I get a lot of e-mails asking about "health Testing"; so, this month I thought I would do a series of entries that deal with an explanation of the different "health testing" we do as breeders. Since the most complex and hardest to understand at times is the testing we do for Hip Dysplasia, let's start with it.
What is Canine Hip Dysplasia (CHD)?Canine Hip Dysplasia can affect millions of dogs each year and can also result in debilitating orthopedic disease of the hip. Many dogs will suffer from osteoarthritis, pain, and lameness costing owners and breeders millions of dollars in veterinary care, a shorten lifespan and reduced quality of life for affected dogs. The occurrence of HD is well documented in Mastiffs as well as many other large and giant breeds and is also prevalent in many toy and small dog breeds as well as cats.
The term
hip dysplasia(HD) can be interpreted as the abnormal or faulty development of the hip. Abnormal development of the hip causes excessive wear of ther joint cartilage during weight bearing, eventually leading to the development of arthritis, often called
degenerative joint disease (DJD) or osteoarthritis. The terms DJD, arthritis, and osteoarthritis are often used interchangeably.
Hip dysplasia was first described in 1937 by Dr. Gerry B. Schnelle in a paper entitled
Bilateral Congenital Subluxation of the Coxofemoral Joints of a Dog. He wrote:
"the condition described herein, rare thought it may be, should be recognized as being congenital and potentially hereditary, and the dog or bitch in which it occurs should be destroyed or sterilized in the eugenic interests of the breed." In 1966, Henricson,Norberg, and Olsson refined the definition of CHD describing it as:
"A varying degree of laxity of the hip joint permitting sublaxation during early life, giving rise to varying degrees of shallow acetabulum and flattening of the femoral head, finally inevitably leading to osteoarthritis." Today, the general veterinary consensus is that hip dysplasia is
hip laxity resulting in osteoarthritis.Just by defination alone, we can see that CHD is a disease of complex factors based primarily on inheritance, and why ethical dog breeders and Veterinarians have attempted to eliminate CHD through selective breeding and care.
What is a Dysplastic Joint?Hip Dysplasia is a terrible genetic disease because of the various degrees of arthritis (also called degenerative joint disease, arthrosis, osteoarthrosis) which it can eventually produce that leads to pain, overall loss of range of motion in the hip joints, and debilitation.
The very first step in the development of arthritis is articular cartilage (the type of cartilage lining the joint) damage due to the inherited bad biomechanics of an abnormally developed hip joint. Traumatic articular fracture through the joint surface is another way cartilage is damaged.
With cartilage damage, lots of degradative enzymes are released into the joint. These enzymes degrade and decrease the synthesis of important constituent molecules that form hyaline cartilage called proteoglycans. This causes the cartilage to lose its thickness and elasticity, which are important in absorbing mechanical loads placed across the joint during movement.
Eventually, more debris and enzymes spill into the joint fluid and destroy molecules called glycosaminoglycan and hyaluronate which are important precursors that form the cartilage proteoglycans. The joint's lubrication and ability to block inflammatory cells are lost and the debris-tainted joint fluid loses its ability to properly nourish the cartilage through impairment of nutrient-waste exchange across the joint cartilage cells.
The damage then spreads to the synovial membrane lining the joint capsule and more degradative enzymes and inflammatory cells stream into the joint. Full thickness loss of cartilage allows the synovial fluid to contact nerve endings in the subchondral bone, resulting in pain. In an attempt to stabilize the joint to decrease the pain, the animal's body produces new bone at the edges of the joint surface, joint capsule, ligament and muscle attachments (bone spurs). The joint capsule also eventually thickens and the joint's range of motion decreases.
No one can predict when or even if a dysplastic dog will start showing clinical signs of lameness due to pain. There are multiple environmental factors such as caloric intake, level of exercise, and weather that can affect the severity of clinical signs and phenotypic expression (radiographic changes). There is no rhyme or reason to the severity of radiographic changes correlated with the clinical findings.
