Which nerve injury produces dorsiflexion weakness with sensory loss between the first and second toes?

• A. Plantarflexion by gastrocnemius-soleus
• B. Inversion of the foot
• C. Loss of sensation between the first and second toes and dorsiflexion weakness
• D. Knee extension

Answer: (C)

Dorsiflexion is driven by the anterior compartment muscles of the leg, especially the tibialis anterior, along with extensor digitorum longus and extensor hallucis longus. These muscles receive their motor innervation from the deep peroneal (deep fibular) nerve. Sensation in the web space between the first and second toes is also supplied by the deep peroneal nerve.

So when weakness of dorsiflexion occurs together with sensory loss specifically between the first and second toes, this pattern localizes to injury of the deep peroneal nerve. It’s a classic sign of deep peroneal nerve involvement, which can occur with trauma to the lower leg or at the fibular neck where the nerve branches.

In contrast, problems with plantarflexion point to the tibial nerve, inversion weakness points to tibialis posterior and tibial nerve, and knee extension weakness points to the femoral nerve, none of which explain the combined dorsiflexion weakness and the precise sensory loss in that toe web space.