What is Hip Dysplasia?

Hip dysplasia (let's call it HD for short) is a malformation of the hip joint, usually seen in medium to large breeds of dogs. This joint is where the top portion of the large bone in the leg (the ball of the femur) meets the curved part of the pelvic bone (the socket or acetabulum). That is why this is called the ball and socket joint.

In the normal dog, the ball and socket joint fit snugly. There is a tiny ligament that keeps the ball attached to the socket, and there is a joint capsule or sac that surrounds the whole area and keeps it bathed in a small amount of nice, thick protective fluid. As a general rule of thumb, at least half of the head of the femur (the ball portion) must fit within the curve of the hip. The top of the ball and the inside of the socket, where the two bones meet, are both lined with smooth cartilage. The cartilage and the fluid in the joint are the two things that allow the bones to move smoothly against one another without creating wear and tear. This is no different than where any two parts of your automobile rub together. If there is enough oil or grease, the parts move smoothly. If not, wear and tear is created, and eventually the parts wear out.

In dogs with hip dysplasia, the ball and socket do not fit properly. Less than 50% of the head of the femur (the ball) fits within the curve of the hip. This causes multiple problems:

- The tiny ligament holding the ball and socket together becomes stretched.

- The sac surrounding the area becomes stretched. The ball portion rubs abnormally against the edges of the socket joint, creating irregularity and tears in the protective cartilage.

- Arthritis sets in as a result of this abnormal wear and tear.

Osteoarthritis is the end result of hip dysplasia. This irreversible arthritis is painful and uncomfortable.

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