Brachymesophalangia-V in five samples of children: a descriptive and methodological study.

The occurrence of brachmesophalangia-V (BMP-V) in 2,012 individuals from five samples of children of different ethnic backgrounds was determined using two indices. Frequencies of BMP-V were analyzed for three variants: BMP-V alone, BMP-V with clinodactyly, and BMP-V with a cone-shaped epiphysis. The two indices used to identify BMP-V indicated highest relative frequencies among Mexican children, moderate frequencies among children of European ancestry (Pennsylvania White, Canadian, West German), and lower frequencies in Pennsylvania Black children. Index 1, based on the ratio of the width to the length of the fifth mid-phalanx, consistently produced higher frequencies than Index 2, based on the ratio of the length of the fifth to the length of the fourth mid-phalanges. Index 1 was also more selective of BMP-alone, while Index 2 selected primarily BMP-V with clinodactyly and/or cone-shaped epiphyses. The differences between indices were largely due to the fact that Index 1, which basically defines shape, selected both the shortest and/or widest mid-phalanges, while Index 2 related actual length differences. It is suggested that Index 2 provided a more suitable criterion of BMP-V in comparative studies, due to possible population differences in phalangeal shape.