The answers to these questions may raise additional questions. For more detailed answers, please explore the relevant areas of this web site or the actual manuscripts listed in the "Scientific Reports" section of this site.
A growing body of scientific information from multiple independent laboratories confirms that the PennHIP method surpasses other diagnostic methods in its ability to measure hip joint laxity and accurately predict the onset of the osteoarthritis (OA) of canine hip dysplasia (CHD). Osteoarthritis is also known as degenerative joint disease (DJD). The PennHIP method can be performed on dogs as young as sixteen weeks of age compared with two years using the standard technique. The data generated by PennHIP allows breeders to confidently identify the members of their breeding stock with the tightest hips and the best breeding potential. Pet owners are able to obtain an estimate of their dog's risk for developing DJD and at the direction of their veterinarian, make lifestyle adjustments for their dog to enhance the quality of their pet's life. The PennHIP interpretation will also permit breeders to assess the progress they are making with their breeding program.
PennHIP is performed only by certified PennHIP veterinarians who have undergone training and have successfully demonstrated their expertise in performing the technique. In addition to the special radiographs developed by PennHIP, the method also incorporates the standard hip-extended view into the interpretation of hip joint integrity. Upon request, your PennHIP veterinarian can provide you with a copy of the hip-extended radiograph for submission to the OFA at the time your dog has PennHIP radiography. You do not have to abandon the OFA view or schedule a separate appointment to have it done.
Through sophisticated biomechanical studies, it was found that the canine hip is loosest when positioned in a neutral or "standing" orientation (also called the stance-phase of weight bearing). It was reasoned that this point is also the optimal patient position for measuring maximal hip joint laxity on a radiograph. Ironically, the standard hip-extended patient positioning was found to put the hip in one of its tightest configurations thereby masking the inherent hip laxity of the dog.
Passive hip laxity measured in the neutral position was radiographically monitored in dogs as they matured. It was shown that 1) the radiographic measurement of passive hip joint laxity by the PennHIP method was accurate in dogs as young as sixteen weeks of age, and 2) hip laxity was the primary risk-factor to predict the development of OA. Specifically, the looser the hip joint according to the PennHIP method, the greater the chance that it will develop OA.
The PennHIP method also incorporates the hip-extended radiograph to evaluate for evidence of OA.
The Penn Hip Improvement Program, PennHIP, is a service provided in conjunction with a worldwide network of over 2000 certified PennHIP-trained veterinarians from 24 countries. PennHIP's primary objective is to reduce the frequency and severity of hip dysplasia in all breeds of dogs. PennHIP is attempting to accomplish this goal through the implementation and widespread utilization of a new stress-radiographic technique (X-ray). Through the network of certified veterinarians implementing this technique, PennHIP is amassing a large scientific database on the etiology (cause), prediction and genetic basis of canine hip dysplasia (CHD).
The PennHIP method is a different way to assess, measure and interpret hip joint status. It consists of three separate radiographs: the distraction view, the compression view and the hip-extended view. The distraction view and compression view, developed by Dr. Smith, are used to obtain accurate and precise measurements of hip joint laxity and congruity, respectively. The hip-extended view is used to obtain supplementary information regarding the existence of osteoarthritis in the hip joint.
To summarize, PennHIP is composed of three major components:
- A diagnostic radiographic technique consisting of 3 radiographs -
- A network of trained veterinarians -
- A medical database for scientific analysis
In 1983, Dr. Gail Smith while at the University of Pennsylvania School of Veterinary Medicine began to research and develop a scientific method for the early diagnosis of CHD. Multiple scientific disciplines - including biomechanics, orthopedics, clinical medicine, radiology, epidemiology and quantitative genetics - have been incorporated during the development of PennHIP. This research resulted in a diagnostic method capable of estimating the susceptibility for CHD in dogs as young as sixteen weeks of age.
In 1993, Dr. Smith established PennHIP, a cooperative scientific initiative, to serve as a multi-center clinical trial of the new hip dysplasia diagnostic technology. The program was successful and quickly grew beyond the capacity and purpose of a university research laboratory. In 2013 PennHIP was acquired from the University of Pennsylvania by ANTECH Diagnostics, Inc. of Los Angeles, CA.
