The Design And Primary Biomechanical Test Of A Novel Dynamic Fixation System For The Lumbar Spine

Part 1.The design of a novel dynamic fixation system for the lumbar spineObjective To design a novel dynamic fixation system for the treatment of the discogenic low back pain.Methods The novel dynamic fixation system is composed of the pedicle screw and connective bar.The connective bar is composed of titanium cluster,titanium ring and semi-hollow titanium cylinder.The titanium cluster is braided with titanium cables of different lengths,diameters and quantities. The gauge of the titanium ring is adjusted according to the effective length of the titanium cluster.Results Two types of the novel dynamic fixation system are manufactured,named as TypeⅠand TypeⅡ.Conclusion According to the concept of dynamic fixation,the novel dynamic fixation system is designed rationally,and is easy to use.Part 2.The primary biomechanical test of the novel dynamic fixation system for the lumbar spineTest 1.The stability of the injured segmentObjective To evaluate the effect of the novel dynamic fixation system on the range of motion(ROM) of the injured segment.Methods Each of the seven fresh adult cadaveric specimens(L1～L5) are injured and destabilized artificially at the L3/4 segment.The ROM of L3/4 segment is measured sequentially in the states of intact, injured,SCOFIX fixation,TypeⅠfixation,TypeⅡfixation,DePuy fixation. Results The ROM of L3/4 segment in the state of injured is much more than in the other five states(p＜0.05).The ROM of L3/4 segment in the state of TypeⅠfixation, TypeⅡfixation and DePuy fixation is more than in the state of SCOFIX(p＜0.05), but less than in the state of intact(p＜0.05).TypeⅡfixation reserves more ROM of L3/4 than TypeⅠand DePuy(p＜0.05).Conclusion After being fixed with the novel dynamic fixation system,the injured segment not only obtains stability,but also retains partial ROM.TypeⅡcan reserve more ROM of the injured segment than TypeⅠ.Test 2.The stability of the adjacent segmentObjective To evaluate the effect of the novel dynamic fixation system on the ROM of the adjacent segment above the fixed level.Methods During the procedure of Test 1,the ROM of L2/3 segment is also measured sequentially in the states of intact,injured,SCOFIX fixation,TypeⅠfixation,TypeⅡfixation,DePuy fixation.Results The ROM of L2/3 segment in the state of injured is less than in the other five states(p<0.05).The differences of the effect on ROM of L2/3 segment are not significant between the state of SCOFIX fixation,TypeⅠfixation,TypeⅡfixation and DePuy fixation(p>0.05).Conclusion The effect on the stability of adjacent segment above the fixed level is not different between SCOFIX,TypeⅠ,TypeⅡand DePuy.Test 3.Fatigue test for the novel dynamic fixation systemObjective To evaluate the short-term fatigue resistance of the novel dynamic fixation system after implantation.Methods After finishing Test 1 and Test 2,each of cadaveric specimen is implanted with TypeⅠagain,and then undergoes the fatigue test under the following conditions:500N axial compressing force,10Nm torsional moment,0.3Hz frequency,10000cycles.The ROM of L3/4 segment is measured sequentially in the states of intact,injured,SCOFIX fixation, TypeⅠfixation,TypeⅠfatigued.Results The ROM of L3/4 segment is not different between the states of TypeⅠfatigued and TypeⅠfixation(p>0.05).Conclusion After being implanted,the novel dynamic fixation system can produce good short-term stability for the fixed segment,which signifying good fatigue resistance.