Biomechanical Evaluation And Preliminary Application In Clinical Practice Of The Bone Cement Injectable Canulated Pedicle Screw

Background: As the world aging population grows, more and more osteoporosispatients need internal fixation for spinal diseases. Pedicle screw fixation technique is mostcommon for posterior spinal fixation as its features of short segment and three columnsfixation. However, decreasing bone mineral density (BMD) and trabecular numbers (Tb. N)and thinning cortical bones lower down the stability of pedicle screw to cause failure of theoperation. How to improve the stability of pedicle screw in osteoporotic vertebral hasbecome a challenge for spinal surgery.According to the previous research, we have designed the bone cement injectablecanulated pedicle screw (CICPS). It has been proved that CICPS can significantly increasethe stability of the pedicle screw, and reduce the risks caused by polymethylmethacrylate(PMMA) leakage or increasing length and diameter of screw. However, does the hollowdesign of CICPS cause any change in mechanical properties? Compared with conventionalpedicle screws (CPS) and DTPSTM(Dream Spine Total Solutions, Dream STS, Seoul,Korea) who has the most advantages in stability of biomechanics? How about the clinicalefficacy of CICPS? None of these is mentioned in the related materials in China or abroad.Objective:1) To observe the distribution of bone cement by X-ray and CT and compare themechanical properties between CICPS and CPS by analyzing the maximum shear stress.2) To compare the biomechanical stability among CICPS, CPS and DTPSTMandanalyze the relationship between bone cement volume and the maximum pullout strength(Fmax) to optimize the volume solution.3) To discuss the safety and efficacy of CICPS by clinical experiments so as toprovide sufficient theretical basis for wide clinical application of CICPS.Methods: 1) Experiments in vitro: Shear stress test is conducted on CICPS and CPS to comparemechanical properties. Four groups of CICPS and DTPSTM, injected with1ml,2ml,3ml,5ml volumes of bone cement, together with CPS are planted in OP biomechanical testblock (BTB). X ray, CT scan and the maximum pullout strength test are conducted tocompare the biomechanical stability among the three screws. The relationship betweenFmax and the volume of bone cement are also analyzed.2) Clinical experiment: From2010to2012,24OP cases have been used CICPS toenhance internal fixation. Complications including bone cement leakage, blockage andinfection are recorded. Visual analog scale (VAS), oswestry disability index (ODI), X-rayand CT (over six months) is followed-up after surgery. The data of clinical manifestation,function of lower limbs, screw pull-out and bone fusion is analyzed. In addition, specialmeasurements were given to spondylolisthesis. The Taillard index (the degree of slip), theslip angle and the disc height were measured on the lateral X-ray view pre-operationallyand follow-up so as to evaluate vertebral reduction and maintenance.Results:1) Experiments in vitroâ‘ Shear stress test: The shear stress of CICPS is significantly less than CPS but it canmeet the spinal fixation requirement.â‘¡Maximum pullout strength test: In OP biomechanical tests block, the Fmax ofCICPS and DTPSTMis significantly greater than CPS. A larger bone cement volumecaused a greater strength in CICPS and DTPSTM. There is a highly positive correlation.When bone cement volume is1ml,2ml,3ml, the stability of CICPS is greater thanDTPSTM. Bone cement is distributed through all the three side holes of CICPS. No rearleakage is observed in BTB. Bone cement in the bone trabeculae forms the compound of"screw-bone cement-bone trabeculae", which fix the screw in the vertebral body. InDTPSTM, bone cement is mainly distributed from the proximal side holes, and the distalside hole is less. When bone cement volume is5ml, the stability of DTPSTMis greater thanCICPS. And the dispersion morphology of bone cement is similar between CICPS andDTPSTM.2) Clinical experimentThe average follow-up time is about7.0months (rang3-23months) with the minimum of three months. Compare to the data before surgery, the evaluation of VAS and ODI isbetter after surgery. Pain and lower limb function change for the better. No bone cementleakage is observed; four cases occure spinal sacral veins leakage without nerve symptoms.All patients have no complications such as infection and embolization. On the lastfollow-up imaging examinations, all pedicle screws do not happen to loose or pull out, andthe pedicle screw fixation system is in position. Six month after the surgery, bone infusionrate reaches100%. The cases of spondylolisthesis, post-operatively the average slippercentage (Taillard index), slip angle are significantly decreased and the disc height issignificantly improved compared to those of pre-operation.Conclusion:1) CICPS can enhance stability in osteoporosis vertebral, significantly better thanCPS and similar products. When the bone cement usage is1ml, CICPS can achievesatisfactory effect on enhancing fixation. By reducing the amount of bone cement, CICPSfinally achieves the object of decreasing the leakage risk.2) Hollow design makes CICPS shear stress lower than CPS, but enough to meet theclinical demand.3) In osteoporosis vertebral, bone cement is distributed in the front of screw, whichcan effectively avoid the complications such as, damaging of burning, leakage andcompressing the nerves.4) CICPS clinical result is favorable and the recovery is desirable. No screw loosingor pull-out case is observed. CICPS is considered as a safe, effective, and easily-operatedinternal fixation option for OP patients.