Articles written to help my puppy people raise their puppies right.
Dealing with behavior problems
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CANINE HIP DYSPLASIA
By Ron Montgomery, DVM, MS
How I treat canine hip dysplasia (CHD) depends on the answer to several questions. First, what is being treated? Hip dysplasia does not equal arthritis. CHD is laxity of the hip joint that develops in juvenile dogs between birth and skeletal maturity. Arthritis (degenerative joint disease [DJD]) is caused by the abnormal biomechanics of a lax hip joint. Hip laxity (i.e., hip dysplasia without DJD) can potentially be corrected by triple pelvic osteotomy (TPO). Arthritis can be treated (e.g., by conservative therapy, femoral head and neck excision [FHNE], artificial hip), but an arthritic hip joint cannot be restored to normal.
The second group of questions deals with the individual dog and the severity of its pathologies. Signalment, history, and a complete physical examination provide most of the answers to these questions. Key issues are the dog's size (e.g., toy to giant), obesity, muscle mass, severity of lameness, activity level (e.g., lap dog versus canine athlete), range of motion, pain, response to medications, radiographic change, and a complete physical examination to identify other pathologies (e.g., cruciate ligament rupture, lumbosacral disease). These issues are critical to the veterinarian and the owner when selecting the "best" treatment for a given dog.
The final group of questions is addressed by a realistic discussion with the client regarding issues including (but not limited to) prognosis, complications, and cost and how these issues fit with the expectations, needs, and limitations of that particular owner and dog. Selecting the "best" treatment for CHD is ultimately the owner's choice. My role in selecting treatment is twofold. First, I do my best to determine all of the pathologies of the dog. Second, I do my best to educate owners about the disease(s) and treatment options that are known to be effective in a large percentage of dogs so that they can reach an informed decision regarding the best treatment for their pet. Although I discuss all treatments that have been proven effective, I will not offer a treatment that I believe is obviously inappropriate for that individual dog (e.g., TPO for a dog with advanced arthritis).
Educating clients begins with answering the question, what is hip dysplasia? As stated, CHD is laxity of the hip joint which develops in juvenile dogs between birth and skeletal maturity (approximately 6 to 12 months of age depending on the dog's size). Hip dysplasia is not caused by a single factor but a combination of factors, including heredity, diet, and exercise level. A specific gene that carries CHD has not been identified. However, approximately 25% of the cause of CHD is attributed to heredity because heredity determines breed and such influences as size and muscularity in family lines. Diet is also a factor as related to growth rate. Feeding juveniles high-calorie diets that promote the rate of growth definitely increases the incidence of CHD. Inadequate pelvic muscle mass in juvenile dogs is also associated with CHD. Exercise is necessary to build muscle mass. However, excessive and/or high-impact exercise may exacerbate stress on a lax hip in the juvenile whose bone length is growing faster than is the muscle strength intended to support the joint.
ARTHRITIS
Uncorrected CHD results in arthritis because of the abnormal mechanical forces placed on a partially or totally luxating joint. Arthritis is often associated with middle-aged dogs because midlife is when clinical signs of arthritis become obvious for many dogs. In reality, some degree of arthritis is usually present by 12 to 18 months of age; I have seen several dogs as young as 8 months of age with advanced hip arthritis due to CHD. The distinction between hip laxity and arthritis caused by hip laxity is important when considering treatment options. Arthritis cannot be "cured" (i.e., restoration of a normal hip joint). Arthritis can, however, be treated by conservative therapy, replacement with an artificial hip, or removal of the joint (i.e., FHNE).
TREATMENT OPTIONS
The four treatment options I discuss for dogs with CHD are TPO, conservative therapy, FHNE, and total hip arthroplasty (THA). Dogs with significant arthritis are not candidates for TPO. In addition, dogs undergoing TPO that weigh less than approximately 40 lb may require a plate configured by the surgeon rather than a Canine Pelvic Osteotomy Plate (Slocum International, Eugene, OR). Similarly, THA implants will not fit dogs weighing less than 40 to 50 lb (depending on the individual's bone size and the implant used). The first question to consider is whether the dog is a candidate for TPO, and, if so, does the client want a TPO? Selecting from the remaining options is influenced by the particulars of the dog, pathology at the time of the examination, and owner preferences and expectations.