There are a number of dysplastic dogs with severe arthritis that run, jump, and play as if nothing is wrong and some dogs with barely any arthritic radiographic changes that are severely lame.FYI-One can not just "look" at the movement of a dog and determine that it does not have CHD. Only through x-rays can we determine if a dog is clear of hip dyspasia. As a breeder, one must evaluate any dog to be bred and determine if it is free of hip dysplasia before breeding!
How do you Test for CHD?One "tests" for CHD by x-raying hips. This simply assures the breeder that the dog being bred does not have CHD. When a breeder health tests for CHD, it is the hope that with each succeeding generation that is bred from clear dogs, the puppies produced should have improved/better hips. OK. So what does these "scores" mean?
To a beginner, just looking at the hip "scores" can be confusing. What do they mean and how are they interprettted? Which ones are best? Here is the United States, the most common methods of evaluating hips is the
OFA (Orthopedic Foundation for Animals) and the
Penn Hip system (University of Pennsylvania Hip Improvement Program). Since many Mastiffs have imported lines from England, we will also look at the system used in the United Kingdom (England) and Austrialia : the British Veterinary Association (BVA). When it comes to testing, various breeders have different opinions to which system is better and many a heated debate can result from discussing the pros and cons of each system. For the purpose of this entery, I will only discuss the basics priniciples of each system so as to provide an explaination.
The most important aspect is to test and vertify your dogs are clear of hip dysplasia before breeding irregardless of the system you use. PERIOD.
I. OFA-Orthopedic Foundation for Animals
I have always used the OFA system to rate and score my dogs' hips. I find it easier to explain to people (puppy buyers) and for most people it makes sense. Please refer to the OFA website at http://www.offa.org/hipgrade.html as my information source. Please note later in this entry I will later compare the Pennhip and BVA to the OFA system I will be using the same definations of Normal and dysplasic terms. The phenotypic evaluationand "ratings" of hips by OFA falls into seven different categories; these categories are the Normal ratings (Excellent, Good, and Fair), Borderline, and Dysplasic (Mild, Moderate, and Severe). Three independent outside evaluations by Orthopedic Radiology Specialists are done for each rating with each classifing the hip intoi one of the 7 phenotype described above. The finial hip grade is decieded by a consensus of these three scores. For example:
(1). Two radiologist report excellent, one good--the finial score would be excellent.
(2). One radiologist reports excellent, one good, and one fair--the finial score would be Good.
(3). One radiologist reports fair, and two report mild--the finial score would be mild.
All normal hip scores (Excellent, Good and Fair) are given OFA Numbers. This information is only accepted by AKC on dogs with pernament identification (tattoos or microcips) and is recorded in the Public domain or open data base (i.e. anyone can look up these results to vertify them--just go to
http://www.offa.org/). X-rays of borderline, mild, moderate and severe dysplasic hip scores are reviewed and a report is sent documenting the abnormal findings. Unless the owner has chosen to allow abnormal scores to be listed in the open data base, dysplasic hip grades are not in the public domain.
Let's look at a visual example and explaination of each rating. The illustrations used below are examples from the OFA site.
Excellent
The Excellent (Figure 1) classification is assigned for superior conformation in comparison to other animals of the same age and breed. There is as deep seated well formed ball (femoral head) which fits tightly into a well formed socket (acetabulum with minimal joint space. There is almost complete coverage of the socket over the ball.
Good
The Good (Figure 2) classification is slightly less than superior (excellent) but a well-formed congruent hip joint is visualized. The ball fits well into the socket and good coverage is present.
Fair
The
Fair (Figure 3) classification is assigned where minor irregularies in the hip joint exist. The hip joint is wider than a Good hip phenotype which is usually due to minor joint incongruency ( i.e. the ball slightly slips out of the socket). There may also be slight inward deviation of the weight-bearing surfaces of the socket(dorsal acetabular rim) causing the socket to appear shallow (Figure 4). This can be a normal finding in some breeds (i.e. Chinese Shar Pei, Chow Chow, and Poodle).
