Hip scoring, dysplasia and osteoarthritis are terms that you may come across frequently when thinking about getting a new puppy, researching new breeds or simply wondering why your own dog is a little bit slower to get up or has an unusual hindlimb gait.
Hip dysplasia is the abnormal development of the coxofemoral (hip) joints. It is a condition seen mostly in larger dog breeds, most commonly German Shepherds, Golden Retrievers and Labradors. However, the condition can occur in any breed and infrequently occurs in cats too.
Hip Dysplasia is not immediately evident at birth. This syndrome is developmental and progresses with age. There is a significant genetic component to hip dysplasia hence the importance of hip scoring and selective breeding. There are however other influences such as environmental influences. A good example of this would be over-feeding. Over-nutrition during a puppy’s first year of life, in which rapid growth of the bones and joints occurs, is thought to contribute to the development of dysplastic hips.
The pathophysiology of hip dysplasia includes multiple variables and the disease can be unilateral or bilateral and range in severity. The coxofemoral joint can be thought of as the ball (the femoral head) and the socket (the acetabulum) joint (see figure 1).
The primary abnormality in these dogs is poor congruency of the coxofemoral joint (figure 2), in other words the ball does not sit in place as it should. This can lead to instability and the abnormal exertion of forces on the cartilaginous linings of the joint.
The earliest changes noted include the erosion of the cartilage on the femoral head and acetabulum, joint effusion where fluid builds up in the joint and thickening of the ligament on the femoral head. These changes cannot be detected with X-rays, however, clinical signs might include a swaying hindlimb gait, reduced range of motion in the hip joints and reluctance to climb stairs. As the disease progresses, the body attempts to stabilise the lax joint by producing new bone around the femoral head, neck and acetabulum (figure 3).
The bone underlying the damaged cartilage hardens, a process known as sclerosis. As more new bone is deposited around the joint, the femoral neck becomes thickened and the head loses its rounded shape. These degenerative changes are collectively called ‘osteoarthritis” and are the cause of pain and reduces mobility.
Unfortunately, there is no method of reversing osteoarthritic changes once they have developed. Treatment options include certain surgical procedures which either remove, alter, or replace the painful, dysplastic joint, or medical therapy to reduce pain and improve mobility. Due to the heritable component, ‘hip scoring’ of higher risk breeds prior to breeding is important. This involved potential breeding animals having a set of radiographs (X-rays – PennHIP) taken by a certified veterinarian or veterinary technician where the hips are forced into both compressed and distracted positions. The radiographs are sent to the USA to measure the degree of laxity of the hips and determine if there are already signs of osteoarthritis. A numerical value called the ‘distraction index’ is then assigned to each dog. Not only does the distraction index quantitively measure the laxity in each joint, it has been shown to correlate with the risk of developing osteoarthritis in the future. This makes in an excellent test for young dogs with PennHip being able to be performed as early as 16 weeks of age.
Hip Dysplasia is a debilitating disease that can significantly limit an animal’s quality of life. Ethical and responsible breeding with testing of potential parents, appropriate early nutrition and limited high intensity activity during growth are all important factors in reducing the incidence of hip dysplasia.
If you are considering a new puppy, have questions about hip scoring or are worried about the hip health of your existing furry friend, consultation with your veterinarian is highly recommended.