Humeral cortical thickness as an index of osteoporosis in women

The combined cortical thickness (C.C.T.) of the left lower humerus has been measured in 254 unselected Caucasian women. The measurement is a simple one to make and the inter-observer error is small. The mean C.C.T. of various age groups has been calculated. This rises successively with decades 20–29 and 30–39 and steadily falls after the age of 50. A lower limit of normal in the 62 individuals between the ages 20 and 39 has been established. In 95 per cent of this age group the C.C.T. falls between 7·5 and 10 mm which we take to be the “normal range”. The narrowness of this range compares favourably with many other physiological measurements and should be useful in clinical work. We believe that bone loss not exceeding 25 per cent can be picked up by this method and in a given individual with serial radiographs taken over a period of time bone loss of less than 10 per cent should be observable.