Prognostic capacity of current diagnostic radiographic parameters for the early diagnosis of hip dysplasia in dogs: repeatability and reproducibility of Laxity Index measurement on stress radiographs obtained with the Vezzoni-Modified Badertscher distension device technique in a large cohort of dogs.

Objective: To evaluate the repeatability and reproducibility of the Laxity Index (LI) measured on stress radiographs obtained with the Vezzoni-Modified Badertscher distension device (VMBDD) technique in a large cohort of dogs. Methods: One-hundred and ninety-five client-owned medium to large breed dogs, aged between 4.5 and 6 months, presented from 2021 to 2024 for screening of hip dysplasia were enrolled in this study. LI for each hip was blindly and independently measured by three observers with different experience on stress radiographs obtained with the VMBDD method. Intra- and inter-observer variability was evaluated. Statistical testing was performed with commercially available software and p-value < .05 was considered significant. Results: Significant difference between all observers was observed at each measurement session with a Linear Mixed Model and the highest mean difference and its standard error (SE) was 0.074 ± 0.008. No significant difference was recorded between more experienced examiners with the ANOVA test and pairwise t-test. Difference was observed between the first and the second measurement sessions (p < 0.001) and first and the third sessions (p = 0.001) in observer 3. Conclusions: In-house evaluation of the LI on stress-radiographs obtained with the VMBDD technique was a repeatable procedure only if performed by examiners with moderate or high experience, but this could not be claimed for examiners with no or minimal experience. Nevertheless, the mean differences could be negligible in clinical setting due to the low impact on the definitive diagnosis. The LI remained a useful measurement to be used in combination with other clinical and radiographic findings for early diagnosis of CHD.