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, restlessness at night, 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. Radiographically, 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. 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 overweight. 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. Administration of drugs (NSAIDs, steroids, PSGAGs, Hyaluronate) or supplements (glucosamine, chondroitin sulfate, manganese) are useful to control discomfort. This is particularly true in the early stages of treatment before the benefits of weight reduction and exercise therapy are realized. The administration of drugs should be at a minimum level (dose and frequency) to achieve comfort. Supplements of glucosamine, chondroitin sulfate and manganese alone or in combination have been shown in vitro as well as in clinical studies to ameliorate discomfort or reduce the dose of drugs needed to control discomfort.
Surgical intervention also is divided into techniques useful in the younger population and those useful in mature dogs. Techniques useful in the younger population include Triple Pelvic Osteotomy (TPO), Double Pelvic Osteotomy, femoral head ostectomy, and possibly total hip replacement. My preference in this aged dog is either a TPO or DPO. The advantage of DPO is that the floor of the pelvic canal is stable is that the ischium does not undergo an osteotomy as in a TPO. This concept allows for greater patient comfort and therefore, the ability to perform a bilateral DPO at the same setting. This reduces postoperative rehabilitation time and allows more rapid return to function. Pelvic osteotomy is used in the group of younger patients to axially rotate and lateralize the acetabulum in an effort to increase dorsal coverage of the femoral head. This procedure is indicated in patients that will lead athletic lives such as the working breeds or in those patients in which the client wishes to arrest or slow the progress of osteoarthritis associated with hip dysplasia. The most favorable prognosis is in patients having minimal existing radiographic degenerative changes and an angle of reduction less than 45 degrees and angle of subluxation less than 15 degrees. The prognosis is less favorable in patients with existing degenerative changes and angles of reduction and subluxation greater than those given above. The details of the technique are beyond the scope of this handout. Briefly, the degree of axial rotation of the acetabulum is set by the previously determined angles of reduction and subluxation. The angle of reduction is the maximum degree of rotation and the angle of subluxation is the minimum degree of rotation. The most commonly used angle of acetabular axial rotation is slightly less than the measured angle of reduction. The pelvis is cut through the pubic brim and body of the ilium. The acetabulum is rotated axially, lateralized and stabilized with the appropriate osteotomy plate. The use of locking technology is an advantage that has decreased post-operative implant failure. Postoperatively the patient is restricted to exercise on a leash only until radiographic healing of the osteotomies is complete.
In the older dogs, my preference is total hip replacement or conservative management. Femoral head ostectomy is an option in cases where conservative management is no longer effective and financial constraints precludes Total Hip Replacement. Advancement in Total Hip Replacement is the advent of cementless systems. Cementless systems have decreased the incidence of acetabular cup loosening and femoral stem loosening. Hybrid insertion with cementless cup and cemented stem are often used in dogs with "stove pipe", i.e., uniform diameter marrow cavity.