Comparison of three-dimensional transient motion characteristics under physiological load between isthmic and degenerative lumbar spondylolisthesis

Objective To observe and compare in vivo segmental lumbar motion between symptomatic L4 isthmic spondy- lolisthesis （IS） patients and L4 degenerative spondylolisthesis （DS） patients during functional weight-bearing activities. Methods Fifteen symptomatic L4 IS patients and fifteen symptomatic L4 DS patients were recruited. Fifteen asymptomatic volunteers were en- rolled as the control group. The L4.5 vertebral segment motion of each subject was reconstructed using three-dimensional computed tomography and a solid modeling software. In vivo, lumbar vertebral motion during functional postures （flexion-extension, left-right twisting and left-right bending） was observed using a dual fluoroscopic imaging technique. The spinal function unit was divided into anterior and posterior segments by the isthmic cleft. Local coordinate systems were established at the vertebral body, to obtain the 6 degree-of-freedom （DOF） intervertebral range of motion （ROM） at L4.5 and the ROM between the anterior and the posterior segments of L4 IS. Results The motion of IS at L4.5 was found to be increased. The migrations along both sagittal and vertical axis were significantly larger than control group （P 〈 0.05）. During left-right twisting, the migration along sagittal axis was significantly larger than control group （P 〈 0.05）; the rotation along vertical axis was significantly larger than DS and control group （P 〈 0.05）. During left-right bending, the migration along frontal axis was significantly larger than DS and control group （P 〈 0.05）. The inter- vertebral ROM at L4.5 showed no significant difference between DS and control group. The migration between anterior and posteri- or segments of IS L4 was larger in standing than supine （P 〈 0.05）. The relative migration along sagittal axis between anterior and posterior segments of IS L4 was significantly larger in flexion than standing （P 〈 0.05）. Conclusion A spondylolytic defect does lead to detectable instability or hypermobility in the lumbar spine compared with degenerative spondylolisthesis and normal group. From supine to standing posture, migration at isthmic cleft along sagittal and coronal axis are identified in IS spondylolithesis. Key words: Lumbar vertebrae;  Spondylolysis;  Biomechanics;  Fluoroscopy