Measurement of bone thickness from radiographs of a metacarpal bone.

The inter- and intra-observer variation for the measurement of the length, external diameter, and internal diameter of the right second metacarpal bone in X-rays of the hand have been studied in two series of 100 consecutive X-rays in old people. The observer variation for length and external diameter were negligible, but that for internal diameter was considerable. There was a consequent considerable variation in the estimate of bone thickness derived from these measurements. The pattern of intra-observer variation was similar, but of smaller magnitude. The possible reason for these findings and method of reducing the consequences of observer variation are discussed.