The authors examined 47 female patients, age 50 - 60 years, with primary and secondary osteope- nia and osteoporosis. In each patients they assessed the bone mineral density (BMD) of the cortical and trabecular bone of vertebrae Th12 to L5 by quantitative computer tonmography (QTC). They did not include in the group patients with deformities of the vertebrae grade one, two and three. These deformities were assessed from a lateral X-ray of the thoracic and lumbar spine. Objective: To evaluate the importance of assessed BMD values of vertebrae from the biomechani- cal aspect. Statistical analysis: Individual groups of assessment of BMD in cortical and trabecular bone for each vertebra were characterized by means of 95 % confidence intervals and their means or median values. Results: The BMD of cortical bone increases from Th12 to L5 almost in a linear fashion. BMD of the trabecular bone declines from Th12 to L3,in L4 abd L5 it rises again.The lowest values were recorded in L3. The greatest decline of BMD of the trabecular bone by 24.05 % in L3 as compared with reference values of the given age groups were not conditioned by deformities of the verteb- rae. The BMD of cortical bone in osteopenic and osteoporotic patients practcally did not differ from reference values for the given age group. Conclusion: From the presented work ensues that deformities of the vertebrae do not occur as long as the BMD of cortical bone is within the range of reference values despite a decline of BMD in trabecular bone. It is thus more important to investigate the material qualities of cortical bone because the risk of fractures of the vertebrae depends on the elasticity and firmness. Critical BMD values of cortical bone assessed by QCT for the development of fractures are not known so far. QTC of vertebrae due to its higher radiation load and financial costs is not a routine densito- metric method. It will be necessary to develop new densitometric methods which will make it possible to assess BMD or another property of cortical bone and assess critical values for the development of vertebral fractures.

        Key words: Osteoporosis - Densitometry - QCT (quantitative computer tomography ) - Biomecha-