To obtain diagnostic radiographs, it is important that the patient and the surrounding musculature be completely relaxed. For the comfort and safety of the animal, this requires sedation and/or general anesthesia. Typically, three separate radiographs are made during an evaluation. The first is the compression view where the femurs are positioned in a neutral, stance-phase orientation and the femoral heads are pushed fully into the sockets. This helps show the true depth of the hip socket and gives an indication of the "fit" of the ball in the socket. The second radiograph is the distraction view. Again, the hips are positioned in a neutral orientation and a special positioning device is used to apply a harmless force to cause the hips to displace laterally. This position is the most accurate and sensitive for showing the degree of passive hip laxity. Passive hip laxity has been shown to be the primary risk factor associated with the development of the osteoarthritis of hip dysplasia. A hip-extended view is also included for the sole purpose of examining for existing joint disease such as osteoarthritis. The PennHIP procedure has been safely performed on thousands of patients.
PennHIP has studied the efficacy of this method from the eight weeks up to three years of age. The PennHIP method can be reliably performed on a dog as young as 16 weeks old. Passive hip laxity at 16 weeks correlates highly with later hip laxity. In other words, a dog's hip laxity at 16 weeks will be much the same at one year, two years or even three years. The accuracy of laxity measurements for German Shepherd Dogs less than 16 weeks of age is not high enough to be of clinical use. Other breeds require study to determine the earliest reliable age of evaluation. For some breeds this age could be less than 16 weeks. Hip laxity after 16 weeks appears to be predictable across breeds tested and PennHIP has established 16 weeks as the earliest age to be given an official PennHIP score.
The looser the joint, as determined by the PennHIP method, the greater is the chance that the hip will develop OA. (The standard hip-extended method actually masks true hip joint laxity and is therefore not as reliable a predictor of hip OA). There are obvious advantages to screening dogs for hip joint laxity at 4 months of age (or six months, 1 year, etc.) as opposed to waiting until 2 years of age. The reliability of the PennHIP method slightly improves with age, with one year being marginally superior to 6 months, which in turn is marginally better than 4 months. For all dogs, we recommend when possible, to use the mean (average) of repeated evaluations to get a more reliable estimate of a dog's hip laxity status (phenotype).
To obtain diagnostic quality radiographs, the musculature around the hip joint must be completely relaxed. For the comfort and safety of the animal, this requires either heavy sedation or general anesthesia. The selection of the individual sedation/anesthesia protocol is left to your PennHIP veterinarian's discretion, so long as the dog is sufficiently sedated to obtain a diagnostic quality radiograph (and, of course, so long as the drugs and dosages used are safe).
After many studies, both in the PennHIP laboratory and in independent laboratories, there is no evidence to suggest that the PennHIP procedure is any more harmful than the standard hip-extended procedure. Certainly, in dogs having extreme laxity and pain associated with inflammation and advanced osteoarthritis of hip dysplasia, any manipulation of the hip (e.g. OFA, PennHIP, routine orthopaedic examination) can potentially cause transient discomfort (1- 2 days). PennHIP is aware of only a handful of cases out of well over 100,000 dogs that have exhibited discomfort after the procedure. All such claims are followed up and no long-term pain or untoward effects have been observed.
The total fee for a PennHIP evaluation is determined by the veterinarian providing the service. It is important to remember that the total service includes sedation/anesthesia, 3 radiographic images, office consultation and all charges associated with submitting the images to AIS PennHIP for evaluation. You will not find it necessary to write a separate check for submission of your dog’s radiographs or for evaluation fees. These charges will be included in the total cost of a PennHIP evaluation.
Your PennHIP veterinarian will likely charge more for PennHIP testing than for an OFA evaluation. PennHIP analysis consists of 3 radiographs rather than one. Also, a certified PennHIP veterinarian incurred costs of training, quality assurance testing and purchasing the necessary equipment.
