Canine hip dysplasia is a very common degenerative joint disease seen in dogs. There are many misconceptions surrounding it. There are many things that we know about hip dysplasia in dogs, there are also many things we suspect about this common cause of limping, and there are some things that we just do not know about the disease. We will cover all of those here and hope to separate out fact, theory, hypothesis, and opinion.

What is hip dysplasia?

To understand what hip dysplasia really is we must have a basic understanding of the joint that is being affected. The hip joint forms the attachment of the hind leg to the body and is a ball and socket joint. The ball portion is the head of the femur while the socket (acetabulum) is located on the pelvis. In a normal joint, the ball rotates freely within the socket. To facilitate movement, the bones are shaped to perfectly match each other, with the socket surrounding the ball. To strengthen the joint, the two bones are held together by a ligament. The ligament attaches the femoral head directly to the acetabulum. Also, the joint capsule, which is a very strong band of connective tissue, encircles the two bones adding further stability. The area where the bones actually touch each other is called the articular surface. It is perfectly smooth and cushioned with a layer of spongy cartilage. In the normal dog, all of these factors work together to cause the joint to function smoothly and with stability.

Hip dysplasia results from the abnormal development of the hip joint in the young dog. It may or may not be bilateral, affecting both right and left sides. It is brought about by the laxity of the muscles, connective tissue, and ligaments that should support the joint. Most dysplastic dogs are born with normal hips, but due to genetic and possibly other factors, the soft tissues that surround the joint start to develop abnormally as the puppy grows. The most important part of these changes is that the bones are not held in place, but actually move apart. The joint capsule and the ligament between the two bones stretch, adding further instability to the joint. As this happens, the articular surfaces of the two bones lose contact with each other. This separation of the two bones within a joint is called subluxation and this, and this alone, causes all of the resulting problems we associate with the disease.

What are the symptoms of hip dysplasia?

Dogs of all ages are subject to the symptoms of hip dysplasia and the resultant osteoarthritis. In severe cases, puppies as young as five months will begin to show pain and discomfort during and after vigorous exercise. The condition will worsen until even normal daily activities are painful. Without intervention, these dogs may be unable to walk at all by a couple years of age. In most cases, however, the symptoms do not begin to show until the middle or later years in the dog's life.

The symptoms are typical for those seen with other causes of osteoarthritis. Dogs may walk or run with an altered gait, often resisting movements that require full extension or flexion of the rear legs. Many times, they run with a 'bunny hopping' gait. They will show stiffness and pain in the rear legs after exercise or first thing in the morning. Most dogs will warm up out of the muscle stiffness with movement and exercise. Some dogs will limp and many will decrease their level of activity. As the condition progresses, the dogs will lose muscle tone and may even need assistance in getting up. Many owners attribute the changes to normal aging, but after treatment is initiated, they are shocked to see much more normal and pain-free movement return.

Who gets hip dysplasia?

Hip dysplasia can be found in dogs, cats, and humans, but for this article, we are concentrating only on dogs. In dogs, it is primarily a disease of large and giant breeds. The disease can occur in medium-sized breeds and rarely even in small breeds. It is primarily a disease of purebreds although it can happen in mixed breeds, particularly if it is a cross of two dogs that are prone to developing the disease. German Shepherds, Labrador Retrievers, Rottweillers, Great Danes, Golden Retrievers, and St. Bernards appear to have a higher incidence, however, these are all very popular breeds and may be over represented because of their popularity. On the other end Greyhounds and Borzois have a very low incidence of the disease.

Hip dysplasia is caused by looseness in the hip joint. The looseness creates abnormal wear and erosion of the joint and as a result pain and arthritis develops. The disease process is fairly straightforward; the controversy starts when we try to determine what predisposes animals to contract the disease. Almost all researchers agree that there is a genetic link involved. If a parent has hip dysplasia, then the offspring are at greater risk for developing hip dysplasia. Some researchers feel that genetics are the only factor involved, where others feel that genetics contribute less than 25% to the development of the disease. The truth probably lies in the middle. If there are no carriers of hip dysplasia in a dog's lineage, then it will not contract the disease. If there are genetic carriers, then it may contract the disease. We can greatly reduce the incidence of hip dysplasia through selective breeding. We can also increase the incidence through selectively breeding. We cannot, however, completely reproduce the disease through selective breeding. In other words, if you breed two dysplastic dogs, the offspring are much more likely to develop the disease, but will not all have the same level of symptoms or even necessarily show any symptoms. The offspring from these dogs will, however, be carriers and the disease may show up in their offspring in later generations. This is why it can be difficult to eradicate the disease from a breed or specific line.

