03/07/2024
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How hip scoring is done worldwide
with Narelle Hammond
Please note that this article may not be current as it was written a few years ago. But it will give you an overview of the Hip scoring system.
There are several methods of evaluating hips worldwide and I will endeavour to explain briefly some of the recognized procedures.
Evaluating hips in Australia is done by a scheme adopted by the Australian Veterinary Association. The system is in use in New Zealand with a similar approach in South Africa(although little information was forthcoming from that country). This program is based on the British scheme, which was developed for German Shepherds by Dr Malcolm Willis.
The recommended age for this procedure is 24 months, but there is flexibility within reason, enabling breeders to assess a potential stud dog/brood bitch before breeding.
To achieve the uniformity required to assess the hips under this scheme, it is normal for the dog to be x-rayed under general anaesthetic. This ensures that the dog is correctly positioned on its back with the hind legs extended and parallel to each other.
The vet performing the examination follows a guide to placing and positioning the dog for the x-ray. If this guide is not followed, the result could be x-rays that are unreadable or perhaps misleading. A good X-ray should show the whole of the pelvis, thighbones, the thighbones laying relatively parallel and the stifles. The X-ray is labelled with the date, owner's name, and dog's identification and the left and right sides of the dog are indicated. The owner, giving a two-generation pedigree and certified by the x-raying vet, completes an accompanying form. Then the x-ray, form and relevant fee are submitted to one of the recognized bodies i.e. the Australian Veterinary Association for assessment.
Each hip area is assessed separately using nine features from Subluxation to Femoral head recontouring (in the ball and socket joint). These features are evaluated according to written guidelines and given a number from zero to six. Zero being normal and 6 grossly abnormal. Therefore, the total points that are possible for each hip is 54 with an overall total for both hips of 108. The scores most often quoted are the total for the right hip, then the total for the left hip in the form of say 1:1 (Oh to be so lucky!) Therefore, the higher the score, the more abnormal the hips. The lower the score the less sign of disease.
The first two areas that are scored, the Norberg angle and subluxation, are considered to be more influenced by environmental factors such as excessive weight, which can give a greater degree of looseness of the ligaments. The other areas scored all involve arthritic changes and are considered to have a high degree of inheritance.
Using this protocol there is no need to give a total score, as this can be misleading. For example, a dog may have a total score of 10, but his right hip could be 10 and his left hip 0.
The score is then compared with information collected for the breed and an assessment is made as to whether your dog is suitable to be bred. The AVA has an average score for most breeds in Australia and your dog is assessed only with others of the breed. For example, your breed’s average score maybe 20 and ideally, one should breed from stock that is no higher than the breed average.
The British Veterinary Association / Kennel Club scheme was first set up some 34 years ago in the United Kingdom, and since then around 150,000 X-rays have been submitted to the BVA for scoring.
Any KC-registered dog can be hip-scored from the minimum age of one year old. A dog may only be hip-scored once, although owners may request a reassessment of the x-ray plates by the BVA’s chief scrutineer.
Originally, hips were recorded simply as 'pass' or 'fail'. Since 1984, however, a more detailed system has been utilized. Hips are currently assessed on nine separate anatomical criteria. Each criterion is scored between zero and six, except for the 'Caudal acetabular edge’, which attracts a maximum score of 5. Any score above zero represents the degree of hip dysplasia present. Each hip is scored separately with a total score for each recorded on the hip certificate.
We now move across the Atlantic to the two recognised methods of evaluation in the USA. The first and oldest method which began in 1961 by the American Veterinary Medical Association and is used by the Orthopedic Foundation for Animals (OFA) in screening and certifying the hip status of purebred dogs.
The purpose of the OFA hip registry is to provide a standardised evaluation for hip dysplasia and to act as a database for the control of hip dysplasia through selective breeding. Currently, the OFA maintains the largest database on hip conformation of any registry worldwide. Since its founding in 1966, OFA has evaluated the hips of many 100’s of thousands of dogs. It is also a non-profit organisation created to assist breeders in addressing the problems of hip dysplasia.
The procedure seems quite simple. The dog is placed under heavy sedation or general anaesthetic and an x-ray is taken with the dog being positioned on its back with the pelvis symmetrical the femurs parallel to one another and approximately parallel to the table, and the patella (knee cap) on the midline.
