Distal Adding-on And Risk Factors In Severe And Rigid Scoliosis

Objective: To identify associated risk factors of distal adding-on in severe and rigid scoliosis.Methods: In this study,48 consecutive patients with severe and rigid scoliosis underwent posterior spinal fusion surgery in an institution from 2008 to 2013.The parameters of preoperative,immediately postoperative,and minimum 2-year follow-up radiographs were evaluated.The patients were grouped into distal adding-on positive and negative at follow-up and risk factors between the two groups were comparatively analyzed.Significant independent risk factors were identified by stepwise logistic regression analysis.Results: The follow-up time was from 24 to 52 months and the average follow-up period was 34.7 months.The average Cobb angle and flexibility of the main thoracic curve(MTC)were 107.4° ± 15.9° and 16.4% ± 10.2% before surgery.Distal adding-on was observed in 12 patients(25.0%)at follow-up.Univariate analysis identified several factors significantly associated with distal adding-on,including age,risser grades,the flexibility of the MTC,the postoperative MTC,the postoperative correction rate of the MTC and lumbar curve,the number of vertebra within fusion segment,the postoperative apical vertebral translation(AVT)of MTC,the postoperative lower instrumented vertebra(LIV)tilt angle,the follow-up MTC and correction rate of the MTC,and the AVT and LIV tilt angle at follow-up.In addition,the change of AVT and LIV-CSVL distance between preoperative and immediately postoperative data,and the change of LIV-CSVL distance between immediately postoperative and follow-up data were significantly different between the two groups.The difference in levels between the LIV and the lower end vertebra(LEV),stable vertebra(SV),deviating vertebra(DV),last touching vertebra(LTV),and last substantially touching vertebra(LSTV)were also risk factors related to distal adding-on.Significant independent risk factors identified by stepwise logistic regression analysis included the correction rate of the MTC immediately after surgery(odds ratio: 1.107,95% confidence interval: 1.024–1.197,P = 0.011)and the difference between the LIV and LTV levels(odds ratio: 0.121,95% confidence interval: 0.028–0.518,P = 0.004).Conclusion: In severe and rigid scoliosis,a high correction rate of the MTC immediately after surgery and the LIV level above the LTV were significantly associated with distal adding-on.