ACR Codes: 4.1
Tarsal coalition is a congenital foot deformity caused by failure of midfoot or hindfoot segmentation in utero. Rarely, tarsal coalition can be associated with a syndrome (hereditary symphalangism, Apert’s acrocephalosyndactyly, and hand-foot-uterus syndrome). It occurs in approximately 1% of the population with a male predominance. Patients with a coalition will usually present as a young adult with foot and ankle pain. Exam findings include limited subtalar motion, pes planus, and shortening or persistent spasm of the peroneal muscles. A coalition can involve any or all of the midfoot and hindfoot joints. The coalition does not have to be osseous as fibrous and cartilaginous bridging of the joint is often the case. Severe cases of tarsal coalition can cause the ankle joint at the tibiotalar articulation to convert from a hindge joint to a ball and socket joint due to limited subtalar motion. The calcaneonavicular joint and the talocalcaneal joints are the most common joints involved. Increased motion at the talonavicular joint causes reactive change and resultant “talar beaking”. This change is more prominent in talocalcaneal coalition than calcaneonavicular coalition. The calcaneonavicular coaltion can be demonstrated radiographically, in the oblique view, as close approximation of the bones with cortical irregularity, broadening, and sclerosis. The talocalcaneal coalition is more difficult to image on plain film and best seen on CT or MRI. The talocalcaneal articulation is comprised of three joints; posterior, middle, and anterior. The coalition can involve all three, but most commonly occurs in the middle joint between the talus and sustentaculum tali.
Reference(s): Manaster BJ, Disler DG, May DA, Musculoskeletal imaging: the requisites 2nd Edition, 2002, 499-503.
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Disease Topic 4526 
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