To obtain the name of a veterinarian in your area who is trained and certified to perform the PennHIP procedure, follow the link to find a certified PennHIP veterinarian. If there is not a veterinarian near you presently, additional veterinarians are currently being trained throughout the country and world.
PennHIP differs from other methods in some very fundamental and important ways:
PennHIP was developed and tested following strict scientific protocols and the results of these studies have been, and continue to be, published in peer-reviewed scientific journals. More than three decades of research and analysis have produced a body of information in support of PennHIP's effectiveness. As with all diagnostic tests, PennHIP's accuracy is not 100%, but in direct comparisons it is far superior to any other available hip dysplasia diagnostic methods. No other method, published or practiced, has similar compelling scientific support.
PennHIP's evaluation protocol quantitatively measures passive hip joint laxity. Based on the degree of laxity, the individual dog's hip laxity is reported on a continuous scale relative to other members of the same breed. This allows breeders to easily identify animals with tighter hips within each breed. Dogs with tighter hips are less likely to develop osteoarthritis (hip dysplasia). Note that the hip evaluation report is not issued in a subjective pass/fail framework.This approach was adopted because some breeds of dogs have few members with hips tight enough to be considered truly OA non-susceptible. In such breeds, genetic progress can be made (while still maintaining adequate genetic diversity) simply by breeding dogs in the tighter half of the population (see Selective Breeding section). Of course, applying greater selection pressure equates to more rapid genetic change toward improved hip status.
Because PennHIP is measuring maximal passive hip laxity, the position of the patient is notably different from the hip-extended position. The legs are in a neutral or stance-phase position rather than the conventional hip-extended position. The hip-extended position has been used for more than 50 years to screen hips for either OA, laxity or both. However, studies have indicated wide diagnostic variability among radiologists in interpreting this view. Further, through biomechanical testing, the hip-extended view was found to mask the underlying true joint laxity therefore the predictive value for CHD of this method was shown to be inferior to the PennHIP procedure.
Heritability is an important statistic relating the proportion of a trait attributable to additive genetic effects when compared to all other sources of phenotypic variation, for example both genetic and environmental factors. In other words, heritability relates the genetic origins of a disease or trait with what is actually expressed or observed outwardly. Heritability is expressed as a number between 0 and 1. From time tested quantitative genetic principles, the higher the heritability, the greater the rate of genetic change that can be derived from the application of selection pressure. The accuracy of a diagnostic test to determine disease (in this case CHD), has profound impact on the value of the heritability statistic. Inaccuracy of a diagnostic test acts to lower the estimate of heritability and therefore the efficacy of breeder selection based on that diagnostic test.
So what are the heritabilities of hip screening phenotypes? The heritability of the diseased phenotype evaluated in the hip-extended view has not been studied in most breeds of dogs in the USA. Each breed population of dogs will have its own inherent heritability relative to the test being evaluated. PennHIP is working with many breed clubs with an interest in determining the heritability estimates for their particular breed. Estimates for the heritability of passive hip laxity (DI) drawn from analysis of full pedigrees for the breeds examined thus far have yielded high values (e.g. for German Shepherd Dogs, heritability = 0.63; Labrador retrievers, heritability = 0.76; and Golden Retriever heritability = 0.60). Such high heritabilities mean that breeders can expect to improve hip status in subsequent generations just by knowing the parental DI’s, a breeding strategy known as mass selection. Of course, even more rapid genetic improvement of canine hips can be accomplished by using Estimated Breeding Values, a method that incorporates the hip status of the relatives of prospective breeding candidates.
Estimates of heritability of the subjective hip-extended phenotype scored from the conventional hip-extended radiograph are available for a few breeds of dogs in the USA. Published reports of heritability estimates tend to be between 0.17 and 0.35 in breeds studied. Low heritability of the hip-extended scoring method and its poor correlation with the prediction of OA are two reasons to help explain the slow change in improving hip status using this method.
The PennHIP method is based on strict quality control. To take PennHIP radiographs, veterinarians must undergo a training and certification process to demonstrate competency. PennHIP films are critically evaluated and the veterinarians are asked to repeat the procedure if the films do not meet PennHIP's stringent standards. The data generated from PennHIP undergoes regular review and statistical analysis so that useful information by breed is available to direct breeding practices and to judge progress toward reducing CHD.
