Dysplasia is the abnormal growth or structure. A hip dysplasia is a genetic condition characterized by alteration and malformation of hip joint. The hip is a ball-and-socket joint; the ball is the head of the femur and the socket is the acetabulum of the pelvis. The hip joint forms the attachment of the hind leg to the body. Hip dysplasia occurs when the ball and socket do not fit snugly; instead it is a loose or partial fit. In a dysplastic hip, the head of the femur fits loosely into a poorly developed, shallow acetabulum.
The bone of the thigh (femur) has a ball that fits into a socket (acetabulum) formed by the pelvis. This type of arrangement forms a very strong joint that allows a great range of motion and weight-bearing. But for it to work properly, the ball must be held deep and snuggly within the socket. There are a series of very strong ligaments and cartilaginous layers that are supposed to do that. When they don't, the pet becomes dysplastic.
Hip dysplasia is a polygenic trait. That is, more than one gene controls the inheritance. Environmental factors such as diet are also involved. It normally occurs in medium to large size dogs although it is also seen in smaller dog breeds as well. Hip dysplasia can begin to develop as early as four months and worsen as puppy ages—or not show up at all until a dog has reached geriatric years. Generally, middle age dogs are more commonly affected by this condition.
Breeds with higher incidence of hip dysplasia include Great Dane, Saint Bernard, Labrador Retriever, and German Shepherd. There is no sex predilection.
The degree of joint looseness or laxation, joint inflammation and duration of the condition directly affect clinical signs and symptoms. Some common signs and symptoms include
Reluctance to run, jump, or climb stairs
Intermittent or persistent hind-limb lameness, often worse after exercise
“Bunny-hopping,” or swaying gait
Narrow stance in the hind limbs (back legs unnaturally close together)
Pain in hip joints
Joint looseness or laxity – characteristic of early disease; may not be seen in long-term hip dysplasia due to arthritic changes in the hip joint
Grating detected with joint movement
Decreased range of motion in the hip joints
Loss of muscle mass in thigh muscles
Enlargement of shoulder muscles due to more weight being exerted on front legs as dog tries to avoid weight on its hips, leading to extra work for the shoulder muscles and subsequent enlargement of these muscles