Canine Hip Dysplasia (CHD) is a crippling disease that affects the hip joints of large and small breeds alike. A dog with hip dysplasia has an abnormally developed ball and joint socket of the hip. The cupped part of the hip is too shallow to cover the ball of the femur. This malformation results in the hips becoming lax, and the femoral head can begin to wear the outside of the hip socket causing the dog pain. 
What causes Hip Dysplasia?
Some dogs are genetically predisposed to have hip dysplasia. A dog whose parents had CHD is much more likely to develop hip dysplasia, but it does not necessarily mean that the dogs will eventually suffer from CHD. There is some debate as to whether or not CHD can also be brought on by the dog’s environmental factors.
Some people believe that large breeds that grow too fast are especially predisposed to get CHD. Also dogs that are too heavy are more likely to suffer from hip dysplasia than those that are kept lean but not starving.
Others feel that dogs who get CHD were born that way and no environmental factors produced the effect.
Until CHD is completely eliminated from the domestic canine these debates will continue. 
What are the signs of hip dysplasia in dogs?
Symptoms of hip dysplasia include lameness, difficulty in standing, walking, or running after getting up, decreased activity, or a ‘bunny-hop’ gait. 
How can I know for sure my dog has CHD?
The only way to check for CHD is to have your vet x-ray your dogs hips. In cases of severe dysplasia your vet will be able to tell from these x-rays if the dog is positive. If the displasia is not obvious then the x-rays can be tested by two different methods.
OFA The most common of the two is getting a v/d (ventral/dorsal) view of the hips. The dog is sedated (usually), placed on its back, and the back feet are grasped and rolled inward. The hips are x-rayed in this position, and the x-rays are sent to the Orthopedic Foundation for Animals (OFA).
The OFA evaluates the x-rays and determines whether or not the dog is HD positive and the severity of the condition. 
PennHip The second method is the newer of the two; it is the PennHip method. In this method all dogs are sedated and x-rays are taken by PennHip certified vets.
PennHip tests the laxity of the hips and is not based upon a pass/fail system like the OFA’s method of testing. 
How can I treat it?
There are several ways to treat CHD. The treatment of the disease depends greatly upon the severity of the CHD, the amount of pain your dog is in, and the amount of money you can afford to spend.
Medication The least expensive way to treat CHD is with medication. Drugs like Rimadyl and Arthricare are good anti-inflammatory/analgesic medications and are easy to administer.
Medication is not a long term solution because, medication meerly suppresses the dog’s pain and doesn’t actually heal or reduce the wear and tear on the joints. However, it can be helpful in senior dogs in which surgery would be risky to keep them mildly comfortable until the end.
Femoral Head Ostectomy (FHO) This is the cheapest operation that is available to treat CHD. An FHO involves the removal of the femoral head (ball). Removing the femoral head eliminates the bone on bone contact that is causing the dog to be uncomfortable. This surgery is recommended for dogs weighing less than 50 pounds but can also be effective in dogs over that weight.
Anti-inflammatory drugs are also recommended in conjunction with this surgery.
Triple Pelvic Osteotomy (TPO) TPO is found to be the best approach to use in young dogs. It involves cutting the pelvis in three places and rotating it to allow normal function with less arthritis. When a TPO is done at the proper developmental stage it can be a lifelong solution to the CHD problem. 
Total Hip Replacement (THR) This is the most expensive of hip surgeries and is recommended for adult dogs that are severely dysplastic. Although it is generally cheaper to have this surgery done at a vet school, the cost still averages about $1000 for each hip.
A THR involves the replacement of the hips with a prosthetic hip which is composed of three parts – the femoral stem, the femoral head, and the acetabular cup.
Over 95% of the dogs who have a THR are able to function normally after the surgery. You get what you pay for. 
How can I prevent CHD?
Although environmental effects (nutrition and exercise) can delay the onset of the physical signs of CHD, it is still a genetic disease. The only way to prevent CHD is to buy from a breeder who is rigorous when it comes to his/her breeding program and breeds only dogs from litters with no CHD. Even then it is impossible to be 100% sure that your dog is not genetically predisposed to get CHD.
Until hip dysplasia is eliminated it is important to keep your puppies lean and avoid excessive exercise (even nomal exercise can increase the amount of physical expression in a dog that is genetically predisposed to CHD).
Avoid calcium supplementation.
Also there is really no conclusive evidence that Vitamin C can prevent CHD, but it can provide some relief to dogs who are dysplastic. 
Biomedtrix – Questions About Total Hip Replacement
Sirius Dog – Canine Hip Dysplasia
More sites dealing with CHD