ESTIMATION OF VERTEBRAL BODY STRENGTH BY DUAL-PHOTON ABSORPTIOMETRY IN ELDERLY INDIVIDUALS - COMPARISON BETWEEN MEASUREMENTS OF TOTAL VERTEBRAL AND VERTEBRAL BODY BONE-MINERAL

The aim of the present study was to investigate the predictive value of bone mineral measurements by dual photon absorptiometry (DPA) in vitro for strength and ash weight of lumbar vertebral bodies in elderly, otherwise nonselected individuals. The material comprised 46 individuals: 26 males (43-95 years) and 20 females (63-95 years) without malignant diseases. Spinal segments, including L2, L3, and L4, were removed en bloc at autopsy. Bone mineral content (BMC) measurements imitating the normal DPA procedure were performed on the segments suspended in a water bath. The segments were measured in toto (BMC(T)) and remeasured after removal of the posterior elements (BMC(B)). The second lumbar vertebral body (L2) was then dissected and sawed below the endplates to obtain samples with planoparallel ends before compression in a materials testing machine. Finally, the bone specimens were incinerated for ash weight estimations. BMC(T) showed significant correlations to vertebral body ash weight (r = 0.79), compressive strength (load, r = 0.69), and stress (load per unit area, r = 0.47). The correlations were improved by removing the posterior elements (BMC(B)-ash weight, r = 0.86, BMC(B)-load, r = 0.74, BMC(B)-stress, r = 0.49). Correction of BMC for differences in vertebral body height (BMC/cm) further increased the correlation coefficients (BMC(B)/cm-ash weight, r = 0.92, BMC(B)/cm-load, r = 0.78, BMC(B)/cm-stress, r = 0.55). We conclude that lumbar BMC is predictive for lumbar vertebral body compressive strength in vitro and ash weight. The correlation coefficient is improved by removing the posterior non-weight-bearing element. Both BMC(B) and BMC(T) corrected for vertebral height give a slightly improved correlation for vertebral body compressive strength.