Hips

The hip joint is a ball and socket joint; the ball is the top or head of the femur (thigh bone) and the socket or acetabulum is a bony cup on the side of the pelvis. This highly mobile joint is stabilized by a ligament, its joint capsule and the surrounding thigh muscles. Hip dysplasia refers to a skeletal disease where the hip develops abnormally and arthritis results. 

At birth, the skeleton is composed mainly of cartilage, which is slowly converted to bone as the puppy grows. During growth, bones are constantly reshaped until the final adult shape is reached. In order for the hip joint to develop normally, the ball (femoral head) must be maintained in the socket (acetabulum) during the critical period of growth. This is the first 6-8 months in most breeds. Puppies with hip dysplasia have a normal hip at birth. As they grow, the bone tends to grow faster than the supporting muscles and soft tissues. The ball begins to slip out of the socket. This is called joint laxity and is the first sign of hip dysplasia. Then, a number of things happen: As the ball slips out of the socket, it hits the edge of the socket causing microscopic fractures and scraping the surface cartilage off the bone. Then the ligament and the joint capsule stretch. As the ball is not sitting tightly in the socket, there is no stimulus for a deep socket to develop so it becomes progressively shallower. The end result is an unstable hip and arthritis.

Hip dysplasia is a genetic disease. Unfortunately, it is more complicated than traits like coat colour where a dominant gene will show up in all offspring carrying the gene and elimination of a problem is as simple as not breeding affected animals. We do not know the exact genetics of hip dysplasia, but we know that transmission involves multiple genes and that dysplastic hips are recessive to normal hips. This means dogs with x-ray evidence of hip dysplasia, regardless of severity, carry the genes for hip dysplasia and should not be used for breeding. It also means dogs with normal hips on x-ray may carry the genes for the disease and you may have several generations of normal dogs before the problem “suddenly” appears in your line. While it is difficult to eliminate, we can decrease the incidence of hip dysplasia by only breeding dogs with normal hips. Breeding studies have shown breeding 2 dysplastic dogs results in 85-95% dysplastic puppies, breeding a normal dog to a dysplastic dog, results in approximately half of the puppies affected and breeding two normal dogs will result in about one third of the puppies having hip dysplasia. The percentage of normal pups improves with each generation the disease is absent.

Breeding to, remove hip dysplasia from your line is also complicated by the role environment plays in the expression of the disease. Most of the research performed in this area has examined modifying the disease through nutrition. There is strong evidence that nutritional modifications can delay the onset or lessen the severity of hip dysplasia, and even prevent dogs with a strong genetic potential for hip dysplasia from developing the disease.

Disclaimer: Your veterinarian is the most qualified person to answer all of the questions you have about your pet’s health. Nothing in this article should be construed as medical advice regarding any individual animal’s condition.

© Copyright April 18, 1999. Contact Myra Ehrman at for permission to re-use material.