[Changes in form and structure of vertebrae as a manifestation of mechanical loading (author's transl)]

In 240 autopsy cases of both sexes, aged between 19 and 88 years and with no evidence of clinically manifest bone disease, the structure of the spongy bone and the external form of the 3rd and 5th lumbar vertebrae were investigated quantitatively and morphometrically on the basis of high-contrast X-ray images of 100 mu-thick polished bone sections, using the Leitz texture analysis system. The structure of the spongy bone was analysed on the basis of the parameters volumetric density, surface density and specific surface in horizontal "fifths", the form being determined by measuring the greatest and smallest heights and widths. In the individual "fifths", the structural parameters manifest a "stepped" distribution, the highest values being in the outer, the lowest values in the middle "fifths". With increasing age, this distribution pattern flattens to differing degrees so that, in old age, only the outer"fifths"differ from the middle and inner"fifths". The form parameters of the vertebrae reveal an age-independent constant heigh and an age-dependent increase in maximum width. The vertebral bodies are subjected mainly to compressive forces and represent a compound construction of spongy bone and fluid-filled medullary cells. The inhomogeneity of the vertebral structure is the constructional equivalent of the intravertebrally regionally differing mechanical forces. Also the structure of the residual spongy bone resulting from the age-dependent remodelling process, is oriented to these mechanical forces. Despite the considerable intravertebral remodelling of structure, the form of the vertebral bodies remains largely constant. The increase in maximum width is based on an increase in the tensile forces acting upon the outer edges of the vertebral bodies consequent upon degenerative intervertebral disc changes.