title: Prediction of scoliosis correction with thoracic segmental pedicle screw constructs using fulcrum bending radiographs.
abstract: METHODS
  A retrospective series of 35 idiopathic scoliosis patients underwent spinal fusion with a segmental thoracic pedicle screw system.
  
  
  OBJECTIVE
  To evaluate the amount of scoliosis correction with segmental pedicle screw constructs, and assess whether the fulcrum bending radiograph can predict surgical correction.
  
  
  BACKGROUND
  The fulcrum bending radiograph is highly predictive of actual curve correction based on hook or hybrid systems. However, its predictive value in segmental pedicle screw fixation systems has not been reported.
  
  
  METHODS
  Patients diagnosed with Lenke type 1A and 1B thoracic idiopathic scoliosis who underwent posterior spinal fusion with segmental pedicle screw constructs by single surgeon from January 2000 to December 2005 were reviewed. The fulcrum flexibility rate (FFR) and correction rate were compared. Stepwise linear regression analysis was done and a prediction equation for the postoperative Cobb angle was developed.
  
  
  RESULTS
  Thirty-five consecutive patients were included. Age at surgery was 14.8 years. Twenty scoliosis deformities were flexible, 15 were rigid. All patients had at least 2-year follow-up. The average preoperative Cobb angle was 58 degrees , fulcrum bending Cobb angle was 28 degrees , and postoperative Cobb angle 15 degrees and 16 degrees at 1 month and 2 years, respectively, after surgery. There was significant difference between FFR (51%) and correction rate at 1 month (72%) and 2 year (70%) after surgery. The difference between fulcrum bending corrective index of flexible (122%) and rigid (203%) curves was statistically significant. Stepwise linear regression analysis showed: Predicted postoperative Cobb angle = 0.012 + 1.75 x age - 0.212 x FFR (R = 0.69, P < 0.01).
  
  
  CONCLUSIONS
  Thoracic pedicle screw constructs achieved better scoliosis correction compared with fulcrum bending radiographs. The fulcrum bending corrective index achieved was significantly greater in rigid than flexible curves. The postoperative Cobb angles could be calculated with a predictive equation.
authors.affiliation: Department of Orthopaedics and Traumatology, The University of Hong Kong, Hong Kong, China. lcheung@hkucc.hku.hk
authors.forename: Wai Yuen
authors.initials: WY
authors.lastname: Cheung
authors.forename: Lawrence G
authors.initials: LG
authors.lastname: Lenke
authors.forename: Keith D K
authors.initials: KD
authors.lastname: Luk
mesh_terms: D000293:Adolescent; D001863:Bone Screws; D005260:Female; D006801:Humans; D016268:Internal Fixators; D008297:Male; D011859:Radiography; D012044:Regression Analysis; D012189:Retrospective Studies; D012600:Scoliosis / Q000000981:diagnostic imaging / Q000601:surgery*; D013123:Spinal Fusion / Q000295:instrumentation / Q000379:methods*; D013904:Thoracic Vertebrae / Q000000981:diagnostic imaging / Q000601:surgery*; D016896:Treatment Outcome