[IN VIVO THREE-DIMENSIONAL TRANSIENT MOTION CHARACTERISTICS OF THE SUBAXIAL CERVICAL SPINE IN HEALTHY ADULTS].

OBJECTIVE: To observe the in vivo three-dimensional (3-D) transient motion characteristics of the subaxial cervical spine in healthy adults.

METHODS: Seventeen healthy volunteers without cervical spine related diseases were recruited for this study, including 8 males and 9 females with a mean age of 26 years (range, 23-41 years). The vertebral segment motion of each subject was reconstructed with CT, and Rhinoceros 4.0 solid modeling software were used for 3-D reconstruction model of the subaxial cervical spine. In vivo cervical vertebral motion in flexion-extension, left and right bending, left and right rotation was observed with dual fluoroscopic imaging system (DFIS). Coordinate systems were established at the vertebral center of C₃-₇ to obtain the intervertebral range of motion (ROM) and displacement at C₃,₄, C₄,₅, C₅,₆, and C₆,₇. The X-axis pointed to the left along the coronal plane, the Y-axis pointed to the back along the sagittal plane, and the Z-axis perpendicular to the X-Y plane pointed to the head. The ROM along X, Y, and Z axises were represented by rotation in flexion-extension (α), in left-right bending (β), and in left-right twisting (y) respectively, and the displacement in left-right direction (x), in anterior-posterior direction (y), and in proximal-distal direction (z), respectively.

RESULTS: In flexion and extension, the displacement in anterior-posterior direction of C₆,₇ was significantly less that of other segments (P < 0.05), but the displacements in left-right direction and in proximal- distal direction showed no significant difference between segments (P > 0.05); the ROM values in flexion-extension 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 left-right twisting of C₄,₅ was significantly larger than those of C₅,₆ and C₆,₇ (P < 0.05), but the ROM value in left-right bending showed no significant difference between segments (P > 0.05). In left and right bending, there was no significant difference in the displacement between other segments (P > 0.05) except that the displacement in anterior-posterior direction of C₃,₄ was significantly larger than that of C₄,₅ (P< 0.05), and that the displacement in proximal-distal direction 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 left-right twisting of C₃,₄ was significantly larger than that of C₅,₆ and C₆,₇ (P < 0.05). In left and right rotation, the ROM value in left-right twisting 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: The intervertebral motions of the cervical spine show different characters at different levels. And the 6-degree-of-freedom data of the cervical vertebrae are obtained, these data may provide new information for the in vivo kinematics of the cervical spine.