| BackgroundLong segment lumbar fixation systems were applied to treat scoliosis and spinaldegenerative disease conventionally[1-4]. But it could not provide enough strength tocorrect severe spinal deformity usually[5-7]. In addition, the mobility of intervertebraljoint adjacent to long segment fixation system would be increased compensatory,whichcould lead to segment degeneration,it was often in need of secondary surgery. In order toobtain reliable fixation stability and prevent segment degeneration,the distal end of longsegment fixation system was extended to pelvic conventionally[1-2]. As a traditionalspinal-pelvic fixation technique, sacral screws with poor anchoring force could be easilypulled out, therefore the incidence of pseudarthrosis was very high[2], especially inpatients with osteoporosis[8]. Iliac screws with longer trajectory and more reliablestability had become the ideal choice of spinal-pelvic fixation system. However, thetraditional lumbar-sacral-iliac fixation system was difficult to execute because of thecomplicated anatomic structures in lumbosacral region,as a result, the risk of lumbosacralspine surgery was increased obviously.Therefore it has become the research foucs ofspinal-pelvic fixation system to simplify the surgical procedure while keeping solidstability and low risk of fixation failiure. ObjectiveTo design a noval spinal-pelvic fixation system, analyze the stability and stressdistribution of the noval fixation system via biomechanical experiments, provide aconvenient and reliable spinal-pelvic fixation system to lumbosacral spine surgeryfinally.Methods1.The design of the noval spinal-pelvic fixation systemOn the basis of lumbar-sacral fixation system, double heads L5pedicle screws(6.5mm×45mm) were applied, the lateral head of L5pedicle screw and the iliac screwwere connected by a pre-curved short rod to create a parallel construct of lumbar-sacraland lumbar-iliac.2. Experiment methods6adult lumbar-pelvic embalmed specimens were prepared.The interspinousligament and zygapophyseal joints from L2to S1were cut through. L1vertebra andIschium were embedded with dental base acrylic resin powder.Experimental groups:(1)unfixed group: lumbar-pelvic specimens without anyfixation device;(2)lumbar fixation group: fixation system from L2to L5;(3)lumbar-sacralfixation group: fixation system from L2to S1;(4)lumbar-sacral-iliac fixation group:fixation system from L2to S1to iliac screw;(5) novel fixation group:the novel fixationsystem was installed according to the method above.The embedded L1vertebral body was fixed to action chuck of biomechanical testingmachine (SBM2000) to execute movements of flexion, extension, lateral bending androtation with8Nm pure moment. In order to diminish the effects of viscoelasticity, eachaction was repeated three times, only the last time was applied.Testing items:(1) The operation time of novel fixation group andlumbar-sacral-iliac fixation group.(2)Mobility: two marker balls were placed in front ofL2and L5vertebral body respectively, the mobility of L2and L5level were measuredwith action recorder.(3)Stress: resistance strain paster was fixed on the neck of L5pedicle screws, S1screws, iliac screws, and on the middle of lumbosacral fixation rods (L5-S1). The strain value of each measure point was detected with resistance straingauge,then the strain value was converted to stress according to Hooke’s law=E (E: modulus of elasticity, ETi6Al4V=16.5GPa,: stress,: strain).3.Statistical analysisSPSS13.0was applied. The operation time was analysised with T test,the value ofmobility and stress were analysised with Krushkal-Wallis test.Results1.The operation time to install the novel fixation system was shorter than thelumbar-sacral-iliac fixation system obviously, there was significant difference (P﹤0.05).2. Mobility of L2level: In all conditions, the mobility of L2level in lumbar-sacralfixation group, lumbar-sacral-iliac fixation group, novel fixation group were obviouslyreduced compared with unfixed group; In conditions of flexion, lateral bending, rotation,the mobility of L2level in lumbar fixation group were obviously lower compared withunfixed group; In conditions of lateral bending, rotation, the mobility of L2level inlumbar-sacral-iliac fixation group and novel fixation group were obviously decreasedcompared with lumbar fixation group; there were significant differences all above (P﹤0.05).3. Mobility of L5level: In all conditions, the mobility of L5level in lumbar-sacralfixation group, lumbar-sacral-iliac fixation group, novel fixation group were obviouslyreduced compared with unfixed group; In conditions of flexion, lateral bending, rotation,the mobility of L5level in lumbar fixation group were obviously lower compared withunfixed group; In all conditions, the mobility of L5level in lumbar-sacral-iliac fixationgroup, novel fixation group were obviously decreased compared with lumbar fixationgroup; In conditions of flexion, lateral bending, rotation, the mobility of L5level inlumbar-sacral fixation group were obviously reduced compared with lumbar fixationgroup; there were significant differences all above(P﹤0.05).4. Stress of L5pedicle screws: In all conditions, the stress of L5pedicle screws inlumbar-sacral fixation group, lumbar-sacral-iliac fixation group, novel fixation groupwere obviously reduced compared with lumbar fixation group, there were significant difference (P﹤0.05).5. Stress of S1screws: In all conditions, the stress of S1screws inlumbar-sacral-iliac fixation group and novel fixation group were obviously reducedcompared with lumbar-sacral fixation group, there were significant difference (P﹤0.05).6. Stress of iliac screws: In all conditions, there were no significant differencebetween lumbar-sacral-iliac fixation group and novel fixation group in the stress of iliacscrews(P﹥0.05).7. Stress of lumbosacral fixation rods (L5-S1): In conditions of flexion andextension, the stress of lumbosacral fixation rods (L5-S1) in lumbar-sacral fixation groupand novel fixation group were obviously reduced compared with lumbar-sacral-iliacfixation group; In conditions of lateral bending and rotation, the stress of lumbosacralfixation rods (L5-S1) in novel fixation group were obviously decreased compared withlumbar-sacral fixation group and lumbar-sacral-iliac fixation group; there weresignificant differences all above(P﹤0.05).Conclusion1. The lumbosacral stability of long segment fixation system can be improved byspinal-pelvic fixation systems, the stress load in the proximal screws can be effectivelyreduced by distal end screws.2.The novel spinal-pelvic fixation system is convenient,reliable lumbosacralstability can be provided, the L5pedicle screws, S1screws, lumbosacral fixation rods(L5-S1) can be protected effectively when applying the novel fixation system,thebreaking rate of rods and screws would be decreased which is beneficial to lumbosacralfusion. |
PDF Full Text Request