| BackgroundSpinal manipulation (SM) is very popular in the patients and it has been more and more attention by clinical doctors. Even it has assured efficacy, however, its basic research of modern medicine is very weak, and lack of modern basic theory. So, SM does not give a strong sense of scientific for people. Now, SM has a range of different types, different operations, and lack of standards, norms and unity. SM also can lead to same damages with low incidence and serious consequences. So, the security problem and lack of modern basic theory hinder the development and popularize of SM.In recent years, the effect of intervertebral disc nucleus pulposus pressures by SM become a hot spots of biomechanical mechanism study of SM. Some researches think SM can reduce the pressure of intervertebral disc nucleus pulposus, even can remove some nerve root compression from protruded nucleus pulposus. However, another studies support opposite conclusions. Furthermore, there is no uniform standard to the position of cervical spine when do spinal manipulation, and neutral position, extension position and flexion position were choose voluntary by doctors. So, the clinical effect can not be promise in this situation.Moreover, there is also no uniform standard to wrench time in the process of SM. A few seconds or teens seconds? Different articles have different opinions. However, it is very important for treatment effect to the position of cervical spine and wrench time in the process of SM. A reasonable approach in patients with appropriate cervical position,rotate angle,passive range of motion and operational time can reduce the operational resistance, and improve the safety and accuracy of SM.It is very significance for mechanism and security of SM to study the suffered payload size, force relations and security load size of cervical motion segment in cervical spine manipulation. And this research cannot carry out by way of human cadavers, the emergence and applications of finite element analysis can provide a technology which can solve such problems for us. As far as we known, this is no material research with three-dimensional finite element analysis about cervical SM (CSM).ObjectiveThis study monitors the change of cervical nucleus pulposus pressures by biomechanical methods simulate CSM which under the different cervical positions and different wrench time. Meantime, it can immediately display the stress and displacement of the structure of cervical spine on the process of CSM by 3-D reconstruction and finite element analysis techniques. So, it cans 1. This study not only can verify and clarify the change of cervical nucleus pulposus pressures under SM, and reveal the efficacy mechanism of SM, but also can enhance the basic theory of SM, and it can be used to guide clinical diagnosis and treatment.2. Selecting the appropriate cervical position and wrench time in SM can clarify some clinical confusion, optimizing the operation method of SM, and improve the clinical efficacy and security.3. It also can provide a theory basis to standardization and scientific of SM, and to explore new ideal of SM research. Intuitive and visual three-dimensional finite element technique could also facilitate the teaching of SM.Methods(1) We simulated the CSM with stretch and rotation by fresh cervical specimens at MTS machine. We also monitored and recorded the change of cervical nucleus pulposus pressures (CNPP) in C3/4,C4/5 and C5/6 under the process of CSM by pressure sensor system.(2) The change of CNPP which under the process of CSM at 5 different cervical spine positions with extension 20°,extension 10°,neutral position,flexion 10°,flexion 20°were monitored and recorded. Further more, The change of CNPP which under the process of CSM at 3 different wrench time with 0.06s,0.11S,0.16s were also monitored and recorded.(3) The change of CNPP which under the process of CSM at the interaction effect between 5 different cervical positions and 3 different wrench times were monitored and recorded.(4) A normal young men's cervical spine were scanned by spiral CT with 1mm intervals, and the image have been entered into the computer by di.com format. A three-dimensional finite element model of C3/4-C6/7 which containing 31,533 nodes and 149,226 units were gradual reconstructed and grid by Mimics,Geomagic and MSC.Patran software.(5) The CSM was decomposed by principium of manipulation. The parameters of mechanics were analyzed by the finite element system. The change of intra-stress distribution and displacement were displayed in C3/4-C6/7 model simultaneously during simulating manipulation. Results1. The whole tendency of CNPP which under the process of CSM was a bigⅤtype change. The CNPP when simulate cervical suffered the gravity of head (physiological state) was higher than before start. The CNPP decreased slowly firstly, and then, it was maintained low level when simulate pulling manipulation. The CNPP were increased at rotating stage, and reduce quickly at wrenching stage, and rise fast when return the neutral position under the process of CSM, those change of CNPP formed a small V-shaped. The CNPP were keeping the same pressure after finished CSM, but, it was higher than physiological state. There were significantly different CNPP between four stages of CSM (F=5498.956, p<0.001).2. There were also significantly different CNPP between five cervical postions in the CSM (F=1371.216,p<0.001).The C3/4,C4/5,C5/6 CNPP under CSM were reduced in turn at cervical spine position from flexion 20°,flexion 10°,neutral position,extension 10°to extension 20°. More over, There were also significantly different CNPP between three wrench times in the