A girl presented with foot injury and gave history of forceful eversion of foot. Which of the following structure is affected the most?

Explanation

## Correct Answer: D. Deltoid ligament Forceful eversion of the foot is the key mechanism here. Eversion is the movement that turns the sole of the foot outward (laterally), which is the opposite of inversion. When eversion is forceful, the medial structures of the ankle are stretched and stressed. The **deltoid ligament** (also called the medial collateral ligament) is the primary medial stabilizer of the ankle joint. It comprises four components: tibionavicular, tibiocalcaneal, anterior tibiotalar, and posterior tibiotalar fibers. During forceful eversion, the deltoid ligament is maximally stretched and bears the brunt of the injury, making it the most commonly affected structure. This is in contrast to inversion injuries, which damage the lateral ligaments. The deltoid ligament is stronger and thicker than the lateral ligaments, but when eversion forces are applied, it is the structure directly opposing that movement. In Indian orthopedic practice, eversion ankle sprains are less common than inversion sprains, but when they occur, they typically involve deltoid ligament injury and may be associated with syndesmotic involvement or medial malleolus fractures. ## Why the other options are wrong **A. Calcaneofibular ligament** — The calcaneofibular ligament is a lateral ankle ligament that is primarily stressed during **inversion** injuries, not eversion. During eversion, this lateral structure is actually relaxed and protected. This is a classic NBE trap—students confuse ankle ligament injuries with the direction of foot movement, selecting lateral ligaments for eversion injuries. **B. Anterior talofibular ligament** — The anterior talofibular ligament (ATFL) is the most commonly injured ligament in ankle sprains, but these are **inversion** injuries. ATFL is lateral and is damaged when the foot turns inward. In eversion injuries, ATFL is not stressed; instead, medial structures bear the load. This option exploits the high frequency of ATFL injuries in general ankle trauma. **C. Posterior talofibular ligament** — The posterior talofibular ligament is another lateral ankle ligament that is injured in inversion mechanisms, particularly in severe or rotational inversion injuries. It is not the primary structure affected in eversion. Selecting this reflects confusion between the direction of foot movement and the anatomy of ankle ligament injuries. ## High-Yield Facts - **Eversion injury** → **deltoid ligament** (medial); **inversion injury** → lateral ligaments (ATFL, CFL, PTFL). - **Deltoid ligament** has four components: tibionavicular, tibiocalcaneal, anterior tibiotalar, and posterior tibiotalar fibers. - **Eversion ankle sprains** are less common than inversion sprains in Indian clinical practice but carry higher risk of syndesmotic injury and medial malleolus fracture. - **ATFL** is the most frequently injured ankle ligament overall, but only in **inversion** mechanisms, not eversion. - **Deltoid ligament injury** may present with medial ankle swelling, pain on eversion stress test, and positive anterior drawer sign if syndesmosis is involved. ## Mnemonics **EVERSION = MEDIAL (Deltoid); INVERSION = LATERAL (ATFL/CFL/PTFL)** Eversion (sole turns OUT) → medial ligament (Deltoid) is stretched. Inversion (sole turns IN) → lateral ligaments are stretched. Think: the ligament on the side being stretched gets injured. **Deltoid = 4 Fibers (T-T-A-P)** Tibionavicular, Tibiocalcaneal, Anterior tibiotalar, Posterior tibiotalar. Use when describing deltoid anatomy in exams. ## NBE Trap NBE exploits the high frequency of inversion ankle injuries (ATFL damage) by placing lateral ligament options prominently. Students who memorize "ATFL is the most common ankle ligament injury" without understanding the mechanism (inversion vs. eversion) will select options A, B, or C reflexively. ## Clinical Pearl In Indian emergency departments, eversion ankle injuries are often missed because they are less common and may be initially attributed to "simple ankle sprain." However, they carry a higher risk of associated syndesmotic injury and medial malleolus fracture, requiring careful imaging (stress radiographs or MRI) and longer rehabilitation. Always ask about the direction of foot movement during injury. _Reference: Bailey & Love's Short Practice of Surgery (Ankle Ligament Injuries); Robbins Pathologic Basis of Disease (Musculoskeletal Trauma)_