Selective Fusion In Adolescent Idiopathic Scoliosis With Lenke 1A Type:An Analysis Of Risk Factors For Adding-on Phenomenon

ObjectivesTo identify the outcomes and evaluate possible risk factors for adding-on phenomenon following selective fusion in Lenke 1A type AIS and to investigate the optimal strategy to choose the lowest instrumented vertebra(LIV).MethodsA total of 43 patients were included in this study(15males,28 females,12-18 years old,average16).And the follow-up period reached at least 1 year,(12-50 months,mean time26.5 months).Radiographical parameters were measured and compared to see if they were different in two group(Adding-on and Non Adding-on).The occurrence of distsal adding-on was counted.A multiple logistic regression model was build to identify independent risk fators.Different treatment strategy for choosing LIV were compared in adding-on group and no Adding-on group,in order to find the optimal way to choose the lowest instrumented vertebra(LIV).ResultsOut of 380 patients reviewd,43 patients met the inclusion criteria.10 of these(23.26%)met the criteria for adding-on,and were classified in the adding-on group,the remaining 33 patients were included in the no adding-on group.The mean Cobb angle was 50.1°±11.3°before surgery,and 8.1°±4.3°at follow-up,the MT correction rate was 86.9%±6.7%.Preop LIV+1 deviation ?Lunbar flexibility? L4 subtype ?Preop Pelvic tilt in coronal plane and the difference in levels between LIV and LTV?LEV?SV were significantly associated with adding-on in Univariate analyses.Logistic regression model showed that Preop LIV+1 deviation(Preop LIV+1 deviation>10mm,OR=10.812,wald=4.930,P=0.026),Gap between LIV and LTV <1,OR =9.017,wald=4.239,P =0.04;1AR:1AL,OR=9.744,wald=3.951,P =0.047 were independent risk fators.ConclusionsIncidence of Adding-on increased when LIV+1deviation>10mm dramatically.Classifying the difference between L4 subtype may reduce the adding-on phenomenon.The LIV is so important to significantly associate with adding-on.Surgeon should fuse the spine to LTV+1,with the shorter fusion segment and saving more mobility,meanwhile,avoiding the adding-on phenomenon...