**Core Concept:** The common peroneal nerve is a motor and sensory nerve that arises from L4, L5, and S1 spinal nerve roots. It is responsible for the motor function of the extensor muscles of the ankle, knee flexor muscles, and sensory function in the lateral aspect of the leg and dorsum of the foot. The common peroneal nerve passes through the lateral aspect of the head of the fibula, where injury can occur.

**Why the Correct Answer is Right:** Injury to the common peroneal nerve at the lateral aspect of the head of the fibula results in the loss of function of the extensor muscles of the ankle, knee flexor muscles, and sensory function in the lateral aspect of the leg and dorsum of the foot. This is due to the nerve fibers being damaged or severed, disrupting their function.

**Why Each Wrong Option is Incorrect:**

A. Injury to the common peroneal nerve at the lateral aspect of the head of the fibula would not typically result in the loss of sensation in the sole of the foot, as this sensory function is primarily supplied by the tibial nerve.

B. While injury to the common peroneal nerve can lead to weakness in the extensor hallucis longus muscle, it would not cause the loss of flexion of the knee, which is primarily supplied by the descending branch of the lateral femoral cutaneous nerve.

C. Injury to the common peroneal nerve at the lateral aspect of the head of the fibula would not lead to the loss of sensation in the medial aspect of the foot, as this sensory function is supplied by the superficial fibular nerve.

D. While injury to the common peroneal nerve can result in loss of sensation in the lateral aspect of the leg, it would not cause the loss of ankle dorsiflexion, as this function is primarily supplied by the tibial nerve.

**Clinical Pearl:** It is essential for medical professionals to understand the distribution of sensory and motor functions of peripheral nerves to accurately diagnose and manage nerve injuries. Injuries to the common peroneal nerve can have significant functional implications for the patient, and a thorough understanding of the affected nerve's anatomy and function is necessary for appropriate treatment and rehabilitation strategies.