Treating painful hips: nonsurgical and surgical modalities (Proceedings)

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Treating painful hips: nonsurgical and surgical modalities (Proceedings)

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Aug 01, 2011

Hip Dysplasia

Hip dysplasia is an abnormal development of the coxofemoral joint. The syndrome is characterized by subluxation or complete luxation of the femoral head in the younger patient while in the older patient mild to severe degenerative joint disease is present. Laxity in the hip joint is responsible for the early clinical signs and joint changes. Subluxation stretches the fibrous joint capsule, producing pain and lameness. When the surface area of articulation is decreased, this concentrates the stress of weight bearing over a small area through the hip joint. Subsequently, fractures of the trabecular cancellous bone of the acetabulum can occur, causing pain and lameness. The cancellous bone of the acetabulum is easily deformed by the continual dorsal subluxation of the femoral head. This piston-like action causes a wearing of the acetabular articular surface from a horizontal plane to a more vertical plane causing subluxation to worsen. The physiologic response to joint laxity is proliferative fibroplasia of the joint capsule and increased thickness of the trabecular bone. This relieves the pain associated with capsular sprain and trabecular fractures. However, the surface area of articulation is still decreased causing premature wear of articular cartilage, exposure of subchondral pain fibers and lameness. This may occur early in the pathologic process or later in life. There are two general recognizable clinical syndromes associated with hip dysplasia: (1) patients 5 to 16 months of age, (2) patients with chronic degenerative joint disease. Patients in group 1 present with lameness between 5 to 8 months of age. Symptoms include difficulty when rising after periods of rest, exercise intolerance and intermittent or continual lameness. The majority of young patients will spontaneously improve clinically around 15 to 18 months of age. This clinical improvement is due to pain relief as proliferative fibrous tissue prevents further capsular sprain, and increased thickness of the subchondral bone prevents trabecular fractures. If symptoms occur later in life, they may include difficulty in rising, exercise intolerance, lameness following exercise, atrophy of the pelvic muscle mass, and a waddling gait with the rear quarters. Physical findings in the younger group of patients include pain during external rotation and abduction of the hip joint, poorly developed pelvic muscle mass, and exercise intolerance. Hip exam performed under general anesthesia will reveal abnormal angles of reduction and subluxation reflecting excessive joint laxity. Physical findings in the older group of patients include pain during extension of the hip joint, reduced range of motion, atrophy of the pelvic musculature, and exercise intolerance. Radio graphically, there are seven grades of variation in the congruity between the femoral head and acetabulum established by the Orthopedic Foundation for Animals. Excellent, good, fair, and near normal are considered within a range of normal. Dysplastic animals fall into the categories of mild, moderate, and severe. It is important to note that clinical signs do not always correlate with radiographic findings. Recently, patients have been evaluated using a distraction index where the degree of hyperlaxity is measured and correlated with standards for each breed.

Treatment is dependent upon the age of the patient, the degree of patient discomfort, physical and radiographic findings, client expectations of patient performance, and financial capability of the client. Conservative treatment is beneficial to a large number of patients in both the young and older patient groups. Conservative management is divided into acute management and long term management. When a dog exhibiting signs of hip dysplasia enters the clinic, it is generally because they have sprained the hip joint. The dysplastic joint is either hyperlax (young dog) has a limited range of motion (mature dog). In either case, the joint is easily sprained and the dog that is presented with symptoms has generally overused (sprained) the hip joint. The management of the case at this time period is the same as treating any other acute sprain. Rest, physical therapy, and non-steroidal analgesics will relieve signs in the majority of patients. Rest is just that!!!, controlled activity with slow walking on a leash only. There should be NO free activity for 2 weeks. Physical therapy includes cold therapy for the initial 1-4 days. Commercial cold packs are the most convenient and precise way to apply cold therapy. The application of cold should only be 5-10 minutes. NSAIDs recommended by the author are: 1. Aspirin (Ascriptin), carprofen (Rimadyl), etodolac (Etogesic), Deracoxib (Deramax). I would not recommend any other "over the counter NSAIDs). The advantage of aspirin (25mg/kg TID) is the low cost. The disadvantage of aspirin is the low efficacy and incidence of GI upset. Aspirin is a COX 1 inhibitor; inhibition of COX 1 de-regulates the balance of normal homeostasis giving rise to a higher incidence of side effects. Aspirin should always be given with a small amount of food. Preferably, give a dose late in the evening so higher blood levels are present early in the morning. Carprofen (1mg/lb BID or 2mg/lb OD) is FDA approved for use as an anti-arthritic medication in the dog. It too should be administerd with a small amount of food. Carprofen is a COX 2 inhibitor accounting for a low incidence of side effects. Carprofen is very effective in controlling discomfort associated with hip dysplasia. The attending veterinarian must always consult with owners relative to side effects of any NSAID. NSAIDs can cause serious side effects and even death in some humans and animals. There is a reported incidence of liver failure in dogs having been given carprofen. The common age of dogs afflicted is most commonly mature adults (8yrs) but liver failure can occur in any age. Although the incidence of liver failure is very low, the clients must be advised of this possibility. Etodolac (Etogesic) is also an NSAID aproved by the FDA for use in the dog. It too is very effective in controlling pain associated with arthritis in dogs and is administered 1/day (4-7mg/lb). Deracoxib is just recently approved for orthopedic pain in dogs. It is highly COX 2 selective which reportedly decreases the incidence of side effects. The attending veterinarian must emphasize that REST and PT are the most important considerations when treating an acute sprains.

Following the acute phase of treatment, the attending veterinarian must consult with the owner regarding long term management of the dysplastic dog. The foundation for long term management of any arthritic joint is weight control, exercise therapy, and anti-inflammatory drugs or supplements. The majority of mature dogs with hip discomfort are over weight. Studies have shown a significant improvement in function if an ideal target weight is achieved. The foundation for weight control is exercise therapy, diet, and owner behavior modification. There are a number of excellent commercial diets on the market. The owner in conjunction with the dog undergo behavior modification. This is a weight reduction program; their dog will be hungry. The owner must not feel guilty but must understand the long term benefits of weight reduction. Convincing evidence might be pictures showing the outcome of previously treated dogs. The attending veterinarian should become familiar with them and chose one or two for use in their clinic. Exercise programs aimed at developing pelvic muscles should begin gradually. Swimming (if available) develops endurance and flexibility. Repetitions of sit-stand exercises also increase endurance and flexibility. Standing, forced flexion-extension exercises (squats) develop strength as does walking uphill with leg weights. If available, an underwater treadmill is an excellent method of exercise. The warm water relaxes sore muscles, the buoyancy lowers joint load, and the water resistance increases work effort.