Hip dysplasia literally means an abnormality of the development of the hip joint resulting in a joint that is misshapen and which does not function as it should. The degree of abnormality of the joint can vary greatly in affected dogs and it is interesting to note that dogs which are not required to do much, or indeed any active work, may have adequate or almost normal hip function in spite of changes in the joint.
The situation is of course much different in a gun dog that may well be worked extensively throughout the shooting season. Even a slight abnormality of the hip joint could result in a lame dog and one unfit for purpose. For the gun dog owner then, an understanding of how hip dysplasia develops and how it can be avoided is of great importance.
Bones and joints must not be considered as static structures. Like all other organs in the body they are made up of living tissue and like most other organs and tissues they undergo their most rapid period of change while the puppy is actively growing. When fist born, all puppies appear to have a similar conformation of the hip joint. However those that go on to develop hip dysplasia start to develop a laxity or instability of the hip joint at a very early age. The reason for this is that the development of the joint, which is controlled by the dog's genes, proceeds abnormally. As the puppy grows other factors such as the size of the dog, its growth rate, its diet and the type of and amount of time spent exercising also start to have an affect on the developing joint.
Puppies tend to be constantly active and this can at an early age cause inflammation in the lax hip joint. This happens because the joint capsule and other supporting structures of the lax joint get stretched causing damage to the synovial membrane (which is the inner layer of the joint capsule). The resulting synovitis (inflammation of the synovial membrane) results in a thickening of the joint capsule and an increase in the amount of synovial fluid. These changes can help to reduce the laxity of the joint to some degree. However this secondary inflammation in the joint causes pain which can manifest itself as lameness. From an early age puppies can, depending on the amount of joint abnormality, be lame on one or both hind legs or walk with an abnormal gait, often "bunny hopping" as they run around.
As the puppy grows in size the hip joint continues to develop abnormally and the laxity gets worse. The teres ligament that runs from the head of the femur to the acetabulum, (and which is also covered by synovial membrane), can become stretched or even ruptured allowing further laxity to develop in the joint. The joint can some times become so loose that the head of the femur can partly or even fully dislocate. All this excessive movement allows the bone of the femur and acetabulum to rub against one and other. This can result in erosions of the bone on the edge of the acetabulum that the body tries to heal with new bone formation.
Pain in the joint continues to cause lameness, and without proper use of the limb, muscle development does not proceed as it should. Reduced muscle mass around the hip joint means that the soft tissue support of the joint is also reduced. Continued remodelling of the joint results in a flattened deformed femoral head and a shallow acetabulum.
All of these changes take place during the growing phase of the puppy. Remember that both hips need not be affected equally. The puppy may be lame on, or favour, only one leg. In sever cases puppies are usually lame on both hind legs, reluctant to climb or jump, and not able to exercise properly. On examination there is usually evidence of pain in the joint when the leg is extended backwards or gentle lifted to the side. At this stage a click can sometimes be heard or felt as the loose femoral head jumps back into the acetabulum. This click is called Ortolani's sign. If the puppy does try and do something to strenuous it can damage the already weakened joint even more and present with sudden severe lameness in one or both legs.
By the time the puppy reaches one year of age its growth rate will have slowed right down as the bones have nearly finished growing. By this time the joint will have stabilised to a degree because of thickening of the joint capsule and an increase in the muscle mass around the hip joint. The joint however is still abnormal, has a reduced range of movement and is often a source of discomfort. In an attempt to reduce the weight on its hip joints the dog will often shift more of its weight to the front legs and as a consequence have well muscled up forequarters. At this stage the clinical signs shown will often depend on the amount of exercise the dog is doing. If the dog is resting most of the time it may appear relatively normal. However it will not be able to do a hard days work.
Once the dog becomes adult, further changes happen much more slowly and are dependent on both the weight of the dog and the amount of exercise it has. The joint space narrows, the articular cartilage is eroded and there is a progressive increase in new bone formation. Although hip dysplasia may be suspected from the clinical signs, diagnosis needs to be confirmed radiographically by your veterinary surgeon. If confirmed the treatment options can also be discussed at this time. Treatment can be either conservative or surgical. Conservative treatments vary but all include a strictly reduced exercise regime. Surgical options range from resection of the pectineus muscle all the way through to total hip replacement. Treatment will hopefully allow an affected dog to live out its life as a housedog or pet but should not be considered as an option for a dog that you wish to work.
From the preceding discussion it can be seen that hip dysplasia is a condition that develops in the growing pup and that the full extent of its severity may not be fully evident until the pup is about one year of age. It is also during this time period that time and money may be spent to start training the pup for its roll as a working gun dog. What we don't want is the cost of buying a puppy and then the investment of time, effort and money in training only to find that at about a year of age the dog has hip dysplasia. Although the causes of hip dysplasia are multifactorial because there is an underlying inherited breed-disposition we can look at the parents and grand parents to get some idea of how likely a pup is to develop the condition. In the United Kingdom we can do this by looking at the their Hip Dysplasia Scheme Score.
The idea behind the scheme is that radiographs of dog's hips are examined for signs of hip dysplasia. This examination involves detailed evaluation of the anatomical features of the joint and any pathological changes. The information is then used to produce a score for each hip joint. In the United Kingdom screening is controlled by the British Veterinary Association and the Kennel Club using the BVA/Kennel Club Hip Dysplasia Scheme. For the scheme to be as successful and meaningful as it can it is important that as many dogs as possible be radiographed and these be submitted for scoring. Even if the dog is not going to be used for breeding purposes, or it is thought that the dog has hip dysplasia, its hip score helps to give a truer picture of the prevalence of hip dysplasia. This in turn gives the breed geneticist as much information as possible, which can only be good for the breed.
