Percutaneous Cement-augmented Pedicle Screw:A Biomechanical In Vitro And Cohort Study

Objectives:1.To assess the biomechanical stability of percutaneous cement-augmented pedicle screw with cement augmentation in different bone mass density,and to investigate the link between the stability of bone-screw interface and the degree of vertebral osteoporosis.2.To compare the percutaneous cement-augmented pedicle screw(PCPS)and conventional pedicle screw(CPS)in the treatment of spondylolisthesis with osteoporosis via a retrospective cohort study,and to investigate the safety and effect of percutaneous cement-augmented pedicle screw.Methods:1.Four kinds of biomechanical test materials in different density were used to mimics the lumbar vertebrae of osteoporosis.65 CPSs and 65 PCPSs were divided into four groups and inserted into the biomechanical materials.Then we measured the maximum axial pullout strength,maximum non-axial compressive stress and fatigue strength of the bone-cement interface.We compared the biomechanical stability between the PCPS and CPS and investigated the link between the stability of the bone-screw interface and the degree of vertebral osteoporosis.2.From January 2014 to March 2018,a retrospective study of 88 patients with spondylolisthesis and osteoporosis treated with minimally invasive transforaminal lumbar interbody fusion(MIS-TLIF)using the conventional pedicle screw(CPS group,n=52)and the percutaneous cement-augmented pedicle screw(PCPS group,n=36)was performed with a follow-up of 30 months(range,10-58 months).Clinical outcomes(preoperation,3,6,and 12 months after the operation and the final follow-up),overall changes in slip degree,and interbody fusion rates were evaluated via questionnaires and radiographic parameters.We compared the effect between these two pedicle screws.Results:1.Compared with CPSs,PCPSs can effectively improve the maximum axial pullout strength,maximum non-axial compressive stress and fatigue strength with the osteoporosis.As the decrease of bone mass density,the stability of cement-augmented pedicle screw could be affected and showed a decrease.When the BMD was lower than 50 mg/cm~3,the stability of cement-augmented pedicle screw would be same as the conventional pedicle screw.2.The average age of CPS group(52 members,12 males and 40 females)was 67.3±6.55,and they were followed for 36.6 months approximately.Compared with CPS,the average age of PCPS group(36 members,2 males and 34 females)was 65.9±9.38,and they were followed for 15.4 months approximately.(1)The clinical score(VAS,ODI and JOA),Taillard index and intervertebral space height were significantly improved in both groups compared with the preoperative assessment(p<0.001).(2)There were no significant differences in operative time,blood loss,X-ray time and the diameter and length of screws between the two groups(p>0.05).(3)No significant differences in scores were found between the two groups at any time(p>0.05).(4)Imaging results at postoperation revealed greater postoperative improvement in the Taillard index in the PCPS group(7.04%±3.11%)compared with the CPS group(13.12%±3.81%,p<0.001).(5)No significant differences in the interbody fusion speed or rates were found between the two groups.(6)In the PCPS group,cement leakage occurred in 22 of 97 screws(22.7%),and symptomatic cement leakage was not found.Conclusions:1.The PCPS shows a remarkable improvement of fixation strength compared with conventional pedicle screw.However,with the reduction of BMD,the enhancement of strength of the PCPS will decrease.When the BMD was lower than 50 mg/cm~3,the stability of cement-augmented pedicle screw would be same as the conventional pedicle screw.Accordingly,when the PCPS was used applied to the serious osteoporosis,the other strategy to reinforce the fixation strength,including injection dose and timing,should be investigated.2.MIS-TLIF combined with the PCPS provided greater improvement in slip reduction than did MIS-TLIF combined with the CPS.Moreover,this technique did not influence interbody fusion rates.Although several patients experienced asymptomatic PMMA leakage,the overall efficacy was definite and effective.Overall,MIS-TLIF combined with the PCPS is an effective and safe technique for the treatment of spondylolisthesis with osteoporotic spine.