Thickness of bone formed at remodeling sites in normal human iliac trabecular bone: variations with age and sex

The thickness of the bone walls formed at completed remodeling sites was estimated by morphometry in iliac trabecular bone from 85 normal individuals (48 women and 37 men) aged 18-90 years. The mean three-dimensional (3-D) wall thickness was 59.4 +/- 5.9 micron. No sex difference was observed. The wall thickness decreased with age: Thickness (micron) = 65.56 micron - 0.14 micron/yr X age (yr). This reduction may lead to a loss of bone with increasing age. The coefficient of variation in completed wall thickness between individuals of the same age was 7%. The factors controlling the thickness are largely unknown, but it was noted that the intraindividual distributions of linear 3-D wall thickness (proportional to the mass of the wall) were symmetric, while distributions of reciprocal 3-D thickness (proportional to the conductivity for oxygen and waste products) were markedly rightskewed. A subgroup comprising 42 individuals aged 18-56 years had been double labeled with tetracycline. The average 3-D calcification rate was 0.63 +/- 0.11 micron/day. No relationship to age or sex was demonstrated. Based on the estimates of completed wall thickness and calcification rate, the mean duration of calcification at remodeling sites was calculated to be approximately 100 days.