Triple Pelvic Osteotomy
Triple pelvic osteotomy is intended for dogs with minimal arthritis because the procedure's goal is to correct hip luxation/subluxation and thus prevent or at least slow the progression of arthritis-not to treat arthritis after it is present. Will all dogs with a positive Ortolani sign develop crippling arthritis? No. Can the veterinarian predict for a particular animal how crippling the arthritis will become and how soon? Although the severity of hip laxity, muscle atrophy, and lost range of motion are suggestive, the answer is again no. TPO is an appropriate option for owners who do not want to risk debilitating arthritis. I believe TPO performed before arthritis is present is the best treatment for hip dysplasia because it corrects the actual problem, prevents or substantially reduces future arthritis, and preserves the natural joint.
The ideal candidate for TPO is a dog that is 6 to 12 months of age with a positive Ortolani sign and without radiographic signs of arthritis. Because such dogs typically have minimal clinical signs, identifying those dogs that may benefit from TPO means educating owners to bring their dogs to the veterinarian at 6 to 9 months of age, before significant arthritis has developed.
The hip examination should include an Ortolani test and sedation for radiography and a repeat Ortolani test. A positive Ortolani sign is hip luxation/ reduction and, by definition, is diagnostic of CHID. If TPO is being considered, the severity of arthritic change must be determined. The earliest clinical sign of arthritis is pain at full extension. Clinical signs of more advanced arthritis include loss of extension and abduction, muscle atrophy, and an indistinct Ortolani sign (suggestive that the dorsal rim of the acetabulum is eroding). Radiographs are needed to help determine if there is too much DJD for TPO to- be considered. The standard ventrodorsal radiograph with legs extended and internally rotated is the minimal view recommended. The addition of the dorsal acetabular rim (DAR) view allows the best evaluation of the DAR. Radiography may also identify the occasional dog that has luxated or subluxated hips but does not yield a positive Ortolani sign. Positioning must be perfect (requiring sedation), however, to diagnose subluxation by radiography alone. Radiography alone is not sufficient to diagnose normal hips. A radiograph in the Orthopedic Foundation of America position (hips extended and internally rotated) may reduce the hip completely, but that does not mean the Ortolani sign will be negative. Remember that radiographs are static in contrast to hip laxity, which is dynamic.
Triple pelvic osteotomy surgery has been described elsewhere," and only a few nuances of the procedure will be described here. I use a rongeur (5-mm Love-Kerrison or Ruskin) to remove a width of pubis, thus avoiding contact between the two sides of the osteotomy that may hinder rotation of the acetabular segment and avoiding possible entrapment of the urethra. Rongeurs used subperiosteally allow the best depth control and protect adjacent structures. A reciprocating saw is used to accurately place the ischial osteotomy from the medial extent of the ischiatic tubercle to the lateral aspect of the obturator foramen. This orientation places the ischial cut in a sagittal plane, which facilitates rotation and avoids the lack of control that can occur with a Gigli wire or the fissures that can result from using the wedge-like osteotome (especially a thick, dull one). Excessive synovial fluid is aspirated, and the joint capsule is imbricated to facilitate reduction. The angle of rotation needed can be estimated from the angles of luxation and reduction, but the final determination is made based on which angle prevents a positive Ortolani sign intraoperatively. A Kern forceps placed on the ischium provides easy rotation of the acetabular segment. A 2.7-mm screw is placed in the small hole on the acetabular side of the Canine Pelvic Osteotomy Plate for additional purchase. Several serious complications are possible with TPOs; however, when the procedure is performed by a surgeon trained in the technique, these complications are infrequent. The most common complication is progressive DJD.
Although I and others have had satisfactory results in dogs older than 12 months of age with mild to moderate radiographic changes, owners should be very aware that the risk of poor results due to arthritis increases with age. Any arthritic changes present at the time of surgery will not be corrected by TPO, and moderate to severe arthritis at the time of surgery may be self-perpetuating despite stabilization of the hip. At this time, 18 months is the oldest age at which I will offer TPO, and this is only if there are minimal clinical and radiographic signs of DJD. Many dogs presented for TPO have some degree of arthritis. How much DJD is too much is a subjective decision based on issues including clinical signs, radiography, age, and others. Any DJD warrants a lengthy discussion with the owner regarding the poorer prognosis. At a relatively early point in the progression of DJD, TPO should not be offered as an option.
Conservative Therapy
If TPO is not an option or is not chosen by the owner, conservative therapy is begun to minimize the clinical effects of DJD. Conservative therapy is adequate for the lifetime of some dogs. If conservative therapy fails, then FHNE or THA are the remaining options.
