In-rive study of rotational characteristic of human lumbar segments

Abstract

Objective To measure the vertebral rotational centers in sagittal and transverse plane. These data may be quite valuable for the design of artificial disc. Methods Ten healthy volunteers of 40-60 years old were recruited under IRB approval and informed consent. Three-dimension lumbar spine models of L_2, L_3 and L_4 were reconstructed from MR scans. Spine motions were then reproduced using combined dual fluoroscopic imaging system (DFIS) and MR scan technique during flexion-extension and left-right twisting of the body. Based on the geometrical features of the vertebrae, ranges of motion (ROM) of 3 representative lo-cations were measured from anterior to posterior, the vertebral body center, the spinal cord canal center and the spinous process tip. Rotational centers of the vertebral segments were then located by calculating the point of zero ROM. Results Motion patterns: The ROMs of L_2 with respect to L_3 (L_(2,3)) and L_(3,4) increased pro-portionally from anterior to posterior locations. During flexion-extension motion, the vertebral body center moved within a range of 0.6 mm, while the spinous process tip moved within 7.5 mm in the sagittal plane. During left-right twisting, the vertebral body center moved within 1.0 mm, while the tip moved within 1.6 mm in the transverse plane. No statistical differences were found in the ROMs between L_(2,3) and L_(3,4). Rotational centers: the rotational centers of flexion-extension in sagittal plane for both L_(2,3) and L_(3,4) segments were located at posterior one-third of the vertebral body. The rotational centers of both L_(2,3) and L_(3,4) segments were located approximately 30 mm anterior to the front edge of the vertebral body. Conclusion The anterior portion of the vertebrae was found to have smaller ROM than the posterior portion. The vertebra rotates with the center of rotation located at approximately the posterior one-third of the vertebral body in sagittal plane. However, the vertebra rotates in transverse plane with respect to a point about 30 mm in front of the vertebra. The data indicated that the different portions of the vertebra have distinct motion characters during different motions. Key words: Lumbar vertebrae; Rotation; Intervertebral disk; Prosthsis design