The Great Hip Debate

Written by: Andrea Hobe

Congenital hip dysplasia (CHD) has been called the leading genetic health problem in dogs today. In broad terms dysplasia is an inherited disease that affects laxity (looseness) of the joints. It is polygenic meaning it appears to be controlled by more than one gene. In an ideal world, there would be a genetic test we could utilize to determine whether a dog would develop hip dysplasia later on in life or if it would pass it on to its offspring. However, because it is affected by multiple genes, work on genetic testing for CHD has been challenging. In the meantime, scientists and veterinarians have been using physical tests, such as OFA and PennHIP, to see if a specific dog has or is more prone to develop the disease.

Hip testing, whether it be through OFA or PennHIP, is a useful tool for making sound breeding decisions towards improving the Bearded Collie breed as a whole. Because dysplasia can come from many different genes, we will probably never be able to entirely eradicate it. However, if we allow health testing to influence our breeding decisions we can certainly lessen the number of dysplastic animals in our gene pool.

There are two main organizations that offer hip testing in the United States – Orthopedic Foundation for Animals (OFA) and the University of Pennsylvania Hip Improvement Program (PennHIP). There is much controversy over which program is more accurate at diagnosing and predicting hip dysplasia. The following is a brief summary of each:

  • OFA radiographs can be done by any licensed veterinarian and can be done once the dog is two years old (a preliminary report can be done for younger animals but they will not receive an OFA number). The OFA recommends chemical restraint to the point of muscle relaxation, however it is not required. The test is based on one view (hip-extended). The hip grades of Excellent, Good and Fair are within normal limits and are given OFA numbers. Radiographs of Borderline, Mild, Moderate and Severely dysplastic hip grades are not issued OFA numbers and are not made public unless requested by the owner.
  • PennHIP radiographs can only be performed by certified individuals who have undergone a specific training and evaluation process. To maintain strict quality control, PennHIP radiographs must be performed under sedation, however, general anesthesia is preferred. They claim to be accurate in puppies as young as sixteen weeks of age. The PennHIP process consists of three views – a hip-extended view, a compression view and a distraction view. Instead of a grade, PennHIP issues a distraction index for each hip, which is basically a percentile ranking of that dog’s hips compared to other dogs of the same breed. For example, a Bearded Collie with a 90% has tighter hips than 90% of all other Bearded Collies that have been tested. PennHIP does not make specific breeding recommendations, however they propose breeding only those dogs in the top 50%. At this point, there are only 56 Bearded Collies in the database; however, PennHIP is gaining popularity with both breeders and veterinarians. With increased participation, PennHIP should be able to give a strong evidence-based recommendation as to a dog’s breeding potential as it relates to CHD.

Inarguably, PennHIP maintains a much more accurate database as to the existence of hip dysplasia as a whole, and is thus a better tool for improving the breed. In order to maintain the integrity and validity of the PennHIP method, all radiographs are required to be submitted for evaluation. This prevents data corruption which can occur when only the better test subjects are submitted for review. OFA allows the veterinarian and owner to review and pre-screen the films prior to submission, diluting the field from which health decisions are currently made. If you were to look at a group of dogs from an OFA database, you would see mostly ‘passable’ scores, giving a false impression of sound hips across the board. What you wouldn’t see are the dogs who had radiographs taken but did not have them submitted for fear they might not get an acceptable score. This alters the overall picture of breed health altogether. The skewed percentage of ‘normal’ dogs in the OFA database may significantly slow the progress of decreasing the prevalence of hip dysplasia. It is difficult to improve the breed as a whole if breeding decisions are not based on an accurate representation.

The evaluation and grading processes of the two organizations differ greatly. OFA sends the radiograph to three different veterinarians who visually review and assign a grade to the film based upon the veterinarians’ opinion as to how much of the femoral head (the ball-shaped piece of bone located at the top of the thigh bone) lies within the socket. The median of those three scores is the grade that is assigned. Researchers have shown a wide variation in consistency in regards to OFA’s grade assignments. Not only might one radiologist disagree with another, but may even contradict himself and give different grades to the same film on different occasions. Unfortunately, the hips are evaluated as a cumulative whole and no further information as to the general structure of the hips are given.

PennHIP uses a computer program to measure and evaluate the joint laxity, thus removing any room for human error. While the computer measures and calculates the distraction index, PennHIP veterinarians visually examine the radiographs in order to get more detailed information about the hip. In addition to the distraction index, PennHIP provides owners with a detailed evaluation report including notes on any degenerative joint disease, cavitation and any other abnormal findings. This information can be very useful when selecting breeding stock as you can breed to correct any irregularities or weaknesses and build upon the strengths of your breed.

A recent study shows that 80% of dogs evaluated as ‘normal’ by the OFA were found to have hip laxity by PennHIP testing that predisposed them to developing hip osteoarthritis in the future*. Results of this study suggest that OFA’s test procedures and scoring methods underestimates a dog’s susceptibility to osteoarthritis. By basing their evaluations solely on the hip-extended radiograph, OFA is approaching hip dysplasia from a narrow point of view. Many veterinarians have learned to manipulate the dog in order to generate more favorable results. PennHIP, on the other hand, evaluates a dog’s hips from three different positions, physically compressing and distracting the hips to precisely demonstrate the laxity in each hip. PennHIP believes this is a much better indicator of current and future hip dysplasia susceptibility.

It is important to note that hip testing is not just for breeding dogs! Unfortunately, many ‘pet’ owners do not feel the need to check their dog’s hips. Early detection of hip dysplasia allows an owner to be proactive about treatment, whether that be through medication, supplements, fitness and/or nutrition. These preventative measures can certainly help the dog to live a longer more comfortable life, allowing a Beardie to bounce comfortably for many years to come.

*Powers MY, Karbe GT, Gregor TP, McKelvie PJ, Culp WT, Fordyce HH, Smith GK. Evaluation of the relationship between Orthopedic Foundation for Animals’ hip joint scores and PennHIP distraction index values in dogs. J Am Vet Med Assoc 2010; 237: 532-541.