| BackgroundWith the population aging,lumbar degenerative diseases symptomized with low back pain or leg pain have growing effects on people life.Fusion procedure has been a standard treatment for lumbar degenerative diseases.However,there have been increasing reports on the complications after lumbar fusion procedure.In recent decades,nonfusion procedure has been developed to reduce these complications and hybrid surgery has been developed to prevent adjacent segment degeneration.PEEK rod is a novel semi-rigid pedicle-based dynamic fixation that has been widely used in posterior lumbar surgery in recent years.It has been reported that fusion procedure by PEEK rod could achieve satisfactory clinical outcomes.However,no study is available for nonfusion or hybrid lumbar procedure by PEEK rod.ObjectiveThe current study is to explore the feasibility and validity of nonfusion and hybrid surgery by PEEK rod for degenerative lumbar diseasses by finite element analysis and clinical studies.The puspose of the first part is to investigate the intervertebral disc pressure and range of motion of lumbar spine before and after implantation of PEEK rods by finite element analysis.The purpose of the second part is to assess the clinical outcomes and radiographic changes of nonfusion procedure by PEEK rods.The third part of the study is to further compare the clinical effects and radiographic parameters especially adjacent segment changes of hybrid procedure by PEEK rods with fusion procedure by titanium rods.MethodsThe dicom data of the CT scan on a healthy male volunteer were imported to Mimics 13.0(Materialise,Shanghai,China)software.Specified CT image intensity was selected before the Region growing was applied.Then the reconstruction of the whole lumbar spine was accomplished by different pixels in different tissue by Calculate 3D.Then the STL files exported from Mimics was imported in the Geomagic 10(Geomagic,North Carolina,the United States).The posterior fixation was reconstructed by Pro/E Wildfire 1.0(PTC,the United States).The IGES files of the surface model of L1-S1 were imported into Ansys 13.0(Ansys,the United States)to establish the L1-S1 finite element models.A total of six models were established in the current study: the intact model,L4/5 nonfusion fixation by PEEK rod,L4/5 fusion fixation by PEEK rod,L4/5 fusion fixation by titanium rod,L3-5 nonfusion fixation by PEEK rod,L3-5 hybrid fixation by PEEK rod.Then 350 N compressive force was loaded on the surface of L1 vertebral body,40 Nm was applied to mimic the driving moment in the flextion and extension,lateral bending and axial rotation movement.The intervertebral pressure and range of motion at L2/3,L3/4,L4/5 level were recorded during the tests.A total of 38 patients from February 2012 to October 2012 were enrolled in the current study.The enrolled patients were diagnosed with lumbar degenerative diseases such as lumbar disc herniation,lumbar spinal stenosis,lumbar spondylolysis.All the patients were treated with nonfusion procedure by PEEK rod with decompression procedure if necessary.The Oswestry Disability Index(ODI)scores and Japanese Orthopaedics Association(JOA)scores were recorded preoperatively,one week postoperatively,three months postoperatively,six months postoperatively,12 months postoperatively and 24 months postoperatively.The disc height index and range of motion were also recorded.The integrity of PEEK rods was observed by three dimension reconstruction of CT scans.A total of 64 patients diagnosed with lumbar degenerative diseases from September 2012 to June 2013 were enrolled in the current study.All the patients were randomly assigned to the PEEK rod group or titanium group.In the PEEK rod group,the patients undertook hybrid procedure,while in the titanium group,the patients undertook interbody fusion procedure.The primary parameter for clinical outcome was ODI.The minimal clinically important difference(MCID)was set to be 10 points.The intervertebrae bone fusion was evaluated by CT reconstruction,successful fusion was defined as continuous bone formation between upper and lower endplate.Disc degeneration on the adjacent segment was evaluated by Pfirrmann classification on MRI scans.At least 8 points improvement in ODI scores was designed in the current study,standard deviation of preoperative ODI scores was about 9 points.Type Ⅰ error α was set to be 0.05 and TypeⅡerror β was set to be 0.1.It was estimated that 10% patients would lost to follow-up.Based on these premise,a total of 58 patients were needed for the current study.The intra-and inter-group consistencies were calculated by Fless Kappa value.Results The established finite element model was proven to be effective.The range of motion at the L3/4 level was 9.0°during flexion and extension in the intact model.When added titanium rod fixation at the L4/5 