Congenital onychodysplasia of the index fingers.

Twenty-two fingers of 13 patients had dysplastic nails. Four types of congenital onychodysplasia of the index fingers such as anonychia, rudimentary, split rudimentary (polyonychia), and micronychia were found in five, three, eight, and six fingers, respectively. Narrowing at the distal end of the affected distal phalanx (lack of the cresent-shaped cap), and a Y-shaped bony projection were characteristic features seen on x-ray films. There were no associated ectodermal abnormalities. Syndactyly was a relatively common associated hand anomaly. Some cases of congenital onychodysplasia of the index fingers were inherited. These findings suggest that impediments to the membranous ossification center can lead to a dysplastic crescent-shaped cap with nail anomalies.