| Epidemiological studies have revealed that lumbar degenerative discdiseases are often found in the lower lumbar levels of L4-5and L5-S1.Clinical reports have indicated that there may be pathological differencesbetween the L4-5and L5-S1motion segments. For example, morelumbar degenerative spondylolisthesis is found at L4-5and lumbar discherniation is more common at L5-S1. In general, altered vertebral motionhas been widely assumed to be a biomechanical factor causing spinalpathology. Therefore, numerous in-vitro and in-vivo studies have beenconducted in order to understand spinal kinematics and to specify thevertebral motion features related to various disc diseases. However,accurate dynamic motion characteristics of L4-5and L5-S1in6degrees-of-freedom (6DOF) are still not clearly described in theliterature.Recently, a3D fluoroscopic imaging technique has been intensivelyapplied to investigate the6DOF range of motion (ROM) of lumbarsegments at various weight bearing static postures. Since bending andlifting motions have been described as common daily living activities thatplay an important role in pathological lower back pain, we sought toinvestigate the in-vivo motion pattern of the human lumbar spine dynamically during weight-lifting from a flexion position to fullextension position using this3D fluoroscopic imaging technique.Objective：This study investigated in-vivo motion of the lumbar spine during aweight-lifting activity.Methods：Ten asymptomatic subjects (5males and5females, aged from40to60years) were recruited for this study. The presences of any spinaldisorders, symptoms, or anatomic abnormalities were used as indicationsfor exclusion from the study.Each subject was scanned in a supine, relaxed position by MRI. TheMR images of the spinal segments were imported into a solid modelingsoftware program for construction of a3D anatomical lumbar model,including L2, L3, L4, L5, and partial S1,Thereafter, each subject performed the following weight-liftingactivity in view of the dual fluoroscopic system.An extension motion,from a flexed position of45°to maximal extension, with each handholding an eight pound dumbbell. A custom-made frame was used to limitpelvis motion during the activity.The in-vivo positions of the vertebrae during the lifting motion werereproduced in the Rhinoceros solid modeling software using the3Dmodels of the vertebrae and the orthogonal fluoroscopic images. This was done by recreating the geometry of the dual-orthogonal fluoroscopicsystem in the solid modeling program. The pair of fluoroscopic images ofthe spine captured during the experiment were imported into themodeling software and placed in calibrated orthogonal planes toreproduce the actual positions of the image intensifiers of thefluoroscopes.After reproducing the in-vivo vertebral positions using the3Danatomic vertebral models, the relative motions of the vertebrae wereanalyzed using right hand Cartesian coordinate systems constructed at theendplates of each vertebra.The relative motions of the proximal vertebrae with respect to thedistal vertebrae were calculated at four vertebral levels: L2-3, L3-4, L4-5,and L5-S1.In this study, we investigated the rotation (flexion-extension, left-rightbending, and left-right twisting) and translation (anterior-posterior,proximal-distal, and left-right) of each vertebral level during the weightlifting motion. Five positions along the dynamic lifting activity wereselected for analysis:0%(45°flexion),25%,50%(upright),75%, and100%(maximum extension). The vertebral positions in a non-weightbearing supine position, collected during MRI scanning, were used as areference to calculate vertebral motions. A repeated measures ANOVAwas used to compare the dynamic ranges of motion of all vertebral levels during the activity. Statistical significance was set at p <0.05. When astatistically significant difference was detected, a Newman-Keuls posthoc test was performed. The statistical analysis was done usingsoftware (Statistica, Statsoft, Tulsa, OK).Results：The total motion of the lumbar spine, measured as L2relative to S1,showed29.8±8.2°of extension from initial flexion to maximal extension.The individual extensions of each motion segment were similar:7.1±2.9°,7.0±3.7°,8.0±3.4°, and7.7±2.3°for L2-3, L3-4, L4-5and L5-S1levels,respectively.The ranges of posterior translation were similar between L2-3andL3-4,1.7±1.0mm and2.1±1.0mm, respectively. L4-5had a posteriortranslation range of2.9±1.5mm, which was significantly higher than thatof L5-S1(1.4±1.1mm)(p<0.05). The range of proximal-distal translationof L5-S1was2.8±0.9mm and significantly larger than L4-5(1.7±0.7mm)(p<0.05).Conclusion:This study used a fluoroscopic system to investigate dynamic lumbarspine extension during a weight-lifting condition. We found that differentvertebral levels appear to behave differently. Specifically, the L4-5motion segment showed the largest anterior-posterior translation andL5-S1showed the largest proximal-distal translation during the activity. The observed higher anterior-posterior translation at L4-5might be abiomechanical factor related to why adult degenerative spondylolisthesisoccurs more often at the L4-5level than the L5-S1level. the largestanterior-posterior translation of L4-5which could be related to the factthat lumbar disc herniation is seen more often at these segments. Theresults may provide insight into our understanding of physiologicallumbar motion characteristics and lumbar disease developmentmechanisms. Future studies should investigate pathological lumbarpatients preoperatively and postoperatively during dynamic functionalactivities so as to help improve both understanding and treatment oflumbar diseases. |
PDF Full Text Request