title: The Norberg angle is not an accurate predictor of canine hip conformation based on the distraction index and the dorsolateral subluxation score.
abstract: Canine hip dysplasia (CHD) is a common complex trait characterized by abnormal hip joint development. Hip joint laxity, an early characteristic of CHD, results in degeneration of the joint due to mechanical trauma, which is a clinical problem mostly in medium to large breed dogs. Clinical signs include pain, decreased activity and lameness. A retrospective, multi-center, cross sectional study of 437 dogs was performed to determine if a Norberg angle (NA) ≥105° accurately predicts a non-dysplastic hip based on a distraction index (DI) cut-off of ≤0.3 or a dorsolateral subluxation (DLS) score cut-off of ≥55%. The predictive capacity of the NA against a DI ≤0.3 or a DLS score ≥55% was assessed using area under the receiver operator characteristic (ROC) curve analysis. The ROC curve of NA for the prediction of a DI ≤0.3 was 0.59 (95% CI=0.50-0.69) and for the prediction of DLS score ≥55% was 0.69 (95% CI=0.63-0.75). Optimizing the specificity of the NA to ≥80% for prediction of a DI ≤0.3 and a DLS score ≥55% gave a cut-point for the NA of ≥112° and 108.7°, respectively. In conclusion, at the cut-point of 105°, the NA is not an accurate measurement to score normal or abnormal hips, based on the DI or DLS score. Application of screening methods for CHD based on hip laxity, such as the DI or the DLS score, would help to remove additional dysplastic dogs from the breeding pool or the NA criterion should be higher when selecting unaffected dogs for breeding.
authors.affiliation: Department of Veterinary Sciences-CITAB, University of Trás-os-Montes and Alto Douro, Quinta de Prados, 5000-801 Vila Real, Portugal. Electronic address: anaritagasparmv@gmail.com.
authors.forename: Ana R
authors.initials: AR
authors.lastname: Gaspar
authors.affiliation: Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853, USA.
authors.forename: Galina
authors.initials: G
authors.lastname: Hayes
authors.affiliation: CIBIO-InBIO-Centro de Investigação em Biodiversidade e Recursos Genéticos, Universidade do Porto, Campus Agrário de Vairão, Rua Padre Armando Quintas, n° 7, 4485-661 Vairão, Portugal.
authors.forename: Catarina
authors.initials: C
authors.lastname: Ginja
authors.affiliation: Department of Veterinary Sciences-CITAB, University of Trás-os-Montes and Alto Douro, Quinta de Prados, 5000-801 Vila Real, Portugal.
authors.forename: Mário M
authors.initials: MM
authors.lastname: Ginja
authors.affiliation: Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853, USA.
authors.forename: Rory J
authors.initials: RJ
authors.lastname: Todhunter
mesh_terms: D000818:Animals; D003430:Cross-Sectional Studies; D004285:Dogs; D005260:Female; D006619:Hip Dysplasia, Canine / Q000000981:diagnostic imaging* / Q000209:etiology; D006621:Hip Joint / Q000000981:diagnostic imaging* / Q000473:pathology; D008297:Male; D012372:ROC Curve; D011859:Radiography / Q000662:veterinary; D012189:Retrospective Studies; D012680:Sensitivity and Specificity
keywords: Canine hip dysplasia; Distraction index; Dorsolateral subluxation score; Norberg angle