The word "dysplasia" means abnormal growth or structure. If your dog has canine hip dysplasia, the leg bone and pelvic (hip) bone don't fit like a ball into a catcher's mitt because the cup formed by the pelvic bone is too shallow. The leg bone slides out of the pelvic socket and may dislocate. Painful arthritis can develop in your dog. Dysplasia can occur in one or both of your dog's hips. Dysplastic hips are one type of degenerative joint disease (DJD) in dogs.
Large breed dogs are prone to hip dysplasia, including St. Bernards, German Shepherds, Labrador Retrievers, Golden Retrievers, and Rottweilers. Genes, nutrition, and environment contribute to the development of canine hip dysplasia.
The hip, or coxofemoral joint (from coax for hip and femoral for the femur thigh bone), is where the spine and upper body meet the leg. Three bones fuse together to make the hip bone: the sacrum, which embraces the lower spine; the ilium which forms the portion we sit on; and the acetabulum, which forms the sides. The acetabulum has a deep groove like a catcher's mitt into which the top of the large thigh bone, the femur, sits. This is a ball and socket joint, and the head of the femur rotates like a ball within the hip (acetabular) socket. The femur is held in the socket by hip muscles and by the round ligament that directly attaches the femur to the acetabulum. The bones are covered with cartilage, bathed with synovial fluid, and sealed inside a synovial membrane. The cartilage and synovial fluid work to cushion movement so that the bones don't jar together when your dog runs or jumps.
Canine hip dysplasia is a problem for dogs and their owners because it causes severe pain and immobility. If your dog has hip dysplasia, he or she will struggle to get up, to climb stairs, to get into a car, and to squat to urinate and defecate. Many dogs lose their good natures because of immobility and pain. The relationship you have with your dog deteriorates because your dog won't feel like playing, and it becomes an effort to do anything with your dog since he or she needs to be lifted and carried.
There are over 400 dog genetic diseases, and canine hip dysplasia is one of the most significant. It is a polygenetic disease, meaning more than one gene is involved. Some breeders certify their dogs have good genetics by submitting X-rays to the Orthopedic Foundation for Animals (OFA) or to the University of Pennsylvania Hip Improvement Plan (Penn HIP). Dogs certified as good or excellent by OFA or Penn HIP are less likely to produce puppies carrying genes for hip dysplasia.
Cats don't develop hip dysplasia very often, but they frequently develop joint problems. The most common locations for joint problems in cats are the elbows and ankles.