Borderline
For the Borderline classification, there is no clear cut consensus between the radilologists to place the hip into a given category of normal or dysplasic. There is usually more incongruency present than the usually minor amount found in a Fair, but there are no arthritic changes present that definanetly place the hip joint in the dysplasic classifications. There may also be a bony growth present on any of the areas of the hip anatomy that can not be accurately assessed as being an abnormal arthritic change or as a normal anatomic variant for that individual dog.
To increase the accuracy of a correct diagonsis, it is recommended to repeat the x-rays at a later date (usually 6 months). This allows the radiologist to be able to compare the orginal film with the most recent film over a given time period and assess for progressive arthritic changes that would be expected if the dog was truely dysplasic. Most dogs with this score (over 50%) show no change in hip conformation and recieve a normal rating; usually a Fair.
Mild Dysplasia
In Mild Canine Hip Dysplasia (Figure 5) there is signifcant sublaxation presemnt where the ball is partially out of the socket causing anincongruent increase joint space. The socket is usually shallow and only partially covers the ball. There are usually no arthritic changes present if the dog is young ( 24 to 30 months of age), and there is an option to resubmit x-rays when the dog is older so it can be reevaluated a second time. However, most dogs will remain dysplasic showing disease progression with early arthritic changes. Since HD is a chronic, progressive disease, the older the dog, the more accurate the diagonsis of HD (or the lack of HD).
Moderate Dysplasia
In Moderate Canine Hip Dysplasia there is significant sublaxation present in the joint socket with the ball barely seated into a shallow shoket caused marked joint incongruency. There are secondary arthritic bone changes usually along the femoral head and neck (called remodeling), acetabular rim changes (called oseophytes or bone spurs) and various degrees of trabecular bone pattern changes called sclerosis. Once arthritis is reported, one can expcet continued progression of arthritis over time.
Severe
A Severe Hip Dyplasia (Figure 6) is assigned where radiographic evidence of marked dysplasia exists. There is significant subluxation present where the ball is partly or completely out of a shallow socket. Like moderate HD, there are also large amounts of secondary arthritic bone changes along the femoral neck and head, acetabular rim changes and large amounts of abnormal bone pattern changes.
II. PennHIP
In 1983, Dr Gail Smith from the University of Pennsylvania School of Veterinanry Medicine devloped a new method for the early diagonsis of CHD. The research conducted in his lab proved his new method to be capable of estmating the susceptibility for CHD in dog as young as 16 weeks.
In 1993, Dr. Smith established PennHIP to serve as a multi-center of clinical trial of his new hip dysplasia diagnostic technology. The program was sucessful and quickly grew beyound the capabiolities of a university research lab. Initailly, PennHIP was licensed to outside biotech companies but PennHIP has recently been reaquired by the University of Pennsylvania and is now a not-for-profit organization.
Some breeders use and prefer the PennHIP exam since it can be used on dogs as young as 16 weeks of age. It gives a breeder an advantage of a tool for early evaluation and looking at joint laxity (losseness) which is the greatest risk factor for the development of DJD.
Before PennHIP, the definations of CHD were vague as to the degree or amount of laxity requires to develop arthritic changes.
the degree of hip joint laxity, as measured by the PennHIP method has been shown to be the most important risk factor in determining whether a dog is prone to developing CHD. Please refer to the PennHIP website,
http://www.pennhip.org/ for more information.
PennHIP is a different way to assess, measure and interpret hip joint laxity--ie. another method of evaulating hips and diagonsising hip dysplasia. Where the OFA method uses just one view ( the hip-entended view), PennHIP uses three seperate x-rays: the distraction view, the compression view and the hip-extended view. Please refer to the pictures below for an example of each different x-ray view on the same dog.
Distraction View Compression View
Hip-Extended View
(This is also them same view used by OFA)
If you look at the x-rays above, in each view you will notice that the joint laxity (looseness) is very diferent. Although each view is of the same dog, please note that the laxity is much greater in the distraction view than in the hip-extended view. On the average, the distraction vies has been shown to revel 2.5-11 times more hip laxity (depending on the breed) than the hip-extended view. Using the comparsion of the three views allows the PennHIP method to measure hip joint laxity with greater percision than the hip-extended method alone.
