The normal metacarpal index.

Normal values for the metacarpal index (MCI) in British children and adults have been determined. In infancy before the appearance of the metacarpal epiphyses the index is constant up to about two years of age (5.2 in males and 5.5 in females). During childhood the index rises to reach a peak at about 16 years, and then falls slightly during adult life. The curves produced are almost identical to those previously found in black children, and one set of values may be used for children of either ethnic origin. The left hand should be used to calculate the MCI, and the results expressed as either below the mean for age, or in terms of percentile for age above the mean. Curves are presented showing percentile values. No attempt should be made to produce a clear distinction between normal and abnormal indices, but the percentile value used in conjunction with other clinical findings in the assessment of Marfan's syndrome and other skeletal conditions associated with arachnodactyly.