title: Reliability of goniometry-based Q-angle.
abstract: OBJECTIVE
  To establish the stability reliability, precision, and minimum value for detecting real differences for quadriceps angle (Q-angle) measurements based on standardized protocols and surface goniometry.
  
  
  METHODS
  An intratester reliability study.
  
  
  METHODS
  University research laboratory.
  
  
  METHODS
  Fifty-two healthy, young, relatively lean adults (25 men and 27 women) from the university community with no history of knee injury.
  
  
  METHODS
  Q-angle was assessed with surface goniometry on 2 separate occasions separated by 48 hours. Subjects assumed a supine position with: (1) extended hips and knees, (2) neutral hip rotational position, (3) neutral foot position, and (4) isometrically contracted quadriceps femoris muscles. The axis of a manual extendable-arm goniometer was placed over the center of the right patella with the proximal arm situated over the anterior-superior iliac spine and the distal arm over the center of the tibial tuberosity.
  
  
  METHODS
  Stability reliability was calculated with use of intraclass correlation (ICC, 2-way random model) and precision was calculated by standard error of measurement (SEM). The 95% limits of agreement also were calculated to estimate the minimum detectable difference in Q-angles. The lowest acceptable ICC was set at ≥0.70 for stability reliability.
  
  
  RESULTS
  The following ICC (SEM) values were found: all subjects = 0.88 (1.0°), men = 0.77 (1.0°), and women = 0.85 (1.0°). The 95% limits of agreement were 3° for the same 3 groups.
  
  
  CONCLUSIONS
  The surface goniometry protocol described herein appeared to be reliable for relatively lean young men and women. Although measures were precise to 1.0°, it appears a difference of 3° may be needed to detect a real difference in Q-angles when measured in this fashion.
authors.affiliation: Musculoskeletal Dynamics Laboratory, Roane Field House 171, The University of Memphis, Memphis, TN 38160-3464(⁎). Electronic address: lweiss@memphis.edu.
authors.forename: Lawrence
authors.initials: L
authors.lastname: Weiss
authors.forename: Bradley
authors.initials: B
authors.lastname: DeForest
authors.forename: Kelley
authors.initials: K
authors.lastname: Hammond
authors.forename: Brian
authors.initials: B
authors.lastname: Schilling
authors.forename: Lucas
authors.initials: L
authors.lastname: Ferreira
mesh_terms: D000328:Adult; D053587:Arthrometry, Articular / Q000592:standards*; D005260:Female; D006621:Hip Joint / Q000033:anatomy & histology* / Q000502:physiology; D006801:Humans; D007719:Knee Joint / Q000033:anatomy & histology* / Q000502:physiology; D008297:Male; D016059:Range of Motion, Articular; D015203:Reproducibility of Results; D055815:Young Adult