# Tarsal Coalition > Tarsal coalition for NEET-PG Orthopaedics: calcaneonavicular and talocalcaneal bars, anteater and C-signs on radiographs, and peroneal spastic flatfoot. - Canonical URL: https://prepelephant.com/topics/neet-pg/orthopaedics/tarsal-coalition - Exam / course: NEET-PG · Subject: Orthopaedics - Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team - First published: 2026-10-14 - Last updated: 2026-10-14 - Reference basis: Campbell's Operative Orthopaedics; Apley's System of Orthopaedics and Fractures - How to cite: "Tarsal Coalition", PrepElephant, https://prepelephant.com/topics/neet-pg/orthopaedics/tarsal-coalition ## Direct answer Tarsal coalition is an abnormal fibrous, cartilaginous or bony connection between two tarsal bones that restricts subtalar motion and produces a rigid flatfoot. The calcaneonavicular and talocalcaneal forms are the most frequent types, and the talocalcaneal bar is the classic cause of peroneal spastic flatfoot. Symptoms typically begin in later childhood and adolescence, and they are first treated with immobilisation and orthoses. ## What you must remember - **Calcaneonavicular coalition:** a bar between the calcaneus and navicular, classically producing a painful flatfoot with limited subtalar motion. - **Talocalcaneal coalition:** a bar between the talus and calcaneus, usually at the middle facet, closely linked with peroneal spasm. - **Peroneal spastic flatfoot:** spasm of the peroneal muscles that makes the hindfoot rigid and painful during walking. - **Anteater sign:** on the lateral radiograph, a beak-like anterior calcaneal projection that indicates a calcaneonavicular bar. - **C-sign:** on the lateral radiograph, a C-shaped outline of the talus and calcaneus that suggests a talocalcaneal coalition. - **Presentation:** a painful, stiff flatfoot that worsens with running and activity, often noticed in adolescence. - **Confirmation:** CT with sagittal and coronal reconstructions defines the extent of the bar before surgery. ## A stepwise evaluation of a stiff flatfoot An 11-year-old boy has a painful flatfoot that worsens with running and has lost subtalar movement. The evaluation distinguishes a coalition from a flexible, postural flatfoot. 1. **Test the hindfoot:** check subtalar inversion and eversion, because loss of motion in a painful flatfoot raises suspicion of a coalition. 2. **Look for spasm:** palpate the peroneal tendons and watch whether the foot becomes rigid and painful during walking, which suggests peroneal spasm. 3. **Obtain targeted views:** oblique and lateral radiographs of the foot are taken, with a Harris heel view when the subtalar joint is in question. 4. **Read the signs:** the anteater sign on the lateral view points to a calcaneonavicular bar, while the C-sign points to a talocalcaneal coalition. 5. **Confirm with CT:** sagittal and coronal reconstructions show the exact site, thickness and extent of the bar, which is needed before any surgical planning. 6. **Choose the treatment:** immobilisation, orthoses and anti-inflammatory drugs come first, with resection and interposition for suitable bars, and arthrodesis reserved for established arthritis. ## Where the exam tries to catch you Examiners test the radiographic signs and the syndrome of spastic flatfoot. - **Trap:** calling every painful adolescent flatfoot flexible and postural. — **Correct:** a rigid flatfoot with loss of subtalar motion and peroneal spasm points to a tarsal coalition. - **Trap:** matching the anteater and C-signs to the wrong coalition. — **Correct:** the anteater sign relates to the calcaneonavicular bar and the C-sign to the talocalcaneal coalition, so each is remembered with its site. - **Trap:** operating before a trial of immobilisation and orthoses. — **Correct:** symptoms often settle with a period of immobilisation, so conservative care comes before resection. ## Frequently asked questions ### Which tarsal coalitions are the most frequent? The calcaneonavicular and talocalcaneal coalitions are the most frequent types of tarsal coalition. Calcaneonavicular coalition classically presents with a painful flatfoot, while talocalcaneal coalition is more closely linked to peroneal spasm. ### What is peroneal spastic flatfoot? Peroneal spastic flatfoot is a painful, rigid flatfoot caused by spasm of the peroneal muscles, most classically in talocalcaneal coalition. The spasm fixes the hindfoot in valgus with lateral pain, and it may improve once the underlying coalition is treated. ### What does the anteater sign indicate in tarsal coalition? The anteater sign on a lateral radiograph indicates a calcaneonavicular coalition, in which the anterior calcaneus projects like the snout of an anteater towards the navicular. Recognising it helps distinguish this bar from a talocalcaneal coalition, which shows a different sign. ### When is surgery considered for tarsal coalition? Surgery for tarsal coalition is considered when symptoms persist despite immobilisation, orthoses and anti-inflammatory treatment. Resection of a suitable bar with interposition is performed for symptomatic coalitions, while arthrodesis is reserved for established arthritis.