**Core Concept**
The question requires understanding of the anatomical course and function of the **tibial nerve**, which is a branch of the **sciatic nerve**. The tibial nerve is responsible for motor and sensory functions in the lower limb, particularly in the posterior compartment of the leg.

**Why the Correct Answer is Right**
Since the tibial nerve is severed on the posterior aspect of the tibia, the patient will likely exhibit signs of denervation of the muscles it supplies, including the **gastrocnemius** and **soleus** muscles. This would lead to weakness or paralysis of these muscles, resulting in an inability to plantarflex the foot.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the tibial nerve injury would not directly affect the dorsal flexion of the foot, which is primarily controlled by the **peroneal nerves**.
**Option B:** This option is incorrect because the tibial nerve injury would not cause paralysis of the muscles responsible for knee extension, which is primarily controlled by the **femoral nerve**.
**Option C:** This option is incorrect because the tibial nerve injury would not directly affect the sensation on the anterior aspect of the leg, which is primarily supplied by the **saphenous nerve**.

**Why Each Wrong Option is Incorrect (Continued)**
**Option D:** This option might seem plausible but considering the specific injury to the tibial nerve, the most direct and significant impact would be on the motor functions it controls.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that the tibial nerve controls the muscles responsible for plantarflexion of the foot. An injury to this nerve can result in **foot drop**, where the patient is unable to plantarflex the foot, leading to a characteristic gait abnormality.

**Correct Answer:** D. Foot drop