Canine hip dysplasia is a disease of dogs that causes looseness, abnormal development and arthritis of the hip joint. The hip joint is a ‘ball-and-socket’ type joint. The ‘ball’ is the uppermost part of the thigh bone, or femur, and is called the ‘head’ of the femur. The ‘head’ is connected to the rest of the bone by the ‘neck’. The ‘socket’ is part of the pelvic bone, and is called the ‘acetabulum’. Normally, the ball, or head of the femur, fits very tightly within its socket, or acetabulum. With hip dysplasia, this fit becomes loose and the joint partially dislocates, or subluxates. This subluxation can cause discomfort, abnormal development and arthritis, later in life. Hip dysplasia is usually a bilateral disease, which means both hips are often affected.

Canine hip dysplasia (CHD) is an extremely common disease today, despite over 25 years of organised effort to reduce its incidence. Most commonly, CHD affects the large and giant breeds, although any breed can be affected.

EVOLUTION OF CHD

Hip dysplasia is not a congenital disease in dogs. This means that puppies are not born with loose hips, unlike human infants who usually have the problem at birth. In puppies, the looseness, or laxity, develops at around 3-4 months of age. Laxity alone can cause soreness in some dogs, usually in puppies 6 – 10 months old. Since the head of the femur is not seated well in its socket, the surrounding tissues are asked to provide more support than they are capable of, especially during exercise. These tissues can stretch and tear causing discomfort. Between the ages of 6 months – 2 years old, arthritis could begin and progress for the life of the pet. Severe arthritis also causes soreness, which usually occurs in the older dog who may have had problems as a puppy or who never showed any previous signs at all. Arthritis is the body’s response to inflammation and hip laxity. The most notable changes that occur are the progressive thickening of the tissues around the joint and the production of bone around the head of the femur and acetabulum.

CAUSES OF CHD

The specific mechanisms which cause CHD are not known. Genetics certainly plays a role, however, the specifics of how the disease is passed from one generation to the next, is very-complex and not completely understood. For example, puppies born from a breeding pair with hip dysplasia, although more likely to have the disease, may be completely normal. Similarly, normal breeding pairs, although more likely to have normal puppies, may produce offspring with severe hip dysplasia. This complexity with regard to genetics has frustrated efforts to eliminate the disease completely, and has led people to believe that environmental factors are responsible for disease expression, as well.

Nutrition and growth rate are considered to be important environmental factors related to CHD. There is strong evidence, from a number of studies, that dogs who are overfed, and gain weight too rapidly, are predisposed to CHD. This seems to be most important for large or giant breeds in the first 6 months of life. There is good evidence showing that puppies who grow more slowly have less chance of acquiring CHD. Feeding premium puppy-foods, ‘free-choice’ to puppies, is not recommended, especially with large breed dogs, Additionally, providing vitamin or calcium supplements, is not recommended for puppies who are fed a balanced nutritionally complete dog food. Most reputable dog foods, even those for adult dogs, have all the vitamins and minerals puppies need.

SIGNS AND SYMPTOMS OF CHD

Dogs showing signs of soreness with CHD can be any age and any size. However, most of the dogs are large, weighing from 45 – 90 pounds (20 – 40 kg). Whether young or old, the signs of CHD are similar. Most commonly, an owner will notice that their pet is reluctant to exercise, work or play.

Common complaints in part or combination of are:

• Limping or short-strided steps in the rear legs.
• Slow to get the rear-end up off the floor.
• Slow to lie down.
• Difficulty with climbing stairs or jumping.
• Tends to ‘warm out’ of the lameness (limping), which is worst when the pet first gets up, morning stiffness.
• Swaying gate when walking.
• Bunny hopping when running.
• Tends to be worse after heavy exercise, usually the next day.
• Some days are better than others, often cold and wet days are worse.

DIAGNOSIS OF CHD

The Young Dog (under 1 year of age)

Deciding which tests to use when evaluating a dog for CHD depend significantly on the patient’s age. As mentioned, younger dogs with CHD, tend to have laxity without much arthritis. Therefore, with younger dogs, the primary goal toward diagnosing CHD is detecting hip joint laxity. Palpation, or careful manipulation of the hip, is an extremely important tool. There are certain manipulation tests that are very sensitive at identifying laxity of the hip joint, occasionally the patient needs to be sedated, or anaesthetised, in order to permit careful and gentle manipulations. Radiographs (x-rays) can also be very helpful when trying to identify laxity in the hip joint.

The Older Dog (over 1 year of age)

As mentioned, older dogs with CHD, tend to have arthritis, and less notable laxity. In these older dogs, the primary goal toward diagnosing CHD is detecting evidence of hip joint arthritis. Radiographs are the best method and can provides a sensitive indicator for even the earliest signs of arthritis.

TREATMENT OF CHD

Conservative Treatment of CHD

Conservative therapy has three-major components:

1. Weight control
2. Use of anti-inflammatory & other drugs
3. Exercise Programs

Weight control is extremely important. Obesity causes excessively high forces to be transmitted through already abnormal hips. Soreness may be exacerbated, and arthritis accelerated, in dogs that are overweight. The appropriate weight and diet program for your dog can be obtained from your veterinarian or from a veterinary nutritionist. In most veterinary practices there are free weight clinics run by trained veterinary nurses.

