title: Comparison of quadriceps angle measurements using short-arm and long-arm goniometers: correlation with MRI.
abstract: OBJECTIVE
  To compare the reliability of quadriceps-angle (Q-angle) measurements performed using a short-arm goniometer and a long-arm goniometer and to assess the accuracy of goniometer-based Q-angle measurements compared with anatomic Q angles derived from magnetic resonance imaging (MRI).
  
  
  METHODS
  An intra- and interobserver reliability study.
  
  
  METHODS
  University hospital.
  
  
  METHODS
  Eighteen healthy subjects with no history of knee pain, trauma, or prior surgery were examined.
  
  
  METHODS
  Two physicians, blinded to subject identity, measured Q angles on both knees of all subjects using 2 goniometers: (1) a short-arm goniometer and (2) a long-arm goniometer. Q angles were derived from axial MRIs of the subjects' hip and knees.
  
  
  METHODS
  The intra- and interobserver reliabilities of each goniometer were assessed using the intraclass correlation coefficient (ICC). The comparison between clinical and MRI-based Q angles was assessed by using the ICC and a paired t-test.
  
  
  RESULTS
  Intra- and interobserver reliabilities of the long-arm goniometer (intraobserver ICC, 0.92; interobserver ICC, 0.88) were better than those of the short-arm goniometer (intraobserver ICC, 0.78; interobserver ICC, 0.56). Although both goniometers measured Q angles that were moderately correlated to the MRI-based measurements (ICC, 0.40), the clinical Q angles were underestimated compared with the MRI-based anatomic Q angles (P < .05).
  
  
  CONCLUSIONS
  The results of this study suggest that, although reproducible Q-angle measurements can be performed using standardized patient positioning and a long-arm goniometer, methods to improve the accuracy of clinical Q-angle measurements are needed.
authors.affiliation: Department of Radiology, Stanford University, Stanford, CA; James H. Clark Center, Rm S-355 MC 5450, 318 Campus Dr, Stanford CA 94305-5450, USA. cdraper@stanford.edu
authors.forename: Christine E
authors.initials: CE
authors.lastname: Draper
authors.forename: Kelvin T L
authors.initials: KT
authors.lastname: Chew
authors.forename: Roberta
authors.initials: R
authors.lastname: Wang
authors.forename: Fabio
authors.initials: F
authors.lastname: Jennings
authors.forename: Garry E
authors.initials: GE
authors.lastname: Gold
authors.forename: Michael
authors.initials: M
authors.lastname: Fredericson
mesh_terms: D000328:Adult; D053587:Arthrometry, Articular / Q000295:instrumentation; D004867:Equipment Design; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000033:anatomy & histology*; D008279:Magnetic Resonance Imaging; D008297:Male; D052097:Quadriceps Muscle / Q000033:anatomy & histology*; D055815:Young Adult