Hip dysplasia is the number one cause of hind limb lameness in dogs and results in an arthritic condition of the hip joint which is initially caused by a laxity (looseness) in the hip joint itself. This joint is a ball and socket joint in which the head of the thigh bone (femur) fits into a cup-like depression (acetabulum) in the pelvis. The laxity is associated with the tissues which surround and hold the joint in place, that is, the tendons, ligaments, connective tissue, and muscle, and this laxity leads to bony abnormalities of the ball and socket. While the laxity of the joint is not thought to change much with time, the presence of joint instability causes abnomal wear and tear on the cartilage lining of the joint with subsequent development of arthritis as the dog ages. Indeed, the Orthopedic Foundation for Animals (OFA) believes that there is little change in the test for dysplasia after 4 months of age; however, they require testing at two years of age or older for certification purposes, to err on the side of caution.Clinical signs can be extremely variable -- from no symptoms to severe lameness. Severity of arthritic changes on radiographs (X-rays) does not necessarily correlate with degree of lameness. Diagnosis is made from radiographs of the hip joint (from the pelvis to the kneecap) and does require sedation or anesthesia. Positioning of the dog is critical for proper evaluation. The radiographs are evaluated by veterinary radiologists specially trained for this task. The dogs are graded as excellent, good, fair, borderline, or mildly, moderately, or severely dysplastic. A newer method of evaluating hip joint laxity called PennHIP has been developed at the University of Pennsylvania School of Veterinary Medicine. This involves a different method of positioning the dog and uses a distraction device that is fitted to the dog during the procedure. Three views are taken, including a compression view, a distraction view and the standard (OFA) extended view. From the radiographs, the dog is assigned a DI or distraction index from 0-1.0, with values of 0.3 or below considered NOT at high risk for developing dysplasia. The dog is also ranked with other members of its breed in a percentile. (A dog ranking in the 80th percentile has 20% of its breed showing tighter hips.) This test can be performed at 16 weeks of age, but the originators of the method admit greater reliability if the test is performed later (at one year). Hip dysplasia is thought to be genetically determined in part, but the mode of inheritance has not been established, since multiple genes and environmental factors such as nutrition and rapid growth may play a role in its development. While some have questioned the frequency and severity of hip dysplasia in the boxer, many owners are now testing their dogs. The OFA currently reports the boxer as 67th in incidence of dysplasia (among breeds where over 100 dogs have been tested) with 2.9% of boxers testing excellent and 11.3% dysplasitic. The OFA Web Site athttp://www.offa.org, or the PennHip website at http://www.vet.upenn.edu/ResearchCenters/pennhip/what_is_ph.html are sources of additional information. This and other information is best discussed with your own veterinarian.