Ron Hines DVM PhD 4/29/06

Hip Dysplasia is a common problem in my practice. Scientific articles that discuss canine hip dysplasia refer to it as CHD. Hip dysplasia is a disease of large breeds and short-faced small breeds such as Bulldogs, Boston Bulldogs, Shia Tzus and Lhasa Apsos. Persian and Main Coon cats are also often dysplastic. Hip dysplasia in dogs is a polygenic trait, which means that a number of genes are involved in producing the problem.

The hip is a ball and socket joint. Hip dysplasia is a situation in which the ball of the femur, the bone between the knee and the hip, and the socket of the pelvis into which it fits are abnormally loose and flattened (see diagram). The ball of the femur is called the femoral head and the socket of the pelvis into which it fits is called the acetabulum. These two structures form the joint in which the ball rotates firmly within the socket, held together by elastic ligaments called the joint capsule. To further strengthen the joint, a round ligament runs from the center of the ball to the center of the acetabulum. In a normal dog, the bones are shaped to perfectly to match each other. In dysplasia the fit is loose and no longer perfect. There are all degrees of hip dysplasia, ranging from very slight changes, which cause no lameness or limp, to severe cases in which the entire architecture of the joint is lost to arthritis. In these cases the round ligament and ligaments of the joint capsule are stretched, allowing the ball to wobble (subluxation) or slip entirely out of the acetabulum (luxation). Although hip dysplasia almost always affects both legs, whichever side is the worst shows the lameness or limping.

The areas within the joint that touch are coated with a slick cartilaginous coating called the articular hyaline cartilage surfaces. In a normal joint, they are very smooth and cushioned with layers of fibrous cartilage. In a normal dog, all of these factors work together for smooth and stable joint function. In a dysplastic joint, these articular layers are eroded off , allowing bone-to-bone contact. When bone rubs on bone, the bone under pressure dissolves while new bone is formed adjacent to it. This is a vicious cycle. As the new bone forms it also rubs on the opposing joint surface. This cycle is called arthritis. It is quite painful. The femoral head that once looked as round and smooth as a billiard ball now becomes flattened, mushroomed an cauliflower-like. The socket or acetabulum looses its depths and becomes shallow as the bone remodels. The areas of bone adjacent to the joint grow new knobs and spicules of bone giving it a characteristic distorted appearance.

Signs Of Hip Dysplasia In Puppies
It is not unusual for signs of dysplasia to occur between 5 and eight months of age. Puppies and juvenile dysplastic dogs tend to hop as they run – much like a rabbit. After periods of exercise these pups will be reluctant to get fully up instead they will sit on their haunches with their legs splayed outward like a frog. They are reluctant to climb stairs and inclines or to stand on their rear legs to reach tabletops or chair seats. When you examine these dogs, their upper thighs and hips are bony and lack muscle mass. They are often cow-hocked, standing with their hocks almost touching. Pups with severe dysplasia stand with their rear legs slightly forward so that their front legs can support more of their weight.

Signs Of Hip Dysplasia In Older Dogs
Many dogs with mild to moderate hip dysplasia do not limp until they are 4 or 5 years old. Some dogs are very stoic and show little sign of lameness until arthritis in the hip is well advanced. These dogs would rather sit than stand. They have trouble rising and can’t keep up with you on walks like the used to. Their problem is worse in cold weather and when the dog has been lying on cement or tile floors. X-rays can be misleading in these dogs in that the degree of joint destruction may not correlate with the degree of pain and lameness.

Nutrition And Dysplasia
It has been found that puppies that reach their final mature body weight a bit later in life do not develop the degree of hip dysphasia found in puppies that are allowed to eat as much as they will. The secret is to keep the puppies growing steadily but to feed them approximately twenty percent less than they would consume free choice.

Since more than genetics are involved, some dogs will not show evidence of dysplasia until they are past breeding age. This is why all dogs should have their hips x-rayed prior to breeding. In severe cases, we often begin to see evidence of lameness when puppies are five to twelve months of age. This can be anything from a slight stiffness when the pup first gets up to reluctance to move and use the legs. As the disease progresses the periods of lameness become longer and the dog’s activity decreases. They may be hesitant to jump across depressions, or to run or climb stairs. With time, the muscles of the thigh also atrophy or wither and the dogs walk with a waddling, Charlie Chaplin motion. The pain associated with this condition is due to the grinding of bone on bone within the joint and adjacent arthritic bone spurs. The degree of discomfort varies from day to day early in the disease but becomes continuous as the condition progresses.

Pathophysiology
Because of loose ligaments, impact within the joint is abnormally jarring. This leads to a degenerative process in which the hyaline cartilage that lines the hip joint is damaged. This damage is the result of lateral forces of the femoral head on the deforming hip socket. Small fractures occur in the cartilage, which cause the release of enzymes that inflame the joint further and inhibit the synthesis of joint-protective compounds called proteoglycans. The cartilage that forms the joint becomes thinner and brittle, which affects its ability to handle the day to day stress of movement and weight bearing. With time, other enzymes are released which interfere with the precursors of proteoglycans or glycosaminoglycans and hyaluronate that make cartilage more resilient to pressure and weight bearing. Inflamed joints lay down new bone within and adjacent to the joint. These bony changes are what we see on x-rays.

