Comparison of the tibia plateau angle between small and large dogs with cranial cruciate ligament disease

Objectives: To compare the conformation of the proximal tibia evaluated on a medio-lateral radiograph between small and large dogs with cranial cruciate ligament disease (CCLD). Methods: Retrospective clinical study with dogs having radiographic evaluation and CCLD confirmed at surgery. The first group (n = 52) was comprised of dogs weighing less than 15 kg and the second group (n = 52) of dogs weighing more than 15 kg. The tibial plateau angle (TPA), the relative tibial tuberosity width (rTTW), and the Z angle were measured on preoperative radiographs with imaging measurement software. Linear mixed models were used to assess the effect of weight, age, sex, and neutered status on radiographic measurements and to estimate interobserver variabilities. Results: The small dog group had a greater TPA (30.1 degrees +/- 5.3; p <0.001 with a mean difference of 4.9 degrees [95% CI: 3.8-6.0]) and Z angle (69.9 degrees +/- 5.6; p<0.001 with a mean difference of 6.1 degrees ([95% CI: 4.9-7.4]) than the large dog group. Sex and neutered status further influenced the TPA and Z angle values. No significant effect was observed on the rTTW values. A strong correlation was found between the TPA and the Z angle (r = 0.61, p <0.001). Variances were not significantly different between observers. Overall the interobserver variability was low suggesting that agreement was good. Clinical significance: Small dogs with CCLD have a steeper tibial plateau than large dogs with CCLD. Sex and neutered status also had an effect on some measured variables. This anatomical difference could influence the surgical technique, which may affect the outcome. The good interobserver agreement suggests the observer is unlikely to influence surgical planning.