Mandatory Film Submission
For optimal validity, it is mandatory that all hip radiographs by PennHIP veterinarians be submitted for analysis and inclusion in the PennHIP database. This policy eliminates "prescreening" radiographs and sending only the best hips for evaluation as is the practice with all global hip-screening methods. This "prescreening" practice, sometimes called "voluntary film submission," has been shown to result in a biased database containing a greater frequency of non-diseased hips than actually exists in the respective dog breeds. Excluding the worst hips leads to a false impression that genetic progress toward reducing the incidence of hip dysplasa is being made.
As technology advances, the veterinary professional community will offer and utilize improved methods of disease diagnosis. The dog breeding community will also endorse those methods that help them achieve their goals of reducing the frequency of hip dysplasia in dogs while maintaining other desirable traits and features. The PennHIP technology and research have been and will continue to be fully presented to the veterinary medical community for its review. PennHIP has been received enthusiastically as a major step toward reducing the frequency of CHD particularly among working and service dog organizations. We encourage and welcome continued scientific examination and comparison of PennHIP to any available or new methods of canine hip dysplasia diagnosis. We emphasize, however, that the forum to debate the relative scientific merits of competing technologies is the peer-reviewed scientific literature and not commercial pamphlets, press-releases in breed club or dog fancy magazines, or web sites. With an understanding of the science to support PennHIP comes acceptance of its superiority over other hip screening methods.
In 1996, the AKC board of directors announced plans to remove all health and genetic information from the official AKC registration and to include it along with PennHIP information in the "Information and Health Database" known as CHIC. This database is managed by the Orthopedic Foundation for Animals and breeders and dog owners may apply to enter PennHIP information for a fee of $25.00. OFA or CERF information is entered into CHIC free of charge. Meanwhile, we continue to work with other organizations, nationally and internationally to present the PennHIP technology and the positive impact it holds for reducing Canine Hip Dysplasia. The PennHIP method has been adopted by several countries and has gained widespread interest internationally. More than 150 service dog agencies globally currently use PennHIP to make breeding and training decisions.
At present there are two surgical procedures (Triple Pelvic Osteotomy and Juvenile Pubic Symphysiodesis) advocated by some veterinary surgeons to prevent the development of osteoarthritis, OA, later in life in dogs with excess joint laxity (loose hips) as a puppy. None of these procedures have undergone rigorous scientific clinical trials to prove the true efficacy in preventing the onset or slowing the development of arthritis in dogs prone to hip dysplasia. Although we at PennHIP are not fundamentally opposed to the use of preventive surgical management of dogs with excessive hip laxity, we feel the wholesale clinical use of purportedly preventive surgical procedures in the absence of adequate clinical testing is premature. We advise caution and suggest that these procedures should be considered “investigational” for now. Veterinarians are free to perform these procedures with full owner consent as to the risks and potential advantages and disadvantages of these procedures. Some well-designed studies are currently underway and we are hopeful to soon have definitive clinical evidence as to the efficacy of preventive surgery for canine hip dysplasia. Preventive treatments would be a welcomed addition to the armamentarium of CHD management.
Research has been able to demonstrate that the PennHIP method surpasses other diagnostic methods in its ability to accurately predict susceptibility to developing the osteoarthritis of canine hip dysplasia. This finding has been corroborated by multiple independent laboratories. The PennHIP method can be performed on dogs as young as sixteen weeks of age compared with two years using the standard technique. The ability to receive an early estimate of a dog's hip integrity is important whether the dog's intended purpose is for breeding, for working or service use, or as a family pet. The data amassed and analyzed by PennHIP will allow breeders to confidently identify the members of their breeding stock with the tightest hips. The PennHIP evaluation will also permit breeders to assess the progress they are making with their breeding program as they strive to reduce the amount of hip laxity in their dogs. Pet owners are able to determine their pet's risk of developing hip OA. This enables them to make lifestyle adjustments for their dog to lower the risk of developing hip OA thereby enhancing the quality of their dog's life.