Hip dysplasia is a congenital disease that, in its more severe form, can eventually cause lameness and painful arthritis of the joints. A combination of genetic and environmental factors cause arthritis and hip dysplasia. It can be found in many animals and, rarely, humans, but is common in many dog breeds, particularly the larger breeds. In the normal anatomy of the hip join, the thigh bone (femur) joins the hip in the hip joint, specifically the caput ossis femoris. The almost spherical end of the femur articulates with the hip bone acelabulum, a partly cartilaginous mold into which the caput neatly fits.
It is important that the bony part of the acetabulum carries the weight of the body, not on the cartilage component because otherwise, the caput can glide out of the acetabulum, which is very painful. Such a condition also may lead to maladaptation of the respective bones and poor articulation of the joint. In dogs, the problem almost always appears by the time the dog is 18 months old. The defect can be anywhere from mild to severely crippling. It can cause severe osteoarthritis eventually as well as compensatory injury to other areas of the body.