title: Predictors of Distal Adding-on in Thoracic Major Curves With AR Lumbar Modifiers.
abstract: METHODS
  Retrospective review of prospectively collected data.
  
  
  OBJECTIVE
  To determine whether the last substantially touched vertebra (LSTV) is a valid lowest instrumented vertebra (LIV) for both Lenke 1 and 2 curve patterns with AR lumbar modifiers, and to identify preoperative risk factors of distal adding-on.
  
  
  BACKGROUND
  Previous studies have recommended selecting the LSTV as the LIV for Lenke 1AR curves (main thoracic curve with A lumbar modifier and L4 tilt to the right (thoracic overhang/King type IV curve).
  
  
  METHODS
  One-hundred sixty patients with a Lenke 1 or 2 curve pattern and AR lumbar modifier who underwent posterior spinal fusion between 2008 and 2012 were reviewed. All patients had minimum 2-year follow up. Patients were identified with distal adding-on between first erect radiographs and 2-year follow up based on previously defined parameters. Factors predictive of the adding-on phenomenon were identified in a multivariate binary logistic regression model.
  
  
  RESULTS
  Twenty-seven patients (17%) were identified as having distal adding-on of their primary thoracic curve; however, only 8 of 89 patients (9%) fused to the LSTV developed adding-on (P = 0.005). Three variables were found to be significant predictors of adding-on: LIV proximal to LSTV (odds ratio, OR 3.63; P = 0.01), Risser zero (OR 4.93; P = 0.02), and C7-CSVL distance <2 cm (OR 3.97; P = 0.01). The risk of adding-on increased as the number of predictors increased from 16% with one risk factor to 80% when all three preoperative risk factors were present (P < 0.001).
  
  
  CONCLUSIONS
  Choosing the LSTV as the LIV in Lenke 1 and 2 curve patterns with an AR lumbar modifier significantly decreases the risk of distal adding-on. Skeletally immature patients, those fused short of LSTV, and those with relative coronal balance preoperatively are at increased risk of distal adding-on between the initial postoperative visit and 2-year follow up.
  
  
  METHODS
  4.
authors.affiliation: Children's Orthopedics of Atlanta, Atlanta, GA.
authors.forename: Joshua S
authors.initials: JS
authors.lastname: Murphy
authors.affiliation: Department of Orthopedics, Rady Children's Hospital, San Diego, CA.|Department of Orthopedics, University of California, San Diego, CA.
authors.forename: Vidyadhar V
authors.initials: VV
authors.lastname: Upasani
authors.affiliation: Department of Orthopedics, University of California, San Diego, CA.
authors.forename: Burt
authors.initials: B
authors.lastname: Yaszay
authors.affiliation: Department of Orthopedics, University of California, San Diego, CA.
authors.forename: Tracey P
authors.initials: TP
authors.lastname: Bastrom
authors.affiliation: Department of Orthopedics, University of California, San Diego, CA.
authors.forename: Carrie E
authors.initials: CE
authors.lastname: Bartley
authors.affiliation: Department of Orthopedics, Shriners Hospital for Children, Philadelphia, PA.
authors.forename: Amer
authors.initials: A
authors.lastname: Samdani
authors.affiliation: Department of Orthopedics, Columbia University, New York, NY.
authors.forename: Lawrence G
authors.initials: LG
authors.lastname: Lenke
authors.affiliation: Department of Orthopedics, Rady Children's Hospital, San Diego, CA.
authors.forename: Peter O
authors.initials: PO
authors.lastname: Newton
mesh_terms: D000293:Adolescent; D001863:Bone Screws; D002648:Child; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008159:Lumbar Vertebrae / Q000601:surgery*; D008161:Lumbosacral Region / Q000601:surgery; D008297:Male; D011183:Postoperative Complications / Q000209:etiology; D011237:Predictive Value of Tests; D011859:Radiography / Q000379:methods; D012189:Retrospective Studies; D012307:Risk Factors; D012600:Scoliosis / Q000175:diagnosis* / Q000601:surgery*; D013123:Spinal Fusion / Q000379:methods; D013904:Thoracic Vertebrae / Q000601:surgery*; D016896:Treatment Outcome