PennHip

PennHIP: Method for Early Screening for Canine Hip Dysplasia and detection of hip arthritis.

Canine Hip Dysplasia (CHD) is the most common, heritable orthopaedic problem seen in dogs. It affects virtually all breeds of dogs but is especially problematic in large and giant breeds.

Clinically, the disease manifests itself in one of two ways:

1. A severe form that typically afflicts the younger animal and is usually characterised by marked pain and lameness.
2. A more chronic form with more gradual onset of clinical signs such as mild intermittent pain, stiffness and a restricted range of motion in the hips as the dog ages.

It is well recognised that the current diagnostic methods of hip evaluation are associated with disappointing progress in reducing the frequency of CHD.

In 1983 Dr. Gail Smith from the University of Pennsylvania School of Veterinary Medicine, developed the PennHIP method of hip joint assessment.

PennHIP allows us to accurately predict which dogs will develop hip dysplasia and so develop hip arthritis, as well as provide a very accurate assessment of which dogs should be used to breed with in order to eliminate hip dysplasia.

PennHIP assessments can be carried out from 16 weeks of age.

The PennHIP method has great advantages over the standard Australian CHD diagnostic method that evaluates dogs at one year or older.

FAQ about PennHIP 

What is PennHIP?

PennHIP is a scientific method to evaluate a dog for its susceptibility to develop hip dysplasia. The radiographic procedure involves a special positioning of the dog so that the dog's "passive hip laxity" can be accurately measured. In simple terms, passive hip laxity refers to the degree of looseness of the hip ball in the hip socket when the dog's muscles are completely relaxed.

Research has shown that the degree of passive hip laxity is an important factor in determining susceptibility to develop Degenerative Joint Disease (DJD) later in life. Radiographic evidence of hip DJD, also known as osteoarthritis, is the universally accepted confirmation of CHD.

Please visit the PennHIP website for more information.

How was PennHIP developed?

The development of PennHIP has involved multiple disciplines including biomechanics, orthopaedics, clinical medicine, radiology, epidemiology and population genetics. The first phase of development involved sophisticated biomechanical testing to determine the optimal patient position for measuring hip laxity. By monitoring passive hip laxity in dogs as they matured, it was discovered that hip laxity was the primary factor in the development of the DJD characteristic of CHD. That is, the radiographic expression of DJD was statistically significantly correlated with the degree of measured passive hip laxity.

In addition, the CHD prediction was shown to be acceptably accurate in populations of puppies as young as sixteen weeks of age. Moreover, the correlation between passive hip laxity and subsequent hip DJD was shown to increase over the four month figures when hips were evaluated at six months and twelve months of age. In addition, no other method used to evaluate CHD has undergone similar rigorous testing through controlled scientific studies to determine diagnostic accuracy.

How does PennHIP differ from evaluation methods which use the Hip Extended Position?

PennHIP differs in some very fundamental and important ways.

1. PennHIP was developed and tested following strict scientific protocol and the results of these studies have been published (and continue to be) in peer-reviewed scientific journals. More than a 2 decades of research and analysis has 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 diagnostic method.

2. Passive hip laxity is objectively measured and the resulting Hip Evaluation Report is not issued in a pass/fail framework. PennHIP specifically measures passive joint laxity and includes the quantitative measurement in its report. Based on the degree of laxity, the individual dog is then ranked relative to other members of the same breed. For example, a dog receiving a ranking in the 70th percentile means that 30% of its breed members have hips that are tighter. This allows breeders to easily identify those animals with tighter hips within each breed. Studies show that dogs with tighter hips are less likely to develop CHD and pass that genetic tendency on to future generations.

3. Because PennHIP is measuring maximal passive hip laxity, the position of the patient is very different from the hip extended position.

4. The hip extended position has been used for more than thirty years to screen hips. Current studies show a wide variation between the scores readers of the hip extended view produce. Furthermore there is no study to show that any reduction in the incidence of hip dysplasia has occurred improvement using the hip extended view.

Most importantly, the heritability of the diseased phenotype scored in the hip extended view has not been studied in most breeds of dogs. Knowledge of heritability is critical to determine whether selection pressure will produce genetic change. Estimates for the heritability of passive hip laxity drawn from analysis of full pedigrees for the breeds examined thus far in the studies show high values (for German Shepherd Dogs, heritability 0.61).

5. The PennHIP method is based on strict quality control. To take PennHIP radiographs, veterinarians must undergo training and a certification process to demonstrate competency. The data generated from PennHIP undergoes regular review and statistical analysis so that useful information, by breed, is available to judge progress toward reducing CHD. For optimal validity, it is mandatory that all PennHIP radiographs be submitted for analysis and inclusion in the PennHIP database. This policy eliminates the practice of pre-screening radiographs and sending only the best for evaluation, resulting in biased hip data for any given breed.

What happens to my dog during a PennHIP Evaluation? 

