Hip dysplasia is a well-known condition in dogs. Less is known about feline hip dysplasia (FHD) since few studies have been done. The authors decided to explore the demographics of FHD using the Orthopedic Foundation of America (OFA) as a large data set. Since the large majority of cats reviewed were Maine Coon, the study focused on the findings for this breed.
The clinical presentation of FHD is often gradual which includes signs of subtle behavioral changes such as inactivity or aggression, lack of response to human attention, reluctance to go up and down stairs, and resistance to handling. The age of onset is typically between 3 months and 3.5 years. Upon physical examination, there may be evidence of muscle atrophy in the hindquarters, restricted hip motion, and crepitus or pain on joint manipulation in more severe cases.
The OFA hip score uses the American Veterinary Medical Association grading system: 1 = excellent, 2 = good, 3 = fair, 4 = borderline dysplasia, 5 = mild dysplasia, 6 = moderate dysplasia, and 7 = severe dysplasia. This study placed cases in two categories, those without FHD (scores 1-3) and those with FHD (scores 5-7). There is another public and voluntary registry for Maine Coon cats for FHD called PawPeds (https://www.pawpeds.com/healthprogrammes/hd/html). PawPeds uses a four-level grading system: normal, grade 1 (mild dysplasia), grade 2 (moderate dysplasia) and grade 3 (bad dysplasia).
In the OFA registry, there were 2732 unique cats in which 2708 (99.1%) were Maine Coons. The variables analyzed were sex, month/season of birth, and hip dysplasia score. While a few other studies of FHD in cats demonstrated the majority of cases were domestic shorthair cats, the reason why Maine Coon cats made up nearly all of the cases in this database is likely due to reports of hip dysplasia as a specific problem in this breed.
The study results showed the overall prevalence of FHD was 24.9% (635/2548) and was slightly higher in males (279/1023 [27.3%]) than females (356/1525 [23.3%]). The youngest cat with FHD was 4 months of age. More severe dysplasia was present in older cats. Bilateral FHD was 56% of the cases evaluated and were more severe than unilateral cases. There was no age difference noted among the cats. Month/season of birth and geographic region of origin had no influence on FHD prevalence.
The authors caution about extrapolating this data to other groups of Maine Coon cats and other breeds. More information is needed in other breeds and geographical locations to better understand the demographics of feline hip dysplasia. (VT)