The decrease in the amount of trabecular bone which is seen with age cannot solely be explained by thinning of trabeculae but must also be due to a loss of structural trabecular bone leading to a discontinuity in the trabecular network. Due to the complex architecture and the anisotropy of bone it is difficult to demonstrate this structural change by conventional histomorphometry. Unbiased stereological estimators can however be obtained from anisotropic structures when using vertical sections and a specially designed anisotropic test system. This combined with a new and unbiased stereological parameter for bone structure the star volume can be of major importance in clarifying histological changes of bone structure. The star volume is defined as the mean volume of all the parts of an object which can be seen unobscured in all directions from a particular point with the mean value taken over all points inside the object. It is defined for any type of objects including cavities like marrow space and networks like the trabecular system. Measurements are performed using a frame and a grid with points and lines. The material investigated was the first lumbar vertebra obtained from two females and six males with ages 26 to 75 years without malignant or metabolic bone diseases. The sampling procedure was as required for vertical sections. Results did show a highly significant, five-fold increase in the star volume of the marrow space with age;​ no such age correlation was found for the star volume of the trabeculae. The only explanation for such an increase in the size of the marrow space is by removing or perforating trabecular bone.

In conclusion, the star volume is a promising estimator and may be of importance in elucidating the pathogenesis of architectural bone changes;​ it is the only parameter which gives a direct and stereologically unbiased estimate of a characteristic size of the marrow space. To confirm its superiority as a parameter for structural changes in trabecular bone, it has to be applied to larger groups including patients with osteopenia and to be compared with direct estimators of physical competence of bone.