What is hip dysplasia?

Hip dysplasia is the abnormal formation of the hip joint due to abnormal development during growth. This results in a joint that is unstable and develops degenerative joint disease (osteoarthritis) at a rapid rate.

Hip dysplasia occurs in many species. I know dogs, cats and people with hip dysplasia. It seems to occur frequently in dogs, especially large dogs. Many breeds like St. Bernards, retrievers, and German Shepherd Dogs appear to be overrepresented, but all breeds can be affected. Some breeds, like the sight hounds (greyhounds, salukis, whippets) are rarely affected.

The reason for different breeds having different tendencies is genetic. There is a strong genetic component to this abnormal growth. Many breeds have had strong human selection for certain traits. This selective pressure often brings along undesirable traits in addition to the desirable traits.

Hip dysplasia appears to be a multiple factor disease. The rate of growth seems to play an important role. The faster a large or giant breed dog grows, the greater the tendency for that dog to have bone and joint problems.

The hip is a ball and socket type joint. The ball is the femoral head on the femoral neck, and the socket is the acetabulum of the pelvis. The ligament of the head of the femur and the joint capsule surrounding the entire joint hold these structures together. The muscles surrounding the joint also tend to compress the ball into the socket.

With hip dysplasia, several abnormalities are commonly seen. Likely, the most important is the acetabulum being too shallow or having an abnormal shape. This causes the socket to provide less congruity with the femoral head, allowing the head to slide around or even to pop out partially or completely. The femoral neck is often short and at an abnormal angle. The joint capsule and ligament of the head of the femur are often stretched.

The body does not like joint instability, so it tends to lay down new bone in an attempt to stabilize the joint. The concurrent inflammation causes cartilage damage. The resulting degenerative joint disease causes pain leading to decreased use of the joint and leg causing muscle wasting. The muscle wasting does not allow the body to protect the joint as well leading to more stresses and pain.

Hip dysplasia develops as the body grows. The severity of the hip dysplasia determines when the problems will become apparent. I have seen 3-month-old puppies that could not walk because the femoral heads have completely come out of the acetabulum. On the other end of the spectrum, some dogs with very mild hip dysplasia only show symptoms when they reach old age, even though they have had hip dysplasia their entire lives.

Hip dysplasia can be diagnosed radiographically at any age, but a dog cannot be diagnosed free of hip dysplasia until 2 years of age. Taking these radiographs should be done under heavy sedation or anesthesia. The goal is to make the hips look as bad as possible radiographically so hip dysplasia is not missed when choosing breeding animals.

Prevention of hip dysplasia is best achieved through selective breeding. When choosing a dog, a pedigree of at least 5 generations diagnosed free of hip dysplasia should be a criterion. The Orthopedic Foundation for Animals is a central certification organization for this. This will not guarantee a hip dysplasia free animal, but will greatly reduce the risks. Additionally, controlling the rate of growth in very large breeds seems to help.

There are several means of treating hip dysplasia. To actually treat the disease, surgery is required. There are several procedures available for different stages of disease. Medical therapy is also common. Weight control, anti-inflammatory and joint protective drugs, exercise and physical therapy are the mainstays. These only help control the disease and symptoms. Nothing can make the hips normal.

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