Nutrition: Experimentally, we can increase the severity of the disease in genetically susceptible animals in a number of ways. One of them is through obesity. It stands to reason that carrying around extra weight will exacerbate degeneration of the joint in a dog with a loose hip. Overweight dogs are therefore at a much higher risk. Another factor that may increase the incidence is rapid growth in a puppy during the ages from three to ten months. Experimentally, the incidence has been increased in genetically susceptible dogs when they are given free choice high protein, high calorie diets. In a large study done in 1997, Labrador Retriever puppies fed a high protein, high calorie diet free choice for three years had a much higher incidence of hip dysplasia than their litter mates who were fed the same high calorie, high protein diet, but in an amount that was 25% less than that fed to the dysplastic group. As might be expected, however, the free choice group was significantly heavier at maturity and averaged 22 pounds heavier than the control group. Because obesity is also a risk factor, this study may be difficult to interpret.

I have yet to see a study that links an increased incidence of hip dysplasia in dogs fed a normal diet of commercial puppy food versus a specialty diet formulated for just large breed dogs. There have also been studies looking into protein and calcium levels and their relationship to hip dysplasia. Both of these studies were able to increase the level of hip dysplasia by feeding increased amounts of calcium and protein. But once again, the studies of puppies fed greatly increased amounts over normal recommended values and compared them to animals fed decreased amounts. They failed to compare puppies fed a normal amount of food that had the recommended amount of protein, fat, and calcium to those fed a diet with slightly less protein, fat, and calcium (similar to those 'large breed puppy foods' that are now flooding the market). I have yet to see a study that links an increased incidence in hip dysplasia in dogs fed a normal diet of commercial puppy food versus a specialty diet formulated just for large breed puppies.

Exercise: Exercise may be another risk factor. It appears that dogs that are genetically susceptible to the disease may have an increased incidence of disease if they over-exercise at a young age. But at the same time, we know that dogs with large and prominent leg muscle mass are less likely to contract the disease than dogs with small muscle mass. So exercising and maintaining good muscle mass may actually decrease the incidence of the disease. Moderate exercise that strengthens the gluteal muscles, such as running and swimming, is probably a good idea. Whereas, activities that apply a lot of force to the joint are contraindicated. An example would be a jumping activity such as playing Frisbee.

Diagnosis of hip dysplasia in dogs that are showing clinical signs of arthritis and pain is usually made through the combination of a physical exam and radiographs (x-rays). If a dog is showing outward signs of arthritis, there are usually easily recognized changes in the joint that can be seen on radiographs. In addition, the veterinarian may even be able to feel looseness in the joint or may be able to elicit pain through extension and flexion. Regardless, the results are straightforward and usually not difficult to interpret.

However, about half of the animals that come in for a determination on the health of their hip joints are not showing physical signs, but are intended to be used for breeding. The breeder wants to ensure that the animal is not at great risk for transmitting the disease to his or her offspring. There are two different testing methods that can be performed. The traditional and still most common is OFA testing. The other newer technique is the PennHip method.

OFA: The method used by the Orthopedic Foundation for Animals (OFA) has been the standard for many years. The OFA was established in 1966, and has become the world's largest all-breed registry. The OFA maintains a database of hip evaluations for more than 475,000 dogs. Radiographs are taken by a local veterinarian under specific guidelines and are then submitted to the OFA for evaluation of hip dysplasia and certification of hip status. Since the accuracy of radiological diagnosis of hip dysplasia using the OFA technique increases after 24 months of age, the OFA requires that the dog be at least two years of age at the time the radiographs are taken. They also recommend that the evaluation should not be performed while the female is in heat. To get the correct presentation and ensure that the muscles are relaxed, the OFA recommends that the dog be anesthetized for the radiographs. OFA radiologists evaluate the hip joints for congruity, subluxation, the condition of the acetabular margins and acetabular notch, and the size, shape, and architecture of the femoral head and neck. The radiographs are reviewed by three radiologists and a consensus score is assigned based on the animal's hip conformation relative to other individuals of the same breed and age. Using a seven point scoring system, hips are scored as normal (excellent, good, fair), borderline dysplastic, or dysplastic (mild, moderate, severe). Dogs with hips scored as borderline or dysplastic are not eligible to receive OFA breeding numbers.

