| [Background]Degenerative lumbar scoliosis (Degenerative lumbar scoliosis, DLS) is defined as Cobb angle greater than 10 ° of scoliosis in lumbar coronal plane after skeletal maturity. Its occurrence is approximately 6% among over 50 years old. With the aging of society, degenerative lumbar scoliosis has increasingly common occurrence and has become the important reason for low back pain, leg pain and neurogenic claudication in elderly. Nowadays we usually consider that degenerative lumbar scoliosis occurs mainly because of asymmetrical lumbar disc degeneration, disc wedging produce and reduced disc height asymmetry in the different segments, which lead to the facet joints force increasing asymmetrically. The lumbar asymmetry degeneration and loading finally cause lumbar spine malformations in a three-dimensional plane.In normal physiological conditions the lumbar interveterbral disc can bear the load in front of the spine.The annulus fibrosus also has many biomechanical properties such as resisting stretch, shear and torsion, which plays an important role in maintaining the integrity of the intervertebral disc. The biomechanical research of annulus fibrosus can help we easily grasp interveterbral disc biomechanical properties in motion segment in clinical diagnosis so as to formulate appropriate treatment project. Now we widely recognized that disc asymmetrical degeneration is the leading cause in degenerative lumbar scoliosis and play a decisive role in the degenerative lumbar scoliosis.Because the specific mechanisms for the development of degenerative lumbar scoliosis is still unclear, some scholars have try to create a scoliosis model by changing the disc only in animal studies. Meanwhile, as we known that human specimens of degenerative lumbar scoliosis are very difficult to obtain, so it is difficult to study directly in human specimens of degenerative lumbar scoliosis. Thus in the experiment we will resect intervertebral disc asymmetrically in L2-L3 segment of human specimens, which simulate the asymmetrical lumbar intervertebral disc degeneration in degenerative lumbar scoliosis.Then we will observe the range of motion (range of motion, ROM), (Neutral zone, NZ) in lumbar spine and the facet joints force. The object of this experiment is to understand the mechanism of intervertebral disc and facet joints in degenerative lumbar scoliosis and explore the biomechanical role of the spine after lumbar intervertebral disc resection.[Objective]1. To explore the effect on facet joint force after intervertebral disc asymmetricaldiscectomy in L2-L3 lumbar segment.2. To explore the effect on lumbar stability after intervertebral disc asymmetricaldiscectomy in L2-L3 lumbar segment.[Methods]1 Materials and methods1.1 Experiment materialsSeven fresh cadavers spine without spinal disorders were made into seven L2-L3 functional units excluding some soft tissue such as the muscle and fat, but intervertebral disc, ligament, facet joint capsule and bone structure were kept intact. Specimens were sealed with double plastic bags and stored at -20℃ refrigerator. Seven hours before the experiment the specimens were taken from refrigerator and thawed at room temperature naturally. The specimens at both ends were embedded with denture gypsum powder. During the experiment we sprayed the specimens at any time so that the specimen kept moist.1.2 Experiment equipmentsThe three-dimensional spinal testing machine, Optotrak Certus three-dimensional motion measurement system(NDI company, Canada), force distribution measurement system, the 6900 type of pressure sensor slice(Tekscan company, USA)1.3 Biomechanical testing1.3.1 Experiment groupsThree groups included Intact disc group(Intact),1/4 Discectomy group(l/4 Discectomy),1/2 Discectomy group(1/2 Discectomy).According to the principle of randomization, three specimens were resected in the left disc and four specimens were resected in the right disc.1.3.2 Model preparationWe measured disc diameter by vernier caliper and vertically cut in 1/4,1/2 of disc diameter with a knife. Then cut in parallel endplates in order to 1/4 and 1/2 discectomy. Four infrared markers were connected in the L2 and L3 vertebrae by Kirschner. ROM was recorded by applying Optotrak Certusthree-dimensional motion measurement system. A sharp knife was used to incise the both facet jonit capsule of L2-L3 segment. Then pressure sensor about 14 mm x 14 mm size was inserted into the facet joint space to record the facet joint force.1.3.3 Biomechanical testingThe specimens were applied with pure moment of 7.5 N-m during flexion/extension(FE), lateral bending(LB) and axial rotation(AR) respectively three times using 1°/s speed by spinal testing machine. Finally the ROM, neutral zoneand facet joint force in L2-L3 segment were analyzed in the third cycle.1.4 Data analysisSPSS20.0 statistical software was used to analyze different group data by repeated measures analysis of variance and compare between groups by Bonfferoni test, then compare the data of two sides in the same group by paired t test. A P value 0.05 is considered statistic significant.