P. 589

A. Pozzi1
1Clinic for Small Animal Surgery, Department of Small Animals, Vetsuisse-Faculty, University of Zurich
Hip dyplasia (HD) is a common multifactorial, developmental disease of the hip joint in dogs. The disease has variable incidences depending on the breed and is a common cause for presentation of a dog with lameness. It is important for the veterinarian to have
an understanding of the etiology, pathophysiology, biomechanics, diagnostic techniques, and treatment options associated with HD. The veterinarian must
be able to explain the rationale behind diagnostic
and breeding programs, as well as, advise the client concerning treatment.
Many causes of HD have been proposed and investigated. It is now known that there is a genetic component to the disease. Dogs are predisposed
to development of HD through a polygenic mode of inheritance. Affected dogs are predisposed to developing a biomechanical imbalance between muscle mass and skeletal stresses on the hip joint. However, other factors including nutrition, hormonal in uences, cell and matrix abnormalities, and environmental factors may be equally important in the development of HD. The dogs that are genetically predisposed to HD develop laxity in the hip as a result of a biomechanical imbalance between the forces on the joint and the associated muscles mass. The
laxity leads to incongruity in the joint, which eventually results in osteoarthritis. It is important to remember that the hip joint is normal at birth. During the  rst 60 days
of life, the muscles and nerves are functionally limited.
If the stresses of weight-bearing and activity exceed
the elastic limit of these tissues, the joint laxity results in irreversible incongruity during development. Stabilization of the hip is afforded by muscles, joint capsule, the round ligament, and the homeostatic hydrostatic pressure in the joint. When joint congruity is lost by insuf ciency of these structures, changes in joint shape can only be accomplished by the production or resorption of bone.
Diagnosis of HD is based on signalment, history, complete general physical examination, complete orthopedic examination, neurologic examination, and radiography. Traditionally, dogs presenting with signs of HD have been divided into 2 groups. Dogs of less than 12 months of age often present with a sudden onset of clinical signs including decreased activity, hip pain, gait alteration, and/or lameness attributed to joint effusion, ligament strain, synovitis, acetabular microfractures,
and/or articular cartilage loss. Older dogs most often present with chronic and insidious signs attributed
to osteoarthritis. Clinical signs in these dogs include lameness (especially after exercise), joint crepitus, restricted range of motion (especially extension), and muscle atrophy. It is important to remember that each dog must be evaluated on an individual basis as many clinical signs can vary and overlap between groups.
In the young dog early diagnosis is crucial. Both palpation technique and speci c radiographic techniques can be useful. Palpation techniques are helpful in establishing a diagnosis and deciding on a treatment plan. The Ortolani sign is a very useful technique for determining hip joint laxity and gaining information for potential treatment options. The technique can be performed on awake or sedated patients, but best results are obtained in anesthetized dogs. We strongly recommend that all patients of susceptible breeds be palpated for the Ortolani sign when anesthetized for neutering.
Speci c radiographic techniques have been developed to measure laxity in young dogs.
The University of Pennsylvania Hip Improvement Program (PennHIP) radiographic technique is a stress radiographic method intended to provide a quantitative means of determining hip laxity before the dog is 24 months of age. This method is intended to provide early and optimal predictive value by correlating joint laxity with subsequent incidence of CHD. A compression and a distraction
view are obtained using the PennHIP compression- distraction device with the patient under deep sedation or general anesthesia. The distance between the center of the acetabulum and the center of the femoral head is measured on both views using templates or gauges. This distance is divided by the radius of the femoral head; a numerical value between 0 and 1, the distraction index, is determined. The distraction index quantitates passive joint laxity. In some breeds, an increase in the distraction index has been correlated with an increased incidence
of OA associated with CHD. The dorsal acetabular
rim (DAR) radiographic view is another technique that was developed to evaluate the DAR using standard radiographic equipment and technique. The DAR
view was designed to address the failure of standard ventrodorsal and lateral radiographic techniques to isolate the weight-bearing portion of the acetabulum.
The value of the DAR view is in evaluating the DAR
for damage and secondary OA changes, correlating palpable joint laxity with observable radiographic  ndings, and displaying acetabular  lling. This technique has been proposed to provide an objective, reproducible method for determining whether a hip is normal, dysplastic, or injured by trauma.
An Urban Experience

   587   588   589   590   591