Okay, let's tackle this question. The patient has a sudden onset of intense pain in the left calf and ankle after a tennis injury. He heard a snap, fell, and can't walk. On exam, there's tenderness, induration, and an irregular mass in the mid-calf. The question is asking about the type of abnormal ankle movement present.

First, I need to figure out what the injury is. The classic presentation here is a posterior tibial tendon tear. The posterior tibial tendon is crucial for inversion and plantarflexion. When it tears, you lose the ability to invert the foot and plantarflex the ankle. So the abnormal movement would be excessive eversion because the antagonist muscle (peroneals) isn't being opposed.

The options aren't given, but common ones in such questions usually include inversion, eversion, dorsiflexion, or plantarflexion. The key is knowing that posterior tibial tendon rupture leads to loss of inversion, so the foot would evert more than normal because the peroneals aren't balanced by the posterior tibialis.

Now, checking other possibilities: Achilles tendon rupture would present with loss of plantarflexion, not inversion. Anterior tibialis issues affect dorsiflexion. Peroneal nerve injury affects eversion, but the question is about the tear causing the opposite. So the correct answer is eversion.

**Core Concept**
This question assesses knowledge of musculoskeletal anatomy and biomechanics, specifically the role of posterior tibial tendon in ankle and foot movement. The posterior tibial tendon is the primary inverter of the foot and stabilizer of the medial longitudinal arch. Its injury leads to loss of inversion control and dynamic arch support.

**Why the Correct Answer is Right**
A posterior tibial tendon rupture would result in **excessive eversion** of the ankle. The posterior tibialis muscle acts synergistically with the flexor hallucis longus to invert the foot. When this tendon is torn, the peroneus longus and brevis (which evert the foot) become unopposed, leading to a "too many toes sign" and eversion. The palpable mass in the mid-calf is likely a retracted tendon or hematoma from the acute tear.

**Why Each Wrong Option is Incorrect**
**Option A:** *Excessive dorsiflexion* is incorrect because the anterior tibialis, not posterior tibialis, primarily dorsiflexes the ankle.
**Option B:** *Excessive plantarflexion* is incorrect—plantarflexion is driven by the gastrocnemius and soleus, not the posterior tibialis.
**Option C:** *Excessive inversion* is incorrect—the posterior tibialis is the *primary* inverter; its rupture would cause weakness in inversion, not excess.

**Clinical Pearl / High-Yield Fact**
Posterior tibial tendon dysfunction (PTTD) is a common cause of adult-acquired flatfoot. Acute rupture often occurs in middle-aged athletes due to sudden inversion trauma. A key physical exam finding is the inability to perform single-limb heel raises (positive "too many toes sign" when the foot everts excessively).

**Correct Answer: C. Excessive eversion**

✓ Correct Answer: B. Dorsiflexion