BIOLOGICALLY MEANINGFUL DETERMINANTS OF THE INVITRO STRENGTH OF LUMBAR VERTEBRAE

Applying unbiased stereological methods and a new stereological parameter, star volume of cancellous bone, the bone structure of the first vertebral body was examined and compared with the compressive strength of the second lumbar vertebra. The material came from eight males, aged 33-69 years (mean 49 years) and seven women, aged 22-87 years (mean 52 years) without malignant or metabolic bone disease. From these individuals, first and second lumbar vertebral body were obtained at autopsy. The heights and weights of the individuals were recorded. The following structural parameters were estimated on undecalcified, seven-mu-m, Goldner-Trichrome stained vertical sections: fractional volume of trabecular bone (BV/TV%), mean trabecular thickness (Tb.Th.l1-mu-m), trabecular star volume (V* tr mm3), marrow space star volume (V* m.space mm3), and mean thickness of the lateral cortical ring (mu-m). The compressive strength of whole vertebral body, mean cross sectional area (cm2), and ash density (g/cm3) were estimated and the data were compared to bone histomorphometric estimates. A significant decrease with age for all parameters was found except for marrow space star volume, which increased. With compressive strength as the dependent variable and all other parameters as independent variables, it was shown by standard multiple regression analysis that the in vitro tested compressive strength could be predicted from mean cortical thickness, mean cross sectional area, and marrow space star volume or ash density with a multiple, squared coefficient of regression (r2) of 0.95 when the height and sex of the individual were known. The hierarchical multiple regression analysis disclosed that besides age and sex, which had been entered at first, mean cortical thickness and trabecular star volume were of next importance with a multiple, squared coefficient of regression (r2) of 0.81 to 0.90. The present study, which includes individuals over a large age-span, suggests that mean thickness of the lateral cortical ring may be of major importance for the compressive strength of whole vertebral bodies. It has to be shown, however, if this is also the case in individuals of identical sex and in the same age span, as well as for patients with osteoporosis.