**Question:** Foot drop is due to injury of:

A. Sciatic nerve
B. Common peroneal nerve
C. Tibial nerve
D. Muscle weakness

**Core Concept:**

The core concept in this question is the anatomy and function of the major nerves supplying the lower limb muscles, specifically the ankle and foot. These nerves are responsible for providing motor innervation to the relevant muscles, allowing for normal ankle and foot movements.

**Why the Correct Answer is Right:**

Foot drop, also known as axonal neuropathy or motor neuron disorder, is characterized by weakness or paralysis of the ankle dorsiflexors and foot eversion. In this case, the correct answer is **B. Common peroneal nerve**. The common peroneal nerve is one of the major nerves that supply the lower limb muscles, specifically the muscles of the ankle and foot. It arises from the ventral ramus of the sciatic nerve and innervates the anterior compartment of the thigh, lateral compartment of the leg, and the posterior compartment of the leg and foot. Injury to the common peroneal nerve results in foot drop due to the loss of motor function in the muscles that flex the ankle and invert the foot (e.g., the fibularis tertius, extensor digitorum brevis, and flexor digitorum longus muscles).

**Why Each Wrong Option is Incorrect:**

A. Sciatic nerve (option A) is incorrect because the sciatic nerve is the largest peripheral nerve in the human body, supplying motor and sensory functions to the lower limbs. Foot drop is not a direct consequence of sciatic nerve injury.

C. Tibial nerve (option C) is incorrect because the tibial nerve is primarily responsible for innervating the muscles of the posterior compartment of the leg, which is different from the muscles responsible for ankle dorsiflexion and foot eversion.

D. Muscle weakness (option D) is incorrect because the question specifies that foot drop results from injury to a specific nerve, not generalized muscle weakness. While muscle weakness may be present in other conditions causing foot drop, the correct answer focuses on the specific nerve involved.

**Clinical Pearl:**

Understanding the role of the common peroneal nerve and its function in ankle dorsiflexion and foot eversion is crucial in clinical practice. This knowledge helps in diagnosing, treating, and managing patients with foot drop due to nerve injuries or neuropathies. Early recognition and management of foot drop can prevent complications such as contractures, deformities, and falls, ultimately improving the patient's quality of life.