The x-ray is forwarded to OFA and is initially screened for correct positioning and technique. If the X-ray is not satisfactory, it is returned to the referring vet for re x-ray.
Three certified veterinary radiologists then evaluate the acceptable X-rays independently and an agreement is reached as to what category the dog fits into. The hips are evaluated for subluxation, femoral head and neck remodelling, acetabular rim and edge changes and any degenerative joint diseases. The average report time is 15 days.
The categories are easy to understand. Normal hips are classified as follows.
Excellent, which is superior hip joint conformation as compared with other individuals of the same breed and age.
Good, this is well-formed hip joint conformation as compared with other individuals of the same breed and age.
Fair, which refers to minor irregularities of hip joint conformation as compared again with other individuals of the same breed and age. Each of these categories is eligible to receive an OFA number.
Borderline X-rays are graded as marginal hip joint conformation of uncertain nature concerning hip dysplasia and it is recommended that a repeat evaluation take place in 6 to 8 months.
Dysplastic hips are graded as follows:
Mild, which shows radiographic evidence of minor dysplastic changes in the hip joints.
Moderate, which is well-defined radiographic evidence of dysplastic changes of the hip joints and severe which are marked radiographic changes of the hip. These categories do not receive a number.
For over thirty years, this same X-ray view has been used to subjectively grade hips and try to predict which dogs are less likely to develop hip dysplasia. Breeders hoped that through this method, only the best hips would be used and removing the others from the breeding program would eliminate hip dysplasia. Unfortunately, there is still up to a 25 % chance of producing a puppy with hip dysplasia when using the OFA method of hip evaluation.
In 1983, a second method of hip evaluation was introduced in the United States. Dr Gail Smith, an orthopaedic surgeon at the University of Pennsylvania School of Veterinary Medicine, began researching early diagnosis of canine hip dysplasia. Through this research, Dr Smith created the PennHip method for measuring joint laxity or looseness of the joint, which is the major cause of degenerative joint disease.
PennHIP stands for the University of Pennsylvania Hip Improvement Program and is a multifaceted x-ray for hip evaluation. The technique assesses the quality of the canine hip and measures the quantity of hip joint laxity. The PennHIP method claims to be more accurate than the OFA method in its ability to predict the onset of osteoarthritis. Osteoarthritis, better known as degenerative joint disease, is the hallmark of canine hip dysplasia.
The PennHIP method is unique for several reasons. It appears to be more than just another X-ray technique. There is a network of vets trained to perform the PennHIP method properly, which assures that standard protocols are used in obtaining films and it helps to ensure accurate data. The X-rays are made by certified PennHIP-trained vets worldwide and are sent to the PennHIP central analysis centre for evaluation. The resulting information is stored in a database, which is constantly monitored. Therefore, as more information becomes available, the PennHIP centre will be able to obtain more precise answers to questions about the cause, prediction and genetic basis of canine hip dysplasia.
The PennHIP centre also publishes its findings in veterinary journals, which are then distributed to all PennHIP members. It also shares this information with interested breed clubs and other publications directed at the dog enthusiast.
The PennHIP method is a very different way to assess measure and interpret hip joint status. It requires three separate X-rays. The distraction view, the compression view and the standard hip extended view. Dr Smith developed the first two views to obtain accurate and precise measurements of the hip joint laxity and congruity (fitting), respectively. The third view was used to obtain further information regarding the existence of degenerative joint disease. Interestingly, Dr Smith found that the hip extended view could possibly mask some of the hip laxity. Therefore, he determined that a neutral position, where the dog in fact was positioned as though it was standing, best showed maximum laxity. Additionally, this position produced a more accurate and consistent reading.
The evaluation method is not a pass or fail. Each dog is graded compared to other dogs of that breed. A distraction index is calculated from the x-ray. This is the measure of potential movement of the femoral head (ball joint) in the hip socket. The smaller the distraction index is the tighter the hip. For example, if the distraction index were .26, it would be a very tight hip. If the distraction index were .87 it would be a very loose hip.
There is strict quality control with PennHIP and due to the necessity of using special positioning devices to demonstrate hip laxity, all x-rays are taken with the dog under heavy sedation or general anaesthetic. Also for continued ongoing research purposes, all X-rays that are taken must be submitted for evaluation. This stops any corruption of information that can occur when x-rays are checked and only the best ones are submitted for evaluation.
