Radiographic Restoration of Sagittal Spinopelvic Alignment after Posterior Lumbar Interbody Fusion in Degenerative Spondylolisthesis
|School||Hebei Medical University|
|Keywords||Degenerative spondylolisthesis spinopelvic parameters posterior lumbar interbody fusion slip angle sagittal spinopelvic alignment|
Objective: Lumbar degenerative spondylolisthesis is defined as slippageof a lumbar vertebra with an intact neural arch and occurs mostly at L4–L5inadults older than40years. Degenerative spondylolisthesis was characterizedby a high pelvic incidence and sacral slope, and those parameters might playan important role in the pathomechanism of degenerative spondylolisthesis.The basic deformities of degenerative spondylolisthesis are forward slippageof the vertebral body, segmental kyphotic angle, and loss of disc height.Correction of those deformities during surgery will subsequently affect thespinopelvic parameters. The purpose of this study was to analyze thespontaneous changes in spinopelvic parameters after surgical correction ofdegenerative spondylolisthesis and to determine which deformity is mostresponsible for changes in spinopelvic alignment.Methods: We retrospectively reviewed patients with L4-L5degenerativespondylolisthesis from January2010to July2012at our institute.Spondylolisthesis was defined as the L4vertebra has slipped forward>10%.The operation was performed on those who had persistent low back pain,radicular pain, or neurological claudication in spite of conservative treatmentfor at least3months. Patients with a history of previous spine surgery, surgeryat more than1level, vertebral fracture, retrolisthesis, or degenerative scoliosiswere excluded. At last,53patients were included in this study. All patientsunderwent posterior lumbar interbody fusion surgery. Patients’ scheduledregular follow-up visits were recommended at1,3,6, and12monthspostoperatively, and then annually. All patients were examined clinically andradiographically before surgery and during follow-up. The preoperative andfinal follow-up data were assessed. Clinical outcomes were evaluated by asking patients to quantify the back pain on a visual analogue scale (VAS)from1to10(1, no pain;10, worst possible pain). Patients were divided intotwo groups based on if changes of VAS≥3or not, and postoperativespinopelvic parameters were compared statistically between the two groups.Each patient had a standing lateral radiograph including the T12vertebra andthe femoral heads. The spinopelvic parameters and deformity parameters weremeasured on the radiographs. Sagittal spinopelvic parameters included sacralslope (SS), pelvic tilt (PT), lumbar lordosis (LL), and L1axis S1distance(LASD). Deformity parameters included slip degree (SD), slip angle (SA), andheight of the intervertebral disc (HOD). The correction of deformity and thesubsequent changes in spinopelvic parameters were calculated and analyzed.We also investigated the correlation between the postoperative correction ofdeformity and the spontaneous changes in spinopelvic parameters. Data wereanalyzed using the Statistical Package for the Social Sciences (version13.0forWindows; SPSS, Chicago, IL, USA), A P-value of <0.05was considered to bestatistically significant.Results: A total of53patients were enrolled in this study. The mean ageof the patients at surgery was58.3years (range,41-78years). Fifteen patients(28.3%) were men, and38patients (71.7%) were women. The mean follow-upperiod was23.8months (range,12-42months). In the analysis ofpostoperative correction of focal deformity, the SD decreased from16.5±5.2mm to5.1±3.3mm, the SA increased from7.3±5.9degrees to14.6±4.8degrees, and the HOD increased from8.3±3.0mm to13.9±2.5mm. Alldeformity parameters showed significant changes after surgery (P<0.01). Inthe analysis of postoperative change in spinopelvic parameters, the SSincreased from38.8±7.1degrees to43.6±7.2degrees, the PT decreased from20.2±8.3degrees to15.3±7.8degrees, the LL increased from58.0±10.4degrees to62.3±9.9degrees, and the LASD moved posteriorly from25.1±18.9mm to20.1±19.2mm. All spinopelvic parameters were restored significantlyafter surgery (P<0.01). Patients showed a relief of back pain after surgery.VAS score for all patients was6.1±2.3before surgery and decreased to 2.4±1.7at the final follow-up assessment. Patients were divided into twogroups based on changes of VAS. The group with changes of VAS score≥3included30patients, and showed significantly higher SS and LL, and lowerPT compared with the other group, in which there were23patients withchanges of VAS score <3. In the analysis of correlation between correction offocal deformity and changes in the spinopelvic parameters, there weresignificant correlations between restoration of the SA and improvement of LL(r=0.32, P=0.02), improvement of SS (r=0.29, P=0.03), and decrease ofPT (r=-0.29, P=0.03). However, the correlation between restoration of SAand decrease of LASD were poor. Besides, the correction of the SD and HODdid not have significant correlation with changes in any spinopelvicparameters (P>0.05).Conclusion: After correction of the focal deformities, the sagittalspinopelvic alignment changed subsequently: the center of gravity has aposterior displacement, the pelvis tilts forward, sacral endplate become morevertical and global lumbar achieves larger lordosis. This was reflected bydecreased PT and LASD, increased SS and LL. Patients with better relief inback pain showed higher SS and LL, and lower PT. It seems that the clinicaloutcome is associated with the postoperative spinopelvic alignment. surgicalcorrection of degenerative spondylolisthesis using posterior lumbar interbodyfusion and posterior instrumentation resulted in significant changes inspinopelvic parameters. Among those deformity parameters, the SA wassignificantly correlated with spontaneous increase of LL and SS, and decreaseof PT. We suggest that surgeons should consider these parameters, especiallythe SA, in the surgical treatment of degenerative spondylolisthesis.