Relationship between degenerative joint disease and hip joint laxity by use of distraction index and Norberg angle measurement in a group of cats

Objective - To determine the relationship between degenerative joint disease (DJD) and passive laxity of the hip joint in a group of cats. Design - Prospective study. Animals - A select (nonrandomized) group of 78 cats. Procedure - Standard hip-extended radiographic views and compression and distraction views of the pelvis were obtained from cats during sedation. Radiographs were evaluated, using an Orthopedic Foundation for Animals (OFA)-like scoring system for dogs. Passive joint laxity was measured, using Norberg angle (NA) and distraction index (DI). Hip laxity in cats with DJD was compared with hip laxity in cats without DJD. Results - Hip dysplasia (HD) was subjectively diagnosed radiographically in 25 of 78 (32%) cats using the OFA-like scoring system. Nineteen cats had mild HD, 4 had moderate HD, and 2 had severe HD. Fifteen of the 25 cats with HD had DJD. The NA ranged from 56 to 105. The mean NA in cats with DJD was (84°) significantly lower than in cats without DJD (95°). The DI ranged from 0.2 to 0.84. The mean DI for cats with DJD was (0.6) significantly higher than that for cats without DJD (0.49). Cats with a DI < 0.4 did not have DJD. Cats had an increased likelihood of having DJD with increased laxity in the coxofemoraf joint, as measured by NA or DI. Clinical Implications - The mean NA for radiographically normal cats (92.4°) was lower than that in radiographically normal dogs (103°). The overall mean DI for cats in this group (0.51) is similar to dogs of breeds with high joint laxity, such as the Labrador Retriever (0.5). As in dogs, there is a relationship between DJD and laxity in the hip joint of cats.