Canine hip dysplasia is a common developmental disease of puppies. It usually affects both hips and is seen in many different breeds. It is considered a multifactorial disease with a strong hereditary component but also influenced by environmental factors.

The underlying disease in canine hip dysplasia is a laxity in the structures that hold the hip joint together. A puppy with the disease is born with normal hips. As the puppy develops however, the support ligaments and joint capsule that keep the normal joint tight become too loose.

This results in the femur pulling away from the acetabulum of the pelvis, a condition we term subluxation because the joint is starting to luxate but doesn't completely luxate. This subluxation of the hip joint occurs every time the puppy takes a step.

In a normal hip joint, the head of the femur sits inside the acetabulum and is well covered on the top by the dorsal acetabular rim. When a puppy has a dysplastic hip and the joint subluxates, the head of the femur puts excessive pressure on the edge of the dorsal acetabular rim which it is not able to handle. This leads to microfracturing of the dorsal acetabular rim over time. When the head of the femur subluxates, it also rubs the cartilage off of the head of the femur exposing the bone below the cartilage surface. In puppies, subluxation of the hip leads to stretching and tearing of the joint capsule and ligaments in the hip which causes swelling and pain. As the dog gets more mature, it is the wearing away of the cartilage and arthritis development within the joint that leads to pain.

Hip dysplasia in dogs is primarily determined by hereditary factors. This means that dogs that carry the genes for canine hip dysplasia will pass them on to their offspring. Even dogs that show no signs of the disease may carry the genes for it and if bred to another dog that is a carrier, could have offspring with the disease. This is a large reason why controlling hip dysplasia in dogs is so difficult. Recommendations are to screen both parents and all offspring in high risk breeds and to not breed any dog that shows signs of being a carrier.

Whether or not a dog shows signs of hip dysplasia is also influenced by environmental factors with the main one being nutrition as a puppy. Abundant food consumption as a puppy has been shown to shorten the time to first appearance and increase the severity of hip disease. While overfeeding itself doesn't cause hip dysplasia, it does maximize the trait expression in genetically susceptible dogs. The mechanism of how this works is not known. Recommendations for high risk puppies are to limit food consumption to 25% less than what is normally fed for the first year of life.

Robert Vonau is a board certified veterinary surgeon with a mobile surgery practice in Denver, CO. If you would like to learn more about hip dysplasia in dogs or other topics in veterinary surgery, check out my site at http://www.petsurgerytopics.com

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