A Mixed Osseous-Fibrous Talocalcaneal Coalition With a Posterior Extra-articular Bridge in a Nine-Year-Old: Resection via a Posteromedial Approach Augmented With Fat Interposition.

Tarsal coalition is a congenital condition and is an often underrecognized cause of pediatric foot pain, most frequently involving the calcaneonavicular and talocalcaneal joints, while mixed-type coalitions are exceptionally uncommon and are rarely reported. We present the case of a nine-year-old boy with progressive left foot pain and limping, unresponsive to conservative treatment. Imaging confirmed a mixed-type talocalcaneal coalition with both bony and fibrous components. Surgical management consisted of osteotomy, coalition resection, and fat interposition via a posteromedial approach, chosen for its direct access to the posterior and medial facets while minimizing tendon and neurovascular risk. Preoperatively, the patient demonstrated hindfoot valgus of 13.28°, restricted subtalar motion, and Oxford Ankle Foot Questionnaire for Children (OxAFQ-C) scores of 12.5% (physical), 56.3% (school/play), and 55% (emotional). At four weeks postoperatively, subtalar mobility had improved to increased eversion and inversion, hindfoot alignment was corrected, and the patient was scheduled for muscle strengthening, functional retraining, and dynamic weight-bearing physiotherapy. By four months, OxAFQ-C scores had risen to 83.3%, 87.5%, and 87.5%, respectively, reflecting significant functional recovery and enhanced quality of life.