Probably the most important reason for PennHIP's increasing popularity is that it can be performed on dogs as young as sixteen weeks of age compared to two years by the standard method. The information generated by PennHIP allows breeders to confidently identify the dogs in their breeding program that at an early age have the best hips therefore the best breeding potential.
Further, north to Canada, we have the OVC (Ontario Veterinary Clinic) program, which is in association with the University of Guelph in the province of Ontario.
The number of X-rays taken depends upon the breeder and the position of the X-rays depends on the individual vet but in most cases, the same format as OFA is implemented.
Certification by OVC can only be done when the dog turns 18 months of age and at that time; the dog is given a yes or no grading. The dog is sedated and x-rayed by the breeder's local vet and these are forwarded along with the dog's registration number, exact age and identification to the University of Guelph where a panel of veterinary radiologists headed by Dr Paul Rennock determines the outcome.
Assuming that the dog is clear with a yes grade, a number is given along with a letter sent directly to the breeder, which says, "that this dog in my opinion does not show evidence of HD".
However, a breeder may have a promising young puppy and decide to x-ray at between 6 - 9 months. These X-rays are referred to as preliminary X-rays and cannot be certified by OVC but it can give the breeder a general idea of the condition of the hips at that time. The rationale behind this is if a young dog showed a preliminary hip score that is unsatisfactory, then the breeder would be inclined to sell the pup as a pet rather than wait until it could be certified by OVC at 18 months of age.
Interestingly, there is much controversy over the OVC versa OFA schemes and it has been known to happen that dogs have been approved OFA and not OVC and vice versa, even with the same x-rays.
On the other side of the globe, we have the countries of Europe, except the UK that work under the control of the FCI.
The FCI has developed a rating system for canine hip dysplasia, but to complicate matters, individual countries have their own systems. In the main, however, these systems can be related to the FCI system. As far as I can determine, in all European countries, the presented X-rays are always evaluated and graded. The only way to avoid this is for the owner of the dog to withhold the X-rays.
The Netherlands is considered to have the most demanding hip evaluation scheme of any European country. The youngest age which the x-rays can be assessed and graded is 12 months for small to medium-sized dogs and 18 months for large breeds. Two different X-ray positions are required similar to the British scheme and the results are forwarded to a central panel at the Hirschfeld Institute for official evaluation and grading. There are four principles in the evaluation. The Norberg value, the shape and junction of the hip joint and the bone malformation. All these areas are evaluated and reported and although the results are compiled and go to a central database, they are not automatically sent to the Kennel Club. The owner controls whether the results are sent and must give permission for it. All results are published once received by the controlling body.
The grading for the Norberg value starts at 40 which is the ideal and the number decreases as the hips show increased signs of degeneration from CHD. Also a letter ie. A, B, C, D, and E, are issued with a plus (+) or minus (-) grading with the letter. Therefore a 10 E (++) grading would be a real problem.
The German system is different again. Each of the three Kuvasz clubs has their own vet, who checks and evaluates the X-rays; therefore, this can lead to discrepancies. The German system compares with Canada's OVC program although there is only one x-ray required, which is the stretched position. All results are automatically reported to the club and published. These clubs also have the power to withhold pedigrees if the results are not by the breeding rules.
In Hungary, currently, the vet that has taken the X-ray performs the evaluation. Although there is a trend developing that because more dogs are being evaluated now than in the past, the program is likely to change soon.
The Scandinavian countries follow the FCI grading system with A being excellent and E being unacceptable to breed. In Finland, for example, some 6000 X-rays were taken in 1999 so the awareness of the importance of hip scoring is encouraging. The Finnish Kennel Club's veterinarian (currently Dr Annie Liman) assesses the x-rays and the recommendation to all vets is that all x-rays are sent to the KC for grading. The dog is normally only sedated with one clear, good x-ray required. The minimum age of the dog is the same as explained previously in the Netherlands.
Unfortunately, within the FCI system, results cannot be compared easily, because of the differences in interpretation. There are many examples of dogs being evaluated by both the Dutch and German systems with the differences being quite marked. For example, the Dutch evaluation can indicate an inferior result, whereas the German evaluation can rate the same dog CHD-free in Germany.
