title: Reproducibility of thoracic kyphosis measurements in patients with adolescent idiopathic scoliosis.
abstract: BACKGROUND
  Current surgical treatment for adolescent idiopathic scoliosis (AIS) involves correction in both the coronal and sagittal plane, and thorough assessment of these parameters is essential for evaluation of surgical results. However, various definitions of thoracic kyphosis (TK) have been proposed, and the intra- and inter-rater reproducibility of these measures has not been determined. As such, the purpose of the current study was to determine the intra- and inter-rater reproducibility of several TK measurements used in the assessment of AIS.
  
  
  METHODS
  Twenty patients (90% females) surgically treated for AIS with alternate-level pedicle screw fixation were included in the study. Three raters independently evaluated pre- and postoperative standing lateral plain radiographs. For each radiograph, several definitions of TK were measured as well as L1-S1 and nonfixed lumbar lordosis. All variables were measured twice 14 days apart, and a mixed effects model was used to determine the repeatability coefficient (RC), which is a measure of the agreement between repeated measurements. Also, the intra- and inter-rater intra-class correlation coefficient (ICC) was determined as a measure of reliability.
  
  
  RESULTS
  Preoperative median Cobb angle was 58° (range 41°-86°), and median surgical curve correction was 68% (range 49-87%). Overall intra-rater RC was highest for T2-T12 and nonfixed TK (11°) and lowest for T4-T12 and T5-T12 (8°). Inter-rater RC was highest for T1-T12, T1-nonfixed, and nonfixed TK (13°) and lowest for T5-T12 (9°). Agreement varied substantially between pre- and postoperative radiographs. Inter-rater ICC was highest for T4-T12 (0.92; 95% CI 0.88-0.95) and T5-T12 (0.92; 95% CI 0.88-0.95) and lowest for T1-nonfixed (0.80; 95% CI 0.72-0.88).
  
  
  CONCLUSIONS
  Considerable variation for all TK measurements was noted. Intra- and inter-rater reproducibility was best for T4-T12 and T5-T12. Future studies should consider adopting a relevant minimum difference as a limit for true change in TK.
authors.affiliation: Spine Unit, Department of Orthopedic Surgery, Rigshospitalet, University of Copenhagen, Blegdamsvej 9, Copenhagen East, 2100 Denmark.
authors.forename: Søren
authors.identifier: 0000-0002-8234-9948
authors.initials: S
authors.lastname: Ohrt-Nissen
authors.affiliation: Department of Orthopedics and Traumatology, The University of Hong Kong, Professorial Block, 5th Floor 102 Pokfulam Road, Hong Kong, SAR China.
authors.forename: Jason Pui Yin
authors.initials: JPY
authors.lastname: Cheung
authors.affiliation: Spine Unit, Department of Orthopedic Surgery, Rigshospitalet, University of Copenhagen, Blegdamsvej 9, Copenhagen East, 2100 Denmark.
authors.forename: Dennis Winge
authors.initials: DW
authors.lastname: Hallager
authors.affiliation: Spine Unit, Department of Orthopedic Surgery, Rigshospitalet, University of Copenhagen, Blegdamsvej 9, Copenhagen East, 2100 Denmark.
authors.forename: Martin
authors.initials: M
authors.lastname: Gehrchen
authors.affiliation: Department of Orthopedics and Traumatology, The University of Hong Kong, Professorial Block, 5th Floor 102 Pokfulam Road, Hong Kong, SAR China.
authors.forename: Kenny
authors.initials: K
authors.lastname: Kwan
authors.affiliation: Spine Unit, Department of Orthopedic Surgery, Rigshospitalet, University of Copenhagen, Blegdamsvej 9, Copenhagen East, 2100 Denmark.
authors.forename: Benny
authors.initials: B
authors.lastname: Dahl
authors.affiliation: Department of Orthopedics and Traumatology, The University of Hong Kong, Professorial Block, 5th Floor 102 Pokfulam Road, Hong Kong, SAR China.
authors.forename: Kenneth M C
authors.initials: KMC
authors.lastname: Cheung
authors.affiliation: Department of Orthopedics and Traumatology, The University of Hong Kong, Professorial Block, 5th Floor 102 Pokfulam Road, Hong Kong, SAR China.
authors.forename: Dino
authors.initials: D
authors.lastname: Samartzis
keywords: Adolescent idiopathic scoliosis; Agreement; Flexibility; Intra-class correlation; Kyphosis; Limits of agreement; Mixed effects model; Radiograph; Reliability; Repeatability coefficient; Reproducibility; Sagittal; Thoracic