To obtain diagnostic radiographs it is important that the patient and the surrounding hip musculature be completely relaxed. For the comfort and safety of the animal this requires a general anaesthesia. Typically, three separate radiographs are made during an evaluation. The first is a 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 laxity. Passive laxity has been shown to correlate with the susceptibility to develop DJD. A hip extended view is also included for the sole purpose of examining for any existing joint disease such as osteoarthritis. The PennHIP procedure has been safely performed on thousands of patients.

How does this benefit me as an owner or breeder of dogs?

Scientific data confirms that the PennHIP method surpasses other diagnostic methods in the ability to accurately predict susceptibility to developing CHD. The method can be performed on dogs as young as sixteen weeks of age compared with 1-2 years using the standard technique.

The data generated by PennHIP will allow breeders to confidently identify the members of their breeding stock with the tightest hips. The PennHIP interpretation 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 assess their pet's risk of developing CHD and make their lifestyle adjustments for their dog, if necessary, to enhance the quality of their pet's life.

How can I get the name of a PennHIP Veterinarian to get answers to additional questions?

If in the Melbourne metropolitan area, contact the Clinic. If viewing this website from any other location and you need to obtain the name of a veterinarian near you, please visit the PennHIP website.

Definition of PennHIP Terms

Acetabulum

The "socket" component of the hip.

Canine Hip Dysplasia (CHD)

A developmental, degenerative condition affecting the ball and socket of the hip. Conventionally diagnosed radiographically by the presence of degenerative changes and/or subjugation of the hip. While the precise role of subluxation in the development of CHD has been poorly studied and remains controversial, radiographic evidence of osteoarthritis is undisputed confirmation of CHD.

Certified PennHIP Member

A veterinarian who has been trained in the PennHIP method and has successfully passed the quality assurance exercises demonstrating competence and repeatability in performing the PennHIP evaluation method.

Compression View 

One of three radiographic views taken during a PennHIP evaluation. During compression the femoral head is pushed fully into the acetabulum. This view is included for purposes of accurately indicating hip landmarks and to demonstrate joint congruity - how well the femoral head fits into the acetabulum.

Degenerative Joint Disease (DJD)

A degenerative condition of the hip characterised by one or more of the following: cartilage damage, joint effusion, synovitis, periarticular osteophyte formation (bone spurs), subchondral bony sclerosis and ultimately bony remodelling. DJD is synonymous with osteoarthritis and its radiographic presence in the hip is considered diagnostic of CHD.

Distraction Index (DI)

DI is a measurement of maximal passive hip laxity. It is a unit less number between 0 and 1. A smaller number DI means less laxity (tighter hips) and less susceptibility for DJD. A DI of 0.5 is interpreted to mean that the femoral head is 50% displaced from the acetabulum. DI has been shown to correlate strongly with a dog's probability of developing hip DJD.

Distraction View 

One of three radiographic views made during a PennHIP evaluation. Dogs are heavily sedated or under general anaesthesia. A special "distraction device" is placed between the legs with the dog on its back. The device acts as a fulcrum to apply a harmless lateral distractive force to the hips. The legs are positioned to optimize the measurement of passive laxity. The amount of hip laxity is quantified using the distraction index.

Functional Hip Laxity

Hip laxity or hip excursion that occurs during weight bearing activity such as walking, running or jumping. Functional hip laxity is associated with the development of high joint stresses that cause cartilage damage and ultimately DJD. While it would be very useful to know the onset and magnitude of functional hip laxity, it is a dynamic condition that is not possible to measure either clinically or experimentally.

Heritability

Heritability indicates the proportion of phenotypic variation that is due to addictive genetic effects. It expresses the extent to which phenotypes (eg. CHD) are determined by the genes transmitted from the parents. Heritability is not a biological constant and will likely vary by breed. Higher heritability means faster genetic change through selective breeding. The DI phenotype is highly heritable (0.61 for German Shepherd dogs) and indicates that DI is a promising criteria on which to base the selection of breeding stock.

Hip Extended Position

One of three radiographic views made during a PennHIP evaluation. The hip extended position is included for purposes of evaluating the hips for existing degenerative joint disease. It is not a reliable position for showing true passive laxity.

Hip Laxity Profile

Hip laxity profile refers to the "current" distribution of passive hip laxity (D1) within a breed. It allows the breed or the individual dog to be compared to other breeds or other individuals within the same breed. Combining this information with radiographic evidence of DJD within a breed facilitates a breed specific determination of CHD susceptibility. In addition, regular monitoring of changes in hip laxity profiles over time permits an assessment of the progress of selective breeding attributable to the PennHIP procedure.

Osteoarthritis

See DJD

Passive Hip Laxity

This refers to the hip laxity that is measured in a dog that is sedated and non-weight bearing. Since it is not possible to measure "functional hip laxity", all hip evaluation methods assess (subjectively or objectively) the magnitude of passive hip laxity.

PennHIP 

PennHIP stands for University of Pennsylvania Hip Improvement Program.

PennHIP encompasses the overall evaluation method, the network of veterinary providers, analytical and support staff as well as an extensive database of hip and breed evaluation data.

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