ntroduction

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

 

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On the right side of this normal pelvis we have outlined 2 important anatomical 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.

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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.

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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.

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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.

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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.

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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.

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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.