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 o f bone mineral measurements by dual photon absorptiometry (DPA) in vit ro for strength and ash weight of lumbar vertebral bodies in elderly, otherwise nonselected individuals. The material comprised 46 individua ls: 26 males (43-95 years) and 20 females (63-95 years) without malign ant 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 remeasure d after removal of the posterior elements (BMC(B)). The second lumbar vertebral body (L2) was then dissected and sawed below the endplates t o obtain samples with planoparallel ends before compression in a mater ials testing machine. Finally, the bone specimens were incinerated for ash weight estimations. BMC(T) showed significant correlations to ver tebral body ash weight (r = 0.79), compressive strength (load, r = 0.6 9), and stress (load per unit area, r = 0.47). The correlations were i mproved by removing the posterior elements (BMC(B)-ash weight, r = 0.8 6, 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 th e 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 B MC is predictive for lumbar vertebral body compressive strength in vit ro and ash weight. The correlation coefficient is improved by removing the posterior non-weight-bearing element. Both BMC(B) and BMC(T) corr ected for vertebral height give a slightly improved correlation for ve rtebral body compressive strength.