Among the following, the structure that passes deep to the flexor retinaculum is?
**Core Concept**
The flexor retinaculum of the ankle is a fibrous band that forms the roof of the tarsal tunnel, which contains several important neurovascular structures. The correct answer requires knowledge of the anatomy of the tarsal tunnel and the structures that pass through it.
**Why the Correct Answer is Right**
The tibial nerve and the posterior tibial artery are the two most significant structures that pass deep to the flexor retinaculum. The tibial nerve is a branch of the sciatic nerve and is responsible for innervating the muscles of the posterior compartment of the leg. The posterior tibial artery is a major artery that supplies blood to the foot and is a continuation of the popliteal artery. Both of these structures are contained within the tarsal tunnel and are subject to compression by the flexor retinaculum.
**Why Each Wrong Option is Incorrect**
* **Option A:** The flexor hallucis longus tendon does not pass deep to the flexor retinaculum; it passes through the inferior tibiofibular joint.
* **Option B:** The posterior tibial vein does not pass deep to the flexor retinaculum; it is located superficial to the flexor retinaculum.
* **Option D:** The flexor digitorum longus tendon does not pass deep to the flexor retinaculum; it passes through the tarsal tunnel but is located superficial to the tibial nerve and artery.
**Clinical Pearl / High-Yield Fact**
The tarsal tunnel syndrome is a condition that occurs when the flexor retinaculum compresses the tibial nerve and/or the posterior tibial artery, leading to pain, numbness, and weakness in the foot and toes.
**Correct Answer:** C. The posterior tibial artery and tibial nerve.