Biomechanical Motion Characteristics of Lumbar Motion Segments : Effects of Radial Tear of the Annulus Fibrosus / 대한척추외과학회지

ABSTRACT

STUDY DESIGN: Lumbar disc degeneration and segmental instability of the lumbar spine are causes of low back pain. Disc degeneration causes specific changes of the intervertebral disc, and could affect anatomic variations of end plate and vetebral body. However, the exact relationship between degenerative changes of the intervertebral disc and segmental motion characteristics is not known. It is known that radial tears of the annulus fibrosus initiate or accompany degenerative process of nucleus pulposus and the motion segment. It is hypothesis of this study that the existence of radial tear in the annulus fibrosis affects 3 dimension motion characteristics of motion segment. For the purpose, the degree of intervertebral disc degeneration is newly classified by existence of radial tear. Then, the resulting biomechanical motions are investigated. OBJECTIVES: To investigate effects of disc degeneration by the classification on kinematic motions of the motion segment from human lumbar spine and to suggest a quantified method to determine spinal instability in vivo. MATERIALS AND METHODS: A total of 60 spinal motion segments from human lumbar spine was used for this study. To measure 3 dimensioal motion of the motion segments, Vicon system(Oxford, England) with 3 cameras reflective markers and VAX station was used. 6 kinds of pure moments(flexion, extension, right and left axial rotation, and right and left lateral bending) were applied to the motion segments using dead weight for each loading step. At the end of test(maximum loading), motion segments were frozen for anatomical study. For making clear the degree of the degeneration of the disc, a new classification based on MRI results was used Grade 1 is a normal young disc without tear; Grade 2 is a normal aging disc without radial tear; Grade 3 is a degenerative disc with radial tear; and Grade 4 is a severely degenerative disc with radial tear and other degeneration such as showing decreased disc height. RESULTS: The upper lumbar specimens with radial tears has increased flexion motions as compared to the normal group. Also, the right and left axial rotation in radial tear group increased as compared to the normal group. However, there were no statistical differences in other motions. For the lower lumbar specimens, there were no significant differences in measured motions in all directions between the normal and radial tear groups CONCLUSIONS: These results suggests that the segmental motions are affected by radial tear in the intervertebral disc. Thus, the radial tear in the annulus fibrosus of lumbar intervertebral disc could cause the instability of lumbar spine. Further research is required to determine the relationship between other structural changes and biomechanical characteristics, and future studies should include in vivo investigations to correlate these findings to patients'symptoms.