A Study On The Biomechanical Distribution Regulation Of The Compressive Strength Of The Endplate And Related Factors

Objective:To study characteristics and regulation of biomechanical distribution of different sites of the lumbar endplate and comprehensively study the mechanical strength of bony endplates in corresponding region of adjacent vertebra to investigate the relationship between biomechanical characteristics and various factors of the lumbar intervertebral disc and its adjacent structures of Chinese people.Materials and methods:Twenty-seven adult fresh specimens with no history of back surgeries or trauma were selected from16males and11females. Their mean age at death was44.3±7.7years old (31-57years old). T12-S1segments were selected for MRI scanning; then, the specimens were placed in a refrigerator at-20℃for cryopreservation. They were thawed at room temperature before the experiment. There were a total of7452test points of324endplates of189vertebras. Coordinate systems were created directly for each endplate surface. It was divided into the inner, middle and outer layer using circular access of points (corresponds to the sampling position in our study—tensile test in annulus fibrosus of intervertebral disc). Applying Zwick Z2.5computer-controlled electronic universal testing machine (2KN, Zwick Roell), continuous compression loading was conducted on23test points of each endplate with a hemispherical pressure head3mm in diameter (3mm downward pressure at a speed of0.2m/s). Taking the value of the maximum compression force and its displacement values, the compression force-displacement curve was recorded using the computer. A statistical analysis was conducted on the data using SPSS18.0statistical software.Results:The lumbar endplate maximum compression force-displacements were listed as follows:in inner layer, dL was2.24±0.66(mm)(Fmax193.55±55.63(N)-Fmax); in middle layer, dL was2.25±0.62(mm)(Fmax204.48±58.21(N)-Fmax); in outer layer, dL was2.18±0.63(mm)(Fmax206.64±61.94(N)-Fmax); and in the center test point, dL was2.07±0.66(mm)(Fmax187.73±52.09(N)-Fmax). When the compression force reached its peak, there was significant difference between the age and the displacement in all three groups (P<0.05), while there was significant difference only between the age and the maximum compression force in inner layer(p<0.05). In all three group, there was significant difference between the gender and the maximum compression force (P<0.05), while there was significant difference only between gender and the displacement at that point in outer groups (p<0.05). When the compression force peaked, there was significant difference between the disc degeneration and the maximum compression force/the displacement at that point in all groups (P<0.05), as well as between the modic changes and the maximum compression force/the displacement at that point in all group (P<0.05).Conclusion:The maximum compression forces of all layers of lumbar endplates are statistically different. The maximum compression force of each layer of lumbar endplates and Modic changes in neighboring endplate are significantly correlated, being decreased layer by layer. This study can provide reference data for the biomechanical study of the integrity of people discs. However, the sample size is insufficient, remaining to be further supplemented.