3. Darryl N. Biery DVM, Diplomate ACVR1, 4. Michelle Y. Powers DVM, Diplomate ACVS1, 5. Frances Shofer PhD1, 6. Thomas P. Gregor BS1, 7. Georga T. Karbe med.vet.1, 8. Mischa B. McDonald-Lynch DVM1, 9. Richard H. Evans DVM, MS3, 10. Richard D. Kealy 1Department of Clinical Studies, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA 2Nestle Research Center, St. Louis, MO 3Veterinary Pathology Services, Aliso Viejo, CA Vet Surg January 2012 41 1 Objective To determine the chronology of radiographic signs of canine hip dysplasia (CHD), specifically joint laxity and secondary osteoarthritis (OA). Study Design Longitudinal cohort study. Animals Paired littermates, 48 Labrador retrievers. Methods Conventional, ventrodorsal, hip-extended (HE) radiographs were evaluated yearly for CHD according to the subjective criteria of the Orthopedic Foundation for Animals (OFA). PennHIP screening was performed at 2 years of age to assess joint laxity by distraction index (DI). Histopathologic evaluation of coxofemoral joints was performed at the dogs’ natural end of life. Results Coxofemoral subluxation, as identified on the HE radiograph occurred by 2 years of age and not thereafter. Accuracy of OFA-criteria scoring was poor: 55% of dogs scored “normal” at 2 years of age became radiographically dysplastic by the end of life (45% negative predictive value, NPV); 92% of the dogs scored as normal at 2 years of age had histopathologic OA of CHD (8% NPV). The DI predicted all 48 dogs to be susceptible to OA of CHD and 98% had radiographic or histopathologic OA by the end of life. Conclusion OFA-criteria score was profoundly influenced by environmental factors, such as diet restriction and age, reducing its value as a selection criterion. DI measurements were not influenced by dietary treatment suggesting higher trait heritability.

• Hip