Evaluation of the association between medial patellar luxation and hip dysplasia in cats

Objective - To investigate the association between hip dysplasia (HD) and m edial patellar luxation (MPL) In cats. Design - Cross-sectional prevalence study. Animals - 78 cats. Procedure - A complete history was obtained. Cats were examined to detect M PL and HD. Radiographs of the stifle and hip joints were obtained. Hip join ts were evaluated by use of Norberg angle,distraction index, and scoring co nsistent with that established by the Orthopedic Foundation for Animals. Results - There were 43 male and 35 female cats (mean age. 2.5 years). Elev en cats had clinical signs of disease in the pelvic limbs. Medial subluxati on of the patella (subgrade 1) was seen in 31 of 33 cats with otherwise nor mal stifle joints. Medial patellar luxation was found in 45 of 78 (58%) cat s, and 35 of 45 (78%) had grade-1 MPL. Bilateral MPL was seen in 32 of 45 ( 71%) cats. A weak association existed between MPL and HD, because cats were 3 times more likely to have HD and patellar luxation than to have either c ondition alone. Concurrent MPL and HD were detected in 19 of 78 (24%) cats, and HD was diagnosed radiographically in 25 of 78 (32%) cats (19 mild, 4 m oderate, 2 severe). Eighteen of the 25 cats with HD had bilateral HD. Conclusions and Clinical Relevance - Clinically normal cats may have a cert ain degree of laxity in the stifle joint, evident as medial patellar sublux ation (< grade 1). There is a weak association between MPL and HD, and both conditions may develop, alone or in combination, more frequently than has been reported.