PennHIP® method

Hip Displaysia is the most commonly inherited orthopaedic disorder in dogs.
The PennHIP method enables accurate HD screening and early disease diagnosis in puppies as young as 16 weeks.
The Tierklinik Elversberg is certified and licensed to perform the PennHip method on your dog.

The PennHIP® method is a relatively new radiographic examination on hip dysplasia (HD) .
Compared to the usual FCI method in Europe, the PennHIP® method allows early detection of HD and a differentiated evaluation of the hip joints.

Hip Dysplasia (HD) is the most commonly inherited orthopedic disease in dogs . Unlike many other hereditary diseases, HD is caused by not only one but several altered genes - the HD is thus of polygenic origin. Unfortunately, the altered genes have not been sufficiently identified yet, so that genetic testing for specific matings of breeding dogs is not available yet. In addition to hereditary predisposition also environmental factors such as nutrition and training of the dog, influence the occurrence and severity of HD. Due to the variety of factors that influence the clinical picture, the HD is considered a multifactorial disease.

As there is no specific genetic testing available yet, the breeding value in terms of HD is based on the assessment of the appearance (phenotype) of dog. The FCI prescribes a standardized X-ray examination for many breeds in order to assess the state of their hip.

The FCI method is based on radiological features noted on a radiograph taken of dogs between 1 and 2 years of age. The patients are x-rayed under general anesthesia with extended hind limbs with the two femur bones being parallel to each other. This relatively unnatural posture is the basis for evaluating the degree of HD on the radiographs.

Illustration: standardized radiograph of a hip by FCI

Based on the radiograph, the shape of the femur head, the shape and depth of the acetabulum as well as their congruency to each other are assessed. Furthermore, the so called Norbert angle is measured. In a dog free of HD, the latter amounts to greater or equal 105 degrees. For the overall evaluation, a 5 grades scoring system from A (HD free joint) to E (severe hip dysplasia) has been proposed. 

Illustration: BVA/KC scoring mode for CHD (Flückinger)

The drawback of the FCI method is that only adult dogs can be used for the evaluation. Therefore, HD is often diagnosed too late, especially in respect of breeding purposes. Furthermore, an early detection of the disease is favorable regarding therapeutic measures.

Was ist PennHIP®?

PennHIP® is a relatively new method for canine hip evaluation which was developed at the University of Pennsylvania as part of the Pennsylvania Hip Improvement Programs (PennHIP) and which is used throughout the USA. In 2013 the Antech imaging services (AIS) reserved all rights of this method and the associated database.

First and foremost, the PennHIP® method measures the canine hip laxity in a position natural to the dog. Hip joint laxity is a feature predominantly influenced by genetic factors rather than environmental factors. Therefore this method is suitable for assessing the breeding value in respect to HD inheritance.

Three radiographs are needed for the PennHIP®- method.

1. Hip-extended view: The ‚classical‘ HD radiograph with extended limbs.

2. The compression view: Femoral heads are pressed into the acetabula to determine the "goodness of fit" of the hip joints.

3. The distraction view to determine hip laxity.

For the distraction view, the so called distractor is placed between the patient’s legs. The hind limbs of the dog are pressed against the distractor so that the femoral heads are lifted out of the acetabula. The looser the joint on the distraction view, the greater is the chance that the dog will suffer from HD and OA. The distraction index (DI) is used to measure the joint laxity of the hip joint.

Illustration: compressed hip joint on the left, distracted hip-joint on the right
Illustration: Calculation of the compression and distraction index (Source: AIS PennHIP®)

To calculate the distraction index, the distance between the center of the femoral head and the center of the acetabulum are measured and then divided by the radius of the femoral head. The DI is a number ranging from 0 to 1,0. The probability of developing hip dysplasia with a distraction index less or equal to 0,3 is low. In some breeds, i.e. the Barsoi or the Greyhound, a distraction index of 0,3 is common and not likely to develop HD. A higher DI however increases the risk of osteoarthritis in the joint.

Illustration: Arthritis in the hip joint

When do owners profit of the PennHIP®-method?

  • For pet dogs as part of a medical checkup. Early diagnosis and risk assessment for the development of osteoarthritis following hip dysplasia is of great importance. Early intervention can help prevent or lessen the severity of disease symptoms by changing environmental factors (especially the diet).
  • For breeding purposes. With the PennHIP®-method disease diagnosis in dogs as early as 16 weeks of age is possible. This allows the breeder to select only dogs without a risk-hip for breeding purposes which is of great importance in respect to the genetic inheritance of this disease.
  • For working dogs or service dogs which have to undergo an intense and costly training (i.e. hunting dogs, sport dogs, guide dog), early diagnosis is important.

Of course, older dogs can also be examined by the PennHIP® method. The PennHIP® method is already widespread in the United States.

Are the radiographs officially evaluated?

All x-rays are only officially evaluated. Radiographs are sent directly and digitally to the central AIS PennHIP® interpretation point and the owner receives a certificate of the result as well as the distraction index of their animal. With this index a statistical statement can be made to which probably an osteoarthrosis development in the hip joint of a certain animal is more than likely. 

Illustration: Example of a certificate after the evaluation and comparison with the values of the database ( Source: AIS PennHIP® )

How is the PennHIP®-method performed?

As for the known HD - examination following the FCI standard, anesthesia is necessary for the PennHIP® method. The procedure itself is neither painful nor does it cause any damage.

Summary PennHIP®

  • Up to 80% of the dogs which were graded as HD-free by the known FCI standard method, showed an actual too high distraction index and therefore a moderate to severe HD.

  • The PennHIP method can be reliably performed on a dog as young as 16 weeks old.

  • Early diagnosis of hip dysplasia allows the owner to prevent or treat consequences like pain and arthrosis.

Ihr Ansprechpartner

Dr. med. vet.
Alexander Pack

© Tierklinik Elversberg 2021 | Images: Tierklinik Elversberg, shutterstock