in: ISRO 2024

Explanation

Foot drop is the inability to lift the front part of the foot, a movement known as dorsiflexion.
The deep peroneal nerve innervates the muscles in the anterior compartment of the leg, such as the tibialis anterior, which are the primary dorsiflexors of the ankle.
Damage to the deep peroneal nerve leads to weakness or paralysis of these muscles, resulting in the characteristic foot drop and a high-stepping gait.
This nerve is a terminal branch of the common peroneal nerve, which is the most frequently injured nerve in the lower limb, often due to its superficial position around the neck of the fibula.

Option A: The tibial nerve controls the muscles for plantar flexion (pointing the foot down), which is the opposite action of what is affected in foot drop.
Option B: The femoral nerve innervates the anterior thigh muscles (quadriceps), which are responsible for knee extension. Its function is unrelated to the movements of the foot and ankle.
Option D: The lateral cutaneous nerve of the thigh is a purely sensory nerve; it has no motor function. Damage to it causes sensory disturbances but no muscle weakness.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Lower limb peripheral nerve function and associated clinical deficits as background academic context rather than a clinical decision trigger.
Nurses must assess for foot drop in at-risk patients, such as those with prolonged bed rest, leg casts, or recent hip/knee surgery, by checking gait and the ability to dorsiflex the foot.
Key nursing interventions for foot drop include using positioning aids like foot boards or high-top sneakers, and applying ankle-foot orthoses (AFOs) or splints to maintain the foot in a neutral position, preventing contractures.
Patient safety is a primary concern, as foot drop significantly increases the risk of tripping and falls. Nurses should implement fall precautions and educate the patient and family on safe ambulation techniques.

How to Approach the Question

First, identify the key clinical sign in the question stem: "Foot drop".
Translate this clinical sign into its underlying physiological deficit. Foot drop means an inability to perform dorsiflexion (lifting the foot and toes upward).
Recall or deduce the muscle group responsible for dorsiflexion. This is the anterior compartment of the leg.
Access your knowledge of lower limb neuroanatomy to identify the nerve that innervates the anterior compartment muscles. This is the deep peroneal nerve.
Evaluate the other options to confirm they are incorrect. The tibial nerve controls plantar flexion, the femoral nerve controls knee extension, and the lateral cutaneous nerve is sensory only. This confirms your choice.

Concept Tested & Keywords

Concept Tested: Lower limb peripheral nerve function and associated clinical deficits.
Stem keywords: Foot drop, damage, nerve
Lead-in keywords: caused by, which of the following
Negative lead-in flag: false

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E6 Anatomy BDChaurasia V2 10e Part 1 pp. 121-123, 104-106

E6 Nursing Fundamentals Potter Perry 12e Part 4 p. 132-134