A 45-year-old male is treated at the hospital after he fell from his bicycle. Radiographic examination reveals fractures both of the tibia and the fibula. On physical examination the patient has a foot drop, but normal eversion. Which of the following nerves is most likely injured?,
**Core Concept**
The patient's symptoms suggest an injury to the nerve responsible for innervating the muscles that control foot movement, specifically dorsiflexion. This is a peroneal nerve injury, which is commonly associated with fibular fractures due to its close anatomical relationship with the fibula.
**Why the Correct Answer is Right**
The peroneal nerve, a branch of the sciatic nerve, provides motor innervation to the muscles responsible for dorsiflexion (tibialis anterior, extensor digitorum longus, and extensor hallucis longus) and eversion (peroneus longus and peroneus brevis). In this case, the patient has foot drop, indicating weakness in dorsiflexion, but normal eversion, which is consistent with a peroneal nerve injury. The peroneal nerve wraps around the neck of the fibula, making it susceptible to injury in cases of fibular fractures.
**Why Each Wrong Option is Incorrect**
* **Option A:** The tibial nerve is responsible for innervating the muscles that control plantarflexion, not dorsiflexion. Damage to the tibial nerve would result in weakness in plantarflexion, not foot drop.
* **Option B:** The common peroneal nerve is a branch of the sciatic nerve, and its injury would result in symptoms similar to those described in the patient, including foot drop and weakness in eversion.
* **Option D:** The sural nerve is a branch of the tibial nerve and is responsible for sensory innervation to the lateral side of the foot and the little toe. It is not involved in motor control of foot movement.
**Clinical Pearl / High-Yield Fact**
In cases of fibular fractures, it is essential to examine the patient for signs of peroneal nerve injury, including foot drop and weakness in eversion. Early recognition and treatment of peroneal nerve injury can significantly improve patient outcomes.
**Correct Answer: C. Common peroneal nerve.