title: Radial head translation measurement in healthy individuals: the radiocapitellar ratio.
abstract: OBJECTIVE
  We hypothesized that the radiocapitellar ratio (RCR) is a valid and reproducible method to assess radial head translation in healthy individuals and that the normal RCR of healthy individuals is 0%.
  
  
  METHODS
  Lateral radiographs of the elbow were examined in 40 healthy patients. The measurement method of the RCR was the displacement of the radial head (minimal distance between the right bisector of the radial head and the center of the capitellum) divided by the diameter of the capitellum. Intraobserver and interobserver reliability was evaluated using intraclass correlation (ICC).
  
  
  RESULTS
  The RCR was 4% ± 4% (range, -7% to 19%). The mean RCR of 4% measured in this cohort represents an anterior displacement of 1 mm in a capitellum of 25 mm. Intraobserver reliability was good (ICC, 0.72) and interobserver reliability was fair (ICC, 0.52). A significant side-to-side correlation was observed (r = 0.4, P = .009). No difference was identified between men and women, and no correlation was identified between age and the RCR. The standard deviation of the centered RCR measurements was 3%, which represented the variability of RCR measurements.
  
  
  CONCLUSIONS
  The results of this study confirm the traditional belief that in the normal elbow, the radial head is generally aligned towards the capitellum on lateral radiographs. Accordingly, a RCR observed outside the ranges of 1 mm posterior (-5%) to 3 mm anterior (13%) in a 25 mm capitellum suggests a misalignment at the RC joint of the elbow. The RCR method to assess RC joint translations has demonstrated a normal distribution in healthy individuals and good reliability.
authors: Hôpital du Sacré-Cœur de Montréal, Montréal, QC, Canada. dominique.rouleau@umontreal.ca
authors: Dominique M
authors: DM
authors: Rouleau
authors: Emilie
authors: E
authors: Sandman
authors: Fanny
authors: F
authors: Canet
authors: Ali
authors: A
authors: Djahangiri
authors: Yves
authors: Y
authors: Laflamme
authors: George S
authors: GS
authors: Athwal
authors: Yvan
authors: Y
authors: Petit
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D004551:Elbow Joint / Q000000981:diagnostic imaging*; D005260:Female; D005542:Forearm / Q000000981:diagnostic imaging / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D011859:Radiography; D011884:Radius / Q000000981:diagnostic imaging*; D012016:Reference Values; D015203:Reproducibility of Results; D012399:Rotation; D055815:Young Adult