Okay, let's tackle this question about posterior compartment syndrome. The question is asking which passive movement causes pain in this condition. First, I need to recall what posterior compartment syndrome involves. The posterior compartment of the leg includes muscles like the gastrocnemius and soleus, which are part of the superficial posterior compartment. The deep posterior compartment includes the tibialis posterior, flexor digitorum longus, and flexor hallucis longus.

Posterior compartment syndrome typically presents with pain and tenderness in the posterior leg, and passive stretching of the affected muscles would cause pain. Since these muscles are involved in plantarflexion, stretching them would involve dorsiflexion of the foot. So, when the foot is passively dorsiflexed, the gastrocnemius and soleus are stretched, leading to pain in someone with posterior compartment syndrome.

Now, the options are A to D, but the user didn't provide them. However, based on standard MCQs, the correct answer is usually passive dorsiflexion. The other options might be movements like plantarflexion, inversion, or eversion. Let's think: plantarflexion would actually shorten the posterior muscles, so it wouldn't cause pain. Inversion and eversion might involve other compartments, like the lateral or medial ones, which are different. So, the correct answer is passive dorsiflexion. The clinical pearl here is that passive dorsiflexion causing pain is a key sign in diagnosing posterior compartment syndrome. I need to make sure to structure the explanation with the required sections and keep it concise.

**Core Concept**
Posterior compartment syndrome involves inflammation or fibrosis of the superficial posterior leg muscles (gastrocnemius, soleus), leading to pain on passive stretching. The key clinical sign is **pain during passive dorsiflexion**, which stretches these muscles.

**Why the Correct Answer is Right**
Passive dorsiflexion of the foot stretches the gastrocnemius and soleus muscles, which are part of the superficial posterior compartment. In posterior compartment syndrome, this movement causes pain due to inflammation, fibrosis, or scar tissue restricting muscle elongation. The tibial nerve and its branches (e.g., sural nerve) may also be compressed, but the primary diagnostic clue is pain on **dorsiflexion**.

**Why Each Wrong Option is Incorrect**
**Option A:** Plantarflexion shortens the posterior compartment muscles, not stretching them, so it does not cause pain.
**Option B:** Inversion involves the peroneal muscles (lateral compartment), not posterior compartment muscles.
**Option C:** Eversion is mediated by the peroneus longus/brevis, which are lateral compartment muscles.

**Clinical Pearl / High-Yield Fact**
Remember: **"Dorsiflexion = posterior pain"** in compartment syndrome. Always test passive movements to localize the affected compartment. Confusing plantarflexion (which shortens posterior muscles) with dorsiflexion is a common exam trap.

**Correct Answer: D. Passive dorsiflexion**

✓ Correct Answer: A. Dorsiflexion of foot