Hip dysplasia is the condition where the development of the ball (the head of the femur/thighbone called the caput femoris) and the socket in the pelvis (called the acetabulum) does not grow uniformly during the early developmental stages of the pup. This results in a loose joint, which is followed by degenerative joint disease or osteoarthritis.
In a normal hip the ball and the socket fit snugly and are lined with healthy cartilage that enables a smooth fit and enabling a wide range of movement.
In the case of hip dysplasias the ball is not held tightly by the socket, so it fits loosely or even worse only fits partially into the socket. The ball or socket can also not be smooth and round, but misshapen, which causes abnormal wear and tear or friction as the joint moves. The body will react by laying down new cartilage, but cartilage repair is a slow process because there are no blood vessels in these tissues, which means degradation will get worse over time and will not support the dog's bodyweight adequately. This leads to the joint becoming inflamed, and so a cycle of cartilage damage, inflammation and pain starts.
Causes and Effects
Hip dysplasia can be caused by an ill fitting femur into the pelvic socket, or develop due to poorly developed muscles in the pelvic area. The large and giant breeds of dogs are most susceptible to hip dysplasia, though there are many other breeds that also suffer from this phenomenon.
To reduce pain a dog will typically reduce the movement of that hip, so it is common to see such a dog "bunny hopping", where both hind legs move together or the dog will appear to be stiff all the time.
The cause of hip dysplasia in dogs are generally considered to be an inherited genetic trait. A Norwegian study that concluded in 2012 has conclusively proved that environmental factors play a large role in the occurence of hip dysplasia in dogs[1]. The study monitored 500 dogs and included four breeds, the Newfoundland, the Labrador Retriever, the Leonberger, and the Irish Wolfhound. The study found that pups born during spring and summer (cold Norwegian weather would result in less exercise by the pup), and that dogs that lived on acreage or small farms had a lower risk of developing hip dysplasia. The study also found that dogs that had to climb steps on a daily basis were at an increased risk of developing hip dysplasia. The labradors appeared to develop hip dysplasia later in life than the other three breeds.
A 2013 in the US has conclusively proved that early neutering of Golden Retrievers more than doubled the risk of developing hip dysplasia later in the animal's life[2]. The authors were careful to stress that this does not mean the results can be extrapolated to other breeds, but I believe it is safe to say that delaying neutering of your dog until adulthood, will increase the health of you dog in later years, especially if the animal is of a breed with genetic susceptibility to hip dysplasia. Other environmental factors that lead to the development of this problem is:
- Overweight condition
- Joint injury at a young age
- Overexertion of the hip at a young age
- Ligament tears at a young age
- Repetitive motion on a forming joint (such as jogging with too young a pup
Symptoms
Dogs with hip dysplasia may exhibit the following signs and symptoms:
- Decreased activity
- Decreased range of motion
- Difficulty or reluctance rising, jumping, running or climbing stairs
- Lameness in the rear end
- Looseness in the joint
- Narrow stance
- Swaying, "bunny hopping" gait
- Grating in the joint during movement
- Loss of thigh muscle mass
- Noticeable enlargement of the shoulder muscles as they compensate for rear end muscle loss
- Pain
- Stifness or soreness after rising from rest
- Partial or full dislocation of the hip joint
Summary
In summary it is apparent that the correct treatment of your young pup, especially if it is of a breed with a known historic susceptibility to hip dysplasia, is very important. It is important to exercise your pup carefully, but not overexert it. Also it appears to be wise to postpone neutering of your dog to adulthood to ensure you do not interrupt the important role that the gonadal hormones play in your pup's development. For some tips on exercising your dog see our blog post article on the importance of walking your dog or our tips for runners.