Canine Hip dysplasia

Hip dysplasia is characterized by faulty development of the hip (hip) joint that initially presents as varying degrees of joint laxity (looseness) and later is manifested as femoral and acetabular remodeling and degenerative joint disease (osteoarthritis). Thus, the disease clinically appears, and is treated, differently in the young versus old dog.

Etiology:
Dog owners and breeders need to distinguish between the "genotype" or genetic coding of the dog and the "phenotype" or way the dog looks (size, body type, weight, etc). Hip dysplasia is a multifactorial disease of heritable origin. Additionally environmental factors, particularly overall increased energy level and increased percentage of calcium in the diet, contribute to development of the phenotype of dysplastic hips. Thus, the chances of a dog developing hip dysplasia are decreased by selective breeding of parents without the genetic tendency for hip dysplasia, and by changing the nutrition of the growing dog. Selective breeding is enhanced by performing predictive tests such as OFA certification or the PennHipR score. To minimize the chances of developing the dysplastic phenotype, dietary calcium should be maintained in the range of 0.9 to 1.6% dry matter, and the animal's caloric intake should be monitored to keep the puppy from becoming overly fat. Overall protein levels, vitamin C intake, vitamin D intake and other nutritional factors have no known effect, either positive or negative, on development of hip dysplasia.

Pathophysiology:
Hip dysplasia is initiated as a disparity between primary muscle mass and disproportionately rapid skeletal growth. Hip joint instability leads to subluxation (partial dislocation) of the acetabulum and femoral head. Bone changes such as thickened femoral neck, bone spur formation, or sclerosis of the acetabulum occur secondarily to the poor fit of the hip joint.

Clinical Signs:
Lameness of the hind limb varies from barely-detectable gait abnormalities to non-weight-bearing lameness. Lameness is especially evident after exercise periods. A "bunny-hopping" gait is often seen in affected young dogs and is characterized by simultaneous advancement of both hind limbs while running. Young dysplastic dogs often lay on their belly with limbs outstretched behind them. Pain is often elicited during full extension of the joint by a veterinarian. Hip dysplasia is not generally an acute lameness, but one of slow progression of lameness severity.

Diagnosis:
The diagnosis of hip dysplasia is suspected based on findings of hip laxity in young animals and pain on hip palpation in older animals, and confirmed by radiographs of the hip. The "Ortilani sign" is a test your veterinarian may perform during examination of your dog. Presence of the "Ortolani sign" indicates joint laxity in a young animal, but does not mean necessarily that the dog will develop hip dysplasia. Absence of the Ortolani sign indicates a normal hip or advanced degenerative joint disease precluding movement of the femoral head out of the acetabulum.

Radiographs
Radiographic (X-ray) changes associated with hip dysplasia range from subluxation of the femoral head to severe degenerative joint disease (arthritis). Animals less than 10 months of age often exhibit only varying degrees of subluxation (figure 1). Clinical significance of the degree of subluxation is based on breed, age, and clinical signs of the dog. Generally, subluxation where <25% of the head of the femur is in the acetabulum on ventrodorsal radiographs is considered severe and leads to rapid development of secondary degenerative joint disease. Milder degrees of subluxation may also lead to degenerative joint disease. Animals older than 10 months of age develop radiographic changes of degenerative joint disease at varying rates depending on the degree of subluxation. Radiographic signs of degenerative joint disease include flattening of the head (ball) of the femur, a shallow acetabulum (hip joint socket), bone spurs on the femoral neck and femoral margin of the joint capsule, narrowing of the joint space and subchondral sclerosis of the femoral head and acetabulum (figure 1).

A              B                     C

Figure 1A represents normal hip conformation
Figure 1B is a dog with subluxation of the hips at 4 months of age
Figure 1C is the same dog as above (1B) at 4 years of age with advanced arthritis of the hips.