level,the range of motion at the L3/4 level increased to 12.5°.When added hybrid fixation by PEEK rods,the range of motion at the L3/4 level decrease to 2.5°.The range of motion at the L3/4 level was 6.7°during lateral bending in the intact model.When added titanium rod fixation at the L4/5 level,the range of motion at the L3/4 level increased to 7.4°.When added hybrid fixation by PEEK rods,the range of motion at the L3/4 level decrease to 2.5°.The range of motion at the L3/4 level was 6.0°during axial rotation in the intact model.When added titanium rod fixation at the L4/5 level,the range of motion at the L3/4 level increased to 7.4°.When added hybrid fixation by PEEK rods,the range of motion at the L3/4 level decrease to 2.6°.ResultThe intervertebral stress at the L3/4 level was 5.3MPa during flexion and extension in the intact model.When added titanium rod fixation at the L4/5 level,the intervertebral stress at the L3/4 level increased to 6.0MPa.When added hybrid fixation by PEEK rods,the intervertebral stress at the L3/4 level decreased to 2.4MPa.The intervertebral stress at the L3/4 level was 4.3MPa during lateral bending in the intact model.When added titanium rod fixation at the L4/5 level,the intervertebral stress at the L3/4 level increased to 4.8MPa.When added hybrid fixation by PEEK rods,the intervertebral stress at the L3/4 level decreased to 2.2MPa.The intervertebral stress at the L3/4 level was 4.2MPa during axial rotation in the intact model.When added titanium rod fixation at the L4/5 level,the intervertebral stress at the L3/4 level increased to 4.3MPa.When added hybrid fixation by PEEK rods,the intervertebral stress at the L3/4 level decreased to 2.5MPa.A total of 31 patients with mean age of 56.3 years old completed the final follow-up.There were 12 males and 19 females,with a mean 23.8 months follow-up.The mean ODI score was 51.4 preoperatively,37.8 one week postoperatively,15.2 three months postoperatively,14.4 six months postoperatively,13.2 one year postoperatively and 13.0 two years postoperatively.The mean JOA score was 13.7 preoperatively,15.9 one week postoperatively,22.0 three months postoperatively,22.2 six months postoperatively,23.4 one year postoperatively and 23.2 two years postoperatively.The mean DHI was 0.30 preoperatively,0.32 one week postoperatively,0.31 three months postoperatively,0.30 six months postoperatively,0.29 one year postoperatively and 0.27 two years postoperatively.The mean ROM was 8.8°preoperatively,2.1°one week postoperatively,2.1°three months postoperatively,2.1°six months postoperatively,2.0°one year postoperatively and 1.8°two years postoperatively.One patient demonstrated screw loosing at 12 months follow-up,but was asymptomatic during follow-up.As for hybrid procedure,there were 28 cases in the PEEK rod group and 27 cases in the titanium group who completed the follow-up.The mean ODI score in the PEEK rod group were 52.5±10.6 preoperatively and 14.4±3.2 two years postoperatively,while in the titanium group were 53.2±9.9 preoperatively and 14.9±2.5 two years postoperatively.The mean JOA score in the PEEK rod group were 15.0±2.5 preoperatively and 23.3±0.9 two years postoperatively,while in the titanium group were 15.6±2.2 preoperatively and 23.4±1.2 two years postoperatively.No PEEK rod breakage was detected at the final follow-up.Intervertebral bone fusion was observed in 19 patients in the PEEK rod group and in 20 patients in the titanium group.The Kappa value of intra and inter group consistencies was 0.93 and 0.89,respectively.The intervertebral disc signal changed in 12 patients at the adjacent level in the PEEK rod group.There were two cases from Pfirrmann 3 to 4,six cases from Pfirrmann 4 to 3,four cases from Pfirrmann 3 to 2.The intervertebral disc signal changed in 4 patients at the adjacent level in the titanium rod group.There were two cases from Pfirrmann 3 to 5,two cases from Pfirrmann 4 to 5.One patient in the PEEK rod group developed persisted low back pain at one month postoperatively.The pain was progressive and was diagnosed with cage subsidence seven months postoperatively.Revision surgery was carried out.Then intervertebral debridement and bone grafting was performed.The PEEK rods were replaced by titanium rods.The back pain was relieved immediately after the operation and no back pain developed during the two years follow-up.ConclusionPEEK rod pedicle based fixation could reduce the intervertebral disc pressure and limit the excess mobility.Hybrid surgery by PEEK rod could reduce the disc pressure at the adjacent segment.Nonfusion procedure by PEEK rod could achieve satisfactory clinical effects.Hybrid procedure by PEEK rod has a comparable clinical outcome to fusion procedure by titanium rod and may prevent or reverse the adjacent segment degeneration. |
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