Comparison of radiographic measurements of the patellar tendon-tibial plateau angle with anatomical measurements in dogs. Validity of the common tangent and tibial plateau methods.

OBJECTIVE

To evaluate the validity of the common tangent and conventional tibial plateau angle methods for measuring the patellar tendon angle (PTA) in dogs.

METHODS

Radiographs of cadaveric stifles (n = 20) placed at 135° in true lateral position were obtained to measure the PTA with both methods. A Kirschner wire was inserted perpendicularly to the patellar tendon at its insertion on the tibia and the stifle was dissected. Two Kirschner wires were then used to identify the anatomical landmarks of the tibial plateau. A digital image was obtained of the proximal tibia in true lateral position. Six blinded observers measured each PTA digitally while the anatomical PTA was determined by an independent blinded observer from the angle between the line representing the tibial plateau and the Kirschner wire representing the perpendicular to the patellar tendon. The agreement between the methods was determined statistically from an intraclass correlation coefficient (ICC).

RESULTS

The global ICC for the common tangent method (0.44) and for the conventional method (0.4) indicated that their overall validity is poor. The measurements obtained by common tangentmethod and conventional method were respectively below and above the anatomical measurements. The reproducibility of the PTA measurements based on images of the dissected stifles was very good.

CLINICAL SIGNIFICANCE

Both the common tangent and conventional methods show poor concordance with the anatomical measurement of PTA. Further studies are needed to determine if errors in measurements affect the clinical outcome.