title: Distal Adding on in Lenke 1A Scoliosis: What Causes It? How Can It Be Prevented?
abstract: OBJECTIVE
  To investigate the causes and prevention of distal adding on in Lenke 1A scoliosis.
  
  
  METHODS
  Sixty Lenke 1A patients were included. The authors selected 10 potential risk factors for distal adding on. Postoperative increase in 5 radiographic parameters was used to indicate the extent of distal adding on. The authors then performed correlation analysis between the 10 potential risk factors and the extent of distal adding on, with the aim of identifying the causes of distal adding on. To predict 2-year outcome using preoperative parameters, linear regression models were established. The authors selected 2-year Cobb angle, thoracic apical vertebra center sacral vertical line (CSVL) distance and lowest instrumented vertebra (LIV)-CSVL distance to represent 2-year outcome. Their correlations with 8 preoperative parameters were tested.
  
  
  RESULTS
  Potential risk factors representing either LIV selection or skeletal immaturity were highly correlated with the 5 radiographic parameters, which suggests that LIV selection and skeletal immaturity are causative in connection with distal adding on. The formula for predicting 2-year LIV-CSVL distance was: 2-year LIV-CSVL distance = 9.9 + 0.8 (preoperative LIV-CSVL distance) - 4.2 (Risser sign grade). The model adjusted R2= 0.77.
  
  
  CONCLUSIONS
  In Lenke 1A scoliosis, both LIV selection and skeletal immaturity are highly correlated with distal adding on. In other words, the shorter the extent is of distal fusion, the larger is the distal adding on; the less skeletally mature the patient is, the larger is the distal adding on. When treating skeletally immature patients (Risser sign ≤3) with 1A curves, performing fusion surgeries should be avoided when possible; growing rod treatment may be the optimal treatment choice. For skeletally mature patients, LIV selection should be the first consideration; the preoperative LIV-CSVL distance should be ≤21 mm when the Risser sign grade is 4 and ≤ 26 mm when the Risser sign grade is 5.
authors.affiliation: Department of Orthopaedics E, Aarhus University Hospital, Norrebrogade 44, Aarhus 8000, Denmark; Department of Orthopaedics, Peking University First Hospital, Xishiku Street 8, Beijing 100034, China. Electronic address: yu.wang@ki.au.dk.
authors.forename: Yu
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Department of Orthopaedics E, Aarhus University Hospital, Norrebrogade 44, Aarhus 8000, Denmark.
authors.forename: Cody Eric
authors.initials: CE
authors.lastname: Bünger
authors.affiliation: Department of Orthopaedics E, Aarhus University Hospital, Norrebrogade 44, Aarhus 8000, Denmark.
authors.forename: Yanqun
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Department of Epidemiology, School of Public Health, Nordre Ringgade 1, Aarhus 8000, Denmark.
authors.forename: Chunsen
authors.initials: C
authors.lastname: Wu
authors.affiliation: Department of Orthopaedics E, Aarhus University Hospital, Norrebrogade 44, Aarhus 8000, Denmark.
authors.forename: Haisheng
authors.initials: H
authors.lastname: Li
authors.affiliation: Department of Orthopaedics E, Aarhus University Hospital, Norrebrogade 44, Aarhus 8000, Denmark.
authors.forename: Ebbe Stender
authors.initials: ES
authors.lastname: Hansen
keywords: Adding on; Fusion extent; Lenke 1A; Lowest instrumented vertebra; Scoliosis