Conservative therapy means allowing the DJD to progress; thus the DJD is being treated rather than the CHID. As I use it, conservative therapy is far from "not doing anything" and would be better described as physical therapy. The primary goals of conservative therapy are to promote muscle mass and eliminate obesity. Antiinflammatory drugs (e.g., nonsteroidal antiinflammatory drugs [NSAIDs]) are the least important part of conservative therapy. Promoting muscle mass is known to be important with almost any orthopedic problem, especially regarding the hip where muscles around the normal joint carry a large portion of the weight-bearing forces. Muscle atrophy secondary to hip dysplasia means that a diseased joint is forced to carry more than its normal share of the load, and more weight bearing is shifted to the front legs.
Exercise
Exercise is the key to breaking the progressive cycle of a painful joint, which causes the leg to be used less, resulting in muscle atrophy. Muscle atrophy causes the diseased joint to carry more of the weight-bearing load, which in turn makes the joint even more painful. Exercise does not mean turning the dog loose in the backyard and assuming it is exercising. I recommend a minimum regimen of Monday-Wednesday-Friday exercise, such as leash walks, swimming, or retrieving. Because this program is labor-intensive for owners, it is not for everyone. In my opinion, owners are the best judges of how long their animals should be exercised. However, owners must realize that a beneficial exercise program is analogous to human athletes in training who push their limits and progressively increase the amount of exercise. Exercise will make the dog sore, especially during the first few weeks. However, the benefits of increased muscle mass make this program worthwhile for most dogs.
The type of exercise used depends on the dog. Swimming is best because it exercises muscles without weight bearing. However, swimming is not always a feasible option or may be impractical because of the breed of dog or climate. Retrieving breeds can be exercised by throwing a ball without exhausting the owner (which may cause the exercise program to stop). If the dog walks or trots over to the ball, picks it up, and trots back, then retrieval is a good form of low-impact exercise. However, if the dog runs full speed, slides into the ball like a runner stealing second base, and runs back, then retrieval may be too high impact for that animal. If the choice is between high-impact exercise and not exercising at all, I recommend the exercise.
Obesity Prevention and Correction
Obesity prevention or correction is an important part of conservative therapy and should not be treated as a superfluous issue. Correcting obesity has a substantial impact on the severity of lameness. Weight loss in dogs is difficult; simply telling owners to make the dog lose weight will, in my experience, usually result in failure. Veterinarians need to provide specific instructions: Feed dog food only, provide a specific amount food, and check weight weekly. Find out how many calories per serving the client's brand of dog food contains, and tell owners how much to feed in cups or cans (not in kilocalories per day). The number of calories required daily can be estimated from the following formula: (30 X animal's target weight [kg]) + 70 = Kcal/day resting energy maintenance. The actual number of calories fed should be titrated in relation to the amount of weight loss. Hypothyroidism is relatively common in obese dogs. Based on the Veterinary Medical Database and our endocrinology laboratory, hypothyroidism occurs in about 1% of all dogs tested. I prefer to submit a free thyroxine (T4) test initially because it is the most reliable, even though it is more expensive. Weight loss plans will result in frustration and failure if hypothyroidism is not identified and corrected.
Antiinflammatory Drugs
As mentioned, NSAIDs are the least important part of conservative therapy and should be used as little as possible. I recommend that NSAIDs (e.g., aspirin or carprofen [Rimadyl, Pfizer Animal Health, Exton, PA]) be given no more often than every other day (e.g., Tuesday and Thursday), primarily to help the dog continue the Monday-Wednesday-Friday exercise program. I also recommend other aspirin-based drugs (e.g., Bufferin [Bristol-Myers, New York, NY] or Ascriptin [Ciba Self-Medication, Inc., Woodridge, NY]); however, I do not recommend other NSAIDs, such as acetaminophen or ibuprofen. Adequan (Luitpold Pharmaceuticals, Shirley, NJ) or nutraceuticals can be administered, but steroids should be avoided as DJD is a lifelong disease and steroids are not appropriate for long-term treatment because of their side effects. In my opinion, failure of this type of conservative therapy (i.e., exercise, weight control, limited NSAIDs) is an indication for surgery.
