DIFFERENTIAL-EFFECTS OF BONE-MINERAL CONTENT AND BONE AREA ON VERTEBRAL STRENGTH IN A SWINE MODEL

Since the biomechanical competence of a vertebral body may be closely related to the content and distribution of the bone mineral, we have e valuated the effects of projected vertebral bone area (BA) and bone mi neral parameters [bone mineral content (BMC) or bone mineral density ( BMD)] on their biomechanical competence. We used dual-energy X-ray abs orptiometry (DXA) to assess the bone mineral parameters of 36 swine th oracic vertebrae (T1-T12) and 15 lumbar vertebrae (L1-L5) after remova l of the posterior elements. The failure load, compressive stress, and the stored strain energy of these vertebral bodies were assessed by a uniaxial compressive test using an MTS 810 testing system. Multiple r egression analysis showed a significantly negative effect of BA and si gnificantly positive effect or BMC on the biomechanical competence (co mpressive stress, r(2) = 0.67, P < 0.0001; failure load, r(2) = 0.75, P < 0,0001). However, the stored strain energy was only related to the BMC (r(2) = 0.35, P < 0.0001). The contributory effects of BMC and BA on the biomechanical competence were not equal. The effects of BMC wa s larger than BA in determining the failure load and stored strain ene rgy, whereas the reverse was found for the compressive stress. Using t he log-transformed parameters as the regressors resulted in similar re sults. These results suggested the differential effects of BA and BMC in determining the biomechanical competence of vertebral bodies. We re commend the use of both parameters instead of BMD alone for evaluation of the vertebral biomechanical competence.