"Duplicate calcaneus": a rare developmental defect observed in several skeletal dysplasias

Duplication of the calcaneus is a rarely observed radiographic finding that probably results from delayed coalescence of two primary calcaneal centers of ossification. We performed a review of 2,500 computerized cases of skel etal dysplasias and syndromes with bone involvement in the International Sk eletal Dysplasia Registry, searching for those cases in which a duplicate c alcaneus had been recorded. We found that it was a non-random feature of th ree skeletal dysplasias and groups comprising thanatophoric dysplasia and t he chondrodysplasia punctata and short rib (polydactyly) groups. We conclud e that duplication of the calcaneus should be considered a consistent featu re of these entities and may reflect a more generalized developmental defec t.