Hip dysplasia - a congenital disease

Introduction

Hip dysplasia is a congenital disease that affects mostly large breed dogs. It causes weakness and lameness to the rear quarters, and eventually leads to painful arthritis. This arthritis goes by several names; degenerative joint disease, arthrosis, osteoarthritis.

This disease is so prevalent, and so debilitating, that a special veterinary organization called The Orthopedic Foundation for Animals (OFA) was organized.

Cause

Many factors work together to cause this disease, which is a combination of a dog genetically inclined to get this disease interacting with environmental factors that bring about the symptoms. These environmental factors excess calcium in the diet of puppy food for large breed dogs, along with obesity, high protein and calorie diets, and a lack of or too much exercise. The breeding of dogs that already have hip dysplasia is one of the primary reasons the disease is still present. A dog that has hip dysplasia in one socket is prone to having a problem with the ligaments of the knee in the other leg (anterior cruciate rupture).

Pathophysiology

During the degenerative process the cartilage that lines the hip joint, called hyaline cartilage, is damaged. The damage results from the abnormal forces on the cartilage from the deformed hip socket. Small fractures can occur in the cartilage also. Eventually an enzyme is released that degrades the joint further and decrease the synthesis of an important joint protectant called proteoglycans. The cartilage becomes thinner and stiffer, further compromising its ability to handle the stresses of daily movement and weight bearing. As the problem progresses more enzymes are released, which now affect the precursors to proteoglycans, molecules called glycosaminoglycans and hyaluronate. Lubrication is negligible, inflammation occurs, and the joint fluid can no longer nourish the hyaline cartilage. This viscious cycle continues until pain occurs. The body attempts to reduce this pain by stabilizing the hip joint. New bone is deposited at the joint, both inside and out, along with some of the ligaments and muscle attachments to the area. This causes thickening and a decrease in the range of motion. This is the actual arthritis noted on a radiograph, which will not go away and will continue to progress.

Breed Predispositions

Many dogs can develop hip dysplasia. Dogs that were commonly affected years ago, like German Shepherds and Labrador Retrievers, still get the disease but not as commonly as before.

According to the OFA some of the breeds with the highest prevalence are:

Diagnosis

Hip Dysplasia is diagnosed based on a history of weakness or lameness to the rear legs, especially after exercise or when first getting up after resting. Some young dogs will bunny hop when running, and might lie down on their stomachs with their legs stretched behind them. It is possible to palpate joint laxity on some dogs that are anesthetized (we call this the Ortolani sign). Radiography is the definitive way this disease is diagnosed. It is not perfect though, since a dog can be hip dysplasia free on the radiograph (phenotype), but can be genetically predisposed to the disease (genotype). These dogs have the potential to be carriers of the disease, yet show no symptoms themselves.

Many variables affect the degree of lameness. They include caloric intake, degree of exercise, and weather. To further add to the complication, pets with terrible looking hips on radiographs might act as if nothing is wrong, while others with barely discernible changes on their radiographs might be severely lame.

These are the x-rays of dog with a normal pelvis. The diagram below explains why these hips are normal. View both of them at the same time if possible.

 On the right side of this normal pelvis we have outlined 2 important natomical features. The "U" shaped appearance of the neck (outlined in white), and the full rounded appearance of the head (outlined in black), are normal. They indicate a full socket with a tight fit and no signs of secondary changes due to instability of the ball and socket joint.

 This dog has moderate changes that indicate it has hip dysplasia on the right side. The socket is not as rounded as it could be, and the head of the femur is slightly flattened. Also, the neck of the femur does not have the U shaped indentation that is normal. You can see this better on the closeup views below.

  The arrow points to the thickening in the femoral neck in the abnormal right socket. You can also visualize the slightly flattened appearance of the head of the femur and the fact that it does not fit into the socket as tight as the normal hip marked left.

This is a case of severe hip dysplasia. The arrows point to the thickened femoral neck on each side along with the secondary arthritis occurring on the left side. Notice how flat the sockets are and the lack of rounded appearance of the femoral head. This dog is probably in pain and has a difficult time walking in the rear quarters.

 If left untreated the disease continues to progress, eventually causing a crippling lameness and severe pain. Correcting this problem at an early age might have prevented this.

 Dogs are not the only species that gets hip dysplasia. It can also occur in cats (Maine Coons are commonly affected), although not as common as in dogs.

The white arrows outline the large amount of stool in the colon of the above cat with feline hip dysplasia. It is painful for this cat to squat to have a bowel movement, as a result it gets severely constipated.

Medical Treatment

Environmental

Keeping your dog's weight under control and providing controlled exercise are very beneficial. Going for short walks will give you an idea of your dog's limits. Proper exercise will maintain muscle tone and keep the joints moving and more fluid. Swimming is a superior form of exercise to achieve this goal.

Provide a warm environment and a well padded bedding area are also of benefit. Additional warmth helps chronically infected joints. Hot water bottles are helpful. We don't recommend electric heating pads because of serious burn potential.