Classically, radiographs taken for diagnosis of hip laxity and arthritis were taken with the animal on it's back and the hind limbs extended and internally rotated (OFA position). These radiographs can be sent to the nonprofit Orthopedic Foundation for Animals for certification and grading for the tendency of a breeding animal to develop hip dysplasia. Disadvantages of this method are that the animal needs to be 2 years of age before it can be certified and that the ability of the method (which measures phenotype) to determine genotype of the animal is similar to the heritable tendency for hip dysplasia. Compression and distraction of the hips during radiography (PennHipR) may be more useful in documenting joint laxity, can be used to determine the tendency for hip dysplasia in dogs as young as 16 weeks and may be useful prognostically in many breeds as a sufficient data base is built. Additionally a dorsal rim acetabular view is used by some surgeons to evaluate acetabular (hip socket) conformation.

Differential diagnoses for hip dysplasia include traumatic hip luxation, infectious or immune mediated arthritis, cranial cruciate ligament rupture, degenerative myopathy (older dogs) and femoral head or neck fractures

Treatment:
Treatment is divided into a matrix composed of nonsurgical versus surgical therapies, and young versus old animals. Because of the heritable component of the disease, neutering is recommended for all dogs with confirmed hip dysplasia.

Nonsurgical therapies to relieve pain in all age dogs consist of exercise restriction and nonsteroidal anti-inflammatory therapy. Nonsteroidal antiinflammatories used in dogs include buffered aspirin, carprofen, or etodalac, and the dosage and choice will vary depending on your dog's pain and your veterinarian's preference. Over-the-counter human nonsteroidal antiinflammatories such as ibuprofen and naproxen can be fatal to dogs and should not be used for treatment of arthritis in dogs. Chondroprotective agents, such as glucosamine, have some benefit in selected dogs. Controlled and blinded clinical studies in humans and animals have demonstrated benefits of these substances for prevention and modulation of chronic degenerative joint disease.

Recommended surgical therapies for the young dog (<10 months age) include Triple Pelvic Osteotomy (TPO) and Femoral Head and Neck excision (FHNE). A newer procedure, pelvic symphophodesis, may be useful in very young animals for prevention of clinical signs. Surgical therapies for the older dog include Femoral head and neck excision (FHNE) and Total Hip Replacement (THR). Other techniques have been described for dogs with hip dysplasia, but are not recommended by this author.

Triple Pelvic Osteotomy
Triple pelvic osteotomy (TPO) is a surgical procedure where osteotomies of the pubis, ischium and ilium are performed, the acetabulum is rotated dorsally, and the ilium is stabilized with a bone plate (figure 2). The goal of TPO is to maintain good femoral head and socket conformation and to prevent degenerative joint disease formation. Triple pelvic osteotomy is indicated for large breed dogs with hip subluxation and no radiographic signs of degenerative joint disease. Such dogs are usually less than 10 months of age. Candidates for TPO should have some remaining coverage of the femoral head by the acetabulum. Animals with complete luxation of the hip are not good candidates for TPO. TPO is usually performed one side at a time with 1 month between sides in dogs who are dysplastic in both hips, but some surgeons do both hips at the same time. There are sporadic reports of TPO being performed in older animals with early degenerative signs, but clinical followup of these animals is inconclusive at present. Prognosis of dogs after TPO is good, with 95% returning to normal pain-free function. Dogs are confined to a small cage or pen for 6-8 weeks after TPO surgery to allow the bone of the ilium to heal noneventfully. Limited exercise on a leash only may be allowed 4-6 weeks after surgery by some surgeons.

