title: Intraobserver and Interobserver Measurement Variability of the Rib-Vertebral Angle Difference.
abstract: BACKGROUND
  The rib-vertebral angle (RVAD) differentiates between progressive and resolving infantile idiopathic scoliosis (IIS) curves. Those with a RVAD<20 degrees often resolve without treatment, whereas those >20 degrees often progress and require treatment. The mathematical magnitude of RVAD measurement variability has not been described, and was thus the purpose of this study. It is important to know the reliability of RVAD measurements so as to understand changes that can be attributed to observer error alone.
  
  
  OBJECTIVE
  The purpose of the study was to mathematically determine the intraobserver and interobserver measurement variability of the RVAD difference in IIS.
  
  
  METHODS
  A convenience sample of 50 patients with IIS was selected. The RVAD was measured twice by 7 different observers separated by a minimum of 3 weeks. The 7 different readers chosen to measure the RVAD were 2 orthopaedic residents, 1 pediatric radiologist, and 4 attending pediatric orthopaedic surgeons. The same goniometer was used for all measurements. Intraobserver and interobserver measurement variability was determined using 3 well known used statistical methods.
  
  
  RESULTS
  The 3 different methods used to determine intraobserver and interobserver variability using 95% prediction/confidence limits gave very similar results. Intraobserver variability was ∼24 degrees and the interobserver variability was ∼23 degrees.
  
  
  CONCLUSIONS
  The utility of the RVAD in medical decision-making and counseling of patients with IIS should be approached with caution when used in isolation due to the large measurement variability.
  
  
  METHODS
  Level 3.
authors.affiliation: Departments of Orthopaedic Surgery.
authors.forename: Robert G
authors.initials: RG
authors.lastname: Tysklind
authors.affiliation: Departments of Orthopaedic Surgery.
authors.forename: Karen
authors.initials: K
authors.lastname: Myung
authors.affiliation: Departments of Orthopaedic Surgery.
authors.forename: George
authors.initials: G
authors.lastname: Gantsoudes
authors.affiliation: Departments of Orthopaedic Surgery.
authors.forename: Shyam
authors.initials: S
authors.lastname: Kishan
authors.affiliation: Departments of Orthopaedic Surgery.
authors.forename: Chad
authors.initials: C
authors.lastname: Turner
authors.affiliation: Departments of Orthopaedic Surgery.
authors.forename: Stella
authors.initials: S
authors.lastname: Lee
authors.affiliation: Radiology, Indiana University School of Medicine, and the James Whitcomb Riley Children's Hospital, Indianapolis, IN.
authors.forename: Matthew
authors.initials: M
authors.lastname: Wanner
authors.affiliation: Departments of Orthopaedic Surgery.
authors.forename: Meagan
authors.initials: M
authors.lastname: Sabatino
authors.affiliation: Departments of Orthopaedic Surgery.
authors.forename: Scott
authors.initials: S
authors.lastname: Linger
authors.affiliation: Departments of Orthopaedic Surgery.
authors.forename: Randall T
authors.initials: RT
authors.lastname: Loder
mesh_terms: D002675:Child, Preschool; D005260:Female; D006801:Humans; D007223:Infant; D008297:Male; D055641:Mathematical Concepts; D015588:Observer Variation; D011859:Radiography; D015203:Reproducibility of Results; D012189:Retrospective Studies; D012272:Ribs / Q000000981:diagnostic imaging / Q000473:pathology*; D012600:Scoliosis / Q000000981:diagnostic imaging / Q000473:pathology*; D013904:Thoracic Vertebrae / Q000000981:diagnostic imaging / Q000473:pathology*