Comparison Of Human Lumbar Disc And Facet Joint Stresses And Strains During Two Simulated Spinal Manipulative Treatments

BackgroundSpinal manipulative therapy (SMT) is widely used in the treatment for degenerative lumbar spinal disease with definite therapeutic effect. SMT includes both mobilization and manipulation. However, the indications and contraindications of both mobilization and manipulation are not clear now. This is one of the causes that SMT is doubtful for its effectiveness and safety in modern medicine.It is helpful to know biomechanical characteristics of these two treatments to solve the problem above. So far some is available about the biomechanical characteristics of these two treatments. Force used in mobilization is low velocity, low amplitude, while it is high velocity, low amplitude in manipulation. Spinal manipulation consists of preload phase, thrust phase and resolution phase. However, there is little knowledge of the transmission of stresses and strains across tissues in vivo.The purpose of SMT is to correct vertebral subluxation and restore the joint movement. Lumbar vertebral joints consist of disc and two facet joints. It is significant to know about stresses and strains on the targeted disc and facet joints for discriminating the two techniques biomechanically. To date studies that have investigated the stresses and strains on disc and facet joints during SMT have been lack of dynamic observation, telling the difference in stresses between bilateral facet joints and concerning interactive effects of stresses and strains on discs and facet joints because of defect of study design and testing instruments.ObjectiveThis study includes simulating both mobilization and manipulation on human cadaveric specimens and testing stresses and strains on discs and facet joints during SMT. Data available will be analyzed carefully to tell the generality and individuality in biomechanics of mobilization and manipulation. Based on these data, it is necessary to discuss the safety and effectiveness of these two techniques, so as to provide the basis for clinical use.The study is one part of National Natural Science Foundation Project-’mechanism of spinal manipulative therapy on the interactive effects of stress and strain on intervertebral discs and facet joints’. It includes two experiments.Experiment 1 Comparison of strain on intervertebral discs and facet joints during spinal mobilization and manipulationMethodsTotally 12 adult fresh lumbar spinal specimens (T12-S2) were divided into two groups randomly. SMT was simulated with BOSE material testing machine. Parameters of simulated spinal mobilization:preload angle 15°(speed 3°/s), maximum angle 20°(speed 1°/s),with 9N horizontal force to L5 spinous process. Parameters of simulated spinal manipulation:preload angle 15°(speed 3°/s), impulse angle 20°(impulse speed 33°/s),with 22N horizontal force to L5 spinous process. All specimens were loaded 300N vertically down simulating half weight during SMT. Strain of disc and facet joint capsules (FJC) were measured with GOM optical non-contact measurement system.Results1 Comparison of parameters:Rotation angle ascended first and then descended gently during mobilization, while it ascended quickly to peak during manipulation. The largest angle of mobilization was bigger than that of manipulation (P<0.01). Torque ascended first and then descended gently during mobilization, while it ascended quickly to peak during manipulation. The largest torques during two techniques had no difference (P>0.05).2 Change of strain on discs during two techniques:Strain on discs ascended first and then descended gently during mobilization, while it ascended quickly to peak during manipulation. There was no difference of strain on discs during two techniques (P>0.05).3 Comparison of strain on different discs:There was no difference in strain on L4-5 and L5-S1 disc during two techniques (P>0.05).4 Change of strain on FJC during two techniques:Strain on FJC ascended first and then descended gently during mobilization, while it ascended quickly to peak during manipulation. Strain magnitudes were larger during manipulation than that during mobilization (P<0.05).5 Comparison of strain on bilateral FJC:There was no difference between strain magnitudes on bilateral FJC (P>0.05).6 Comparison of strain on discs and FJC:Strain magnitudes on discs were larger than that on FJC during mobilization (P<0.01). There was no difference in strain magnitudes between discs and FJC during manipulation (P>0.05).Experiment 2 Comparison of stress on discs and facet joints during spinal mobilization and manipulationMethodsSMT was simulated on lumbar spinal specimens according to experiment 1. Stress on left and right parts of discs were measured with micro sensors. Pressures of bilateral L4-5/L5-S1 facet joints were measured with Tekscan system.Results1 Comparison of parameters was the same with experiment 1.2 Space distribution of stress on discs during SMT:The maximal stresses on right part of discs were larger than that on left during two techniques (P<0.05).3 Change of stress on discs during two techniques:Stress on discs ascended first and then descended gently during mobilization, while it ascended quickly to peak during manipulation. The maximal stresses during both techniques were larger than that at the beginning and ending (P<0.05).There was no difference in the maximal stresses on discs between manipulation and mobilization (P>0.05).4 Comparison of stresses on different discs:There was no difference in stress on L4-5 and L5-S1 disc during two techniques (P>0.05).5 Comparison of speeds of change of stress on discs:Ascending speeds of stress on discs during manipulation were faster than that during mobilization (P>0.05).6 Change of stress on facet joints during two techniques:Stress on ipsilateral joints descended first and then ascended during two techniques, while stress on contralateral joints ascended first and then descended. Stress on contralateral joints ascended quickly during manipulation.The minimal stresses on ipsilateral joints during both techniques were lower than that at the beginning and ending (P<0.05). The maximal stresses on contralateral joints during both techniques were higher than that at the beginning and ending (P<0.05).There was no difference in stress on ipsilateral joints between mobilization and manipulation (P>0.05). Stresses on contralateral joints during manipulation were higher than that during mobilization (P<0.05).7 Comparison of speeds of change of stress on facet joints:Speeds of change of stress on contralateral joints during manipulation were faster than that during mobilization (P<0.05). Descending speeds of stress on ipsilateral joints during manipulation were faster than that during mobilization (P<0.05).Conclusion1 Strains on discs and bilateral FJC ascend first and then descend gently during mobilization with small magnitude, while they ascend quickly to peak during manipulation.2 There is no difference in maximal strains on discs during two techniques. There is no difference in maximal strains on different discs during either technique.3 The maximal strains on FJC during manipulation are larger than that during mobilization. There is no difference in maximal strains on bilateral FJC, and there is also no difference in maximal strains on different FJC.4 Stresses on discs ascend first and then descend gently during two techniques. Stresses on ipsilateral joints descend first and then ascend, while stresses on contralateral joints ascend first and then descend. Speeds of change of stresses on discs and joints during manipulation are faster than that during mobilization.5 There is no difference in the maximal stresses on discs between manipulation and mobilization. The maximal stresses on the ipsilateral side are higher than that on the contralateral side. There is no difference in the maximal stresses on different discs during either technique.6 Stresses on contralateral joints during manipulation are higher than that during mobilization. There is no difference in the maximal stresses on different joints during either technique.7 Above all, Discs and facet joints are more likely to be injured during manipulation than mobilization.