Femoral Head and Neck Excision
Femoral head and neck excision (FHNE) is a "salvage" procedure indicated for dogs of all ages and sizes with hip subluxation or degenerative joint disease, but the results are not optimal in larger dogs (>50 lbs). FHNE is a surgical removal of the ball and neck of the femur (figure 3). The use of interpositional muscle flaps, an added surgical part of the surgical technique, remains controversial but are probably not of benefit. FHNE relieves pain to some degree and results in a dog better able to walk, but the animal has no normal hip articulation. Success may relate more to postoperative physical therapy than to patient size; the more use the animal gets from the limb in the first few days to weeks, the better the long-term outcome, so postoperative physical therapy is very important for recovery.. All FHNE's should be radiographed postoperatively for a baseline evaluation. While the exercise allowed the animal should be controlled, leash-controlled exercise is begun soon after FHNE surgery to improve the animal's pain and recovery. Uncontrolled exercise is usually allowed one month following surgery.

Total Hip Replacement (THR)
Total Hip Replacement (THR) is the surgical treatment of choice in adult dogs weighing > 50 lbs to obtain the best functional outcome. THR involves replacement of the femoral head and acetabulum with artificial components and demands advanced technical expertise and equipment, and strict aseptic technique. It provides relief from pain for affected dogs and allows a return to normal activity. Dogs with successful total hip replacement (THR) can be expected to function as family pets, and may return to sporting and other activities. THR has a high success rate (>90%) although complications (infection, dislocation, loosening of implants) are potentially catastrophic.

Indications For Hip Replacement:
The hip in dogs is most often replaced to eliminate pain associated with chronic hip dysplasia. Other common reasons to replace the hip include chronic hip dislocation, severe chronic fracture involving the hip, and arthritis of the hip.

Candidates:
Candidates for THR are typically large breed dogs (>60 lbs) with irreparable disease or injury to the hip joint. The dog must be fully grown (>10 months age) at the time of surgery. To minimize postsurgical complications, candidates should be free from infection of the ears, skin, or organs, and free from neurologic disease.

Procedure:
Total hip replacement is a major surgical procedure. The dog's health is fully evaluated before surgery to minimize the risk of complications. The leg is shaved and scrubbed from the hock (ankle) to the middle of the back in preparation for surgery. The surgical procedure involves removal of the damaged femoral head and acetabulum (socket). The femoral head is replaced with a metal stem cemented into the femur and topped with a metal ball. The acetabulum is replaced with a high-density polyethylene cup cemented into place. Since the bone cement used could serve as a hiding place for bacteria, special precautions are observed to prevent contamination at surgery. The dog is recovered from anesthesia and given medication to prevent pain or discomfort. Average hospital stay is 5 days, and the dog should be kept confined for 8 total weeks after surgery. Radiographs are taken at one month and then yearly thereafter to assess the integrity of the prosthetic joint.

Risks:
Every possible measure is taken to minimize the risk of complications from hip replacement surgery. Reports indicate that complications occur in approximately 8% of cases. The two major risks of the surgery are infection (about 2%), and luxation or displacement of the joint (about 3-5%). Infection of the implants may necessitate removal of the entire prosthesis. Other potential problems include anesthetic complications, nerve damage, or fracture of the femur.

After care:
Proper care after surgery is important if a satisfactory result is to be achieved. The patient's activity must be restricted for 8 weeks to a small area with good footing. Running and jumping is not permitted for the entire 8 week period. Stairs should be avoided. Leash walks are permitted and can gradually be increased in length. The dog is not permitted to be off a leash while outside for the 8 week period.

Prognosis:
The majority of dogs regain full, pain free function after total hip replacement. Satisfactory results are achieved in over 90% of cases.

Pubic symphysiodesis
Pubic symphysiodesis is a recently described preventative surgery for dogs with hip laxity approximately 12-16 months of age. An approach is made to the midline of the pelvis and the symphysis (fusion area between the sides) of the pubis is fused with electrocautery. This procedure results in premature fusion of the symphysis and causes the hip joints to rotate to cover the femoral head during growth, much like the triple pelvic osteotomy surgery does in older animals. The procedure may prevent the development of hip dysplasia in dogs.

Other Techniques for Hip Dysplasia.
Several less-accepted surgical techniques have been described including Pectineal muscle or tendon resection, femoral neck lengthening, and the BOP-Shelf arthroplasty but are not recommended by the author.