Hip Dysplasia is a genetic disease because of the various degrees of arthritis (also called

Transcription

1 Hip Dysplacia Hip Dysplasia is a genetic disease because of the various degrees of arthritis (also called degenerative joint disease, arthrosis, osteoarthrosis) it can eventually produce, leading to pain and debilitation. Hip dysplasia, characterized by an abnormal formation of the hip joint, occurs in many mammals. Both dogs and humans may fall victim to this disease, although it is far more prevalent in dogs. Hip dysplasia in dogs, it is primarily a disease of large and giant breeds. German Shepherds, Labrador Retrievers, Rottweilers, Great Danes, Golden Retrievers, and Saint Bernards appear to have a higher incidence, however, these are all very popular breeds and may be over represented because of their popularity. On the other hand, sighthounds such as the Greyhound or the Borzoi have a very low incidence of the disease. This disease can occur in medium-sized breeds and rarely in small breeds. It is primarily a disease of purebreds although it can happen in mixed breeds, particularly if it is a cross of two dogs that are prone to developing the disease. The symptoms are similar to those seen with other causes of arthritis in the hip. Dogs often walk or run with an altered gait. They may resist movements that require full extension or flexion of the rear legs. Many times, they run with a 'bunny hopping' gait. They will show stiffness and pain in the rear legs after exercise or first thing in the morning. They may also have difficulty climbing stairs. In milder cases dogs will warm-up out of the stiffness with movement and exercise. Some dogs will limp and many will become less willing to participate in normal daily activities. Many owners attribute the changes to normal aging but after treatment is initiated, they are surprised to see a more normal and pain-free gait return. As Page 1 of 14

2 the condition progresses, most dogs will lose muscle tone and may even need assistance in getting up. Hip dysplasia refers to the development of a poor fit between the femoral head and the acetabulum that allows loose movement and altered pressure. These changes result in joint damage, inflammation, and pain. The volume of synovial fluid in the joint increases, and the round ligament that binds the femoral head to the acetabulum becomes enlarged. The normally smooth articular cartilage covering the end of the opposing femoral head and acetabulum is abraded and weakened, and the joint capsule becomes inflamed and thickened. Muscles in the region of the hip joint diminish in bulk and may be affected in other ways as well. As the disease progresses, the bones become damaged and spurs known as osteophytes develop at the bone-cartilage interface. The whole joint is structurally weakened and painful. The perceived pain of hip dysplasia during its early stages is due to stretching of nerve endings and inflammation in the joint capsule and ligament. In its advanced stages the disease progresses to the painful condition of osteoarthritis, or degenerative joint disease. 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). Page 2 of 14

3 Though physical examinations may be helpful, radiography and x-rays are the only means of reaching a definitive diagnosis of CHD. The goal of a physical examination is to determine hip joint laxity, or the degree of looseness in the joint. Looser hip joints are more likely to become dysplastic than are stable ones. Palpation of the hip joint and surrounding areas can provide an estimate of the laxity of the hip joint, but the measurements are subjective and not as definitive as x-rays. See attached sheets, which highlight the statics for each breed and the percentage of Hip dysplasia. Page 3 of 14

4 Excellent Hips Excellent: this classification is assigned for superior conformation in comparison to other animals of the same age and breed. There is a deep seated 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 Hips Good: slightly less than superior but a well-formed congruent hip joint is visualized. The ball fits well into the socket and good coverage is present. Page 4 of 14

5 Fair Hips Fair: Assigned where minor irregularities in the hip joint exist. The hip joint is wider than a good hip phenotype. This is due to the ball slightly slipping out of the socket causing a minor degree of joint incongruency. There may also be slight inward deviation of the weight-bearing surface of the socket (dorsal acetabular rim) causing the socket to appear slightly shallow. This can be a normal finding in some breeds however, such as the Chinese Shar Pei, Chow Chow, and Poodle. Borderline Hips Borderline: there is no clear cut consensus between the radiologists to place the hip into a given category of normal or dysplastic. There is usually more incongruency present than what occurs in the minor amount found in a fair but there are no arthritic changes present that definitively diagnose the hip joint being dysplastic. There also may be a bony projection present on any of the areas of the hip anatomy illustrated above that can not accurately be assessed as being an abnormal arthritic change or as a normal anatomic variant for that Page 5 of 14

