Definition of Hip Dysplasia in Cats
Hip dysplasia is a fairly uncommon, largely genetic disorder in cats that involves abnormal development and subsequent degeneration of one or both hip joints. It is thought that the immature hip joints of affected cats have an inherited predisposition to partially dislocate, causing abnormal forces across the hips, irregularly shaped bones, damaged cartilage, microfractures and, in severe cases, osteoarthritis with crippling lameness and pain.
How Hip Dysplasia Affects Cats
Hip dysplasia is not common in cats. When it does occur, the symptoms are typically the same as those seen in dogs and can be rather subtle. They include rear lameness characterized by a “bunny-hopping” gait, weakness in one or both hind legs, stiffness and soreness after rising from rest, reluctance to be active, hesitance to stand on hind legs, run or jump (up the stairs, onto furniture or counters, etc.), pain, and sometimes an audible clicking sound coming from the hips when the cat rises or walks. Other signs include a narrow rear stance, wasting of the muscle mass in the pelvic area, enlargement of the shoulder musculature from overuse and sometimes a humped or hunched appearance of the spine caused by the shifting of weight to the forelimbs. These signs can be intermittent or persistent and tend to worsen after activity. Obesity and rapid weight gain can exacerbate the lameness and pain.
Causes of Hip Dysplasia
Normally, the upper rounded end of the long thigh bone (the head of the femur) connects tightly and smoothly to a rounded cavity in the pelvis (the acetabulum), forming the ball-and-socket hip joint. Bones provide the strength necessary to support body weight; cartilage ensures a smooth, tight and functional fit between the bones that make up joints. In dysplastic hips, instead of a deep tight fit, the head of the femur is loose or not all the way inside the hip socket, which causes abnormal forces across the hip joint. Defects in the shape of the bones can cause increased wear and tear within the hip joint itself, overloading the articular cartilage and contributing to development of painful, progressive osteoarthritis. There is considerable evidence that genetics play a key role in this disease in both cats and dogs, in combination with as yet unconfirmed environmental factors.
Preventing Hip Dysplasia in Cats
Affected cats should be removed from the breeding population, as should their parents and possibly their siblings. Pelvic radiographs taken even before clinical signs are present may reveal the existence of hip dysplasia. Weight management (to prevent obesity in cats) can also help prevent clinical disease from developing.
Hip dysplasia is not common in companion cats. The various surgical techniques available for treating dogs with this disease may or may not be available to affected cats. Medical management is probably the best option for cats with clinical hip dysplasia.