Pioneering the Diagnosis of Canine Hip Dysplasia View Bellwether Spring 2015 By: John Donges
Published: Feb 27, 2015
The Penn Hip Improvement Program, largely known as PennHIP, has had a fascinating and successful trajectory from lab to private sector patient care. Rigorously developed by Dr. Gail K. Smith, V’74, the program exemplifies the cross-disciplinary nature of work at Penn Vet—drawing not only from veterinary but engineering principles. But as Smith notes, “From the beginning, it’s always been about the welfare of dogs.” Canine Hip Dysplasia (CHD) is a heritable disease that afflicts millions of dogs each year and is a major concern for pet owners, breeders, working dog owners, and veterinarians. CHD is described as the faulty development of the hip, causing excessive wear to joint cartilage; it affects all dog breeds and more than 50 percent of dogs in some of the major breeds. Excessive hip joint laxity leads to osteoarthritis (OA), stiffness, and diminished quality of life, and costs owners and breeders millions of dollars in care and loss of performance. The emotional toll is incalculable. While CHD has been described since the 1930s, Smith’s pioneering research has advanced the ability of veterinarians to identify and treat the condition early in life. PennHIP is a unique method enabling the estimation of OA risk in dogs as young as 16 weeks of age. PennHIP includes three major components: a diagnostic radiographic technique; a network of trained veterinarians; and a medical database for scientific analysis. The multifaceted radiographic screening method assesses the quality of the canine hip and quantitatively measures canine hip joint laxity. Approximately 3,000 veterinarians around the world are trained to perform the PennHIP methodology. Smith charted a distinctive academic path at Penn, which led to groundbreaking work. After completing an undergraduate degree in engineering in 1970, he was interested in pursuing bioengineering, which was not an academic discipline at the time. He was accepted into the VMD-PhD program in 1971 and, after receiving his Penn Vet degree in 1974, went on to earn a PhD in materials science engineering. He completed a residency in orthopedic surgery in 1979 and was appointed to the Penn Vet faculty that same year. As Smith explains, “I chose the veterinary curriculum over medical school because it provided more opportunity for multi-species investigation: the One Health concept.” In the McKay Laboratory in the School of Medicine, he conducted in vitro biomechanical research on the hip, knee, and spine. In 1983, this research led to a theory that became the scientific foundation for PennHIP. It was here that the “surgery, materials, and mechanics all came together,” Smith recalls. “We could understand hip health with a high degree of accuracy and clinical relevance.” In 1993, the PennHIP method was made available to the public as a clinical tool to aid in the control of CHD. In 1996, Smith was issued a patent for the discovery; a second followed in 2013. A large scientific database houses the PennHIP data. As more information becomes available, the PennHIP laboratory is able to obtain more precise answers to questions about the etiology, prediction, and genetic basis of hip dysplasia. PennHIP publishes its findings in scientific journals to share with veterinarians, as well as breed clubs and dog fancy publications. The tools developed by PennHIP help veterinarians and dog breeders to reduce or eliminate CHD through selective breeding strategies. With 20 years of science and 45 peer-reviewed papers to back the PennHIP findings, Smith’s work has not gone unnoticed. For his research and contributions to the advancement of small animal veterinary medicine, Smith has been recognized by the American Veterinary Medical Association and the American Kennel Club. He has also received the prestigious Blaine Award from the British Small Animal Veterinary Association and the Iams Saki Paatsama Award from the World Small Animal Veterinary Association. In the 1990s, the Penn Center for Innovation (PCI) licensed PennHIP to a corporation, with Smith taking it back in 2002 and turning it into a not-for-profit service at Penn Vet. Recently, PCI facilitated the sale of PennHIP to Antech Imaging Services (Antech Diagnostics, Inc.): it is now called AIS PennHIP. As the Director of AIS PennHIP, Smith helps Antech develop web-based teaching modules for an untapped market: everyday pet owners. Tom Gregor and Dr. Pamela McKelvie, longtime members of the PennHIP team, also work for AIS with Smith. Their goal is for this new educational platform to facilitate global training of new PennHIP veterinarians and to make PennHIP information accessible and convenient for dog owners, as well as breeders and vets. “I’m looking forward to PennHIP growing rapidly,” Smith says. “Pain medication for life, even hip replacements, are compromises and cost a lot of money. People would like their dogs to have good hips. Now they’ll be able to measure the risk of their dog developing hip OA and, with their veterinarian’s guidance, implement preventive and palliative strategies early in life.”
Antech Imaging Services explanation of PennHIP
THE PROBLEM
Canine Hip Dysplasia (CHD)
• Is the most commonly inherited orthopedic disease
• Leads to hip arthritis causing pain, stiffness, and diminished quality of life
• Has no medical or surgical cure
• Afflicts more than 50% of the dogs within some breeds
• Clinically affects large breed dogs more severely than smaller breed dogs
THE KEY FACTOR
Hip Laxity
In the 1980’s, researchers at the University of Pennsylvania’s School of Veterinary Medicine pioneered a better diagnostic method to assess hip laxity—the key factor in the development of Canine Hip Dysplasia (CHD).
The hip joint is a ball-and-socket joint, with the ball of the femur (femoral head) fitting into the hip socket (acetabulum). Hip laxity refers to the degree of “looseness” of the ball in the hip socket.
