Cat Hip Dysplasia

Introduction

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 & Prevention

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.

Special Notes

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.

Symptoms & Signs

Hip dysplasia is a fairly uncommon disorder in cats that involves abnormal development and subsequent degeneration of the coxofemoral (hip) joint. It is thought that the immature hip joints of affected cats have a genetic predisposition to subluxate (partially dislocate), causing abnormal forces across the hips, irregularly shaped bones, damaged cartilage, microfractures and, in severe cases, osteoarthritis. It is important for cat owners to recognize the clinical signs of hip dysplasia so that effective treatment options can be pursued as early in the course of the disease as possible. This can be difficult, however, because the signs of hip dysplasia often mimic those of other degenerative disorders.

Symptoms of Hip Dysplasia in Cats

Hip dysplasia is one of the most common skeletal disorders seen clinically in dogs, but is much less common in cats. When it does occur, purebred cats and females are more commonly affected; Maine Coons seem particularly predisposed. Clinical signs tend to show up early, usually between 4 and 12 months of age, although signs of osteoarthritis can first present later in life. The early signs of this disease are caused by looseness in the joints; later signs are related to joint degeneration.
Since hip dysplasia affects the rear limbs, this is where cat owners should look for signs of the disease. The main signs of hip dysplasia are rear lameness characterized by a bunny-hopping or swaying gait, pain or weakness in one or both hind legs, difficulty rising, exercise intolerance, reluctance to run or jump (up the stairs, onto furniture, counters, etc), and sometimes an audible clicking sound coming from the hips when the cat rises or walks (called "crepitus"). Other signs include a narrow hind-end stance, poor pelvic limb conformation and musculature, hypertrophy (enlargement) of the shoulder muscles from overuse and sometimes an arched appearance of the spine caused by the shifting of weight to the forelimbs because the rear end hurts. These signs can be subtle. They can be intermittent or persistent and tend to worsen after activity. Affected cats may seem fine most of the time but be stiff in the morning or after a catnap. Obesity or rapid weight gain can exacerbate the lameness and pain associated with this disease.
Left untreated, hip dysplasia will progress, and the symptoms will become more obvious. Cat owners should be especially aware of signs in kittens as they near maturity, and they should not simply write-off the signs in older cats as a natural decline due to aging. Proper treatment can reduce the discomfort caused by hip dysplasia and allow the cat to remain active and happy.

Diagnosis & Tests

Hip dysplasia is an uncommon, painful and degenerative disease that causes arthritis-like symptoms and general hind end lameness. It is caused by a combination of genetic and environmental factors that lead to laxity (looseness) in one or both hip joints. Diagnosing this disorder can be difficult, because a number of other diseases cause similar clinical signs and must be ruled out before a definitive diagnosis of hip dysplasia can be made.

Diagnosing Hip Dysplasia in Cats

If a cat presents with unilateral or bilateral hind end lameness – especially if it is either an older kitten or an aging adult - the initial veterinary database normally will include blood work (complete blood count and serum chemistry panel run on fresh blood samples), a urinalysis, palpation of the hip joints (this may require sedation or even general anesthesia because of pain) and pelvic radiographs (x-rays). Very specific positioning of the animal for hip radiographs is essential to an accurate diagnosis of hip dysplasia.
There are several ways to detect hip dysplasia, whether or not clinical signs are present. This is important because some breeders may wish to have their cats tested before breeding them. The older and more common method is recommended by the Orthopedic Foundation for Animals (the OFA), which will assess the hips of cats under the same rules, guidelines and fee schedules applicable to dogs. The cat's veterinarian will take radiographs of the hips with the cat in a specific stretched-out position – on its back, with its hind legs pulled back and slightly rotated – and will submit those films to the OFA. There, specialized veterinary radiologists will analyze the radiographs and compare them to a large computerized database of hip x-rays of other cats to determine whether hip laxity exists and, if it does, how severe it is at that point. While this can be done in young cats, the accuracy of this method is much greater if the cat is over 2 years of age when the films are taken.
The other recognized method, called PennHip, is currently only available for assessing canine, not feline, hip dysplasia.
Confirmatory testing might include additional x-rays taken at different views and possibly computed tomography (CT or CAT scan).
Basically, your general veterinarian, perhaps in consultation with a veterinary radiologist, will be able to diagnose whether your cat is affected by hip dysplasia. Whether it is an older cat showing significant symptoms, or a younger cat without clinical signs, there are medical and possibly surgical options available to treat or at least manage this disease in companion cats.

Treatment Options

While there is no cure for hip dysplasia in cats, there are things that can be done to help alleviate discomfort and manage quality of life. The overall goals of therapy are to relieve pain and stabilize the hip joints to return the cat to normal or near-normal function. Depending upon the severity of disease, the veterinarian will recommend a treatment plan that may contain both surgical and non-surgical options.

Non-Surgical Options for Treating Hip Dysplasia in Cats

Cats with mild hip dysplasia frequently respond well to conservative medical management on an outpatient basis. Of course, which treatment protocol to adopt depends upon the cat's age, health, activity level, intended function (companion, show, etc.), the severity of joint laxity, the existence and degree of osteoarthritis, the veterinarian's personal treatment preferences and the financial considerations of the owner. Non-surgical options include physical therapy, dietary management, weight control, activity restriction and use of oral anti-inflammatory and pain management medications. Corticosteroids normally are not recommended as part of a treatment plan for feline hip dysplasia, because despite their beneficial anti-inflammatory effects, they also can cause cartilage damage with long-term use. A number of oral supplements are available to help protect and lubricate joints as well. In many cases, weight loss alone can dramatically reduce the pain and clinical signs associated with hip dysplasia in overweight cats.

Surgical Options for Treating Hip Dysplasia in Cats

There are a number of surgical options for treating hip dysplasia, if less intrusive methods do not accomplish acceptable results. Depending on the severity of the condition in a given cat, its veterinarian may attempt to modify the existing hip joint surgically or instead may opt for a total hip replacement. These surgical techniques are usually (or sometimes exclusively) performed on dogs; whether they are routinely available for affected cats is unclear. A veterinary orthopedic surgeon is the best one to consult about available surgical treatment options for feline hip dysplasia.