The metacarpal index of infants.

Some infants appear to have long fingers, and since arachnodactyly is a feature of Marfan's syndrome, it is important to know whether a baby's long fingers are outside the normal range. In 1960, Sinclair, Kitchin, and Turner observed that arachnodactyly in Marfan's syndrome was related to the length and breadth of the metacarpal bones and showed that the metacarpal index was a useful criterion of arachnodactyly. The index is calculated by measuring the 2nd, 3rd, 4th, and 5th metacarpals. The sum of the lengths is divided by the sum of the breadths, as measured at the midpoint of each metacarpal. Sinclair's measurements were carried out mainly on adults, and it is not known if they are relevant to babies, or to children before the appearance of secondary ossification centres in the metacarpals. The aim of this study was to obtain values for the metacarpal index of children aged 2 years and under, and to compare the normal values with the indices of some infants who were thought to have long or short fingers.