Studies have shown that dogs with looser hips (excessive hip laxity) are at higher risk to develop hip dysplasia than dogs with tighter hips (minimal hip laxity).
THE SOLUTION
AIS PennHIP Hip Improvement Program
The research-based hip-screening procedure known as PennHIP has proven to be the most accurate and precise method to measure hip laxity. It can identify—as early as 16 weeks of age—dogs that are susceptible to developing hip dysplasia. This offers breeders the opportunity to make early decisions on breeding stock, and allows veterinarians to advise pet owners on lifestyle adjustments and preventive strategies to minimize the pain and progression of the disease.
THE PennHIP PROCEDURE
There are two principal innovations in the PennHIP method. First, the dog is positioned on the x-ray table with hips in a neutral orientation, and second, a custom distraction device is applied to reveal the maximum amount of hip laxity. To achieve this, the dog’s muscles are completely relaxed by administering sedation or general anesthesia.
Veterinarians must complete specialized training and quality-control exercises before becoming certified to perform the PennHIP procedure.
A complete PennHIP evaluation includes
office consultation, sedation/anesthesia, and submission of the three PennHIP radiographs to ANTECH Imaging Services for evaluation.
Severe Hip Dysplasia
PennHIP RADIOGRAPHS
PennHIP screening includes three separate radiographs (x-rays). Above are examples of the three PennHIP radiographs of a 15-month-old Labrador Retriever.
HIP-EXTENDED RADIOGRAPH
The dog’s hind legs are placed in “extension.” PennHIP utilizes the hip-extended view to identify radiographic signs of hip arthritis also known as osteoarthritis (OA).
Traditional hip screening methods rely solely on the hip-extended view (photo 1) to evaluate both the presence of hip arthritis and joint laxity (subluxation). Using traditional systems this dog’s hips would be considered normal because the hip-extended view (photo 1) shows no evidence of arthritis or subluxation (laxity). While the hip-extended view can detect existing arthritic changes, it often conceals hip laxity thereby giving a false impression of joint tightness. So, in the absence of arthritic changes, as in this dog, the hip-extended view does not reliably distinguish between dogs that are disease-susceptible and those that are not.
COMPRESSION RADIOGRAPH
The dog’s hind legs are positioned in a neutral, weightbearing orientation and the femoral heads (balls of the femur) are gently seated into the acetabula (hip sockets).
This view can identify critical anatomic landmarks of the hip and determine how well the femoral head fits into the acetabulum.
DISTRACTION RADIOGRAPH
The dog’s hind legs are positioned in the same neutral position as the compression radiograph and a special device is used to reveal the dog’s inherent joint laxity.
This exclusive feature of the PennHIP procedure permits accurate measurement of maximal hip laxity.
When comparing this dog’s hip-extended view (photo 1) to the distraction view (photo 3), the distraction view reveals much greater joint laxity. The PennHIP method uses the amount of joint laxity revealed in the distraction view (photo 3) to tell us that this dog is actually susceptible to developing hip dysplasia and will likely show radiographic evidence of hip arthritis later in life.
HIP SCORING AND REPORT INTERPRETATION
Your PennHIP veterinarian will submit the three PennHIP radiographs to ANTECH Imaging Services for specialized evaluation. A confidential report comprised of the following key parts will be sent to your PennHIP veterinarian: Distraction Index (DI) The DI is a measure of hip laxity—the inherent distance the ball can be displaced (distracted) from the hip socket—and is expressed as a number between zero and one. A DI near zero indicates little joint laxity (very tight hips). A DI closer to 1.0 indicates a high degree of laxity (very loose hips). Dogs with tighter hips are less likely to develop hip dysplasia than dogs with looser hips. A threshold level of 0.30 has been identified, below which hip dysplasia is very unlikely to occur.
ARTHRITIS
The PennHIP report also includes an evaluation of the hip-extended radiograph for evidence of arthritis, confirming a diagnosis of hip dysplasia. For dogs with evidence of arthritis, your PennHIP veterinarian can explain the disease fully and recommend palliative measures. Breed Laxity Profile Ranking Based on the DI, your dog is ranked within its breed. For the dog breeder this ranking helps in the selection of breeding candidates—dogs in the tighter half of the population are recommended for breeding. By selecting breeding dogs with tight hips (lower DI), meaningful progress toward better hips can be made within a few generations.
PennHIP — MAKING A DIFFERENCE
PennHIP is the most accurate hip screening method available and can be safely performed on dogs as young as 16 weeks of age. An early estimate of a dog’s hip integrity is invaluable, whether the dog’s intended purpose is for breeding, for working, or as a family pet. For breeders Information compiled in PennHIP’s international database permits informed selection of breeding stock based on hip tightness relative to other members of the same breed. Breeders can reduce the incidence and severity of Canine Hip Dysplasia (CHD) in future generations of dogs by applying selection pressure towards tighter hips. Among current hip screening methods, PennHIP has the highest heritability value to bring about these genetic changes. For service and working dog organizations Service and working dog organizations were the first to adopt PennHIP as the principal method for hip screening. The investment in training service/working dogs is enormous. The ability to prescreen the dog’s genetic predisposition to CHD is an invaluable tool when evaluating a future service/working dog’s hip integrity. For companion dog owners If your dog is identified to be at risk for CHD, your PennHIP veterinarian can recommend, at an early age, appropriate strategies (diet, medication, and/or activities) to delay or diminish the ultimate course of the disease.
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