title: Postoperative trunk shift in Lenke 1C scoliosis: what causes it? How can it be prevented?
abstract: METHODS
  A risk factor analysis study.
  
  
  OBJECTIVE
  To identify the causative factors for postoperative trunk shift in Lenke 1C scoliosis and investigate how to prevent it.
  
  
  BACKGROUND
  When selective thoracic fusion is performed, postoperative trunk shift is a significant problem in the management of Lenke 1C scoliosis. It is often accompanied by unsatisfactory clinical outcomes and a risk of reoperation.
  
  
  METHODS
  We reviewed all the patients with adolescent idiopathic scoliosis (AIS) surgically treated in our institution from 2002 through 2008. Inclusion criteria were as follows: (1) patients with Lenke 1C curves who were treated with selective thoracic fusion using posterior pedicle screw-only constructs; (2) the lowest instrumented vertebra (LIV) ending at L1 level or above; and (3) 2-year radiographical follow-up. Eighteen radiographical parameters were chosen as potential risk factors. The 18 parameters measured (1) amount of correction obtained by surgery; (2) preoperative position of LIV; (3) magnitude of major thoracic and thoracolumbar/lumbar (MT and TL/L) curves and ratio of MT: TL/L curve; and (4) curve flexibility. Both comparative and correlation analyses were performed. Those parameters that had shown highest correlation with the 2-year thoracic apical vertebra-center sacral vertical line (AV-CSVL) distance were selected to form a linear regression model, by which the correlations were quantified.
  
  
  RESULTS
  Of the 278 patients reviewed, 44 met the inclusion criteria. The parameters that measured the preoperative position of LIV and ratio of MT: TL/L curve showed high correlation with the 2-year thoracic AV-CSVL distance. With regard to the parameters that measured the amount of correction obtained by surgery, only the correction of the thoracic AV-T1 distance showed low correlation. Among the 18 parameters, preoperative lowest instrumented vertebra-lower end vertebra (LIV-LEV) difference and ratio of MT: TL/L Cobb angle were selected to form a formula to help predict postoperative trunk shift. The formula was as follows: 2-year thoracic AV-CSVL distance = -26.6 + 22.7 (ratio of MT: TL/L Cobb angle) - 3.9 (preoperative LIV-LEV difference). The model R2 = 0.55.
  
  
  CONCLUSIONS
  Both LIV selection and ratio of MT: TL/L curve were found to be highly correlated with the onset of postoperative trunk shift in Lenke 1C scoliosis. Amount of correction obtained by surgery, however, did not seem to be an independent causative factor. Postoperative trunk shift is less likely to occur when selecting LEV as LIV and the ratio of MT: TL/L Cobb angle of 1.2° or more.
authors.affiliation: Department of Orthopaedics E, Aarhus University Hospital, Aarhus, Denmark. yu.wang@ki.au.dk
authors.forename: Yu
authors.initials: Y
authors.lastname: Wang
authors.forename: Cody Eric
authors.initials: CE
authors.lastname: Bünger
authors.forename: Chunsen
authors.initials: C
authors.lastname: Wu
authors.forename: Yanqun
authors.initials: Y
authors.lastname: Zhang
authors.forename: Ebbe Stender
authors.initials: ES
authors.lastname: Hansen
mesh_terms: D000293:Adolescent; D001863:Bone Screws; D002648:Child; D005260:Female; D006801:Humans; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging / Q000601:surgery; D008297:Male; D011183:Postoperative Complications / Q000209:etiology* / Q000517:prevention & control; D011859:Radiography; D012189:Retrospective Studies; D012307:Risk Factors; D012600:Scoliosis / Q000000981:diagnostic imaging / Q000601:surgery*; D013123:Spinal Fusion / Q000009:adverse effects / Q000295:instrumentation; D013904:Thoracic Vertebrae / Q000000981:diagnostic imaging / Q000601:surgery; D060726:Torso; D016896:Treatment Outcome; D055815:Young Adult