OFA Certification
The only way to definitively diagnose hip dysplasia is with an x-ray. One dorso-ventral view should be sufficient. This x-ray must be taken with the dog anesthetized or heavily sedated so that positioning is perfect. On x-ray, many dogs that are not lame will show mild to moderate dysplasia. If your dog should be one of the many dogs that suffer from hip dysplasia you have a lot of treatment options to help them live long, comfortable lives. Dog which are to be used for breeding should have this x-ray performed at 24 months of age and sent to the Orthopedic Foundation For Animals for grading and certification. Two criticisms of this test are that one must wait until the dog is two years old to perform it and that the reading of the film is still , somewhat subjective.

The PennHip Diagnostic Procedure
This technique has been available since 1993. It is a useful technique for determining the degree of hip joint laxity in dogs and is more precise than OFA certification. This technique removes all of the guesswork from evaluating canine hip x-rays. It is the best indicator as to whether or not a dog should be used in a breeding program. Because the University of Pennsylvania’s veterinary school found that different breeds have different susceptibility to dysplasia, PennHip evaluates each dog only in comparison to the breed of the dog involved. This test involves pulling the leg away from the body to stretch out the hip joint. Dogs that are prone to hip dysplasia have loose fitting sockets and the degree of looseness is called the Distraction Index. The distraction index is particularly good in detecting dogs early in the disease or dogs that are only slightly dysplastic and whose x-rays look normal when photographed for OFA. It works on dogs as young as sixteen weeks. Three radiographs are taken of the sedated or anesthetized dog, a distraction view, a compression view and a standard ventrodorsal view. The distraction and compression views are taken to obtain precise numerical measurements of joint laxity and conformation. The hip-extended view is used to detect osteoarthritis and distorted joints similar to OFA screening. As of November 2001 there were 977 veterinarians in the United States authorized to perform this procedure. Dogs with a distraction index closest to zero have the tightest hips and are therefore the best to be bred. Dogs with distraction indexes closer to one should not be bred.

Treatment

If your dog comes from a dysplastic line, if hip x-rays taken prior to maturity show evidence of the disease or if you have simply purchased a large breed of dog subject to hip dysplasia how and what you feed your dog is very important. For a start, do not feed the pup puppy chow or a diet with a caloric content of over 2900Kcal/kg. The object of feeding a lower caloric diet is to slow the rate of growth of the puppy. Its final adult weight will remain the same. Feeding approximately three-quarters dog chow and one-quarter cooked vegetables will lower the kilocalories substantially. This gives bones and ligaments time to adjust to the dog’s increasing weight. Also put these dogs on a chondrotin/glucosamine supplement you purchase at WalMart or a neighborhood pharmacy.

If your dog is beginning to show signs of hip dysplasia consider putting it on a diet if it is even slightly obese. Many dogs can easily loose 20% of their weight and the less they weigh, the less burden is placed on their joints. If your dog sleeps on cold concrete, purchase a rubber mat for it to sleep on. If your dog spends most of its time out-of-doors consider making it an indoor family member.

There will come a time when your dog will need some medications to keep it pain-free. All medications that help dysplastic dogs belong to the non-steroidal anti-inflammatory drug class or NSADs. The commonest drug in this category is Aspirin. You can give your dog 4-6 mg/pound of buffered aspirin up to twice a day. This, combined with a few days of inactivity will get your pet through flare-ups. If digestive disturbances occur the drug must be stopped or the dose lowered. The newer anti-arthritic drugs marketed especially for dogs are no better than aspirin in relieving pain but cause much less gastro-intestinal upset. These drugs which are cyclooxygenase-2 (COX-2) selective inhibitors include Rimadyl (carprofen, Pfizer), Etogesic (etodolac, Ft. Dodge), Deramaxx (deracoxib, Novartis), meloxicam (Metacam, Merial) and Zubrin (tepoxalin, Schering Plough). All medications in this class will, on occasion, cause vomiting and diarrhea. There have also been some cases of severe liver, kidney, intestinal and blood formation (dyscrasia) problems associated with COX-2 administration.

I suggest that all my patients with hip dysplasia receive nutritional supplements. One form, polysulfated glycosaminoglycan, or Adequan, is an injectable product. Oral products include chondrotin, glucosamine and omega-3 fatty acid supplements. Omega-3 fatty acids reduce inflammation. The other products supply the building blocks of cartilage.

There are many other scientifically unproven treatments for arthritis in people and pets. Everything from magnets to acupuncture have been used. I cannot tell you that they work, but little is lost in trying them if you wish to.

