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By Margaret Muns DVM
Canine hip dysplasia (CHD) is a joint disease that can be painful and often crippling. It is not a disease of bone, muscle, or ligament. Although it has been associated mostly with large dogs, smaller dogs are not immune. This common genetic disorder can be influenced by a number of factors.
Fortunately, there are quite a few medical and surgical options that can treat dogs with hip dysplasia.
Development of the disease
Dogs with a genetic predisposition for hip dysplasia are born with anatomically normal hips. However, as the dog grows, an abnormal maturation of the hip joint structure occurs. There is an unequal growth between the skeletal and muscular components. The bone literally grows too fast for the muscle mass and the supporting structures. This problem causes varying degrees of looseness in the joint. As the dog bears weight on the rear limbs, the head of the femur bone rubs against the cavity at the base of the hipbone (acetabulum). After continuous rubbing, damage occurs to the joint cartilage. The dog can then develop degenerative joint disease, pain, and lameness.
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 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.
Clinical Signs
The clinical signs exhibited by dysplastic dogs depend greatly on the age of the animal when the clinical disease surfaces, and the presence or absence of degenerative joint disease (DJD). Dogs less than 1-year old tend to have episodes of acute bilateral (or unilateral) lameness in their rear limbs. The signs of lameness become more obvious with exercise or after a minor trauma.
Dog owners frequently report that their pet is having trouble rising, walking, running, or climbing stairs. Typically, the clinical signs wax and wane, depending on the degree of dysplasia. This stage can last for months or years. Many dogs will never show signs of dysplasia until after DJD develops.
Older dogs with DJD will show rear limb lameness and a shifting of the weight to the forelimb. They will have well-developed shoulder muscles, while the rear limbs will be weak and atrophied. The dog will walk with a typical waddling gait, and will be reluctant to exercise. If the dog can run, it will exhibit a characteristic "bunny-hopping" gait. The degree of lameness and weakness can be extremely variable. Many dogs with advanced joint destruction will not show any visible signs at all.
Diagnosis
The diagnosis of canine hip dysplasia requires a complete physical and neurological examination. While a dog is anesthetized, radiographs confirm the presence of CHD. Frequently, CHD occurs with other inherited bone and joint disorders. Therefore, it is crucial to determine any other type of orthopedic or neurological disease. Many diseases can mimic the signs of CHD, such as spinal problems, metabolic diseases (hypothyroidism), immune mediated diseases (rheumatoid arthritis, lupus), bone diseases (panosteitis, OCD), stifle diseases, and multiple joint disease.
Strict radiographic technique and positioning guidelines have been published to avoid misleading results. Since physical inactivity leads to increased hip looseness, dogs should be radiographed only when they are in good condition. It is recommended that the dog be under anesthesia to avoid producing abnormal positioning. The age of the dog must also be considered. Young dogs and puppies normally have looser hips than mature dogs.
Treatment
The treatment for CHD depends on the age of the dog when it is diagnosed. In a young dog without degenerative joint disease, the goal is to prevent cartilage damage and subsequent joint degeneration. There are new drugs available that are designed to prevent cartilage and joint damage.
For an older dog with secondary degenerative joint disease, the goal of medical therapy is to stop the pain associated with the joint destruction. Once degenerative joint disease is present, the goal is to slow down its progression. There is no magic cure for degenerative joint disease, but both young and older dogs can benefit greatly from a few simple conservative therapies.
To maintain muscle strength and cardiovascular health, dogs with hip dysplasia should be encouraged to exercise within the limits of their disease. For example, swimming is an ideal exercise for a dysplasic dog. It allows the dog to get a good workout, without undue stress to the joints. Preventing and treating obesity is also highly beneficial for a dysplasic dog. Obesity increases the stress to the joints and hastens the progression of degenerative joint disease in affected dogs. Keeping the dog in a warm environment with sleeping areas that are well padded can relieve joint stiffness.
Eventually, most dogs with CHD will need medication to relieve the joint inflammation and pain associated with the disease. Several classes of drugs are available for this purpose. The most effective and commonly used drugs are the non-steroidal anti-inflammatory drugs (NSAIDs). Aspirin is the first choice for relieving the pain and inflammation associated with degenerative joint disease. It is inexpensive, readily available, and works well in most cases. If a dog is unresponsive to aspirin, Phenylbutazone or Meclofenaminc Acid (Arquel) can be used.
The side effects associated with NSAID use can be numerous, however, they are usually not common or very severe. The most common adverse reaction is stomach irritation. In extremely sensitive dogs, ulcers can develop. Fortunately, there is a drug that can reduce stomach irritation associated with NSAID. Misoprostal, when given with aspirin, enhances the stomach's normal protective mechanisms, and decreases acid production.
As a last resort, corticosteroids can be used to treat dogs with degenerative joint disease. Although corticosteroids are potent anti-inflammatory drugs, they also cause accelerated joint destruction. Consequently, the joint dysfunction increases, despite the reduced pain and inflammation. Corticosteroids can also produce systemic side effects, such as increased thirst, increased urination, liver disease, and adrenal gland disease.
Recently, a new class of drugs designed to protect the joint has been introduced. Polysulfated glycosaminoglycans inhibit the formation of enzymes known to be involved in the destruction of joint cartilage. They are available either in an injectable or oral form.
A recent study proved that Vitamin C can reduce the inflammation in joints that have been affected with degenerative joint disease.
Surgical Therapy
Numerous surgical procedures are available for the treatment of hip dysplasia. The specific technique used depends on the age of the dog and the presence or absence of degenerative joint disease.
