In Vivo Three-dimensional Transient Motion Characteristics Of The Subaxial Cervical Spine In Healthy Adults

Objective: To observe the in vivo three-dimensional kinematics of the subaxial cervical spine in healthy human beings and compare the difference among different levels.Methods: Seventeen asymptomatic subjects with a mean age of 25.8 years were recruited for this study, A written consent was obtained from each subject prior to the study. The model-based Two-Dimensional to Three-Dimensional registration methods were used in our study. The vertebral segment motion of each subject was reconstructed with three-dimensional computed tomography and solid modeling software Rhinoceros. In vivo cervical vertebral motion during functional postures(flexion-extension, left-right bending, left-right twisting) was observed with dual fluoroscopic imaging. Coordinate systems were established at the vertebral center of C3-C7 to obtain the intervertebral range of motion(ROM) and translations at C3-4, C4-5, C5-6 and C6-7.Results: During the flexion-extension motion: the translations along frontal, sagittal, and vertical axis were 1.7±1.2mm,4.4±1.0mm and 0.6±0.4mm respectively at C3-4,the corresponding rotations along the three axises were 13.2±2.7°,3.6±2.4°,and 3.7±1.8°; the translations along frontal, sagittal, and vertical axis were 1.4±0.9mm,4.9±1.0mm and 0.6±0.3mm respectively at C4-5,the corresponding rotations along the three axises were 17.8±3.9°,2.8±1.9°,and 4.2±2.3°; the translations along frontal, sagittal, and vertical axis were 1.2±0.9mm,4.7±0.9mm and 0.7±0.5mm respectively at C5-6,the corresponding rotations along the three axises were 18.0±2.3°,3.2±1.8°,and 2.8±1.9°; the translations along frontal, sagittal, and vertical axis were 1.5 ± 0.9mm,2.0 ± 0.9mm and 0.6 ± 0.3mm respectively at C6-7,the corresponding rotations along the three axises were 9.9±3.7°,2.8±1.5°,and 2.5±1.7°.The displacement in sagittal axis of C6-7 was significantly less that of other segments(P<0.05), but the displacements in frontal axis and in vertical axis showed no significant difference between segments(P>0.05);the ROM values in frontal axis of C4-5 and C5-6 were significantly larger than those of C3-4 and C6-7(P<0.05), and the ROM value in vertical axis of C4-5 was significantly larger than those of C5-6 and C6-7(P<0.05), but the ROM value in sagittal axis showed no significant difference between segments(P>0.05).During the left-right bending motion: the translations along frontal, sagittal, and vertical axis were 1.6 ± 0.9mm,1.0 ± 0.5mm and 1.0 ± 0.6mm respectively at C3-4,the corresponding rotations along the three axises were 3.8±2.2°,9.2±4.0°,and 9.8±5.1°; the translations along frontal, sagittal, and vertical axis were 1.3±0.7mm,0.7±0.4mm and 1.0±0.5mm respectively at C4-5,the corresponding rotations along the three axises were 2.9±1.6°,8.5±4.0°,and 6.2±2.4°; the translations along frontal, sagittal, and vertical axis were 1.5±0.6mm,0.9±0.5mm and 0.8±0.4mm respectively at C5-6,the corresponding rotations along the three axises were 2.9±2.0°,9.6±4.1°,and 5.2±3.2°; the translations along frontal, sagittal, and vertical axis were 1.8 ± 0.8mm,0.8 ± 0.4mm and 0.6 ± 0.2mm respectively at C6-7,the corresponding rotations along the three axises were 2.3±1.0°,10.3±3.9°,and 5.2±2.8°. There were no significant difference in the displacement between other segments(P>0.05) except that the displacement in sagittal axis of C3-4 was significantly larger than that of C4-5(P<0.05), and that the displacement in vertical axis of C6-7 was significantly less than that of C3-4 and C4-5(P<0.05); no significant difference was shown in the ROM value between segments(P>0.05), except that the ROM value in vertical of C3-4 was significantly larger than that of C5-6 and C6-7(P<0.05).During the left-right twisting motion: the translations along frontal, sagittal, and vertical axis were 1.5±0.8mm,1.7±1.0mm and 0.8±0.4mm respectively at C3-4,the corresponding rotations along the three axises were 5.2±3.7°,5.9±2.9°,and 8.5±4.7°; the translations along frontal, sagittal, and vertical axis were 1.4 ± 0.8mm,1.7 ± 0.8mm and 0.9 ± 0.4mm respectively at C4-5,the corresponding rotations along the three axises were 4.7±2.9°,6.6±3.1°,and 4.6±2.2°; the translations along frontal, sagittal, and vertical axis were 1.4±0.8mm,1.7±0.9mm and 1.1±0.5mm respectively at C5-6,the corresponding rotations along the three axises were 4.6±2.6°,6.1±3.4°,and 7.0±3.7°; the translations along frontal, sagittal, and vertical axis were 1.0±0.6mm,1.8±0.9mm and 1.2±0.6mm respectively at C6-7,the corresponding rotations along the three axises were 3.8±2.3 °,6.1 ± 3.6 °,and 4.1 ± 2.3 °. The ROM value in vertical of C3-4 was significantly larger than that of C4-5 and C6-7(P<0.05), and the displacement and ROM value showed no significant differece between other segments(P>0.05).Conclusion: We used model-based Two-Dimensional to Three-Dimensional registration method to reproduce the subaxial cervical spine in vivo three-dimensional motion in healthy adults and found that the intervertebral motions of the cervical spine have different characters at different levels. And we obtained the six-degree-of-freedom data of the cervical vertebrae, these data may provide us with some new information about the in vivo kinematics of the cervical spine and to be the reference information for the development and application of the cervical prosthesis.