Hydrotherapy can be affective method to reduce weight and keep high level of exercise without straining the already stressed joint. It will increase the muscle mass, which in turn may help to reduce the degree of subluxation.

Anti-inflammatory medication is an important part of conservative therapy especially when soreness flares up. DO NOT treat your dog yourself. Drugs such as Aspirin, and Ibuprofen can be extremely toxic to dogs when given at an incorrect dosage. The metabolism and dosages of some drugs are much different in dogs as compared to people.

Exercise must be controlled for conservative therapy to be effective. “Full-out” running, jumping and rough housing should be prohibited as much as possible. Extended walks or jogs, can be beneficial. When soreness flares up, exercise should be limited for a few days. Some owners mistakenly believe that their pet knows his or her own limits, and will restrict themselves as needed. In general this is not true. It could be argued that many people don’t recognise their own limits, and will “over-do-it” exercising, even though they’re likely to regret it the next day. Most dogs are like these people. If allowed, they will run, jump or play to their fullest ability, even though they are likely to re-injure themselves. Owners must take responsibility for limiting the exercise for their pets. Exercise should not be restricted for too long as this will result in reduced muscle mass, which in turn leads to greater hip loosening and later arthritis. It is important that the muscles “kept in shape” to support the hip joint in its place. This can be achieved by moderate and monotonous exercise and/or Hydrotherapy.

Surgical Treatment of CHD

The three most common surgical treatments of CHD have three different objectives. One objective is to save the dog’s own natural joint by eliminating the laxity and preventing the progression of arthritis. This objective is usually reserved for the younger dogs that still have a joint worth saving. A second objective is to remove the source of the soreness by removing part of the joint itself. The arthritic femoral head and neck are removed and a ‘false-joint’ made of scar tissue and muscle eventually provides, relatively, pain-free movement. The third and final objective is to remove and replace the arthritic femoral head and acetabulum with an artificial joint.

Saving the Natural Joint

• Juvenile pubic symphysiodesis

Juvenile pubic symphysiodesis (JPS) is a relatively new surgery designed to save the natural joint by reducing or eliminating the laxity. Dogs are younger (15-20 weeks old) when this surgery is performed. It is minimally invasive and quick to perform. With JPS an electrical current is driven into the pubis growth plate via an electrosurgery unit. This results in growth retardation of pubic bone and so the acetabulum can be rotated over the head of the femur during the remaining growth period. Success rate is very encouraging if it is performed within the growth period of the dog.

• Triple Pelvic Osteotomy

Triple pelvic osteotomy (TPO) is surgery designed to save the natural joint by reducing or eliminating the laxity, or looseness. If the laxity is eliminated then the arthritis, which would follow, can be prevented. This can be done on dogs that have ended their growth period but are young enough and have no arthritis. With TPO, the pelvis is cut in three places (‘triple osteotomy’ means ‘three cuts in bone’), so the acetabulum, or socket, can be rotated over the head of the femur to prevent it from slipping out of the socket or subluxating. The TPO is not appropriate for all dogs and works best in dogs that have no arthritis present in their hips. Dogs are usually young (6-10 months old) when this surgery is performed, before arthritis has begun. Usually both hips are operated in two separate surgeries, 4 – 8 weeks apart. Most surgeons reserve this surgery for dogs that are sore, and showing many of the signs consistent with CHD described earlier. Exercise must be restricted for 2 – 3 months, to allow the pelvic bones to heal after surgery. The TPO surgery has a good success rate if it is performed on an appropriate candidate; many dogs are improved clinically and arthritis is effectively prevented in some dogs.

Preoperative and six weeks post operative views of the same dog show bone healing at the osteotomy site and good hip conformation. No arthritic changes seen.

Removing the Natural Joint

• Femoral Head and Neck Ostectomy

Femoral Head and Neck Ostectomy (FHO) is designed to eliminate the source of discomfort by removing part of the hip joint. The femur is cut so that the head and neck of the femur are removed (‘ostectomy’ means’ bone is cut and removed’). Scar tissue forms between the femur and acetabulum, where the femoral head and neck used to be; this is called a ‘false-joint’ because motion, between, the bones, is maintained without the ‘true’ ball-and-socket joint. Eventually, this scar tissue provides enough support to permit use of the limb without causing significant discomfort. The FHO surgery is usually performed on older dogs, which already have significant arthritis.

Replacing the Natural Joint

• Total Hip Replacement

Total hip replacement (THR) is designed to eliminate the source of discomfort by replacing the arthritic joint with an artificial joint or hip prosthesis. The arthritic femoral head and neck is removed and replaced with a metal head and stem. The arthritic socket is removed and replaced with a plastic cup. This surgery is performed on skeletally mature dogs that have severe arthritis, conservative treatment is not satisfactory and FHO is not indicated.