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Evaluation of the Norberg Angle Threshold: A Comparison of Norberg Angle and Distraction Index as Measures of Coxofemoral Degenerative Joint Disease Susceptibility in Seven Breeds of Dogs

Authors

  • WILLIAM T. N. CULP VMD,

    1. Department of Clinical Studies, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA, the Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California—Davis, Davis CA, and the Department of Veterinary Clinical Studies, College of Veterinary Medicine, Washington State University, Pullman, WA.
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  • AMY S. KAPATKIN DVM, Diplomate ACVS,

    1. Department of Clinical Studies, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA, the Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California—Davis, Davis CA, and the Department of Veterinary Clinical Studies, College of Veterinary Medicine, Washington State University, Pullman, WA.
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  • THOMAS P. GREGOR BS,

    1. Department of Clinical Studies, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA, the Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California—Davis, Davis CA, and the Department of Veterinary Clinical Studies, College of Veterinary Medicine, Washington State University, Pullman, WA.
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  • MICHELLE Y. POWERS DVM,

    1. Department of Clinical Studies, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA, the Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California—Davis, Davis CA, and the Department of Veterinary Clinical Studies, College of Veterinary Medicine, Washington State University, Pullman, WA.
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  • PAMELA J. MCKELVIE VMD,

    1. Department of Clinical Studies, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA, the Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California—Davis, Davis CA, and the Department of Veterinary Clinical Studies, College of Veterinary Medicine, Washington State University, Pullman, WA.
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  • GAIL K. SMITH VMD, PhD

    1. Department of Clinical Studies, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA, the Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California—Davis, Davis CA, and the Department of Veterinary Clinical Studies, College of Veterinary Medicine, Washington State University, Pullman, WA.
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  • Presented at the 30th Annual Conference of the Veterinary Orthopedic Society, March 2003.

Address reprint requests to Dr. William Culp VMD, Department of Clinical Studies, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA 19104-6010. E-mail: wculp@vet.upenn.edu.

Abstract

Objective— To evaluate the thresholds of 2 radiographic methods used to determine coxofemoral joint laxity in 7 breeds of dogs.

Animals— Three hundred and fifty clinically normal dogs.

Study Design— Retrospective study.

Methods— Hip radiographs from 7 breeds of dogs were randomly selected from a database. None of the dogs had radiographic evidence of degenerative joint disease (DJD). Distraction index (DI) and Norberg angle (NA) were measured on these radiographs and compared with DI and NA thresholds for diagnosing DJD susceptibility derived from the literature and from evaluated Borzois. Dogs with a NA<105° and a DI of ≤0.32 were considered false-positives and dogs with a NA≥105° and a DI of >0.32 were considered false-negatives.

Results— Mean age of all dogs was 22.9 months. Mean NA for all dogs was 99.37°, and mean DI for all dogs was 0.44. Borzoi mean DI of was significantly less than the mean DI of the other 6 breeds. The highest (most hip laxity) Borzoi DI was 0.32, and the lowest (most hip laxity) Borzoi NA was 99°. False-positive and false-negative diagnoses were identified in 6 of the 7 breeds.

Conclusions— Using the NA threshold of 105° (literature established threshold of susceptibility to DJD) resulted in a high percentage of false-negative and false-positive diagnoses. Breeds like the Labrador Retriever and Rottweiler would have large numbers of hip dysplasia susceptible dogs remain in the breeding population based on this NA threshold. False-positive diagnoses were common in breeds like the Australian Shepherd, Borzoi, and German Shepherd effectively eliminating hip dysplasia nonsusceptible dogs from the breeding population.

Clinical Relevance— The NA was not an accurate predictor of DJD susceptibility in these 7 breeds of dogs when using a NA threshold of 105°.

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