The microscopic age changes that occur in human cortical bone were measured by counting the number of osteones, osteon fragments and non-Haversian canals, and estimating the percentage of lamellar bone in four selected 100 power fields in the outer third of the cortex in ground sections from the mid-shaft of the femur, tibia and fibula. Age graphs were derived from 126 specimens covering the age range from birth through 95 years. The best correlation with age by regression analysis was found in the osteon fragment number in the fibula (ρ = 9.74). The use of the regression formula for this factor permits the age to be estimated within ± ten years of the actual age 95% of the time.

An alternative method utilizes a specially devised profile chart to estimate age from the age change graphs. When this method was checked on 56 additional specimens, 87.3% of the estimates were within ± five years of the actual age, and all estimates were within ± ten years.

It was concluded that there are measurable microscopic age changes in the cortex of the major long bones of the leg that can be used to estimate the age of an individual with known accuracy over the entire range from birth to 95 years. This method can be applied to fragmented and incomplete skeletons as well as eroded archeologic skeletons, since only the mid-shafts of leg bones are used.