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


METHODS
Three hundred and fifty clinically normal dogs.


METHODS
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 degrees and a DI of < or =0.32 were considered false-positives and dogs with a NA> or =105 degrees 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 degrees, 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 degrees. False-positive and false-negative diagnoses were identified in 6 of the 7 breeds.


CONCLUSIONS
Using the NA threshold of 105 degrees (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.


CONCLUSIONS
The NA was not an accurate predictor of DJD susceptibility in these 7 breeds of dogs when using a NA threshold of 105 degrees.
Culp
William T N
WT
Department of Clinical Studies, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA, USA. wculp@vet.upenn.edu
Kapatkin
Amy S
AS
Gregor
Thomas P
TP
Powers
Michelle Y
MY
McKelvie
Pamela J
PJ
Smith
Gail K
GK
D000818:Animals; D001947:Breeding; D004285:Dogs; D020022:Genetic Predisposition to Disease; D006619:Hip Dysplasia, Canine / Q000000981:diagnostic imaging* / Q000235:genetics / Q000601:surgery; D011237:Predictive Value of Tests; D011859:Radiography; D012189:Retrospective Studies; D012680:Sensitivity and Specificity