Canine hip dysplasia is a joint problem that can affect any dog but is most common among large breeds. 
Canine hip dysplasia can be caused by hereditary or environmental factors, or a combination of the two. It most often affects dogs under the age of two, although it can affect dogs of any age.
In a healthy, normal hip joint the head of the femur (thigh bone) fits into a hollowed space in the pelvis, or hip bone. Both the head of the femur and the hollow of the hip, or the acetabulum, are coated with cartilage and surrounded by a thick fluid. These two forms of cushioning help the joint to move smoothly. In order for the joint to work properly, the angle of the head of the femur must align with the acetabulum in such as way that the dog's weight is properly supported.
Canine hip dysplasia results when the hip joint relaxes to the point that the properly alignment between the femoral head and the acetabulum cannot be maintained. This causes friction within the joint, often leading to osteoarthritis.
Most dogs afflicted by canine hip dysplasia are born with healthy hips. 
While there are genetic factors involved, not all dogs of breeds prone to hip dysplasia will develop it. Likewise, some dogs of breeds not normally prone to the disorder may develop it as well. Along with genetic factors, two of the biggest contributors to hip dysplasia development appear to be rapid growth and rapid
weight gain.
Dogs diagnosed with canine hip dysplasia may be treated with medicines such as glucosaminoglycans, or may require surgery. Surgical reconstruction of the hip joint is highly successful when it is done while a puppy is still growing. For cases of canine hip dysplasia diagnosed after a dog has finished growing, pain management is generally the main course of action. In some cases, surgery will still be performed but it may not be as successful as surgeries on younger dogs. In dogs that have finished growing, surgery usually means replacing rather than reconstructing the hip.
