Study Of Correlation Between Sagittal Alignment And Symptomatic Adjacent Segment Degeneration After Posterior Lumbar Interbody Fusion

STUDY DESIGN:Case-controlled studyBACKGROUND:Posterior lumbar interbody fusion（PLIF）is more and more widely used in degenerative lumbar disease,the adjacent segments degeneration（ASD）is one of the most important long-term complication,among which,symptomatic adjacent segment degeneration（SASD）will seriously influence the effect of surgery,even need a revision surgery.Previous studies reported preliminary studies on risk factors of adjacent segment degeneration after lumbar fusion,including long segment fixation,decompression at the adjacent segment without fixation and preoperative adjacent segment degeneration.At the same time,the influence of sagittal balance on the clinical outcomes has been attracting an increasingly attention.However,little is known about the correlation between symptomatic adjacent segment degeneration（SASD）and spinopelvic sagittal parameters.OBJECTIVE:By comparing the difference of spinopelvic sagittal parameters between the case group and the control group pre-operative and the last follow-up,we discussed the correlation between symptomatic adjacent segment degeneration after lumbar fusion and spinopelvic sagittal parameters.METHODS:This was a retrospective 1:5 matched case-control study.25 patients who had undergone revision surgery for symptomatic adjacent segment degeneration（SASD）after L_4-5 or L₄-S₁PLIF and had standing radiographs of the whole spine before primary and revision surgeries were enrolled from January 2013 to October 2017 in the Department of orthopedics of Shanghai Changhai Hospital,including 11 cases of male,14 were female,the average age is55.8 years old（28⁷6 years old）,the average BMI is 26.9Kg/m²（21.6 Kg/m²³7.1 Kg/m²）,in the first surgery,8 cases undergone a L₄-L₅ fixation,while 17 cases of L₄-S₁ fixation,symptoms occurred in the cephalic side in 16 cases,caudal side in 5 cases,4 cases of bilateral side.The interval time between two surgery is 79.6 months（12¹68 months）.Then,measuring the spinopelvic sagittal parameters in the standing radiographs of the whole spine before primary and revision surgeries,including thoracic kyphosis（TK）,total lumbar lordosis（TLL）,low lumbar lordosis（LLL）,pelvic incidence（PI）,pelvic tilt（PT）,sacral slope（SS）,sagittal vertical axis（SVA）,and calculating the ratio of LLL to TLL,marked R_L.As a control group,50 age-,sex-,and pathology-matched patients who had undergone L_4-5 or L₄-S₁ PLIF during the same period,had no signs of SASD for more than 1 years,and had whole spine radiographs at pre-operation and last follow-up were selected,of which 24 were male,26were female,18 cases fixed with L₄-L₅ and L₄-S₁ fixation in 32 cases,the average age at the primary surgery is 55.2 years（32⁸2 years）,the average BMI is 24.8Kg/m²（19.2 Kg/m²³1.4Kg/m²）,the average follow-up time is 78.8 months（12¹60 months）,also measuring the spinopelvic sagittal parameters.RESULTS AND CONCLUSION:No significant difference of demographics of patients was found in case and control group（P>0.05）.In the case group,LLL before the first surgery was smaller than the revision surgery,meanwhile,the number of cases whose R_L<60%becomes more before the revision surgery,the difference was statistically significant.In the control group,all the parameters have no significant differences between the preoperative and final follow-up.In terms of preoperative radiographic parameters,the case group had significantly lower TLL（p<0.01）and significantly higher PT（p<0.05）than the control group,and had significantly more case whose PT-TLL≥10°and SVA>50mm（p<0.05）than the control group.Before the revision surgery,TLL in the case group was significantly lower when compared to the control group（P<0.01）,and RL<60%was seen in 21 of 25 patients（84%）in the case group and in 17 of 50patients（75%,P<0.01）,which was similar to the data pre-operation.The case number of PT-TLL≥10°were significantly higher than the control group.By statistical analysis,preoperative lower TLL and sagittal imbalance（SVA>50mm）were being regarded as the risk factors for the occurrence of SASD;furthermore,R_L<60%post operation has an obvious relevance with SASD,thus,compensatory kyphosis occurring in the adjacent segment following the poor recovery of lordosis in the surgical segment may be one of the reasons for SASD.