The Quadriceps Angle: Reliability and Accuracy in a Fox (Vulpes vulpes) Pelvic Limb Model

Authors


  • Study performed at Department of Small Animal Clinical Sciences, LIFE Faculty, Copenhagen University.

  • Financial support was received from the Danish Kennel Club.

Corresponding Author

James Miles, BVetMed, Universitetshospital for Familiedyr, Dyrlægevej 16, 1870 Frederiksberg C, Denmark

Email: jami@life.ku.dk

Abstract

Objectives

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.

Study Design

Cadaveric radiographic study and computer modeling.

Animals

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 (FMEDIAL) 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 FMEDIAL (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).

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