When dogs born in 1972 to 1980 were compared with dogs born in 1989 and 1990, 60% of the breeds demonstrated a statistically significant decrease in hip dysplasia. At the same time, 68% of breeds had a statistically significant increase in the number of hips scored as excellent. The OFA will also provide preliminary evaluations (performed by one OFA radiologist) of dogs younger than 24 months of age to help breeders choose breeding stock. Reliability of the preliminary evaluation is between 70 and 100% depending on the breed. Results published by the OFA suggest that the incidence of hip dysplasia in certain breeds has decreased as a result of selective breeding programs. When dogs born in 1972 to 1980 were compared with dogs born in 1989 and 1990, 60% of the breeds demonstrated a statistically significant decrease in hip dysplasia. At the same time, 68% of breeds had a statistically significant increase in the number of hips scored as excellent. This information may suggest progress is being made to decrease the frequency of hip dysplasia, but it may simply be that only radiographs from dogs thought to have normal hips are being submitted to the OFA, while those with dysplasia are being screened out by referring veterinarians.

PennHIP: The diagnostic method used by the University of Pennsylvania Hip Improvement Program (PennHIP) uses distraction/compression radiographic views to more accurately identify and quantify joint laxity. Radiographs of the hip joints are taken with the dog under heavy sedation. Two views are obtained with the hind limbs in neutral position to maximize joint laxity. Weights and an external device are used to help push the head of the femur further into or away from the acetabulum. The amount of femoral head displacement (joint laxity) is quantified using a distraction index (DI). The DI ranges from 0 to 1 and is calculated by measuring the distance the center of the femoral head moves laterally from the center of the acetabulum and dividing it by the radius of the femoral head. A DI of 0 indicates a very tight joint. A DI of 1 indicates complete luxation with little or no coverage of the femoral head. A hip with a distraction index of .6 is 60% luxated and is twice as lax as a hip with a DI of .3. When the DI was compared to the OFA scores for 65 dogs, all dogs scored as mildly, moderately, or severely dysplastic by the OFA method had a DI above .3.

Hip joint laxity as measured by the DI is strongly correlated with the future development of osteoarthritis. Hips with a low DI are less likely to develop osteoarthritis. Hips with a DI below .3 rarely develop osteoarthritis visible on radiographs. Although hips with a DI above .3 are considered "degenerative joint disease susceptible," not all hips with a DI greater than .3 eventually develop osteoarthritis. It is known that some hips with radiographically apparent laxity do not develop osteoarthritis. A means of differentiating lax hips that develop osteoarthritis from those that will not is important in developing a prognosis and making treatment recommendations. In one study, the DI obtained from dogs at four months of age was a good predictor of later osteoarthritis, though the 6 and 12-month indices were more accurate.

To assure quality and repeatability among diagnostic centers using the PennHip technique, veterinarians must take a special training course to become certified. As this technique gains popularity more and more veterinarians are becoming certified.

Surgical Treatment of Hip Dysplasia: There are several surgical procedures available depending on the age and the severity of the joint degeneration.

Triple Pelvic Osteotomy (TPO): TPO is a procedure used in young dogs usually less than 10 months of age that have radiographs that show severe hip laxity but have not developed severe damage to the joints. The procedure involves a surgical breaking of the pelvic bones and a realignment of the femoral head and acetabulum restoring the coxofemoral weight bearing surface area and correcting femoral head subluxation. This is a major surgery and is very expensive but the surgery has been very successful on animals that meet the requirements.

Total Hip Replacement: may be the best surgical option for dogs that have degenerative joint disease as a result of chronic hip dysplasia. Total hip replacement is a salvage procedure that can produce a functionally normal joint, eliminate degenerative changes and alleviate joint pain. The procedure involves the removal of the existing joint and replacing it with a prosthesis. To be a candidate for this procedure the animal must be skeletally mature and weigh at least 35 pounds. There is no maximum size limit. If both hips need to be replaced there is a three-month period of rest recommended between the surgeries. As with the TPO surgery this is a very expensive procedure but has had some very good results.

Femoral Head and Neck Excision: Femoral head and neck excision is a procedure in which the head of the femur is surgically removed and a fibrous pseudo-joint forms. This procedure is considered a salvage procedure and is used in cases where degenerative joint disease has occurred and total hip replacement isn't feasible. The resulting pseudo-joint will be free from pain and allow the animal to increase its activity, however, full range of motion and joint stability are decreased. For best results the patient should weigh less than 50 pounds, however the procedure is often performed on larger dogs.

