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Home » Pumi health

What is canine hip dysplasia?

Submitted by on Mar 17, 2010 – 3:09 PMNo Comment
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Canine hip dysplasia (CHD) is one of the most baffling diseases afflicting dogs today. The word dysplasia is already a little bit intimidating in itself, and non-medical people seem to assume that the disease is very complicated. Actually, the problem is quite simple. It’s the solution that’s everybody’s confused about, the medical profession included. Despite extensive research into the condition, many questions remain unanswered for.

The purpose of this series of articles is to review the current knowledge on the development of hip dysplasia, including factors modifying its development, as well as current diagnostic techniques and treatment options. Furthermore, we will consider its significance in breeding programs by revealing the findings of our extensive research into the hip dysplasia situation in the Finnish and Hungarian pumi population. This is part one in our series on canine hip dysplasia.

Hip jointHip dysplasia is a disease that affects the development of the hip joint in a young dog. (Dysplasia, a Greek word used in medicine, simply means “abnormal formation”, so it is necessary to always name the affected joint when we talk about an actual disease.) To understand the condition, let’s look first at the hip joint of the dog. It forms the attachment of the hind leg to the body with a “ball and socket” joint. The ball portion is the head of the femur, the long
bone between hip and knee. The socket, called the acetabulum, is located on the pelvic bone. These two form the joint of a normal dog where the ball rotates freely within the socket. To facilitate movement, the bones are shaped to perfectly match each other with the socket surrounding the ball.
To strengthen the joint, the two bones are held together by a ligament going directly from the femoral head into and attaching to the acetabulum. Also attaching to both bones and completely encircling the joint is the joint capsule. This thick band of connective tissue additionally acts to hold the bones together. The area where the bones actually touch each other is called the articular surface. It is perfectly smooth and cushioned with a layer of spongy cartilage. In the normal dog, all of these factors work together for smooth and stable joint function.

Puppies are born with perfectly normal hips as described above. The ball-and-socket joints of an affected puppy radiographically appear to be structurally and functionally normal at birth, so the hips of an affected puppy are indistinguishable from a normal puppy at birth. Hip dysplasia is brought about by theabnormal development of the soft tissues that surround the joint as the puppy grows, i.e. the laxity of the muscles, connective tissue, and ligaments that should support the joint. The most important result of the change is that the two bones are not held in place but actually move apart. The joint capsule and the ligament between the two bones also stretch, adding further instability to the joint. As this happens, the articular surfaces of the two bones lose contact with each other. The slight separation of the two bones of the joint is called subluxation; this causes all of the resulting problems we associate with this disease.

BAll-and-socket jointIt is important to remember that if two bones lose their normal position in relationship to each other within any joint, their articular surfaces no longer correctly contact each other. The surrounding muscles of the dog’s joint work to force the bones back together but they are never totally successful. Because of the dog’s weight, the femoral head often rides up onto or over the rim of the socket. With every movement of the leg, there are now two abnormal areas of bone grinding against each other instead of contacting on a smooth articular surface.

Hip dysplasiaWherever these bones come in contact, new abnormally-shaped bone will grow. It is a vicious cycle; new bone growth causes further irritation which causes more abnormal bone growth. This is what we refer to as arthritis and it is usually a very painful condition. The femoral head that once looked like a smooth billiard ball now looks more like a head of cauliflower. The acetabulum (socket) that was once deep enough to enclose the femoral head is now shallow due to the grinding away of the rim. The edge is covered with bone spurs. As the condition progresses, more new abnormal bone forms and along with it comes further pain and distortion of the bone.

There are infinite variations of abnormality - ranging from only very slight changes from normal to complete dislocation, affecting either or both the right and left hip joints. The signs of hip dysplasia usually start to show between 5 and 13 months of age and range from mild discomfort to extreme pain when using the hind limbs. Signs of hip dysplasia in young dogs are generally thought to be from small irritations or even minor fractures occurring in the bone spurs that form around the socket. Fractures may be caused by the pup’s increasing weight or exercise.
Sudden periods of discomfort usually follow prolonged activity or when the dog gets up or lies down. Later in life the signs become more consistent, noted daily regardless of activity levels. Adult dogs that are in severe
pain will usually decrease their activity. They are unwilling to run or climb stairs and, with decreased use, the muscles of their rear legs atrophy and become weakened. A few will learn to alter their gate and posture, often showing little or no signs of discomfort even though the bone changes, the arthritis of the deformed joints and chronic irritation are severe.

Hip dysplasia is a disorder that has been proven, positively, to have a genetic basis. How much of a genetic origin in each case can vary – studies have shown that CHD’s heritability factor ranges from .25 to .85. A condition that is completely determined by genetics, for example gender, has a heritability factor of 1. A condition totally unaffected by genetics, for example a burn, has a heritability factor of zero. In view of this, 0.25 to 0.85 is a significant genetic contribution.

The heritability factor for a given dog is the result of a combination of the heritability factors from each parent. Simply put, if the parents are carrying genetic material for hip dysplasia, so will the offspring. The greater the genetic contribution for loose hips or malformed bone or abnormal muscle mass from the parents, the greater the chances for hip dysplasia in the offspring.

The expression of hip dysplasia in any dog has other determinants, though; genetics play only a varying role in the total picture. The effect of the developing dog’s environment (including nutrition, physical activity, even bedding) does play a role in the clinical, observable signs of hip dysplasia, although just like the genetic component
the effects of environment are variable and not completely understood. It is possible for a dog with known genetic components for hip dysplasia to not show any clinical signs of trouble if the environmental factors are favorable. So the dog can be dysplastic and not show observable signs of it until middle or old age – that is, only after it has been used for breeding.

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