According to PenHIP, since CHD is a developmental disease (meaning it is not present at birth, but develops with age) a breeder or owner may be able better predict which puppies may have hip problems later in life by looking at the degree of hip laxity.
A PennHIP rating is given as a numerical rating and gives a rating for each hip individually ( a rating for the right hip vs. the left hip) and an overall percentage rating that is breed specfic-i.e it will tell you where your dog "ranks" among other Mastiff results. However it should be noted that the "pool" of results used for this rating is not as generalized or as large as OFA. Often breeders may use PennHipp to get a rating for a dog that has failed it's OFAs--thus the "pool" of dogs that this average is pulled from may be slightly skewered.
You will not see a "fail" rating for a PennHipp unless the dog is severely dysplasic. Thus the "%" ratings can be misleading to an unknowing puppy buyer.
IMO-if a dog does not have a 90% rating--I'm not interested in breeding to it. A rating of 30 to 50% may actually be rated "dysplasic" by OFA terms and scores. Please keep this information in mind when looking at PennHipp scores.
There is no clear cut "excellent", "good" or "fair" with pennhipp and the related range is going to vary from breed to breed. IMO--way too confusing for the average puppy buyer.
(Please note :At the bottom of this entry I will give a table that correlates OFA , PennHIP , FCI, SV and BVA results. I found it very helpful to me! The PennHip scores are an approximation for the Mastiff breed only. In order to be as accurate as possible--I did not try and "rate" the dysplasic scores--only the passing scores.)
III. British Veterinary Association (BVA)
Often as Mastiff breeders, we find it difficult to find Mastiffs from England that have "health" testing done--esp. hips! Why? Until recently in England, there has been very little emphasis placed on clearing dogs of health issues before breeding. Health and Soundness was not necessarily a goal with all breeders. With the advent of improved methods to complete health testing, and an international interest in the importing of health tested dogs; we now see more of the dogs being bred in England that are being health tested.
The BVA system is the one most commonly available in the United Kingdom (England) with most veterinary clinics having experience in using this method. Since no repeat submissions are allowed, it is best if one uses a clinician who has a good deal of experience in doing this exam and the proper equipment to obtain good quality x-rays. Dogs must be at least 12 month old to be BVA scored, but 18 months gives a more reliable result for large breeds (i.e. Mastiffs) and is the sugessted age for this test.
When evaluating a BVA score, it is important too take into account how the score is made up. Both hips should be more or less symmetrical; a significant difference in the two hips can either be genetic or the result of trauma. On the printed report a notation is made relating to positioning and film quality.Each hip scored on 9 different aspects. Scores in the first 3 boxes indicate the conformation of the hip (shape of the head, neck and socket), scores in the remaining 6 boxes indicate secondary changes/arthritiis/DJD. Healthy dogs should have 0's in the last 6 boxes.
Here is an example of how a reporting form would appear.
Thus, the higher the BVA score the greater the degree of dysplasia. I have provided a comparison to the OFA ratings in the table at the end of this entry.
How can I compare the different ratings?
Of course, any rating is subjective to human error. No system of testing is perfect--but it is the best we have to use at present. The mode of Hip dysplasia is unknown, but is believed to be recessive in nature--i.e. an dog can carry the gene and still be "normal". Thus, it is possible for "clear" parents to produce a puppy with hip dysplasia.
Health testing simply aids a breeder in eliminating dogs that are affected. At present there is no DNA test for CHD, so NOT breeding affected dogs is our best answer to improving the overall hips of any given breed.
Please note in the table below how each of the different evaluation methods (OFA, PennHIP, FCI (used in Europe) , SV (used in Germany) & BVA (used in UK and Australia) results compared to each other. Please note the PennHipp scores are an approximation for the Mastiff breed only.