Again, in the younger dog without DJD, the goal is to relieve pain and slow the degeneration process. The pectineal myotomy procedure attempts to decrease pain by releasing tension on the joint capsule. The advantages of this procedure are that it greatly increases joint function, while significantly decreasing pain. The main disadvantage of the procedure is that it does nothing to stabilize the joint. Consequently, it does not prevent the development of DJD.
The actual biomechanics of the hip joint can be corrected by performing either pelvic or intertrochanteric osteotomy surgeries. The various pelvic osteotomy techniques all strive to reposition the cavity at the base of the hipbone (acetabulum) so that it fits better over the femoral head. On the other hand, the intertrochanteric osteotomy technique is done to reposition the femoral head so that it fits better into the acetabulum. Pelvic osteotomies are very difficult and extensive surgeries, while the intertrochanteric osteotomy is more conservative. Both surgeries are limited for use in dogs without DJD, and whose bones are still growing.
For an adult dog with DJD, total hip replacement is the surgery of choice. Candidates for hip replacement surgery must be carefully screened. Dogs who are not clinically lame are not operated on, regardless of how bad the hips look radiographically. The dog must also be free of any other metabolic, neurologic, and musculoskeletal disease. In most cases, the worst hip is done first. Often, this will resolve the lameness, even if the dog has bilateral disease. If signs persist, the second hip can be done later. In general, excellent results are seen after hip replacement surgery.
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The TPLO procedure is based on the leveling of the tibial plateau to eliminate the cranial tibial thrust produced by axial loading of the CCL-deficient stifle. A radial osteotomy of the proximal extremity of the tibia is made as one looks at the stifle in the mediolateral plane. The proximal fragment of the tibia is then rotated so as to level the cranial to caudal slope of the tibial plateau. The osteotomy is then fixed with a specialized bone plate and screws. The results of over 20 000 TPLO procedures at several institutions worldwide, which continue to provide positive results on the procedure's efficacy, were presented to Congress delegates. However, results do not suggest that other techniques should be abandoned. Data were presented showing that 6 mo postoperatively, weight-bearing in 68 Labrador retrievers, as measured by force plate analysis, was not significantly different between TPLO repairs and extracapsular repairs
.Causes of cranial cruciate rupture in dogs
· Cruciate ligament rupture can occur in all ages of animals, including very young dogs. The etiology of this problem is multi-factorial. Bow-legged conformation, patellar luxation, narrow intercondylar notch, trauma, nonisometric ligament attachments to the bones, and steep tibial plateau are contributing factors.
· Bow-legged hind limb conformation and medial patellar luxation cause excessive internal tibial rotation which strains the ligament and may lead to cranial cruciate ligament rupture.
· The cranial cruciate ligament passes through the intercondylar notch of the femur bone. A narrow intercondylar notch can impinge the cranial cruciate ligament which results in continual friction and fraying of the ligament.
· Ligaments must be attached to isometric points on the bones. This means that the ligament is not stretched during extension versus flexion or visa versa. If the bone growth is such that these isometric points are altered, increased forces are exerted on the ligament, which results in permanent elongation of the ligament with resultant instability of the joint.
· The slope of the tibial plateau plays a significant role in stressing the cranial cruciate ligament. The steeper the plateau slope, the greater the forces that are exerted on the cranial cruciate ligament. A comparative example is this: greater force is required to pull a wagon up a steep hill than on a level surface. A steep slope results in repeated maximal loading of the ligament, which ultimately stretches the ligament beyond its elastic phase into the plastic phase resulting in permanent elongation and weakening of the ligament.
Methods of Repair
· Many repair methods exist for cranial cruciate rupture. Extracapsular repair has been the most popular technique for a number of years. Many extracapsular techniques exist, however most surgeons use the "Flo" and the lateral imbrication technique. Board-certified Surgeons in the United States have recognized that these and many other traditional techniques do not allow dogs to return to working or athletic activities without lameness. In our experience, dogs treated with the tibial plateau leveling osteotomy (TPLO) technique have an excellent chance to successfully return back to these types of activities.
Progression of Arthritis
· Another study evaluated the progression of degenerative joint disease in dogs following intra- and extra-capsular surgical techniques and a group of cranial cruciate ligament deficient dogs having no surgery. Interestingly, all groups of dogs developed the same degree of degenerative joint disease. In contrast, a study that evaluated the progression of arthritis in dogs receiving the TPLO versus the imbrication technique demonstrated four times less progression of degenerative joint disease with the TPLO technique. We have also noted in our clinical cases that arthritic changes in most cases progresses very slowly or is arrested.
Very young dogs and cruciate injury
· One of the challenges that the orthopedist faces is rupture of the cranial cruciate ligament in very young dogs (6 months or less). As mentioned above, arthritic changes progress rapidly with the traditional techniques that have been used in the past. As a result, this is not an ideal treatment. The standard TPLO is also not ideal for very young dogs either, as the growth plate is cut during the procedure, which may result in continued flattening of the tibial plateau as the dog grows.
Dynamic tibial plateau leveling procedure
· A new technique, called the dynamic tibial plateau leveling procedure (TPLP), can be used to treat cranial cruciate ligament rupture in growing immature dogs. The timing of the surgery is critical, and is specific to the breed of dog. This technique involves placing a screw in the cranial aspect of the growth plate of the tibial plateau. Growth is stopped at this region of the tibial plateau, yet the caudal aspect continues to grow. Over time the tibial plateau angle is leveled. The amount of leveling of the plateau is dependant on the preoperative tibial slope and the age of the dog at which the procedure is performed.
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