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CANINE HIP DYSPLASIA
Overview
Canine Hip Dysplasia is a condition which begins in immature dogs with instability or a loose fit of the hip joint (Figure 1). The hip joint laxity is responsible for early clinical signs and joint changes. The abnormal motion of the hip stretches the fibrous joint capsule and ligament connecting the head of the femur to the pelvis, producing pain and lameness. The acetabulum (the hip socket) is easily deformed by continual movement of the femoral head. Micro fractures of the acetabular bone may occur, causing further pain and lameness in the immature dog. The dog’s physiologic response to joint laxity is proliferative fibroplasia or thickening of the joint capsule and formation of osteophytes or new bone on the rim of the acetabulum and the femoral neck (Figure 2).
Figure 1. Hip dysplasia present in young animals as instability of the hip joint. As the dog bears weight, the head of the femur (the “ball”) comes out of the acetabulum (the “socket”) as far as the joint capsule and ligament will allow. The joint capsule and ligament gradually get stretched allowing the femoral head to come out of the acetabulum even further.
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Figure 2. The result of the instability in the joint is abnormal wear of the cartilage. Cartilage wear leads to the formation of osteophytes (bone spurs) and joint capsule thickening, which are the characteristic signs of osteoarthritis or degenerative joint disease.
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These responses help to stabilize the hip joint. The new bone formation is visible on radiographs and considered to be osteoarthritis or degenerative joint disease (Figure 3).
Figure 3. A pelvic radiograph of a dog with degenerative joint disease (osteoarthritis) of the hips secondary to hip dysplasia.
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The osteoarthritis progresses over the life of the dog. However, radiographic signs of osteoarthritis do not always correlate with clinical function.
Causes
Causes of hip dysplasia are considered to be multifactorial; including both hereditary and environmental factors. Rapid weight gain and growth through excessive nutritional intake may encourage the development of hip dysplasia. Mild repeated trauma causing synovial (joint lining) inflammation may also be important.
Incidence and Prevalence
The incidence of hip dysplasia is greatest in large breed dogs. Two populations of animals show clinical signs of lameness: (1) patients 5 to 10 months of age, and (2) patients with chronic degenerative joint disease.
Signs and Symptoms
The clinical signs of hip dysplasia are lameness, reluctance to rise or jump, shifting the weight to the forelimbs, loss of muscle mass on the rear limbs, and pain when the hips are manipulated. Dogs may show clinical signs at any stage of development of the disease, although many dogs with hip dysplasia do not show overt clinical signs. Some dogs are painful at 6 to 8 months of age but recover as they mature. As the osteoarthritis progresses with age, some dogs may show clinical signs similar to people with arthritis such as lameness after unaccustomed exercise, lameness after prolonged confinement, and worse problems if they are overweight.
Risk Factors
Risk factors for CHD include breed (genetic), rapid growth and nutrient excesses.
When to Seek Veterinary Advice
Some veterinarians recommend radiographing the hips at 6 months of age to help identify dogs with hip dysplasia early enough to perform a triple pelvic osteotomy. For many dogs, the owners seek veterinary surgery advice when the dog has been consistently lame, and has not responded to medical therapy. Many of the surgical treatments for hip dysplasia are performed by surgical specialists. Find an ACVS Veterinary Surgeon.
Exam, Screening Tests, and Imaging
Physical examination includes an evaluation of lameness and palpation of the hips. Many dogs are painful when the hip joint is extended by pulling the leg back. The standard radiographic view for diagnosis of hip dysplasia is the ventrodorsal view of the pelvis with rear limbs extended symmetrically and rotated inward to center the patellas over the trochlear grooves. (Figure 3) The dog must be heavily sedated or anesthetized for proper relaxation and positioning. The Orthopedic Foundation for Animals, a screening agency for canine hip dysplasia, will certify a dog after 2 years of age. Stress radiographs can be used to detect breed susceptibility to hip dysplasia as early as 4 months. A dorsal acetabular rim view can be used to define the angle and condition of the dorsal acetabular rim when evaluating a dog for candidacy for a triple pelvic osteotomy.
Differential Diagnosis
A number of neurologic and orthopedic problems cause similar clinical signs to those seen with hip dysplasia. In immature dogs, lameness caused by panosteitis, osteochondrosis and occasionally partial or complete cranial cruciate ligament injury must be differentiated from hip dysplasia. In older patients it is necessary to rule out pain and lameness associated with pressure on the nerve roots in the lower back and lameness associated with rupture of the cranial cruciate ligament, polyarthritis, or bone neoplasia (cancer) conditions before attributing clinical signs to hip dysplasia. Many dogs have hip dysplasia evident on radiographs, yet the lameness is caused by another problem.
Complications Caused By The Disease
The primary complication caused by hip dysplasia is the development of osteoarthritis or degenerative joint disease. Dogs with unstable hips secondary to hip dysplasia are also more likely to dislocate a hip with minimal trauma, such as falling while running in the yard.
