Reconstruction of the formative site in iliac trabecular bone in 20 normal individuals employing a kinetic model for matrix and mineral apposition

Abstract

A stereologic procedure for the reconstruction of matrix and mineralized bone growth curves at formative sites in trabecular bone is presented. Iliac crest bone biopsies obtained from twenty normal individuals after tetracycline double-labeling were investigated histomorphometrically. Corresponding values for osteoid width and apparent distance between bone markers and width of mineralized bone walls were classified using a sector plotting system. Observed structure widths were converted to three-dimensional structure thicknesses by a stereologic unfolding procedure. Osteoid thickness, calcification rate, and fractional labeling of osteoid varied characteristically with increasing wall thickness and permitted the construction of curves describing the time-dependent variations in matrix and wall thicknesses.

The mean thickness of completed walls was 61.9 ± 1.5 μm (SE), and the mean bone formation period (Sigma_f) was 145 days (124–168; 95% confidence interval.). The initial appositional rates for bone matrix (2.1 μm³/μm²/day) (1.4–2.9) and bone mineral (1.1 μm³/μm²/day) (0.4–1.9) declined gradually toward zero at the end of Sigma_f. The initial mineralization lag time was 15 days (12–24) and increased to a maximum of 27 days during the first 45% of Sigma_f. Thereafter, it decreased gradually toward zero. The height of the osteoblast nuclei gradually declined from 6.7 ± 0.5 μm at the start of bone formation to 1.2 ± 0.1 μm at the end.

The study demonstrates that it is possible to reconstruct growth curves for trabecular bone walls based on three-dimensional values for structure thicknesses using different sections for light and fluorescence microscopy and avoiding classification according to osteoblastic nuclear morphology. This more detailed description of the bone remodeling sequence is important for the planning of treatment of different metabolic bone diseases. The techniques described make it possible to assess bone mineral balance at the BMU level and may give further insight into the mechanisms by which different hormones and drugs influence bone remodeling.