[Results]We observed the ipsilateral facet joint did not have force during axial rotation under intact disc status, while the contralateral facet joint was under pressureand went through maximum pressure at maximum ROM. The force of left and right facet joint during axial rotation rose alternately. The contralateral facet joint hardly went through pressure during lateral bending while the ipsilateral facet joint was under pressureand went through maximum pressure at maximum ROM. During extension the facet joint force at both sides went through pressure and went through maximum pressure at the same time at maximum ROM. During flexion the facet joint force at both sides hardly went through pressure, so we did not analyze the force.The facet joint force during lateral bending was 15.45 N and the facet joint force during axial rotation was 60.94 N under intact status. There was no significant difference in force between both sides during lateral bending and axial rotation(P>0.05), but during extension the force at one side (13.73 N)was larger than the other side(7.81 N) (P<0.05). With the disc resected largely, there was significant difference between different group. During extension, a significant increase in facet joint force under discectomy status was found at side of not discetomy under 1/4 discectomy status(P<0.05). During lateral bending, not only the facet joint force at both sides under 1/2 discectomy status increased significantly than that under intact status, but also a significant increase in facet joint force was found at side of not discetomy under 1/4 discectomy status(P<0.05). During axial rotation, only facet joint force at side of not discetomy under 1/2 discectomy status increased significantly(P<0.05).Under intact disc status the ROM was respectively 6.40°,3.37°,10.13°and 3.96°during flexion, extension, lateral bending and axial rotation. There was no significant difference in ROM between both sides under intact disc status,1/4 discectomy status or 1/2 discectomy status during lateral bending and axial rotation(P>0.05). With the disc resected largely, there was significant difference between different group. Except during flexion, ROM under 1/4 discectomy and 1/2 discectomy status were larger than that under intact status in all motion directions (P<0.05).During extension, the neutral zone under 1/2 discectomy status increased significantly than that under intact disc status(P<0.05). There was no significant difference in neutral zone under among intact disc status,1/4 discectomy status and 1/2 discectomy status(P>0.05). The neutral zone under 1/4 discectomy and 1/2 discectomy status were larger than that under intact status during lateral bending(P<0.05), but there was no significant difference in neutral zone under between 1/4 discectomy status and 1/2 discectomy status(P>0.05). During axial rotation, the neutral zone under 1/2 discectomy were larger than that under intact status and 1/4 discectomy status(P<0.05), but there was no significant difference in neutral zone under between intact disc status and 1/4 discectomy status(P>0.05).[Conclusions]1. The asymmetric lumbar discectomy can increase the ROM during extension, lateral bending and axial rotation as well as enlarge the facet joint force asymmetrically, which indicate that the instability of lumbar spine and the increase of facet joint force resulted from asymmetric degeneration of the disc might lead to the backache.2. We should retain the integrity of the annulus fibrosus as much as possible to prevent from the the significant increase of facet joint force and instability of lumbar spine after surgery when removing the nucleus pulposus or cutting out the annulus fibrosus.3. The facet jonit force of asymmetrical change reflects better the asymmetrical spinal injury than the ROM of symmetrical change when disc suffering from asymmetrical injury. But with the disc injured more largely, the facet joint force and ROM gradually increase and both can reflect the severity of spinal injury. |
PDF Full Text Request