Hip dysplasia (canine)

In dogs, hip dysplasia is an abnormal formation of the hip socket that, in its more severe form, can eventually cause lameness and arthritis of the joints. It is a genetic (polygenic) trait that is affected by environmental factors. It is common in many dog breeds, particularly the larger breeds, and is the most common single cause of arthritis of the hips. During growth, both the ball (the head of the femur, or thighbone) and the socket in the pelvis (acetabulum) must grow at equal rates. In hip dysplasia, this uniform growth during puppyhood does not occur. The result is laxity (looseness) of the joint, followed by degenerative joint disease (DJD) or osteoarthritis (OA), which is the body's attempt to stabilize the loose hip joint. In the normal anatomy of the hip joint, the almost spherical end of the femur head (the caput, or caput ossis femoris) fits into the acetabulum (a concave socket located in the pelvis). The bony surfaces of the femur head and of the acetabulum are covered by cartilage. While bones provide the strength necessary to support body weight, cartilage ensures a smooth fit and a wide range of motion. Normal hip function can be affected by congenital conditions such as dysplasia, trauma, and by acquired diseases such as osteoarthritis and rheumatoid arthritis. The hip could have major contractions from dysplasias. The caput is not deeply and tightly held by the acetabulum. Instead of being a snug fit, it is a loose fit, or a partial fit. Secondly, the caput or acetabulum are not smooth and round, but are misshapen, causing abnormal wear and tear or friction within the joint as it moves. The body reacts to this in several ways. First, the joint is continually repairing itself and laying down new cartilage. However, cartilage repair is a relatively slow process, the tissue being avascular, so the joint may suffer degradation due to the abnormal wear and tear, or may not support the body weight as intended. The joint becomes inflamed and a cycle of cartilage damage, inflammation and pain commences.