Definition of Hip Dysplasia

Hip dysplasia is a common disorder in domestic dogs that involves abnormal development and/or degeneration of the coxofemoral (hip) joint. “Dysplasia” simply means an abnormality of development in terms of size, shape or organization of mature cells in the body. The “hip” is the area of the body around the articulation of the large, long thigh bones (the femurs) and the pelvic bone. The “hip joint” is the ball-and-socket joint formed between the head of the femur bone (called the ball of the femur) and a concave “socket” area of the pelvis called the acetabulum. It is thought that the immature hip joints of affected dogs have a genetic predisposition to subluxate (partially dislocate), which means that the ball of the femur comes out of the socket, causing abnormal forces across the hips, irregularly shaped bones, damaged articular cartilage (cartilage around a joint), microfractures and, in severe cases or in cases that start in mature dogs, degenerative joint disease. Another name for degenerative joint disease is osteoarthritis. Both terms refer to the progressive, noninflammatory and irreversible deterioration of articular cartilage.

Causes of Hip Dysplasia

Genetics almost certainly influence the occurrence of hip dysplasia in dogs, although the exact contribution of genetics is unclear. A combination of complex hereditary and environmental factors probably leads to looseness (laxity) of the hip joint, which in turn causes that joint to become unstable and accelerates the progressive degeneration of bone and cartilage. Young dogs who are predisposed to hip dysplasia usually are born with hips that appear normal but are not. Conformational abnormalities usually can be seen radiographically (by x-ray) within the first few weeks of life, and by 6 months or so young dogs typically start showing signs of rear limb lameness and gait abnormalities. Mature dogs that develop hip dysplasia later in life tend not to have conformational deformities of their pelvis from birth. Instead, they develop progressive joint degeneration as they age - basically the equivalent of osteoarthritis of the hip joint.

Prevention of Hip Dysplasia

According to current research, the best way to prevent hip dysplasia is to screen animals and remove them from the breeding population if they have radiographic evidence of hip dypslasia. This is still somewhat controversial, because dogs with excellent hips can produce dysplastic puppies, and dysplastic parents can produce puppies with excellent hips. However, since a genetic component to this condition is strongly suspected, cautious breeders will not use dysplastic dogs in their breeding programs, nor will they repeat particular breedings that produced dysplastic offspring. In addition, young, rapidly growing large and giant breed puppies should not be fed a diet that is extremely high in energy/protein, as that can contribute to growth-related bone, joint and cartilage disorders. All dogs should have their weight managed to prevent obesity, which can put undo stress and pressure on hips and other joints.

Special Notes

In young dogs, hip dysplasia usually is caused by conformational abnormalities that cause a “poor fit” between the head of the femur and the pelvic acetabulum, which in turn causes laxity of the hip joint. In older dogs, hip dysplasia typically is related to progressive degeneration and deterioration of bone and cartilage in the hip joint over time.