Pectineal Myectomy: This is a somewhat controversial treatment for patients with chronic hip dysplasia. The pectineus is one of the muscles attaching the femur to the pelvis. By cutting and removing this muscle, the tension on the joint and joint capsule are reduced. This offers some pain relief for some patients but doesn't slow the progression of the disease. There are possible complications with this procedure and with the introduction of the newer, better procedures this surgery is rarely performed anymore.

Medical Treatment of Hip Dysplasia

Because hip dysplasia is primarily an inherited condition, there are no products on the market that prevent the development of hip dysplasia. Medical treatment has greatly improved in the last several years thanks to the introduction and approval of several new drugs used to treat osteoarthritis. Because hip dysplasia is primarily an inherited condition there are no products on the market that prevent the development of hip dysplasia. I very often get asked if a certain product will prevent hip dysplasia but I always must answer "no". Through proper diet, exercise and supplemental glucosamine you can decrease the progression of degenerative joint disease but the looseness in the joint will not change significantly as a result of any supplement.

Medical management is indicated for young dogs with a sudden onset of clinical signs and for older dogs with chronic osteoarthritis. Because of the high cost involved with many surgeries, medical management is many times the only realistic option for many clients. Medical management is a multifaceted treatment. For the best results, several of the following treatments must be instituted. For most animals, I began with the first recommendations and work my way down this list as needed to control the pain and degenerative joint disease.

Weight Management: Weight management is the first thing that must be addressed. All surgical and medical procedures will work much better if the animal is not overweight. Considering that up to half of the pets in the U.S. are overweight there is a fair chance that many of the dogs with hip dysplasia are also overweight. Getting the dog down to it's recommended weight and keeping it there may be the most important thing an owner can do for their pet. However this may be the hardest part of the treatment, but it's worth it. Very few dogs can drive to MacDonalds, work a can opener, or open the refrigerator, so you the owner are controlling what the dog eats. If you feed your dog less it will lose weight.

Exercise: Exercise is the next important step. What we are trying to accomplish here is to restrict the amount of exercising yet still maintain adequate movement to increase or maintain muscle strength. Young active dogs are going to need to be restricted to walks on the leash or short periods of swimming. Older dogs should also participate in these activities to a lesser extent. Too little exercise can be more detrimental than too much in some cases so make sure your dog is getting out daily for some activity. Jumping in all forms is bad for dogs with hip dysplasia. While watching a dog play Frisbee is very enjoyable and fun for the dog, remember that it is very hard on a dog's hip joints. Remember, it is important to exercise daily; only exercising on weekends, for instance may cause more harm than good if the animal is sore for the rest of the week and reluctant to move at all.

Glucosamine and Chondroitin: Glucosamine and chondroitin are two of the drugs that have recently become widely used in treating both animals and humans for osteoarthritis. These products have been around for a while but due to the lack of scientific studies supporting them and the medical profession's resistance to endorse a nutraceutical, they had failed to gain popularity. But due to the overwhelming success in treating patients with osteoarthritis these products have come to the forefront of therapy and are becoming one of the most popular products for treating arthritis today.

Glucosamine is the major sugar found in glycosaminoglycans and hyaluronate, which are important building blocks in the synthesis and maintenance of cartilage in the joint. Chondroitin enhances the synthesis of glycosaminoglycans and inhibits damaging enzymes in the joint.

When a dog has hip dysplasia the joint wears abnormally and the protective cartilage on the surface of the joint gets worn away and the resultant bone to bone contact creates pain. Glucosamine and chondroitin give the cartilage-forming cells (chondrocytes) the building blocks they need to synthesize new cartilage and to repair the existing damaged cartilage. These products are not painkillers; they work by actually healing the damage that has been done. These products generally take at least six weeks to begin to heal the cartilage and most animals need to be maintained on these products the rest of their lives to prevent further cartilage breakdown. Because these products are naturally-occurring compounds they are very safe and show very few side effects. There are many different glucosamine/chondroitin products on the market but they are not all created equal. We have seen the best results and fewest side effects from products that are formulated especially for dogs and that contain pure ingredients that are human grade in quality. Products such as Dr. Foster and Smith's Joint Care and Gluco-C, or the veterinary-sold product Cosequin are several that fit this category.

Buffered Aspirin: Buffered aspirin is an excellent anti-inflammatory and painkiller in dogs (Do NOT give your cat aspirin unless prescribed by your veterinarian). It can be used along with glucosamine/chondroitin products and is safe for long term use. With all aspirin products used in dogs there is a risk of intestinal upset or in rare cases gastric ulceration. Because of these problems it is recommended that if a dog develops signs of GI upset, the product be discontinued until a veterinary exam can be performed. (By giving aspirin with a meal, you may be able to reduce the possibility of side effects.) Using buffered aspirin formulated just for dogs makes dosage and administration much easier. Regular aspirin, Tylenol, and ibuprofen have many more potential side effects and are not recommended without veterinary guidance.

