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Hip Dysplasia--Dogs
BASICS
DEFINITION
Hip dysplasia is the malformation and degeneration of the coxofemoral joints.
Pathophysiology
Hip dysplasia is a developmental defect initiated by a genetic predisposition to subluxation of the immature hip joint. Poor congruence between the femoral head and acetabulum creates abnormal forces across the joint, interferes with normal development (leading to irregularly shaped acetabula and femoral heads), and overloads the articular cartilage (causing microfractures and degenerative joint disease).
Systems Affected Musculoskeletal
Genetics
• Complicated, polygenetic transmission.
• Expression is determined by an interaction of genetic and environmental factors. Heritability index varies with breed (0.25-0.40)
Incidence/Prevalence
• Hip dysplasia is one of the most common skeletal diseases encountered clinically in dogs.
• The actual incidence is unknown and varies with breed.
Geographic Distribution N/A
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SIGNALMENT
Species Dogs
Breed Predilection
• Large breed dogs, including Saint Bernards, German shepherds, Labrador retrievers, golden retrievers, and rottweilers.
• Smaller breed dogs may be affected but are less likely to demonstrate clinical signs.
Mean Age and Range
• Hip dysplasia begins in the immature dog.
• Clinical signs may develop after 4 months of age in some dogs, whereas other dogs present with clinical signs at an older age when degenerative joint disease develops.
Predominant Sex None
SIGNS
General Comments
• Clinical signs are dependent on the degree of joint laxity, amount of degenerative joint disease present, and chronicity of the disease.
• Early clinical signs are related to joint laxity; later signs are related to joint degeneration.
Historical Findings
Reported signs include reduced activity, difficulty rising, reluctance to run or jump or climb stairs, intermittent or persistent hind limb lameness (often worse after exercise), "bunny hopping" or swaying gait, and narrow stance in the hind limbs.
Physical Examination Findings
• Physical exam findings include pain, laxity, crepitus, and diminshed range of motion in the hip joints.
• Other findings are atrophy of thigh muscles and hypertrophy of shoulder muscles.
• Joint laxity (+ Ortolani sign) is characteristic of early hip dysplasia; however, joint laxity may no longer be present in chronic cases due to periarticular fibrosis.
CAUSES
• Hip dysplasia is caused by a genetic predisposition for hip laxity.
• Rapid weight gain, nutrition, and pelvic muscle mass influence the expression and progression of the disease.
RISK FACTORS N/A
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DIAGNOSIS
DIFFERENTIAL DIAGNOSIS
• Degenerative myelopathy
• Lumbosacral instability
• Bilateral stifle disease
• Panosteitis
• Polyarthropathies
CBC/BIOCHEMISTRY/URINALYSIS N/A
OTHER LABORATORY TESTS N/A
IMAGING
• Radiography--ventrodorsal, hip extended radiographs are commonly used for diagnosis of hip dysplasia. Sedation or general anesthesia may be required for accurate positioning. Radiographic signs in early disease include subluxation of the hip joint with poor congruence between the femoral head and acetabulum. The shape of the acetabulum and femoral head are normal initially, however; the acetabulum becomes shallow and the femoral head begins to flatten and the disease progresses. Radiographic evidence of degenerative joint disease eventually develops, including flattening of the femoral head, shallow acetabulum, periarticular osteophyte production, thickening of the femoral neck, sclerosis of the subchondral bone, and periarticular soft-tissue fibrosis.
• Distraction radiographs can be used to quantify joint laxity and may accentuate the laxity for more accurate diagnosis of hip dysplasia.
• Dorsal acetabular rim radiographs allow evaluation of the acetabular rim and assessment of dorsal coverage of the femoral head.
OTHER DIAGNOSTIC PROCEDURES N/A
GROSS AND HISTOPATHOLOGIC FINDINGS
The femoral head and acetabulum appear normal early in the disease. Joint laxity and excess synovial fluid may be appreciated grossly. As the disease progresses, the acetabulum and femoral head are malformed and gross and histopathologic signs of synovitis and articular cartilage degeneration develop. Full thickness cartilage erosion may be present in chronically affected dogs.
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TREATMENT
INPATIENT VERSUS OUTPATIENT
• Treatment options for dogs with hip dysplasia are conservative medical therapy and surgery.
• Preferred treatment depends on the dog's size, age, intended function, severity of joint laxity, the presence or absence of degenerative joint disease, clinician's preference, and the financial considerations of the owner.