Femoral Head and Neck Excision
Femoral head and neck excision is indicated for dogs with hip arthritis when conservative therapy has failed, the dog is too small for THA, or THA is not financially possible. I use a modified Watson-Jones approach, which elevates the vastus muscles off the femoral neck for clear visibility of the entire neck. There are several variations to FHNE surgical technique; however, standard FHNE without a biceps femoris muscle sling yields the best results with the least trauma. Collection of the biceps muscle flap causes considerable morbidity, and the muscle flap between the femur and acetabulum atrophies to the point of not providing a pad within 16 weeks after surgery. In my experience, transposition of the deep gluteal muscle has not been associated with as much morbidity as the biceps femoris muscle flap and is a technique I frequently use with subjectively satisfactory results.
Performing the FHNE before severe muscle atrophy develops is especially important. My impression is that good muscle mass in the affected leg(s) and lack of obesity are at least as important as the dog's body weight relative to prognosis (i.e., lean, well-muscled large dogs can do well after FHNE). Forced exercise (e.g., leash walking) is important as soon as sutures are removed.
Total Hip Arthroplasty
Total hip arthroplasty is indicated for the treatment of clinically significant hip arthritis in dogs with a closed physis at the greater trochanter, which occurs at approximately 9 months of age. Old age alone is not a contraindication. An absolute contraindication is the absence of lameness and/or pain regardless of radiographic appearance. The severity of clinical and radiographic signs of arthritis frequently do not correlate; therefore, treat the dog instead of the radiographs. One caution is to ensure that medications are not masking clinical signs. In my laboratory, force-plate analysis of research dogs indicates that the mean weight bearing of artificial hips is 92% of the normal, preoperative hip. If weight bearing has not decreased (or lameness has increased) to a level comparable to the 92% expected with an artificial hip, then THA may actually worsen the dog's lameness. In addition, the dog would be subjected to the risk of THA complications before conservative therapy should be considered a failure. Conversely, waiting until muscle atrophy is advanced will result in poorer results from surgery, whether it be THA or any other type of orthopedic surgery. My experience with measuring thigh circumference is that muscle mass will not be fully regained if atrophy is severe at the time of surgery.
Another absolute contraindication for THA is infection anywhere (e.g., cystitis, gingivitis). Total hips, especially if cemented, represent a large mass of foreign material that is at risk for surgical and hematologic routes of infection. Relative contraindications include other orthopedic problems (e.g., cruciate ligament rupture), neurologic disease (e.g., lumbosacral instability), and systemic or major organ disease (e.g., neoplasia, renal disease). Extreme remodeling of the hip and/or extreme luxation makes THA technically more difficult and subject to complications. Cemented and cementless artificial hips have proven successful in well over 90% of cases when they are carefully selected and the procedure is performed by a surgeon experienced with the technique.
SUMMARY
Hip dysplasia and DJD are different diseases (albeit CHID leads to DJD) with different treatments. TPO is a treatment for CHID that requires clients to take their dogs to a veterinarian before DJD becomes significant. Conservative treatment, FHNE, and THA are treatments for hip DJD. Client education is important to help the pet owner make informed decisions and to minimize risk factors for CHID with future pets.
Conservative therapy that emphasizes an aggressive exercise program, obesity prevention, and limited use of antiinflammatories is beneficial in the majority of dogs. However, such a program is labor-intensive for the owner and owner compliance must be good to derive benefit. As with any DJD treatment, muscle mass and obesity are critical issues.
FHNE has a high success rate in small dogs. Larger dogs have a higher rate of poor results; however, this does not imply that all, or even most, large dogs have poor results after FHNE. Muscle mass and obesity are especially critical issues when considering FHNE in large dogs.
As with any disease, removing the inciting cause and restoring normal structure and function are preferable. We know intuitively that as good as human-made products can be, nature makes a better Joint than we can. For example, the dynamic coefficient of friction for a normal hip joint is 20 times (2000%) less than that for an artificial hip (ultra-high molecular weight polyethylene [UHMWPE] cup/stainless steel head). In addition, a normal hip has a ligament of the femoral head to help stability, does not produce wear products that lead to "cement disease," does not act as a nidus for infection, and can regenerate in response to normal wear. TPO performed before arthritis develops is therefore the treatment I prefer for big dogs from a purely medical standpoint (i.e., without regard to finances and other considerations).
All of the treatments discussed in this article have pros and cons, are successful in the majority of carefully assessed dogs, and can fail in any individual dog. In addition, it is common for dogs with hip dysplasia and/or DJD to have concurrent orthopedic problems (e.g., osteochondritis dissecans/cruciate rupture). Therefore, thorough examination of the dog and good communication with the owner are imperative in selecting the "best" treatment for an individual dog.