In a newborn with congenital talipes equinovarus, which of the following is the most common associated structural deformity at the subtalar joint?

## Subtalar Joint Pathology in Posteromedial CTEV **Key Point:** The most common structural deformity in CTEV involves **medial rotation and inversion of the talus combined with posterior displacement of the calcaneus**, creating the characteristic "inverted, plantarflexed" foot. ### Anatomical Deformities in CTEV ```mermaid flowchart TD A["Posteromedial CTEV<br/>(95% of cases)"]:::outcome --> B["Subtalar Joint Changes"]:::outcome B --> C["Medial rotation of talus"]:::action B --> D["Inversion of talus"]:::action B --> E["Posterior displacement of calcaneus"]:::action C --> F["Results in varus deformity"]:::outcome D --> F E --> G["Results in equinus deformity"]:::outcome F --> H["Rigid foot in inverted,<br/>plantarflexed position"]:::outcome G --> H ``` ### Structural Changes at Each Joint | Joint | Deformity | Mechanism | |-------|-----------|----------| | **Subtalar (talocalcaneal)** | Medial rotation + inversion of talus; posterior calcaneal displacement | Primary pathology; creates varus | | **Talonavicular** | Medial deviation of navicular; adduction | Secondary to subtalar changes | | **Ankle (tibiotalar)** | Plantarflexion (equinus) | Posterior displacement of calcaneus | | **Midtarsal** | Supination and adduction | Follows subtalar and talonavicular changes | **High-Yield:** The **talus does not rotate laterally** — it rotates **medially**. The calcaneus does not move anteriorly — it moves **posteriorly**. These are the hallmark findings on imaging. ### Radiological Findings 1. **Anteroposterior (AP) view:** - Talus and calcaneus are parallel (loss of normal divergence). - Medial deviation of the navicular and metatarsals (adduction). 2. **Lateral view:** - Talus is plantarflexed (equinus). - Calcaneus is displaced posteriorly and is also plantarflexed. - Talocalcaneal angle is reduced (normally ~25–40°; in CTEV often <15°). **Clinical Pearl:** The **medial rotation of the talus** is the primary deformity; the other changes (inversion, posterior calcaneal displacement, adduction) are secondary consequences. This is why early treatment aims to correct the talus position first. ### Why This Matters for Treatment - **Ponseti method:** Uses serial casts to gradually abduct and dorsiflex the foot, correcting the medial rotation and posterior displacement. - **Surgical correction:** If conservative treatment fails, procedures target the subtalar joint (e.g., triple arthrodesis in older children) to realign the talus and calcaneus.