Laxity index measurement on stress radiographs obtained with the Vezzoni-modified Badertscher distension device technique: repeatability and reproducibility in a large cohort of dogs

Sara Sassaroli^1,2*Francesco Gallorini^3,4Francesco Roggiolani^2,3Alberto Salvaggio^2,3Rosario Vallefuoco⁵Andrea Pratesi⁶Mario Fordellone⁷Elisa Campagnoli¹Angela Palumbo Piccionello¹

• ¹Universita degli Studi di Camerino Scuola di Bioscienze e Medicina Veterinaria, Camerino, Italy
• ²Technevet, Matelica (MC), Italy
• ³Clinica Veterinaria San Silvestro, Castiglion Fiorentino (AR), Italy
• ⁴Policlinico Veterinario Gregorio VII, Roma (RM), Italy
• ⁵Department of Small Animal Surgery Pride Veterinary Referrals, Derby, United Kingdom
• ⁶Veterinary Surgeon, Private Practitioner, Padova, Italy
• ⁷Universita degli studi della Campania Luigi Vanvitelli Dipartimento di Salute Mentale e Fisica e Medicina Preventiva, Naples, Italy

Introduction. The Vezzoni-Modified Badertscher Distension Device (VMBDD) technique is a radiographic method to assess hip joint laxity and is widely adopted in Europe. While the intra-observer and inter-observer variability of the Laxity Index (LI) measured on stress radiographs obtained with the VMBDD technique has been reported, it has never been evaluated in a large cohort of patients. The aim of our study is to assess the repeatability and reproducibility of the Laxity Index measured on stress radiographs obtained using the VMBDD technique in a large cohort of dogs. Methods. Stress-radiographs obtained with the VMBDD method of medium to large breed dogs, aged between 4.5 and 6 months, presented from 2021 to 2024 for screening of hip dysplasia were analyzed. The LI for each hip was blindly measured by three observers with different experience. Intra-and inter-observer significant variability was evaluated to assess repeatability and reproducibility of the LI, respectively. Statistical testing was performed and a p-value < 0.05 was considered significant. Inter-observer and intra-observer Intraclass Correlation Coefficients (ICCs) were evaluated. Results. One-hundred and ninety-five stress-radiographs (390 hip joints) were included. The inter-observer ICC showed moderate agreement (ICC = 0.55, 95% CI 0.50–0.59). EMMeans indicated that Observer 3 consistently provided higher LI values compared to Observers 1 and 2 across all time points (e.g., at T1: 0.484 vs 0.410 and 0.438, p-value < 0.001 for Observer 1 vs Observer 3). The repeatability within each observer were excellent for all three observers (Observer 1: ICC = 0.94, 95% CI 0.93–0.96; Observer 2: ICC = 0.99, 95% CI 0.99–0.99; Observer 3: ICC = 0.95, 95% CI 0.94–0.96). Conclusions. In-house evaluation of the LI on stress-radiographs obtained with the VMBDD technique was a high repeatable procedure, but it was a moderate reproducible measurement due to systematic upward bias by observer with less experience. Nevertheless, the mean differences could be negligible in a clinical setting due to the low impact on the definitive diagnosis.