Among the various physical disorders that can compromise a cat’s ability to move freely about its environment is a painful orthopedic disorder called hip dysplasia (after the Greek word for “malformation”). Compared to its occurrence in dogs and in humans, the condition is rare in felines. But cat owners should nevertheless be aware of its clinical signs and the ways in which the disability can be managed if it should occur.
The condition is a genetically inherited malformation of the ball-and-socket joint that connects a cat’s thigh bone (femur) to its hip. In this case, the “ball” is the knobby top end (femoral head) of the thigh bone, while the “socket” is a cup-shaped cavity (acetabulum) located at the lower end of the hip bone. In a normally formed animal, the femoral head, while fitting snugly within the acetabulum, is free enough to glide and partially rotate to allow a cat to lie down, stand up, climb trees, chase after mice, and so forth.
In a cat with hip dysplasia, the ball and socket are misaligned and loose, which prevents the femoral head from moving smoothly. This partial dislocation, called subluxation, causes the femoral head and the acetabulum to knock and grind against each other. Over time, the constant wear and tear causes the acetabulum to become shallow and the femoral head to become worn, flattened, and misshapen, resulting in an incapacitating looseness of the entire joint. In addition, the constant trauma is likely to eventually foster osteoarthritis, a condition marked by the gradual destruction of cartilage, the rubbery tissue that normally serves to cushion the bone ends.
A specific cause of feline hip dysplasia has not been identified, although the condition is widely thought to have a genetic component, since it seems to be more prevalent in certain breeds, such as Maine Coons. Other factors appear to play a causative role in the development of the disability; it is believed, for example, that obesity significantly increases the pressure on the hip’s supporting structures and may therefore contribute to excessive wear and tear on the joint. For now, however, veterinarians generally agree that the only way to prevent hip dysplasia would be to avoid the breeding of cats that are thought to be genetically predisposed to the condition.
Clinical signs of feline hip dysplasia include limping or other apparent difficulties in walking, avoidance of physical activity, expression of pain if the hip is touched, and persistent licking or chewing at the hip area. A definitive diagnosis of the condition can be achieved by an x-ray of an apparently painful hip joint.
Options are limited when it comes to preventing or treating feline hip dysplasia. “Make sure that your cat is not overweight,” advises Ursula Krotscheck, DVM, assistant professor of small animal surgery at Cornell University’s College of Veterinary Medicine, “and encourage exercising to keep the hip muscles strong. Try to get the animal to jump up on a counter to get its food, for example, or hide the food under a sofa so that it has to crouch in order to find it.” Also, she says, a veterinarian may recommend the use of certain anti-inflammatory drugs as well as dietary supplements containing glucosamine and chondroitin, compounds that may help maintain the strength of an animal’s connective tissues.
Surgical options are also available to relieve advanced cases of hip dysplasia. One option, for example, is a so-called micro total hip replacement, in which the hip joint is removed and replaced with an artificial device. Or, Dr. Krotscheck points out, “You can just remove the femoral head—the ball part of the hip’s ball-and-socket joint—and you do not replace it. The muscles that normally hold those components of the hip will essentially continue to do their job, but without the painful bone-on-bone contact. Although the cat may have a mechanical lameness and the affected limb may be a little shorter after the operation, the leg will have an almost normal range of motion and excellent function. The animal will be able to sit up, run, jump, and engage in normal cat behavior.”