CSM(F=419.530,p<0.001), and it were also reduced in turn at wrench time from 0.06s,0.11s to 0.16s. Further more, three cervical segments also showed in significantly different CNPP (F=84.282, p <0.001), the CNPP were rasied in turn from C3/4,C4/5 and C5/6.3. There were also significantly different CNPP between ench two factors interaction in the four factors including wrench time, cervical postions, cervical segments and CSM stages in the CSM (p<0.001 or p<0.01).4. Except the interaction of wrench time, cervical postions and CSM stages, there were also significantly different CNPP between ench three factors interaction in the four factors in the CSM (p<0.001 or p<0.01). And there was no significantly different CNPP in the interaction of four factors including wrench time, cervical postions, cervical segments and CSM stages in the CSM (F=0.843,p=0.759). 5. The size and the region of stress suffered cervical finite element model were gradual decreased, and then increasing gradually when simulates pulling manipulation. The regions of stress concentration were mainly in C3/4 Zygapophyseak joints and less in C4/5,C5/6 Zygapophyseak joints. Stress concentration was C3/4 nucleus pulposus at C3/4,C4/5,C5/6 nucleus pulposus. With the increased in thrust C4 spinous process, the left bottom of C4 spinous process,the root of C4 spinous process, and the combination area of left root of C4 spinous process and vertebral pedicle appeared stress concentration in turn.In the process of turn right rotate 40°radually, C3-C6 bilateral Zygapophyseak joints,the root of C4-C6 spinous process-,C4-C6 vertebral arch and the lateral side of C4-C6 vertebral body appeared stress concentration in turn; And the stress concentration areas form a sloping-shaped distribution in the view of lateral side; the sizes and the regions of stress in cervical model become the greatest in rotate 40°, and the greatest region occurred in right of C3/4 Zygapophyseak joints; Stress concentration were C3/4 nucleus pulposus and less in C4/5,C5/6 nucleus pulposus at the three nucleus pulposus. Stress concentration areas in nucleus pulposus also rotated follow the process. The size and the region of stress suffered cervical finite element model reduced quickly at the stage of quick return, and the stress drop to least when the model return to neutral position.5. The maximum displacement of cervical finite element model was the middle front of C3 vertebral body at the beginning of the pulling manipulation, and the displacement area were decreased gradually towards surrounding distribution as a center of the middle front of C3 vertebral body. The size and the region of displacement suffered cervical finite element model were gradual decreased, and then increasing gradually when simulates pulling manipulation, and displacement was C3/4 nucleus pulposus at C3/4,C4/5,C5/6 nucleus pulposus in this stage. With the increased in thrust C4 spinous process, the left of C3 vertebral body,the right of C4 vertebral body,C4 vertebral arch and C4 spinous process raised the displacement, and the displacement of C3/4 nucleus pulposus also rotated slightly follow the process. In the process of turn right rotate 40°radually, C3/4 and C4/5 motion segments appeared big displacement, except front of C4 vertebral body. Furthermore, the surrounding part of C3/4,C4/5 nucleus pulposus had the biggest displacement in all three nucleus pulposus model. The sizes and the regions of displacement in cervical model become the greatest in rotate 40°, and the greatest region occurred in superior articular process of C3 and spike of C3 spinous process. The size and the region of displacement suffered cervical finite element model reduced quickly at the stage of quick return, but the displacement not drop to 0 when the model return to neutral position.Conclusion1. The characteristic of changes of CNPP which under the process of CSM was a big V type change, not simply increase or decrease. The CNPP decreased and maintained at low level at simulate pulling manipulation stage. The CNPP were increased at rotating stage, and reduce quickly at wrenching stage, and rise fast when return the neutral position under the process of CSM, The CNPP were keeping the same pressure after finished CSM, However, it was higher than physiological state.2. Different cervical spine position,wrench time and cervical segments at process of CSM had a great effect to the CNPP; and the CNPP of cervical extension position at physiological area is higher than flexion; the longer time, the lower CNPP under the process of CSM from 0.06s,0.11s to 0.16s. The interaction of different cervical spine position and wrench time at process of CSM also have a good effect to the CNPP, and the CNPP was lowest at extension 20°combined 0.16s in the process of CSM, this combination have the most security in our study. 3. Cervical spine model have its unique stress and displacement change rule under the CSM. Zygapophyseak joints suffered the major stress in the cervical spine movement, and It is very important and don't damage easily. Rotation within 40°nder CSM did not injure the normal structure of cervical spine. The different cervical segments (including nucleus pulposus) have different displacement at process of CSM, and even the different part of the same cervical segment also have different displacement. C3/4 and C4/5 motion segments appeared big displacement.4. Cervical nucleus pulposus can appear large displacement and apparent shape change in the process of CSM; this may support the view that change position between protruded nucleus pulposus and nerve roots is one mechanism of SM. |
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