Carprofen (Rimadyl): Rimadyl is a non-steroidal anti-inflammatory developed for use in dogs with osteoarthritis. Carprofen is a very strong and effective pain killer and anti-inflammatory agent. It is a prescription product and because of potential side effects, careful adherence to dosing quantity and frequency must be followed. Many veterinarians throughout the country are requiring periodic bloodwork to be done on animals that are on this product to monitor any developing liver problems resulting from its use. This product is often used initially with glucosamine therapy and then as the glucosamine product begins to work the carprofen dose is reduced or eliminated.

Polysulfated Glycosaminoglycan (Adequan): Adequan is a product that is administered as an injection. A series of shots are given over weeks and very often have favorable results. The cost and the inconvenience of weekly injections are a deterrent to some owners especially since the oral glucosamine products are so effective. This product helps prevent the breakdown of cartilage and may help with the synthesis of new cartilage. The complete mechanism of action of this product is not completely understood but appears to work on several different areas in cartilage protection and synthesis.

Vitamin C: Vitamin C has received a lot of press lately, primarily because of studies done in humans that have linked it to preventing and controlling a variety of diseases. Much of the use in animals has been extrapolated from human medicine. Humans are one of only a handful of species that have a requirement for vitamin C. Dogs and cats synthesize their own vitamin C so this is one area where we probably shouldn't be using human studies as guidelines for treating cats and dogs. We know that vitamin C acts as an antioxidant and is an important nutrient in the synthesis of collagen and cartilage. We also know that Vitamin C is water-soluble and it is very difficult to create a toxicity. Vitamin C does lower the pH of urine and some researchers question the possible long term side effects of over-acidified urine. The benefits of vitamin C in preventing or treating hip dysplasia and joint disease are purely speculative. Using reasonable doses of Vitamin C doesn't appear to be harmful and some day research may show that it is beneficial in animals.

Corticosteroids: Corticosteroids have been used for many years to treat the pain and inflammation associated with osteoarthritis. Corticosteroids act as a potent anti-inflammatory but unfortunately have many undesirable short and long term side effects. Because of these side effects and the advent of newer, more specific drugs, corticosteroids are generally only used in older animals where all other pain control products have failed. Corticosteroids are a prescription product and come in both a pill and injectable form.

When it comes to preventing the formation of hip dysplasia there is only one thing that all researchers agree on, and that is selective breeding is crucial.

There are many different theories on how to prevent the progression of hip dysplasia. As I discussed earlier, nutrition, exercise, and body weight may all contribute to the severity of degenerative joint disease after the hip dysplasia has developed. When it comes to preventing the formation of hip dysplasia there is only one thing that all researchers agree on, and that is selective breeding is crucial. There will be a lot of new information coming forward in the future concerning other factors that contribute to hip dysplasia, but for right now we have to stick to what we know for sure. We know that through selectively breeding animals with good hips we can significantly reduce the incidence of hip dysplasia. We also know that we can increase the incidence of hip dysplasia if we choose to use dysplastic animals for breeding. Breeding two animals with excellent hips does not guarantee that all of the offspring will be free of hip dysplasia but there will be a much lower incidence than if we breed two animals with fair or poor hips. If we only bred animals with excellent hips it wouldn't take long to make hip dysplasia a rare occurrence. If owners insisted on only purchasing an animal that had parents and grandparents with certified good or excellent hips, or if breeders only bred these excellent animals then the majority of the problems would be eliminated. For the best results, buyers should look at three or four generations of dogs prior to theirs to insure that there aren't carriers in the bloodline. Following the newer recommendations for exercise and nutrition may help but will never come close to controlling or eliminating the disease if stricter requirements for certified hips aren't instituted or demanded.

Summary

Hip Dysplasia is a widespread condition that primarily affects large and giant breeds of dogs. There is a strong genetic link between parents that have hip dysplasia and the incidence in their offspring. There are probably other factors that contribute toward the severity of the disease.

Osteoarthritis is the result of degeneration of the joint due to hip dysplasia. Surgical and medical treatments are targeted to prevent and treat the resulting osteoarthritis. The best way to prevent hip dysplasia is through selection of offspring whose parents and grandparents have been certified to have excellent hip conformation.