A point eventually comes when the drugs mentioned are not enough. In these pets the carefully supervised use of cortisone-type drugs will buy extra mobility and time for your pet. Steroids are powerful drugs. The most commonly used ones for arthritic problems are prednisone and prednisolone. They are best given no more frequently than every second or third day. I usually begin at 0.38mg/pound body weight. These drugs relieve inflammation throughout the body but also cause increased appetite and thirst, fluid retention, liver enlargement and other changes. Do not fear cortisone drugs too much. These drugs have saved countless human lives. Any person with an organ transplant or lupus remains on one of them for the rest of their lives. The secret of success with them is to control weight through diet and exercise and to give as little of the medication as infrequently as possible so that you and your pet can enjoy each other’s company for as long as God allows.

Surgery
Four types of surgery are performed to salvage dysplastic dogs.

Pectineus Tenotomy
This older technique was popular in the 1970’s. It involves cutting the pectinious muscle of the groin to lessen the pain of dysplasia. Cutting this muscle is said to decrease the normal pressure that presses the ball of the femur into the acetabular socket. I have never performed this surgery but some veterinarians found it successful in certain cases. However, the relief provided was often temporary. Few veterinarians still perform this surgery.

Femoral Head Excision or Osteotomy
This is surgery, which removes the femoral head. A dense, fibrous attachment then forms between the femur and the pelvis, which replaces the joint and allows pain-free motion. I have performed many of these surgeries and the outcome has been excellent in dogs weighing fifty pounds or less. It can take up to a year for full motion and weight bearing to return but it is a real joy to see these pets racing happily and pain-free once again.
When hip dysplasia affects both legs it is better to operate on both hips simultaneously. This forces the dog to use both rear legs soon after the operation.

In a femoral head excision, the portion of the femur that grinds against the pelvis is removed and soft tissue is placed between the two bones as a cushion. With time, cartilage spans the joint and allows almost natural motion. After surgery, the animal maintains its knee slightly straighter to compensate for the slight shortening of the femur. For the first 3 weeks after surgery I confine the pet to a small cage and have the owner frequently massage the muscles of the leg. By the fifths or sixth week after surgery I encourage as much light activity as possible to prevent further atrophy (withering) of the muscles of the leg. I have the owners passively flex and extend the leg and continue massages four times a day. Dogs and cats do quite well on three legs so it is difficult to get them to start using the repaired leg. Sometimes I resort to taping a sock onto their good rear leg to encourage them to use the newly reconstructed joint. I have also found that swimming really hastens recovery and use of the affected leg. Within six months of surgery almost all dogs lope about as if nothing had happened. I love to do this surgery because it is one of the most successful, heartening and emotionally rewarding procedures I perform.
Every veterinarian’s technique differs. Antibiotic administration and sterility are extremely important when I do joint and bone surgery. In performing this surgery, I incise and peal back the skin of the hip for good visualization of the muscles, ligaments and bone that form the joint. In preparation for the procedure, I locate and mark a large nerve (the sciatic nerve) that runs just posterior to the joint so that I do not injure it. I remove the diseased femoral head with pliers-like tools called rongeurs and file the bone smooth. I relocate surrounding muscle and cartilage as padding between the ends of the bone and then I place several harnesses of stainless steel drilled through the hump (protuberance) on the femur called the greater trochanter. Using suture material and nylon cord that lasts for the rest of the pet’s life, I construct a synthetic joint.

Hip Replacement
The third technique available for dysplastic dogs is a total hip replacement with a prosthetic joint. It replaces the painful arthritic joint and can be performed at any stage of the disease. This process has become routine in humans but cost limit its use in dogs. It is the only technique that works in dogs over fifty pounds with advanced dysplasia. The modular prosthetic hip replacement system used today has three components, a femoral stem, a femoral head, and the artificial acetabulum. Each component has six available sizes, which allow for a custom fit. The components are made of cobalt chrome stainless steel and ultra high molecular weight polyethylene. This procedure is quite expensive and only performed at large veterinary centers. It has a high success rate and changes in the dog’s mobility are nothing short of miraculous.

Triple Osteotomy of the Pelvis
This procedure has been used since the early 1990s. It works best when hip dysplasia is discovered very early before degenerative changes and arthritis become noticeable on radiographs. Dogs need to be seven month old or older to have this surgery. This surgery entails cutting free the socket or acetabulum at three points and rotating it so that the pressure of the femoral head is directly into the cup and not on pressing on it’s upper edge. Metal plates, screws and wire are used to reattach the acetabulum to the pelvis in its new position. Recovery from the operation, which is performed only on one leg at a time, is 6-10 weeks.

An article in the February 1st 2005 issue of the Journal of the AVMA found that hip dysplasia in two breeds commonly affected with the disease was much higher than anticipated. The incidence of hip dysplasia in golden retrievers was 53-73%. The incidence of hip dysplasia in rottweilers was 41-69%.

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