Drugs

Many drugs have been used to control the pain associated with the secondary arthritis that occurs with hip dysplasia. Some of these drugs are extremely effective, and can provide a dog with a high degree of relief from pain.

Buffered aspirin and Ascriptin (aspirin with maalox) are readily available over the counter remedies. Tylenol should not be used in dogs because of its potential for side effects. Tylenol is NEVER used in cats because it can cause a serious disease called methemoglobinemia.

Rimadyl and Etogesic are highly effective prescription medications. The work by inhibiting the release of prostaglandins, leading to less inflammation in the joints. They should be given prior to any bout of exercise. Some dogs will vomit or have diarrhea on these medications. Giving the medication on a full stomach and using GI protectants can minimize this problem. Rimadyl use in labradors should be carefully monitored for signs of liver problems.

Nutraceuticals are popular arthritis treatments, primarily because they are thought of as more natural than drugs. Humanoids use them commonly. They provide the raw material that enhance they synthesis of glycosaminoglycan and hyaluronate. Controlled studies are lacking to determine their true effectiveness. Oral versions take at least one month to become effective. A great advantage is their lack of side effects. Oral versions include Cosequin, Synovicare, Glycoflex, Arthramine, and MaxFlex. Injectable versions include Adequan, a drug that has been used in veterinary medicine, especially in horses, for many years. Injectable versions achieve a more rapid response than oral medications. 

We can't predict which medications will work best in an individual case. Trying different ones, even using some of them in combination, can let you determine which is the best approach in your dog.

 Surgical Treatment

Most cases of hip dysplasia, especially in younger dogs, are treated surgically. One of the surgical specialists we consult with will make the determination of which procedure is the most appropriate. Three main types of surgery are performed.

This area contains graphic pictures of actual surgical procedures performed at the hospital. It may not be suitable for some children (and some adults also!).

1. Femoral Head Ostectomy (FHO)

In this procedure the head (or ball) of the femur is removed. The remaining part of the femur forms a false joint with the muscles, ligaments, and tendons in the area. Even though this false joint is not as good as a real joint, there is a significant reduction in pain. Almost any sized dog can have this procedure even though it is much more effective in smaller dogs. Obese dogs and those with significant loss of muscle do not do as well. Compared to the other types of surgery this one is much more basic, yet many pets that have this surgery return to almost normal function.

This are the hips of Mickey, a very active Australian Shepherd. He has hip dysplasia on both sides. FHO surgery will be performed on his right hip.

After the skin incision is made the muscles are separated to give visualization of the femoral head. It is gently rotated and brought up as far as possible.

A special air powered drill is used to cut the neck of the femur at just the right angle.

The angle in the cut of the femoral neck is apparent. Also present on the head of this femur is a piece of the round ligament, one of the structures that anchors the head of the femur into the socket.

 An opening remains where the head of the femur used to reside. The remaining bone will form a false joint, and return this pet to almost 100% function.

The muscles that were separated and cut are now carefully sutured. These muscles are necessary for normal movement of the false joint that will soon form. 

 This is what remains after the surgery. Mickey healed rapidly after the surgery and is running around as fast as before, according to his worried mom. 

2. Triple Pelvic Osteotomy (TPO)

This surgery is used in large breed dogs no older than 10 months of age. Candidates for this surgery can only have mild hip dysplasia and no signs of secondary arthritis. During the procedure the pelvis is cut and rotated slightly so that the head of the femur has a tighter fit into the socket. Since the pelvis is being cut it needs to be stabilized with bone plates.

The pelvis is cut in 3 locations. The locations of these cuts allows the proper rotation of the hips.

 This is the final result after a TPO surgery. These two plates are angled to provide the proper pelvic rotation.

3. Total Hip Replacement (THR)

In this procedure the neck and head of the femur are replaced with stainless steel or titanium implants. This is a highly specialized procedure performed only by select veterinarians. It is used in young dogs that have achieved most of their skeletal growth and in adult dogs that weigh at least 40 pounds. It can be used in dogs that already have secondary arthritis, unlike the TPO. It has a high success rate but has to be performed carefully because if post operative complications occur they can be disastrous.

This is the end result of the surgery. These implants now make up the ball and socket joint, and will remain fully functional for many years.

An additional treatment modality that has yielded great success in treating hip dysplasia is called VOM. It is a non-invasive and non-painful way to stimulate the nervous system to help the hip dysplasis syndrome.

Prevention

This is achieved by neutering pets that have the disease. Dogs can be screened for this problem by taking radiographs of their hips at 2 years of age. If they are certified free of hip dysplasia by the Orthopedic Foundation of America (OFA), there is much less of a chance they will sire offspring with the problem. It is best to purchase large breed dogs only if their parents are OFA certified to be hip dysplasia free.

No guarantee can be given when breeding hip dysplasia free dogs radiographically that their offspring will not deveop the disease. A dog can be hip dysplasia free on a radiograph, yet still carry the genetic predisposition to this disease that will be transmitted to its offspring.