Which nerve is responsible for innervation of the tibialis anterior muscle, and at what level does it branch from the common fibular nerve?

Explanation

## Deep Fibular Nerve and Tibialis Anterior Innervation **Key Point:** The deep fibular (deep peroneal) nerve is the motor nerve to tibialis anterior. It branches from the common fibular nerve after the common fibular nerve pierces the fibularis longus muscle in the proximal leg, typically 1–2 cm below the fibular head. **High-Yield:** The deep fibular nerve then passes through the anterior compartment of the leg, supplying: - Tibialis anterior (foot dorsiflexion) - Extensor hallucis longus (great toe extension) - Extensor digitorum longus (toe extension) - Fibularis tertius (foot eversion, dorsiflexion) **Mnemonic:** **TEFL** = Tibialis anterior, Extensor hallucis longus, Extensor digitorum longus, Fibularis tertius — all supplied by the deep fibular nerve. ## Common Fibular Nerve Divisions ```mermaid flowchart TD A[Common Fibular Nerve<br/>at fibular head]:::outcome --> B[Pierces fibularis longus<br/>1-2 cm below fibular head]:::action B --> C{Division into branches}:::decision C -->|Superficial branch| D[Fibularis longus & brevis<br/>Lateral leg sensation]:::outcome C -->|Deep branch| E[Anterior compartment muscles<br/>Dorsum of foot sensation]:::outcome E --> F[Tibialis anterior<br/>Extensor hallucis longus<br/>Extensor digitorum longus<br/>Fibularis tertius]:::action ``` **Clinical Pearl:** Compression of the common fibular nerve at the fibular head (e.g., from tight casts, prolonged squatting, or crossing legs) causes **foot drop** — inability to dorsiflex the foot due to tibialis anterior paralysis. This is the most common lower limb nerve compression injury. ## Differential: Superficial vs Deep Fibular Nerve | Feature | Deep Fibular | Superficial Fibular | | --- | --- | --- | | **Motor supply** | Anterior compartment (dorsiflexors) | Lateral compartment (evertors) | | **Key muscle** | Tibialis anterior | Fibularis longus & brevis | | **Sensory** | Dorsum of foot (first web space) | Lateral leg & dorsum of foot | | **Injury sign** | Foot drop | Inversion weakness | **Warning:** Do NOT confuse deep fibular nerve with the superficial fibular nerve — they have opposite motor functions (dorsiflexion vs eversion).