6 individual dog. To increase the accuracy of a correct diagnosis, it is recommended to repeat the radiographs at a later date (usually 6 months). This allows the radiologist to compare the initial 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 truly dysplastic. Most dogs with this grade (over 50%) show no change in hip conformation over time and receive a normal hip rating; usually a fair hip phenotype. Mild Hips Mild Hip Dysplasia: there is significant subluxation present where the ball is partially out of the socket causing an incongruent increased joint space. The socket is usually shallow only partially covering the ball. There are usually no arthritic changes present with this classification and if the dog is young (24 to 30 months of age), there is an option to resubmit an radiograph when the dog is older so it can be reevaluated a second time. Most dogs will remain dysplastic showing progression of the disease with early arthritic changes. Since HD is a chronic, progressive disease, the older the dog, the more accurate the diagnosis of HD (or lack of HD). Page 6 of 14

7 Moderate Hips Moderate Hip Dysplasia: there is significant subluxation present where the ball is barely seated into a shallow socket causing joint incongruency. There are secondary arthritic bone changes usually along the femoral neck and head (termed remodeling), acetabular rim changes (termed osteophytes or bone spurs) and various degrees of trabecular bone pattern changes called sclerosis. Once arthritis is reported, there is only continued progression of arthritis over time. Page 7 of 14

8 Severe Severe Hip Dysplasia: 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. Treatment Simple practical measures may be enough to give comfort to dysplastic animals. Mild exercise such as walking, hydrotherapy, or slow running is beneficial, but excessive activity such as jumping and prolonged running should be avoided. Some analgesic and antiinflammatory drugs can relieve the pain. Such medications do not however halt or reverse the progression of destructive changes in the joint. Injections and even oral administration of carbohydrate polysulfates have shown promise in increasing clinical use as a treatment for dysplastic dogs. These drugs can prevent pain and aid in normal remodeling to improve the contour of the hip joint. Although carbohydrate polysulfates do not cure hip dysplasia, many dogs receive at least some benefit from this treatment. Similarly, nutritional supplements Page 8 of 14

9 have some proven benefits. There are several surgical procedures available to treat hip dysplasia depending on the dog's age, body size, and the severity of the hip joint's degeneration. Triple Pelvic Osteotomy (TPO): TPO is a procedure used in young dogs usually less than 10 months of age that have radiographs that show severe hip laxity, but have not developed damage to the joints. The procedure involves surgically breaking the pelvic bones and realigning the femoral head and acetabulum restoring the weight-bearing surface area and correcting femoral head subluxation. This is a major surgery and is expensive, but the surgery has been very successful on animals that meet the requirements. Juvenile Pubic Symphysiodesis: A less invasive surgery for treating hip dysplasia is called Juvenile Pubic Symphysiodesis. This surgery prematurely fuses two pelvic bones together, allowing the other pelvic bones to develop normally. This changes the angle of the hips and improves the articulation of this joint, lessening the likelihood of osteoarthritis. Early diagnosis is critical, since the procedure must be done before 20 weeks of age, preferably 16 weeks, and before any signs of arthritis are evident. Total Hip Replacement: This may be the best surgical option for dogs that have degenerative joint disease as a result of chronic hip dysplasia. Total hip replacement is a procedure that can produce a functionally normal joint, eliminate degenerative changes, and alleviate joint pain. The procedure involves the removal of the existing joint and replacing it with an artificial joint or prosthesis. To be a candidate for this procedure, the animal must be skeletally mature. With the new micro-prosthetics there is no minimum size limit. In addition, there is no maximum size limit. If both hips need to be replaced, there is a three-month period of rest recommended between the surgeries. As with the TPO surgery, this is an Page 9 of 14

10 expensive procedure but it produces very good results. Most dogs return to a near normal level of activity without pain. Femoral Head and Neck Excision: Femoral head and neck excision is a procedure in which the head of the femur is surgically removed and a fibrous pseudo-joint replaces the hip. This procedure is considered a salvage procedure and is used in cases where degenerative joint disease has occurred and total hip replacement is not feasible or if the expense of a total hip replacement is prohibitive. The resulting pseudo-joint will, in most cases, be free from pain and allow the animal to increase his activity, however, full range of motion and joint stability are decreased. For best results, the patient should weigh less than 40 pounds; however, the procedure may be performed on larger dogs. Page 10 of 14

