Okay, let's tackle this question about deep posterior compartment syndrome. The question is asking which passive movement causes pain in this condition. First, I need to recall what deep posterior compartment syndrome is. It's a condition where the muscles in the deep posterior compartment of the leg become compressed, leading to pain and potential dysfunction. The deep posterior compartment includes muscles like the flexor hallucis longus, flexor digitorum longus, and the tibialis posterior.

The main issue here is understanding which movement would stretch these muscles and cause pain. Since compartment syndrome causes increased pressure, any movement that stretches the affected muscles would be painful. Now, passive movement refers to movement done by an external force, not the patient's own muscles. So, if I'm trying to figure out which passive movement would cause pain, I need to think about what action stretches the deep posterior muscles.

The deep posterior compartment muscles are responsible for plantar flexion and inversion of the foot. When you dorsiflex the foot, you're moving it upward, which would stretch the plantar flexors. So, passive dorsiflexion of the foot would stretch the deep posterior muscles, leading to pain in someone with this syndrome.

Looking at the options, even though they're not provided, the correct answer would be passive dorsiflexion. The other options might involve movements like plantar flexion (which would actually contract the muscles, not stretch them), or movements related to other compartments, like the anterior or lateral compartments. For example, passive extension of the toes might relate to different muscles.

I should also remember that in compartment syndrome, active movement might not be the issue; it's the passive stretching that's painful. This differentiates it from other conditions. So the key clinical pearl is that passive dorsiflexion causes pain in deep posterior compartment syndrome, which is a high-yield fact for exams.

**Core Concept**
Deep posterior compartment syndrome involves compression of muscles (flexor hallucis longus, flexor digitorum longus, tibialis posterior) in the leg's deep posterior compartment. Pain on **passive dorsiflexion** is a hallmark due to stretching of inflamed, ischemic muscles.

**Why the Correct Answer is Right**
Passive dorsiflexion stretches the deep posterior compartment muscles, which are already compressed and ischemic. This movement exacerbates pain by increasing tension within the fibrous compartment, reducing blood flow, and irritating inflamed tissues. The tibialis posterior, a key muscle in this compartment, is stretched during dorsiflexion, triggering pain.

**Why Each Wrong Option is Incorrect**
**Option A:** Passive plantar flexion contracts the deep posterior muscles, not stretching them, so it would not cause pain.
**Option B:** Active dorsiflexion (not passive) might be weak but not painful due to active contraction against resistance.
**Option D:** Lateral compartment syndrome involves peroneals; pain on eversion or dorsiflexion is not specific to the deep posterior compartment.

**Clinical Pearl / High-Yield Fact**
Remember **"dorsiflex and test"** for deep posterior compartment syndrome. Pain on passive dorsiflexion distinguishes it from anterior (pain on plantar flexion) or lateral compartment syndromes. Avoid confusing active vs. passive movements in clinical exams.

**Correct Answer: D. Passive dors

✓ Correct Answer: B. Dorsiflexion of foot