As most of you know, canine hip dysplasia (CHD) is the most common, heritable orthopaedic problem seen in dogs. A previous article in this series discussed CHD and the orthopaedic Foundation for Animals (OFA), however as the University of Pennsylvania Hip Improvement Program (PennHIP) method of CHD evaluation is becoming increasingly more common, I thought it was time to have a closer look at this subject.
In 1983, Dr Gail Smith from the University of Pennsylvania School of Veterinary Medicine began to actively research and develop a new scientific method for the early diagnosis of CHD. Research in Dr. Smith’s lab has introduced evidence that there is a symptom free “carrier” state for CHD and this state is undetectable using standard diagnostic methods. The PennHIP method involves special positioning of the dog so that the dog’s passive hip laxity (degree of “looseness” of the hip ball in the hip socket) can be accurately measured. Research in Pennsylvania has shown that the degree of passive hip laxity is an important factor in determining the individual’s susceptibility to develop Dejenerative Joint Disease (DJD) later in life. Hip DJD, or osteoarthritis, is the universally accepted confirmation of CHD.
Dogs are typically given a general anesthesia, then 3 separate radiographs are taken:
Compression view where hips are pushed into the socket to show the true depth of the socket and give an indication of the “fit” of the head of the femur into the pelvic socket
Distraction view using a special device which is the most accurate view for showing the degree of passive laxity, and
Hip Extended view to examiune for any existing joint disease.
This third view is the view the OFA currently uses to diagnose and grade our dogs hips. PennHIP proponents state that the biomechanics of the extended hip view are such that the radiograph may actually give a false impression of joint tightness, and question the accuracy of this view alone.
Radiographs are taken by a veterinarian who has been trained and certified to take and measure these radiographic views. The PennHIP evaluation results in a numerical Distraction Index (DI), which is a measure of the passive hip laxity, and is expressed as a number between 0 and 1. A DI approaching 0 would indicate no joint laxity and very tight hips, whereas a DI near 1 indicates a high degree of laxity and very loose hips. At the University of Pennsylvania, a “threshold” of tightness has been identified in some breeds, below which hip dysplasia is not found. These radiographic evaluation(s) can be accurately performed on our dogs as early as 16 weeks of age, thus enabling us to evaluate a prospective breeding prospect much earlier. We could, conceiveably, radiograph all littermates and select the one with the tightest hips at 16 weeks for our future breeding stock, and in that way select against the tendancy for our dogs to develop CHD. Working enthusiasts could have a puppy tested prior to purchase to determine if the dogs hips are strong enough to stand up to a lifetime of strain, or if this dog would do better in a home with lifestyle adjustments to minimize disease expression.
International Canine Genetics Inc. (ICG) currently trains and certifies veterinarians in PennHIP methods of evaluation. ICG is currently working with many organizations to present the PennHIP technology and hopes that the PennHIP Distraction Index will someday be included as part of a dog’s registry information, as the dog’s OFA number currently is. Presently, the hip evaluation reports are considered confidential medical information and are released only to the PennHIP veterinarian and the owner of the dog.
I have not had any of my dogs evaluated with this method, however I am considering taking the ICG PennHIP course and becoming certified myself. I will continue to get my dogs OFA certified at 24 months of age or older, but I believe that any and all methods of testing for heritable disease(s) are worthwhile. The more information we have on every individual dog, the better, MORE INFORMED breeding decisions we can make…and I will once again use this forum as an opportunity to encourage ALL breeders to test ALL their dogs for ANY AND ALL types of heritable disease(s), as well as to encourage prospective puppy buyers to DEMAND pups from litters from TESTED parents ONLY!! If education and concern for our dogs won’t change some breeders minds about testing, the threat of losing the almighty buck to breeders who test their breeding stock sure will!!
Dr. Cathy Priddle