Malformation and Degeneration of the Hip Joints in Cats

Hip dysplasia is the failure of the hip joints to develop normally (known as malformation), gradually deteriorating and leading to loss of function of the hip joints.

The hip joint is composed of the ball and the socket. Dysplasia occurs when part of the hip joint is abnormally developed, resulting in dislocation of the ball and socket. The development of hip dysplasia is determined by an interaction of genetic and environmental factors, though there is a complicated pattern of inheritance for this disorder, with multiple genes involved. Affected cats inherit the gene from both parents, even when neither parent has shown any outward predisposition to hip dysplasia.

The incidence of this disorder is relatively rare in cats, but some breeds are more likely to have the genes for hip dysplasia than other breeds. It is more common in purebreds, and more likely in female than male cats. Heavy boned cats, such as the Main coon and the Persian have higher rates than most, but it can affect small boned cats as well. Approximately 18 percent of Maine coon cats are reported to suffer from this condition.

Symptoms and Types

Symptoms depend on the degree of joint looseness or laxity, the degree of joint inflammation, and the duration of the disease.

• Early disease: signs are related to joint looseness or laxity
• Later disease: signs are related to joint degeneration and osteoarthritis
• Decreased activity
• Difficulty rising
• Reluctance to run, jump, or climb stairs
• Intermittent or persistent hind-limb lameness, often worse after exercise
• “Bunny-hopping,” or swaying gait
• Narrow stance in the hind limbs (back legs unnaturally close together)
• Pain in hip joints
• Joint looseness or laxity – characteristic of early disease; may not be seen in long-term hip dysplasia due to arthritic changes in the hip joint
• Grating detected with joint movement
• Decreased range of motion in the hip joints
• Loss of muscle mass in thigh muscles
• Enlargement of shoulder muscles due to more weight being exerted on front legs as cat tries to avoid weight on its hips, leading to extra work for the shoulder muscles and subsequent enlargement

Causes

Influences on the development and progression of hip dysplasia are concurrent with both genetic and environmental factors:

• Genetic susceptibility for hip looseness or laxity
• Rapid weight gain or obesity
• Nutritional level
• Pelvic-muscle mass

Diagnosis

Your veterinarian will perform a complete physical exam on your cat, including a blood chemical profile, a complete blood count, an electrolyte panel and a urinalysis. Inflammation due to joint disease may be noted in the complete blood count. As part of surveying the physical symptoms and fluid work-ups, your veterinarian will also need a thorough history of your cat's health, onset of symptoms, and any possible incidents or injuries that may have contributed to your cat's symptoms. Any information you have on your cat's parentage will be helpful as well, as there may be a genetic link.

X-rays are crucial for visualizing the signs of hip dysplasia. Some of the possible findings may be degenerative disease of the spinal cord, lumbar vertebral instability, bilateral stifle disease and other bone diseases.