Treatment Options
Treatment depends on the dog’s age and degree of discomfort, physical and radiographic findings, and owner’s expectations and finances. Conservative and surgical options are available for juvenile and mature animals with hip pain secondary to hip dysplasia. Most immature animals are best treated with conservative or medical management. Although early surgical intervention with juvenile pubic symphysiodesis or triple pelvic osteotomy may increase the prognosis for long-term acceptable clinical function, approximately 75% of young patients treated conservatively return to acceptable clinical function with maturity. The remaining 25 % require further medical or surgical management at some point in life.
In puppies less than 20 weeks of age, juvenile pubic symphysiodesis (JPS), a technique for stopping the growth of the pubis (part of the pelvis) may be performed to alter the growth of the pelvis and increase the degree of coverage of the acetabulum over the femoral head. Most puppies of this age do not show clinical signs of hip dysplasia, so diagnosis depends upon use of a screening technique for documenting hip laxity, such as Penn Hip, to determine which animals may be candidates for the procedure. Although specific criteria for application of JPS have not been developed, puppies under 20 weeks of age that have palpable and radiographic evidence of laxity on a hip distracted view can be considered for the procedure.
Immature dogs (less than one year) with loose fitting hips, but no arthritic changes can be treated with a pelvic osteotomy (also sometimes called a triple pelvic osteotomy). This procedure involves cutting the pelvic bone in three places and rotating it to stabilize the hip joint and in many cases slow the progression of osteoarthritis. (Figure 4).
Figure 4. A pelvic radiograph of a dog following a triple pelvic osteotomy. The object of this surgery is to create an acetabulum (socket) that is deep enough that the femoral head will no longer tend to come out of the socket at the dog bears weight.
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Immature dogs with osteoarthritis already present will not benefit from this procedure and are treated medically as needed. You should seek veterinary advise on treating the pain and lameness with nonsteroidal anti-inflammatory drugs (NSAIDS). Concurrent treatment with a nutraceutical agent may also be recommended.
Mature dogs with hip dysplasia which are not showing clinical signs do not need medical or surgical treatment. These dogs should be kept slim and encouraged with consistent moderate exercise to develop good muscle mass to support the hips. Mature dogs with occasional lameness can be treated with non steroidal anti-inflammatory drugs and rest when they are lame. If the lameness can be associated with a certain activity, it is best to avoid the activity. After the lameness subsides, a slowly increasing, consistent exercise program should be instituted. If lameness recurs, exercise is decreased and the drugs are administered again. Every effort should be made to maintain the dog at a slim weight. Ideally one should be able to easily feel the ribs. In obese dogs, weight loss alone may alleviate clinical signs. When medical therapy does not provide pain relief and reasonable function, the dog is a candidate for one of two surgical procedures to reconstruct the hip joint. The femoral head and neck ostectomy involves removing the femoral portion of the hip joint. (Figure 5) The joint heals with fibrous tissue and in many cases allows a more pain free existence.
Figure 5. A pelvic radiograph of a dog following a femoral head ostectomy (FHO). The object of this procedure is to eliminate the bone to bone contact of the degenerating hip joint and allow the formation of a scar tissue pseudarthrosis (false joint) which results in less pain
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The total hip replacement (THR) involves replacing the hip joint with a metal and polyethylene prosthesis (Figure 6). This procedure results in the most normal limb function in large dogs. The procedure is expensive because of the implants and the technical requirements of the surgery, and requires a commitment from the owners for follow up care.
Figure 6. A pelvic radiograph of a dog following a total hip replacement (THR). The object of this procedure is to replace the cartilage of the acetabulum (socket) with a polyethylene socket, and the femoral head with a metal prosthesis. Most dogs have excellent return to function following a total hip replacement.
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Potential Complications Following Surgery
Risks of complications after juvenile pubic symphysiodesis are low and failure of the procedure to reduce hip subluxation does not preclude further surgical treatment in the future.
Reported complications after pelvic osteotomy include implant failure, loss of limb abduction, and pelvic outlet narrowing. However, the incidence of complications is low and reports of long-term clinical function are good to excellent.
Results after femoral head ostectomy vary. The prognosis is highly dependent upon patient size and postoperative physical therapy. In large patients, 50% of animals have good or excellent function. The rest of the dogs have varying degrees of lameness, but function is usually improved when compared with preoperative status. Medium and small patients usually have good or excellent limb function.
Total hip replacement results in excellent return to normal function unless complications occur. Complications after total hip replacement include infection, hip luxation, and fracture.
Aftercare for Surgical Patients
After pelvic osteotomy the dog’s activity should be restricted to leash exercise until the osteotomies are healed, generally 6 weeks. Most patients are weight bearing soon after surgery and must be closely confined to prevent overuse of the leg during the healing period.
After femoral head and neck ostectomy, patients are encouraged to use the limb as soon as possible. Physical therapy and controlled exercise to increase the range of motion of the hip is essential for an optimal outcome. It may take up to 6 weeks or longer after surgery for some dogs to show improvement.
After total hip replacement, most patients feel comfortable enough to use the leg because the prostheses are stabilized with bone cement. Many dogs will quickly become too active and must be confined to a small area with activity restricted to leash walking only. The dog should avoid stairs, slippery surfaces and interactions with other dogs. If all goes well, after 4-6 weeks, activity can be slowly increased back to normal.
—Ann Johnson, DVM, MS
Diplomate ACVS
Posted 12/08/2004
Updated 5/15/2008 by Dr. Johnson
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