title: The quadriceps angle: reliability and accuracy in a fox (Vulpes vulpes) pelvic limb model.
abstract: OBJECTIVE
  To evaluate the effect of measurement technique and limb positioning on quadriceps (Q) angle measurement, intra- and interobserver reliability, potential sources of error, and the effect of Q angle variation.
  
  
  METHODS
  Cadaveric radiographic study and computer modeling.
  
  
  METHODS
  Pelvic limbs from red foxes (Vulpes vulpes).
  
  
  METHODS
  Q angles were measured on hip dysplasia (HD) and whole limb (WL) view radiographs of each limb between the acetabular rim, mid-point (Q1: patellar center, Q2: femoral trochlea), and tibial tuberosity. Errors of 0.5-2.0 mm at measurement landmarks alone and in combination were modeled to identify the effect on Q angle. The effect of measured Q angles on the medial force exerted on the patella (F(MEDIAL)) was calculated.
  
  
  RESULTS
  The HD position yielded significantly (P < .001) more medial Q angles than the WL position. No significant difference was observed between Q1 and Q2, but Bland-Altman plots indicated they were not equivalent. Intra- and interobserver agreement was substantial. Q2 errors were inherently greater than Q1: the mid-point and tibial tuberosity are the most important sources of Q angle variability. Increasing Q angles significantly increased the exerted F(MEDIAL) (P < .0001, gradient 1.7%).
  
  
  CONCLUSIONS
  Measurements are reliable, but Q2 is more prone to error than Q1, and the 2 measurement techniques are not interchangeable. Positional errors must be kept below 1.3 mm (Q1) or 0.8 mm (Q2).
authors.affiliation: Department of Small Animal Clinical Sciences, Faculty of Life Sciences, University of Copenhagen, Denmark. jami@life.ku.dk
authors.forename: James E
authors.initials: JE
authors.lastname: Miles
authors.forename: Jane V
authors.initials: JV
authors.lastname: Frederiksen
authors.forename: Bente
authors.initials: B
authors.lastname: Jensen
authors.forename: Jolle
authors.initials: J
authors.lastname: Kirpensteijn
authors.forename: Eiliv L
authors.initials: EL
authors.lastname: Svalastoga
authors.forename: Thomas
authors.initials: T
authors.lastname: Eriksen
mesh_terms: D000818:Animals; D005121:Extremities / Q000033:anatomy & histology / Q000000981:diagnostic imaging / Q000601:surgery; D005260:Female; D005589:Foxes / Q000033:anatomy & histology / Q000601:surgery*; D008297:Male; D010388:Pelvis / Q000033:anatomy & histology* / Q000000981:diagnostic imaging / Q000601:surgery; D052097:Quadriceps Muscle / Q000033:anatomy & histology / Q000000981:diagnostic imaging; D011859:Radiography; D015203:Reproducibility of Results; D013522:Surgery, Veterinary / Q000379:methods / Q000592:standards