What is hip dysplasia?
It is a progressive degenerative condition caused by a “poorly formed hip”. The hip joint is a “ball and socket joint”: the “ball” is the femoral head (top part of the thigh bone) and the “socket” (acetabulum) is in the pelvis. Hip dysplasia occurs when the femoral head does not fit into the acetabulum properly. The pain associated with hip dysplasia is caused when the femoral head pulls away from the joint and rides on the rim of the socket. This is called subluxation (partial dislocation). In response to this instability, the body forms scar tissue and bony changes occur. The ultimate outcome is degenerative joint disease (DJD), i.e. arthritis.
What causes hip dysplasia?
Hip dysplasia is the most common inherited orthopedic disease in large breed dogs. The exact genes involved have not been identified, but it is known that it is polygenic (caused by many different genes). Dogs with hip dysplasia should not be used for breeding, but unaffected dogs can yield dogs with the condition. Nutritional factors (high calorie/ supplemented foods, over feeding, fast growth rate, etc.) and excessive exercise programs (long distance running, jumping, etc.) contribute to hip dysplasia.
How can you screen for hip dysplasia?
Diagnosing hip dysplasia on physical examination is difficult and a presumptive diagnosis at best. Radiographs (x-rays) are necessary. Sedation or anesthesia is required to ensure proper positioning of the dog. Two different techniques are used to evaluate dogs: OFA (Orthopedic Foundation for Animals,) and PennHIP certification. Both of theses organizations have great, informative websites: www.offa.org and www.pennhip.org . With an OFA evaluation, the dog lays on its back with the legs pulled straight back and knees rolled toward each other. This forces the femoral head into the acetabulum. The hip joint is evaluated for conformation (how well the ball and socket fit together, shape of the femoral head and acetabulum), coverage (approximately 60% of the ball must be in the socket) and DJD signs. They will be reported as “Excellent, Good, Fair, Dysplastic”. All evaluations performed in dogs less than 2 years old are preliminary. PennHIP evaluations can be done on puppies as young as 16 weeks. Two radiographs are taken: one with the femoral heads compressed (pushed into the acetabula as far as they will go) and one with the femoral heads distracted (pulled out of the acetabula as far as they will go). A measurement called a distraction index is calculated from these radiographs, the idea being that a tighter fitting hip (one allowing less distraction) is less likely to develop dysplasia. Each dog breed has a different range of distraction indices that are considered acceptable.
How is hip dysplasia treated?
The degree to which the hips are dysplastic does not always correlate with the amount of pain. Since there is no cure for hip dysplasia, the goal of treatment is pain management. Medical management includes anti-inflammatory drugs, acupuncture and nutriceuticals such as glucosamine. Surgical management includes TPO (triple pelvic osteotomy), FHNO (femoral head/neck ostectomy), total hip replacement, and DARthroplasty (dorsal acetabular rim transplant).
B Kramer DVM