Dysplastic Hips
The expression hip dysplasia can be interpreted as the abnormal or faulty development of the hip. Abnormal development of the hip causes excessive wear of the joint cartilage during weight bearing, eventually leading to the development of arthritis, often called degenerative joint disease (DJD) or osteoarthritis (OA). The terms DJD, arthritis and osteoarthritis are used interchangeably.
Canine Hip Dysplasia (CHD) was first described in 1935 by Dr. Gerry B. Schnelle. Dr. Schnelle initially called it “bilateral congenital subluxation of the coxofemoral joint”. It was originally thought to be a rare condition but is now recognized as the most common orthopedic disease in dogs. This radiographic image is the first known example of CHD to be published in a scientific journal.
In 1966, Henricson, Norberg and Olsson refined the definition of CHD describing it as: “A varying degree of laxity of the hip joint permitting subluxation during early life, giving rise to varying degrees of shallow acetabulum and flattening of the femoral head, finally inevitably leading to osteoarthritis.”
Today, the general veterinary consensus is that hip dysplasia is a heritable disease manifested as hip joint laxity that leads to the development of OA. So a knowledge of hip joint laxity is key to predicting the ultimate development of the OA of CHD.
Canine Hip Dysplasia afflicts millions of dogs each year and can result in debilitating orthopedic disease of the hip. Many dogs will suffer from osteoarthritis, pain, and lameness, costing owners and breeders millions of dollars in veterinary care, shortened work longevity, and reduced performance. The occurrence of CHD is well documented in large and giant breed dogs, but there is also evidence that CHD is prevalent in many small and toy breeds as well as in cats.
Hip dysplasia is a disease of complex inheritance, meaning it is caused by many genes and its expression can be affected by multiple non-genetic factors. Veterinarians and dog breeders have attempted to eliminate CHD through selective breeding strategies based on scoring of the standard hip-extended radiograph, however, the reduction of CHD frequency in pure-breed dogs has been disappointing.
Fast facts about Canine Hip Dysplasia
- Canine hip dysplasia (CHD) is the most commonly inherited orthopaedic disease in dogs.
- CHD is a degenerative, developmental condition, leading to painful hip osteoarthritis, stiffness, and diminished quality of life.
- All dog breeds are affected by the disease: in some breeds more than 50% of dogs are afflicted.
- The disease is polygenic and multifactorial meaning that CHD expression is a product of both genes and environmental factors such as body weight and age.
- There is no medical or surgical cure for CHD.
- CHD is a major concern for working dog agencies, pet owners, dog breeders and veterinarians.
Penn Hip is a method of evaluation for the hips of dogs.
Penn Hip evaluate laxity in the hip joint, In other words, the amount of laxity or looseness in a hip joint is related to the chance that a hip will develop OA: the looser the hip, the greater the risk. For this reason, it is important to understand the difference between passive and functional hip laxity.
- Passive hip laxity is subjectively scored or measured on a hip radiograph of a dog while under heavy sedation or anesthesia. The PennHIP method measures passive laxity.
- Functional hip laxity is the pathologic form of laxity occurring during normal weightbearing in dogs with dysplastic hips. Current hip screening methods cannot assess functional hip laxity.
- PennHIP research has shown that passive hip laxity is a clinically useful surrogate for functional hip laxity.
To see how PennHIP measures passive hip laxity, go to the Distraction Index – Measuring Laxity section. For an in-depth discussion of the association between laxity and OA, go to the Laxity and Osteoarthritis section.
Effects of Functional Laxity on Joint Mechanics
Under normal conditions, the sum of the forces on the joint are spread out over a large surface area of cartilage. When laxity (or subluxation) is present in the joint, the force applied by the surrounding muscles actually increases to compensate for the laxity (see middle figure). The sum of the forces exerted on the dysplastic hip is greater than the sum of forces exerted on the normal hip. In addition, the forces on the dysplastic hip are applied over a smaller surface area as shown at the contact point in the figure. The high joint contact stresses produce injury and ultimately result in the loss of delicate articular cartilage. Over time, functional hip laxity results in erosion of the femoral head and flattening of the acetabulum.
Normal Joint
Mechanics
Joint Mechanics with Functional Laxity
Results of Functional Laxity Over Time
The Penn Hip evaluation can allow us to evaluate your dog’s breeding potential as well as help determine the chances of them developing hip dysplasia. If we can catch hip dysplasia early in the process, we have many more options for treatment.
Penn Hip vs. OFA
OFA is an evaluation method that looks for evidence of degenerative joint disease in the hip joint. This is a fairly subjective method and the determination is fail, good, fair or excellent. It will be difficult to decide if we should breed a dog with fair hips or even good. Penn Hip, because it measures laxity will give us a number that can then be compared to other dogs of the same breed to make a better determination of risk of osteoarthritis.
A recent article in the Journal of the American Veterinary Association, showed that the use of OFA evaluation alone did not improve the overall hip scores, but PennHIP Distraction Index values were an effective measurement of hip joint quality for selecting breeding stock, and the addition of Distraction Index values to OFA measurements significantly improved hip joint quality in a population of purpose-bred dogs. To view the abstract click here
If you have any questions or would like to schedule a Penn Hip evaluation, please contact our office.