• Patients are treated as outpatients unless surgery is performed.
ACTIVITY
• Exercise should be limited to the individual tolerance of the patient.
• Swimming is recommended to maintain joint mobility while minimizing weight bearing.
• Physiotherapy (passive joint motion) will reduce joint stiffness and help maintain muscle integrity.
DIET
Weight control is important to reduce the load applied to the painful joint and minimize weight gain associated with reduced
exercise.
CLIENT EDUCATION
• Discuss the heritability of the disease.
• Medical therapy is palliative because the joint instability is not corrected. Joint degeneration often progresses unless corrective osteotomy procedure performed early in the disease.
• Surgical procedures can salvage joint function once severe joint degeneration is present.
SURGICAL CONSIDERATIONS
• Triple pelvic osteotomy is a corrective osteotomy procedure designed to re-establish congruity between the femoral head and acetabulum. The acetabulum is rotated in the immature patient (6-12 months) to improve the dorsal coverage of the femoral head and correct the forces acting on the joint. This will minimize the progression of degenerative joint disease and may allow development of a more normal joint if performed early (before severe degeneration develops).
• Total hip replacement is indicated to salvage function in mature dogs with severe degenerative disease unresponsive to medical therapy. Studies have indicated that pain-free joint function returns after total hip replacement in >90% of cases. Approximately 80% of cases require only unilateral joint replacement for acceptable function. Complications reported after hip replacement include luxation, sciatic neuropraxia, and infection.
• Excision arthroplasty is the surgical removal of the femoral head and neck and is used to eliminate joint pain. Results are consistently better in smaller, lighter dogs (<20 kg), and those with good hip musculature. After joint pain is eliminated, however, a slightly abnormal gait often persists. Postoperative muscle atrophy is common, particularly in large dogs. Excision arthroplasty is primarily used as a salvage procedure when severe degenerative joint disease is present and pain cannot be controlled medically, or when total hip replacement is cost prohibitive.
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MEDICATIONS
DRUGS AND FLUIDS
Medical therapy for hip dysplasia includes analgesics and anti-inflammatory medications to minimize joint pain (and stiffness and muscle atrophy caused by limited usage) and reduce synovitis. The biomechanical abnormality within the hip joint is not corrected, however, and the degenerative process will likely progress. Frequently, medical therapy provides only temporary relief of signs. Aspirin (10-25 mg/kg, q8h-q12h), meclofenemic acid (1.1 mg/kg divided q12h for 1 week, then maintenance) and Piroxicam (10-20 mg daily, taper down to maintenance) have been advocated.
CONTRAINDICATIONS
Corticosteroids should be avoided because of the potential side effects and the articular cartilage damage associated with long term use.
PRECAUTIONS
Gastrointestinal upset may occur with the use of nonsteroidal anti-inflammatory drugs and may preclude their use in individual cases.
POSSIBLE INTERACTIONS N/A
ALTERNATE DRUGS
Polysulfated glycosaminoglycans has been shown to have a chondro-protective effect in dogs with degenerative joint disease but has not been fully evaluated for treatment of hip dysplasia.
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FOLLOW-UP
PATIENT MONITORING
Clinical and radiographic monitoring to assess progression of hip dysplasia is recommended. Clinical deterioration suggests an alternate dosage, alternate medication, or surgical intervention is indicated. Patients treated by triple pelvic osteotomy are monitored radiographically to assess osteotomy healing, implant stability, joint congruence, and progression of degenerative joint disease. Patients treated with hip replacement are monitored radiographically to assess implant stability.
PREVENTION/AVOIDANCE
Hip dysplasia is best prevented by not breeding affected dogs. Pelvic radiographs can help identify phenotypically abnormal dogs but may not identify all dogs carrying the disease. Dam/sire breedings that result in dysplastic offspring should not be repeated.
POSSIBLE COMPLICATIONS N/A
EXPECTED COURSE AND PROGNOSIS
Joint degeneration usually progresses, though most dogs can lead normal lives with proper medical or surgical management.
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MISCELLANEOUS
ASSOCIATED CONDITIONS N/A
AGE RELATED FACTORS N/A
ZOONOTIC POTENTIAL N/A
PREGNANCY
Dogs with hip dysplasia should not be bred. If a dysplastic bitch becomes pregnant, the added weight may exacerbate clinical