11 Some of the environmental aspects that can affect the observable expression of hip dysplasia are the following by T. J. Dunn, Jr. DVM "Nutrition - There are reports that in puppies a restricted calorie intake could restricted the growth rate, and in turn will lessen the potential for the dog to develop hip dysplasia. (I wouldn't suggest doing this to any pup... it makes as much sense as stealing money from your own checking account!) The problem is that some restricted diets restrict the fat and protein content and increase the carbohydrate content of the food. Bad! The real goal should be to keep growing pups from becoming OVERWEIGHT. Restricting fat and protein in a growing pup can be a disaster. A high quality, meat-based diet is absolutely necessary for growing pups, just don't feed so much of it that the pup becomes overweight". "Physical Activity - In a young, growing dog with a genotype (genetic makeup) for CHD who will eventually develop some trouble because of it, will develop more arthritis and have more eventual difficulty if it is highly active physically. Climbing stairs, jumping into and out of pick-up trucks, running with other normal dogs can all subject the growing hip structures to unwarranted stress and trauma and increase future discomfort for the dog. The effects of this excessive activity is worsened in an overweight pup. (In a normal, growing dog, all these activities will not cause hip dysplasia!)". Page 11 of 14

12 "Bedding - There is no scientific proof, but lots of observational conclusions, that pups reared especially during the nursing period on slippery surfaces such as newspapers will be prone to hip difficulties. That is not to say that smooth concrete, wood or newspaper surfaces cause dysplasia, just that they can make a bad situation worse. Better surfaces for newborn pups would be blankets or towels... something they can get a better grip on". Baker Institute for Animal Health Research "The time of appearance and the rate of progression of hip dysplasia are influenced by the growth rate of individual dogs. Studies at the Baker Institute and elsewhere have shown that slowing growth during the early months of life can lessen the severity of hip dysplasia and even prevent it. One study followed two groups of susceptible pups from the time they were eight weeks old until their death. One group of pups was fed nearly 25 percent less food than the second, which were permitted to eat all they wanted of the same diet. Over the course of the 14 year study, data was collected regarding general longevity and the development of hip dysplasia. Not only did the dogs eating a restricted diet live significantly longer than their well-fed counterparts, they developed hip dysplasia at a much lower rate than did the second group. Further, for those dogs on a restricted diet who did develop hip dysplasia, the risk of developing osteoarthritis decreased by 57 percent. This study of course involved a diet restriction that is difficult to enforce for many pet owners. It would be desirable to Page 12 of 14

13 use a less restrictive dietary regime that would confer many of the same benefits this more severe diet did". Daniel C. Richardson DVM Diplomate, American College of Veterinary Surgeons Director, Advanced Research Hill's Pet Nutrition, Inc., Topeka, Kansas A Symposium Held at Western Veterinary Conference "The large and giant breeds are the most susceptible to skeletal disease. Genetics, environment, and nutrition play key roles. Nutritionally, rate of growth, feed consumption, specific nutrients, and feeding methods influence our ability to optimize skeletal development and minimize skeletal disease. Maximizing the growth rate in young, growing puppies does not correlate to maximal adult size; however, it does increase the risk of skeletal disease. The growth phase of 3 to 8 months and possibly the phase prior to weaning are integral to ultimate skeletal integrity. The giant breeds may be limited in their ability to cope with excesses of minerals such as calcium, and the results are abnormal bone remodeling and skeletal disorders. This apparent increased sensitivity makes these breeds somewhat of a monitor of dietary influences". By Margaret Muns DVM "The degree to which CHD is manifested in a particular dog depends on the degree of the animal's genetic predisposition, and the influence of a variety of environmental stresses. The greatest incidence of CHD occurs in the most rapidly growing breeds of Page 13 of 14

14 dogs. Therefore, mix-breed dogs are much less susceptible than highly bred dogs. In most cases, the rapid growth rate of the disease is directly related to young dogs that are fed a high-calorie diet, and therefore develop excess body weight at a rapid rate. These diets only serve to enhance the biomechanical imbalance present in genetically susceptible dogs. Limiting the rate of a dog's growth results in less joint looseness and fewer signs of hip dysplasia. Another major factor in the development of skeletal disease in young growing dogs is too much calcium intake. Excessive blood calcium levels disrupt the normal maturation of both bone and cartilage. Other clinical diseases related to calcium imbalances include osteochondrosis dissecans (OCD), retained cartilaginous cores, radius curvus syndrome, and stunted growth. Dogs that are affected with these syndromes lack the biochemical ability to protect themselves from chronic calcium excess". Page 14 of 14