Measurement of micro-hardness of the human lower cervical vertebrae in vitro

Abstract

Objective To measure and analyze the distribution and significance of the microhardness of the lower cervical vertebrae. Methods The three fresh adult cadaver C3-C7 vertebrae specimens were selected and the soft tissue was removed . Each vertebra was divided into a vertebral body area and an attachment area, and then was cut into three 3 mm-thickness slices (1 in the vertebral body area and 2 in the attachment area) by a high-precision slow saw. A total of 45 bone slices were cut from 15 vertebrae. The Vickers method was used to measure the microhardness values of cortical bone and cancellous bone in different areas of bone sections. Five effective microhardness values were selected for each region, and the average value of all effective values was used to be the hardness value of the region. Results A total of 825 effective hardness values were performed on 15 vertebrae. The hardness range of C3-C7 was (11.10-47.80)HV. The hardness of cortical bone and cancellous bone were (26.04±4.84)HV and(22.92±4.78)HV, respectively. The hardness of cortical bone and cancellous bone in the vertebral body area were (25.46±4.86)HV and (21.10±4.97)HV, respectively. The hardness of cortical bone and cancellous bone in the attachment area were (26.50±4.78)HV and (24.75±3.80)HV, respectively. The bone hardness of the cortical bone/ cancellous bone in the attachment area was higher than that of the cortical bone/ cancellous bone in the vertebral body area, and the difference was statistically significant(t=2.800, 4.978, P<0.05). The microhardness values of the lower cervical vertebrae of three cadavers in different regions were different, but the hardness values of the cortical bone and cancellous bone in the vertebral body area were significantly lower than those in the attachment area. The differences of the hardness in cancellous bone were statistically significant(tA=4.316, tB=2.364, tC=2.107, P<0.05), while in the cortical bone, only Donor B was statistically significant(t=2.498, P<0.05). The distribution of the hardness values in different regions of each vertebrae was consistent with the whole: the hardness value of the vertebral body area was lower than those of the attachment area.The differences of the cancellous bone in C3, C5, C6 and C7 were statistically significant(t=3.220, P<0.05). In the accessory area, the hardness of the superior articular process was significantly lower than those of other regions (F=8.590, P<0.05); in the vertebral body area, the hardness of the lower endplate was significantly higher than those of other regions (F=16.365, P<0.05). Conclusions This study reveals that the microhardness of bone in different regions of the lower cervical vertebrae are different.The bone hardness of the cortical bone/cancellous in the attachment area is higher than that in the vertebral body area. This distribution law is a physiological change which adapts to the stress and strain during the human daily activities. It can provide data support for the modeling of the finite element analysis, 3D printing and preoperative simulation. Key words: Cervical vertebra; Lower cervical vertebra; Vickers hardness; Microhardness; Biomechanics; Hardness tests