The British Veterinary Association and the Kennel Club have issued Hip Dysplasia Scheme Procedure Notes in order to make sure that all the information required is sent to them and that the dogs pelvis is radiographed in a standard position. A certificate to be used for the submission of details and reporting the hip score is provided by the BVA. This certificate is printed on a heavy gauge green paper. The minimum age of a dog for taking and submitting a radiograph is one year. There is no upper age limit. Initially the dog owner would contact their veterinary surgeon to arrange to have the dogs hips radiographed. This is done under general anaesthesia and the veterinary surgeon in question will provide further details about admitting the dog for the procedure. At the time of the radiography the following documents must be made available to the veterinary surgeon:
At some stage prior to the radiography, often on the morning of admission for the procedure, the owner must complete and sign the first section of the certificate "Section A" the Owners Declaration. This is to verify that the details given in this section relate to the dog being submitted, that the details are all correct and that the owner agrees to the results being used by the Kennel Club. The details required are:
The following information is requested but is not mandatory:
The Hip Dysplasia Scheme Procedure Notes detail how the veterinary surgeon should position the dog for the radiograph, what information should be marked on the film, and what sort of image quality is required. The submitting veterinary surgeon then fills in "Section B", the Submitting Veterinary Surgeon's Certificate, after he has checked all the details required by the scheme. The radiograph and the HD Certificate are then sent to the BVA. The current fee for the BVA must be included at the same time. This fee covers the BVA costs, the KC costs and the scrutineers' fee. The veterinary surgeons fee to cover the cost of obtaining the radiograph and processing the required paper work is not included in the BVA fee. Radiographs that do not meet the strict requirements of the scheme are not scored; they are returned to the submitting veterinary surgeon and a radiograph of appropriate quality requested. This is to make sure that there is consistence and a level playing field for all the radiographs submitted for scoring. When subsequent radiographs are submitted a new certificate and a further fee must accompany them.
The results of scoring are normally sent to the submitting veterinary surgeon after about three weeks. Two scrutineers, appointed by the BVA, examine each radiograph and agree the score. Nine separate features are evaluated for each hip using a set of defined criteria. Points awarded for each of the nine radiographic features are added together to give a score for each hip and then the two hips scores are added together to give the final score for the individual dog. The minimum score for each hip is 0 and the maximum is 53. This means there is a range of possible scores from 0 to 106 for each dog. The lower the score the less evidence there is of hip dysplasia. The score is recorded in "Section C", the Certificate of Scoring section, of the certificate which is also signed by the two scrutineers. The radiograph is sent back to the submitting veterinary surgeon with the completed certificate to be given to the owner of the dog. The results for all Kennel Club registered dogs are sent to the Kennel Club for publication. Details may also be sent to a geneticist for statistical analysis.
Once a certificate of HD scoring has been issued for a dog, further radiographs of the dog may not be resubmitted for scoring under the scheme. If an owner feels that the score is incorrect they have the right to appeal. The procedure is that the owner must lodge any application for appeal against the result of a HD score with the BVA, in writing, within 45 days from the date of dispatch of the radiographs from the BVA. The same radiographs used for the initial scoring must be resubmitted by the veterinary surgeon, with an Appeal Certificate and a re-scoring fee to the BVA. The radiograph will be re-scored by the Chief Scrutineer, whose decision is final, and the new score will be reported in the normal way.
How does all of this help us? The fact that hip dysplasia has a genetically transmitted component means that if we look at the Hip Dysplasia Scheme Scores for the parents and grand parents of a puppy we will have a very good idea if it will go on to develop hip dysplasia or not. The lower the scores for the parents and grand parents the less chance there is that the puppy will develop hip dysplasia. Remember that as the causes of hip dysplasia are multifactorial the HD score should only be regarded as an indicator of what might happen. The HD score is not an absolute measurement of what will happen. Many dogs have had their hips scored over the years. For some breeds the number is in the tens of thousands. The BVA/KC have used all this information to calculate a Breed Mean Score for all the breeds scored. The Breed Mean Score is calculated from all the scores, both high and low, recorded for a given breed and thus it gives a representation of the overall HD status for all the dogs of that breed.
When looking to purchase a new puppy or dog find out if both parents have had their hips scored. If grand parents have also been scored then so much the better. The lower the score for these individuals the better the chances that the puppy will not go on to develop hip dysplasia. The current Breed Mean Score for all breeds may be available at your veterinary surgeons or can be found on the BVA web site. It would not be advisable to purchase a puppy from parents whose HD scores are above the Breed Mean Score. Remember the lower the score the better. Another word of caution, remember that although we have just been talking about hip dysplasia many breeds have other inherited disease, don't forget about these when choosing your pup.
The Breed Mean Score is also a very useful tool to help dog breeders select their breeding stock. Only dogs and bitches with HD scores well below the Breed Mean Score should be used for breeding in order to reduce the risk of hip dysplasia. For some breeds were large numbers of individuals have been scored a Breed Median Value has also been calculated; dogs and bitches used for breeding should be selected from individuals well below this figure also. As we have seen clinically sound dogs can have hip dysplasia (and high HD scores) and should not therefore be bred from.