The Effect Of Weight-Bearing Activity On The Center Of Rotation In The Lower Lumbar Spine

Objective:To measure the center of rotation of the lower lumbar spine during a weight-lifting activity and compared with the center of rotation under the physical load. So that the effect of weight-bearing activity on the in vivo motion pattern of the lower lumbar spine will be clear.Methods: fourteen asymptomatic subjects with a mean age of 25 years were recruited for this study(6 males and 8 females, aged between 22 and41 years). The lumbar segment of each subject was CT-scanned to construct 3D models of the L4–S1 vertebrae. Let the normal people take different loads(0, 10Kg) respectively when performming an activity from a lumbar flexion position to maximal extension position. The transient image of the lumbar motion was recorded and introduced into the software to reconstruct lumbar in-vivo motion. Coordinate systems were established at the vertebral body of L4-S1, to obtain the center of rotation(COR) during flexion-to-neutral?neutral-to-extension and the full flexion-extension motion.Results: 1.The range of motion(ROM) during flexion-extension activity at different loads: The translations along frontal, sagittal, and vertical axis were 1.3±1.6mm?2.0±1.7mm?0.3±0.2mm respectively at L4-5 segment,the corresponding rotations along the three axises were 6.1±3.3°?1.6±1.0°?1.7±1.4°, the translations along frontal, sagittal, and vertical axis were 2.0±1.3mm?3.3±1.3mm?0.3±0.2mm respectively at L5-S1 segment,the corresponding rotations along the three axises were 7.5±3.0°?1.6±0.7°?2.4±1.8°;When the normal people take 10 KG loads in the hand, the translations along frontal, sagittal, and vertical axis were 0.9±0.6mm?2.2±1.2mm?0.3±0.3mm respectively at L4-5 segment,the corresponding rotations along the three axises were 4.8±2.2°?2.5±1.1°?1.9±1.7°, the translations along frontal, sagittal, and vertical axis were 1.4±2.0mm?3.4±1.8mm?0.5±0.5mm respectively at L5-S1 segment,the corresponding rotations along the three axises were 8.1±2.7°?1.7±1.2°?2.8±2.1°?There was no statistical differences between these two loading condition at L4-5 and L5-S1 segments. The translation in sagittal axis of L4-5 was significantly less than that of L5-S1 at two different loading condition(P<0.05).And The rotation along frontal axis of L5-S1 was significantly more than that of L4-5 when taking 10 KG loads(P<0.05). 2. The center of rotation during flexion-extension activity at different loads:During flexion–extension, The COR of L4-5 was located about 1.0 mm anterior to the central of the vertebral body, and the COR of L5-S1 was located about 0.7 mm anterior to the central of the vertebral body. While with 10 KG weight in hands, the CORs of both L4-5 and L5-S1 shifted posteriorly by about 0.6 mm and 0.4 mm. There was no statistical differences between these two loading condition. When the COR in flexion and extension were calculated respectively, the translation of the COR at both L4-5 and L5-S1 became larger due to taking loads in hands(P<0.05). In flexion the COR at L5-S1 significantly shifted forward during a weight-lifting activity(P<0.05). These results confirm that compared with nonweight-bearing condition,the translation of the COR was found to be increased when taking 10 KG loads,especially during the flexion-to-neutral motion.Conclusion: These results confirm that compared with nonweight-bearing condition,the translation of the COR was found to be increased when taking 10 KG loads,especially during the flexion-to-neutral motion.