Until very recently, cats were not thought to be affected by hip dysplasia. Well known in many dog breeds as an inherited disorder, cats were felt to be free of the condition. New information and research has shown that this disease does indeed exist in the cat and is likely an inherited disorder. No single gene is thought to be responsible for hip dysplasia in either the dog or the cat, but rather a complex interplay of several genetic factors is involved. We do know that if a cat or dog is found to have hip dysplasia, then both its parents must be either affected or carriers of the defect. Using new information, cat breeders are able to develop breeding programs to minimize the incidence of this problem in their breed.

Hip dysplasia is a disease of the hip joint. "Dysplasia" is a word that means abnormal development of a tissue. The hip is a ball and socket type of joint. The "ball" is the top of the femur (called the "head") which fits into the "socket", the depression in the pelvis called the acetabulum. A normal joint has a close fit of the femur's head into the acetabulum, so that the joint functions smoothly and efficiently. The large muscles of the hip and pelvis help hold the joint in place and allow it to function properly.

In hip dysplasia, parts of the hip joint are abnormally shaped, so that the fit of the ball into the socket is poor. This allows the head of the femur to move easily out of the joint to some degree (called "subluxation" = dislocation). Over time, chronic changes develop in the bones of the hip joint from this abnormal movement and degenerative joint disease may result. In most cases, both hip joints are affected although one may be more severe than the other. Many cats with hip dysplasia go undetected. Due to their small size and the fact that cats are not exercised as much as dogs, along with their natural agility, they may have hip dysplasia and still function normally. In some cats, hip dysplasia is found incidentally when they are x-rayed for another reason. This disease is not obvious at birth, but develops as the young kitten grows.

Some cats with hip dysplasia, especially the more severely affected, will have obvious symptoms and experience pain. These cats may appear to be stiff when they walk and they may be reluctant to jump or climb. They may appear lame from time to time. In some cases, the symptoms only appear after some traumatic event, such as a fall. Cats with clinical symptoms compatible with hip dysplasia can have the diagnosis confirmed with x-rays of the hips. The veterinarian will be able to see various abnormalities in the hip joint associated with hip dysplasia. In some cases, the hip joint has partially or totally subluxated.

Just as in dogs, we can predict that the breeds of cats most likely to have hip dysplasia are the larger, heavy-boned breeds such as the Persian and Maine Coon. It is important to note, however, that hip dysplasia can and does occur in any breed and also in non-pedigreed cats, too. Breeders of dogs at risk for hip dysplasia have long used a screening process to try to identify those dogs at least risk of the disease for inclusion in a breeding program.

The most common screening process is an x-ray taken according to certain specifications that is submitted to the Hip Dysplasia Registry of the Orthopedic Foundation for Animals (OFA) at the University of Missouri, Columbia, Missouri, USA. Veterinarians who are orthopedic specialists review the x-ray and the registry then assigns a grade to the animal being examined. Preliminary evaluations can be done on cats under the age of 2 years, but a final certification is not issued until the cat is over 2 years old. Breeders use the certifications to determine which animals are best selected for breeding. OFA now reviews and grades hips for Maine Coon cats.

Another method of screening cats and dogs for hip dysplasia was developed at the University of Pennsylvania and is called PennHip. This method utilizes a different x-ray procedure designed to measure the degree of laxity, or looseness, in the hip joint. This system is not as readily available to breeders as the OFA system. However, several researchers at the University of Pennsylvania, including Dr. Gail Smith and Dr. Todd Murphy, are one of the few groups looking at hip dysplasia in cats. Since this is a newly recognized problem in cats, one of the first tasks for both OFA and PennHip is to develop a reference for what constitutes normal hips in a cat. Only by knowing what is normal can experts then determine if an individual cat has normal or abnormal hips.

What about treatment for an affected cat? As previously mentioned, many cats with hip dysplasia will show no discomfort at all. If a cat is known to have dysplastic hips and is overweight, weight reduction will reduce the chances that discomfort will be experienced. For cats who are diagnosed with hip dysplasia because they developed clinical signs of lameness and pain, several treatments are available. Veterinarians use anti-inflammatory and pain medications as well as dietary supplements designed to help in joint repair. Restricting exercise, such as limiting access to outdoors or the ability to climb up on objects, can be helpful as well. For severely affected cats, a surgery called a femoral head and neck excision arthroplasty is widely available that removes the damaged tissue. Cats who have had this surgery can usually expect a full return of hip function and freedom from pain and discomfort once post-operative healing has occurred.

References:

1. Cargill J. Hip dysplasia in Maine Coons. The Scratch Sheet, March 1998, pp 18-21.
2. Dohrmann H. Having OFA check your cat's hips. The Scratch Sheet, March 1998, pp. 21-22.
3. Schrader SC and Sherding RG. Disorders of the skeletal system in Sherding RG (editor): The Cat: diseases and clinical management, second edition, WB Saunders, Philadelphia, 1994, p. 1608
4. Smith GK et al. Patellar luxation and hip dysplasia in a group of cats. Proceedings of the First International Feline Genetic Disease Conference, Philadelphia, June 1998.
5. Murphy T. Feline hip dysplasia - how to deal with it. Maine Coon International 14:2, 1998
6. Keller GG and Corley EA. Hip dysplasia: Orthopedic Foundation for Animals data on the Maine Coon cat. The Scratch Sheet, Summer, 1996.

Please Note: The Winn Feline Foundation provides the feline health information on this site as a service to the public. Diagnosis and treatment of specific conditions should always be in consultation with one's own veterinarian. The Winn Feline Foundation disclaims all warranties and liability related to the veterinary advice and information provided on this site.