Experimental Study Of Biomechanical Property Of Cervical Endplate Structure

Objectives1. To study the distribution of biomechanics property of the cervical endplates;2. To study the distribution of biomechanics property in the cervical endplate between the endplate-intact and endplate-removal groups;3. To study the effect of bone mineral density (BMD) on the structural property distributions of cervical endplate;4. To study the effect of disc degeneration (DD) on the structural property distributions in the cervical endplates.Materials and methods12 fresh cervical vertebrae were harvested (11 with C2-Cy and 1 with C3-C7), 8 donors were male and 4 were female. BMD of vertebral body was measured in an AP view using dual energy X-ray absorptiometry (DEXA). The specimens were divided into isolated vertebrae by sectioning the discs through the center. The endplates were cleaned using a scalpel to remove the disc and cartilage tissue, leaving the bony endplate exposed. The specimens were divided into halves and then were mounted in Polymethylmethacrylate (PMMA).According to the objectives above, the specimens were treated as 4 groups:1. 9 cervical vertebrae (50 cervical vertebral bodies) were used to study the distribution of biomechanics property of the cervical endplates;2. 7 cervical vertebrae (42 cervical vertebral bodies) with no BMD difference were selected to study the distribution of biomechanics property in the cervical endplate between the endplate- intact and endplate-removal5groups. These specimens were divided into two groups in random (endplate-intact group=24 vertebral bodies), endplate-removal group=18 vertebral bodies). Bony endplates in the endplate-removal group were abraded to the trabecular using the desk-top type dental engine.3. 9 cervical vertebrae (50 cervical vertebral bodies) were used to study the effect of BMD on the structural property distributions of cervical endplate. According to the BMD, all vertebrae were divided into 3 groups using the k-means method: high BMD group (n=16); middle BMD group (n=24) and low BMD group (n=10);4. 9 cervical vertebrae (50 cervical vertebral bodies) were used to study the effect of disc degeneration on the structural property distributions in the cervical endplates. Grade of disc degeneration was determined using Nachemson's grading scale on 50 cervical vertebrae. According this, all vertebrae were divided into 4 groups: Normal group (n=22), disc degeneration group (DD group) I (n=10), DD group II (n=9), DD group III (n=9).The indentation tests were conducted using a material test system (MTS, model: 858 Mini Bionix, USA). The tests were performed using a 2mm-diameter, hemispherical indenter with a rate of 0.03mm/s to a depth of 2mm. The load through the indenter and displacement of the indenter were recorded at 10 Hz. 20 indentation tests were conducted on each endplate. The location of these test sites were based on a specific coordinate system.The failure load and stiffness at each test site were determined using the load-displacement curves. SPSS was used to analyze the result data:1. Factorial analyses were used to analyze the distribution of the failure load and stiffness across the endplate surface, respectively. AP and LAT test site coordinates served as first two factors. To study the effect of spinal level, level was used as the third factor to compare the distributions of endplates among the difference levels. To study the effect of endplate surface, the cervical endplates (superior vs. inferior) was used as the third factor to compare the distributions of the superior and inferior cervical endplates. AndSNK tests were used to analyze the differences of failure load and stiffness among the AP, LAT coordinates, and levels respectively.2. Independent-Samples T Test was used to analyze the difference between the endplate-intact and endplate-removal groups. Factorial analyses were used to analyze respectively the distribution of the failure load and stiffness across the endplate surface in either endplate-intac...