Influences of endplate removal and bone mineral density on the biomechanical properties of lumbar spine.

PURPOSE: To investigate (1) effects of endplate removal and bone mineral density (BMD) on biomechanical properties of lumbar vertebrae (2) whether the distributions of mechanical strength and stiffness of endplate are affected by BMD. METHODS: A total of thirty-one lumbar spines (L1-L5) collected from fresh cadavers were used in this study. Bone density was measured using lateral DEXA scans and parts of samples were performed with partial or entire endplate removal. All the specimens were divided into three BMD groups. According to endplate integrity of the lumbar vertebrae, each BMD group was then divided into three subgroups: subgroup A: intact endplate; subgroup B: central region of endplate removal; subgroup C: entire endplate removal. The axial compression test was conducted with material testing system at a speed of 2mm/min. The experimental results were statistically analyzed using SPSS 17.0. RESULTS: (1) Significant differences of biomechanical properties occurred among normal BMD, osteoporotic and serious osteoporotic group (P<0.05). (2) Spearman analysis showed that BMD was positively correlated with the failure load and stiffness of lumbar vertebrae. (3) For each BMD group, significant differences of biomechanical properties were found between subgroup A and C, and between subgroup B and C (P<0.05). (4) For each BMD group, there was no statistical difference of biomechanical properties between subgroup A and B (P>0.05). CONCLUSIONS: Entire endplate removal can significantly decrease the structural properties of lumbar vertebrae with little change in biomechanical properties by preservation of peripheral region of the endplate. BMD is positively correlated to the structural properties of the lumbar vertebrae