A Study On The Biomechanical Property Of Lumbar Endplate And Its Relationship With Bone Mineral Density

ObjectiveTo provide experimental basis for the placement of interbody fusion cage, improvement of its design, and related operative procedure by studying the biomechanical distribution and histological structure of lumbar endplate, and the effect of bone mineral density on the failure load of lumbar endplate.MethodThirteen fresh human lumbar spines (L1–L5) obtained from human cadaver with a mean age of 60.5 years (range:30–70) were used in the study. The 65 vertebrae were evaluated with dual energy radiograph absorptiometry. According to the diagnosis standard of osteoporosis, all the vertebrae were divided into 3 groups: normal group (n=35); osteoporotic group (n=16); and serious osteoporotic group (n=14). The specimens were reserved in the refrigerator at minus 20 degrees Celsius and thawed before the experiment. The coordinate system was created directly on the surface of the lumbar endplate, and the indentation tests were conducted using a material testing system (858 mini bionixII, Madison, WI) and a 1.5-mm diameter indenter. The failure load at each site was determined by the load-displacement curve and was defined as the maximum load reaching before a load decrease of greater than 5%. The data were analyzed by SPSS 13.0 software. One-way analysis of variance (α=0.05) was used to study the relationship between the failure load and BMD. Spearman correlation assay was also used to investigate the correlation between them. The factorial analysis of variance was adopted to compare the failure loads of horizontal lines and vertical lines across the lumbar endplates in the 3 groups, respectively. Multiple comparison between the failure loads of the horizontal lines and vertical lines was performed using Student-Newman-Keuls(SNK) test and the significance level was set at 0.05. The effect of bone mineral density on the biomechanical distribution of lumbar endplate in the three groups was also analyzed. Sections of 2-mm thickness were incised from the central regions and peripheral regions of vertebral endplates from 20 cadaver lumbar vertebrae. The sections were fixed in 1% formalin, decalcified, embedded in paraffin, and stained with HE. After the above steps, the sections were observed under 10 times light microscope, and the areas of all the pore structures measured by software INSTUDIO 1.00 were compared by Satterthwaite test with the level of significance set at 0.05. ResultThe peripheral region of lumbar endplate was stronger than the central region(P<0.05). The strongest position of the lumbar endplate was the posterolateral region closest to the pedicles and the failure loads tended to increase from anterior to posterior regions of the lumbar endplates. BMD was positively correlated with the failure load of the lumbar endplate(rs=0.782,P<0.01). The failure load distribution did not change with the BMD decrease. The areas of pore structure in the central region of lumbar endplate were significantly larger than those in the peripheral region (P<0.05).ConclusionIt is necessary that BMD should be measured before operation and implants should be placed in posterior-lateral regions of lumbar endplates so that subsidence syndrome can be reduced as much as possible.The central regions of lumbar endplates were porous, as the fused trabeculae and peripheral regions had fewer and smaller pore structures. The differences in the anatomic structures of different regions are the histologic foundation of biomechanical properties of lumbar endplates.