title: Characterization and Predictive Value of Segmental Curve Flexibility in Adolescent Idiopathic Scoliosis Patients.
abstract: METHODS
  A prospective radiographic analysis of adolescent idiopathic scoliosis (AIS) patients managed with alternate-level pedicle screw fixation was performed.
  
  
  OBJECTIVE
  The objective of this study was to characterize segmental curve flexibility and to determine its predictive value in curve correction in AIS patients.
  
  
  BACKGROUND
  Little is known regarding the distinct segmental curve characteristics and their ability to predict curve correction in patients with AIS.
  
  
  METHODS
  The segmental Cobb angle was measured on posteroanterior standing radiographs and on fulcrum bending radiographs. Radiographs were analyzed preoperatively and at 2 years postoperatively and the curve was divided into upper, mid, and lower segments based on predefined criteria. The segmental flexibility and the segmental fulcrum bending correction index (FBCI) were calculated.
  
  
  RESULTS
  Eighty patients were included with mean age of 15 years. Preoperative mean segmental Cobb angles were 18, 31, and 17 degrees in the upper, mid, and lower segments, respectively. Segmental bending Cobb angles were 6, 13, and 4 degrees, respectively, corresponding to segmental flexibilities of 50%, 47%, and 83% in the upper, mid, and lower segments, respectively (P < 0.001). At 2-year follow up, the mean segmental FBCI were 155%, 131%, and 100% in the upper, mid, and lower segments, respectively (P < 0.001), which suggested that the lower segment of the curve was more flexible than the other segments and that higher correction was noted in the upper segments. A significant, positive correlation was noted between the segmental bending Cobb angle and the segmental FBCI (P < 0.05), whereby the strength of the correlation varied based on the curve segment.
  
  
  CONCLUSIONS
  This is the first study to demonstrate the segmental variations in curve flexibility using the fulcrum bending radiograph in AIS patients. Curve flexibility is not uniform throughout the curve and different segments exhibit greater flexibility/correctibility than others. Segmental flexibility should be considered in assessing AIS patients and in the clinical decision-making strategy to optimize curve correction outcomes.
  
  
  METHODS
  03.
authors.affiliation: Department of Orthopedics and Traumatology, University of Hong Kong, Pokfulam, Hong Kong, SAR, China.|Department of Orthopedics, Shantou University Medical College, Guangdong, China.
authors.forename: Guanfeng
authors.initials: G
authors.lastname: Yao
authors.affiliation: Department of Orthopedics and Traumatology, University of Hong Kong, Pokfulam, Hong Kong, SAR, China.
authors.forename: Jason P Y
authors.initials: JPY
authors.lastname: Cheung
authors.affiliation: Department of Orthopedics and Traumatology, University of Hong Kong, Pokfulam, Hong Kong, SAR, China.|Department of Orthopedic Surgery, Nara Medical University, Kashihara, Nara, Japan.
authors.forename: Hideki
authors.initials: H
authors.lastname: Shigematsu
authors.affiliation: Department of Orthopedics and Traumatology, University of Hong Kong, Pokfulam, Hong Kong, SAR, China.|Department of Orthopedics, Rigshospitalet, Denmark.
authors.forename: Søren
authors.initials: S
authors.lastname: Ohrt-Nissen
authors.affiliation: Department of Orthopedics and Traumatology, University of Hong Kong, Pokfulam, Hong Kong, SAR, China.
authors.forename: Kenneth M C
authors.initials: KMC
authors.lastname: Cheung
authors.affiliation: Department of Orthopedics and Traumatology, University of Hong Kong, Pokfulam, Hong Kong, SAR, China.
authors.forename: Keith D K
authors.initials: KDK
authors.lastname: Luk
authors.affiliation: Department of Orthopedics and Traumatology, University of Hong Kong, Pokfulam, Hong Kong, SAR, China.
authors.forename: Dino
authors.initials: D
authors.lastname: Samartzis
mesh_terms: D000293:Adolescent; D002648:Child; D000066491:Clinical Decision-Making / Q000379:methods; D005260:Female; D006801:Humans; D008297:Male; D065289:Pedicle Screws / Q000639:trends*; D011237:Predictive Value of Tests; D011446:Prospective Studies; D016059:Range of Motion, Articular / Q000502:physiology; D012600:Scoliosis / Q000000981:diagnostic imaging* / Q000503:physiopathology / Q000601:surgery*; D013123:Spinal Fusion / Q000295:instrumentation / Q000639:trends*; D000078783:Standing Position; D013904:Thoracic Vertebrae / Q000601:surgery