Hip Dysplasia

Condition Overview

Hip dysplasia is the most common cause of rear leg lameness in dogs. The highest incidence occurs in large breed dogs including St. Bernards, Newfoundlands, Rottweilers, Chesapeake Bay Retrievers, Golden Retrievers, German Shepherds, Labrador Retrievers, and many others.

Symptoms

Dogs with hip dysplasia are born with hips that appear normal but progressively undergo structural changes. The age of onset is 4 - 12 months. Affected puppies may show pain in the hip, walk with a limp or swaggering gait, bunny hop when running, and experience difficulty in the hindquarters when getting up. Pressing on the rump can cause the pelvis to drop. With the puppy on his back, the rear legs may not extend into the frog-leg position without causing pain.

All symptoms +

Causes

Hip dysplasia is a polygenic trait. This means, more than one gene controls the inheritance. Environmental factors such as diet are also involved. The hip is a ball-and-socket joint, with the ball being the head of the femur (upper leg bone) and the socket is in the pelvis.

Preventing hip dysplasia in a bloodline is absed on selective breeding practices. Hip dysplasia is a moderately inheritable condition. It is 2x more common among littermates who have one dysplastic parent. Experience shows that repeatedly using only dogs with normal hips for breeding stock significantly reduces the incidence of hip dysplasia in susceptible bloodlines.

Diagnosis

An X-ray of the hips is the only reliable way of determining whether a dog has hip dysplasia. Dogs must be 24 months of age or older to be tested. Some female dogs will show subluxation (dislocation) wen X-rayed around an estrus cycle, so OFA recommends not X-raying females around a heat peroid or within 3 - 4 weeks of weaning a litter.

Good X-rays require heavy sedation or anesthesia. The standard view is taken with the dog lying on his back with his rear legs parallel and extended. The knees (stifles) are rotated internally. Care is taken to be sure the pelvis is not tilted.

Hip dysplasia is graded according to the severity of X-ray findings. In ideal hips, the femoral head fits tightly into a well-formed hip socket with a minimum of space between the head of the femur and the hip socket. The hip ball is almost completely covered by the socket.

Normal hips are rated excellent, good, or fair, depending on how closely they match the ideal. Dysplastic hips are rated mild, moderate, or severe. If the findings are not clear, the hips are rated borderline.

In a dog with mild hip dysplasia, the X-rays will show mild subluxation (increased space in the joint) with the hip ball partway out of the socket. There are no changes associated with degenerative arthritis.

In a dog with moderate hip dysplasia, the hip ball is barely seated into a shallow socket. Arthritic changes begin to appear. These include wear and flattening of the femoral head, a rough appearance to the joint surfaces, and the beginning of bone spurs.

In a dog with severe hip dysplasia, the head of the femur is completely out of the joint and arthritic changes are marked. Once arthritis is noted, the condition is irreversible - however, even with arthritis, some dogs are not lame. The onset of lameness is unpredictable, and some dogs may go the rest of their lives with dysplastic hips but no lameness. Others develop lameness as puppies.

A genetic test for hip dysplasia that is applicable for a number of breeds is under development through VetGen. However, the mode of inheritance is still not clearly understood, making the development of this test difficult.

Treatment

Hip dysplasia is treated both medically and surgically. Medical treatment includes restricting activity and giving an NSAID analgesic such as Rimadyl, and a joint chondroprotectant such as Cosequin or Adequan to relieve pain and inflammation and to repair damaged cartilage. Weight loss and moderate exercise are also important.

It is important to exercise lame dogs on a leash and not allow them to run, jump, or play as long as they exhibit pain. Swimming is an excellent exercise that improves muscle mass and joint flexibility without over-stressing the hips.

After reviewing the X-rays, your veterinarian may recommend hip surgery. Early surgery in selected puppies can prevent some cases of degenerative joint disease. Surgery is also indicated for dogs who continue to experience pain and lameness despite medical treatment.

There are 5 surgical options and technical factors determine the choice. Triple pelvic osteotomy and femoral osteotomy are two operations performed on puppies who do not have degenerative joint changes. The goal of both is to position the femoral head more deeply in the acetabulum. Normal joint function is thus maintained and arthritis may not develop, although this is not always the case.

Pectineus myectomy is a relatively simple operation in which all of the pectineus muscle is removed on both affected sides. This operation does not slow the progress of joint disease, but does relieve the pain for some time.

Femoral head and neck excision arthroplasty is an effective operation that provides relief for intractable hip pain. The head of the femur is removed, allowing a fibrous union to replace the ball-and-socket joint. The operation is usually reserved for dogs that weight less than 36lbs.

Total hip replacement is the most effective procedure for dogs 9 months and older who have disabling degenerative joint disease in one or both hips. The operation removes the old joint and replaces it with a new, artificial joint. The procedure requires special equipment and is usually performed by an orthopedic specialist. Good results are obtained in more than 95% of cases.

Dorsal acetabular rim arthroplasty - building up the acetabular rim with bone from other sites in the body to create a deeper socket - is another surgical option that is currently the subject of investigational studies.

Prevention

Preventing excessive weight gain in puppyhood sand keeping the puppy from placing undue stress on the hips will delay the onset of hip dysplasia is many dog with a genetic pre-disposition. It may also lead to a much less severe form of the disease.

Feed puppies a quality food in amounts appropriate for normal growth. Puppies known to be at risk should be fed a calorie-controlled diet. Overweight puppies should be given a calorie-restricted diet.

Feeding a very high-calorie diet to growing dogs can exacerbate a predisposition to hip dysplasia, because the rapid weight gain places increased stress on the hips. Being overweight supports the genetic potential for hip dysplasia, as well as other skeletal diseases. A diet with an imbalance of calcium and phosphorous is bad for bone development.

Inappropriate exercise during the period of rapid bone growth can also spark symptoms of hip dysplasia. Young dogs should be discouraged from jumping up and down from heights in situations where they land on their back legs (such as jumping to catch a ball), and from standing up on their back legs. They should also avoid running on pavement.

The OFA maintains a hip dysplasia registry for purebred dogs. An OFA-certified radiologist will help review hip X-rays taken by your veterinarian and if the conformation of the hips is normal for the breed, certify the dog as excellent, good, or fair and assign him an OFA number. As an optional step, you can have the OFA number added to your dog's AKC registration papers.

The OFA registry is a confidential registry and remains confidential unless the owner marks off on the application that all results may be made public.

Dog breeders often request preliminary evaluation on hip status before selecting puppies for show and breeding stock. The OFA accepts preliminary X-rays for puppies as young as 4 months of age. Their own analysis reveals that these evaluations are about 90% accurate when compared with follow-ups at 24 months of age.

Another method of evaluating hips was developed at the University of Pennsylvania Veterinary School and is now administered by PennHip via the University of Pennsylvania. PennHip X-rays are taken using the traditional OFA views, but additional views are also required. Distraction pressure is applied with special techniques to look for joint laxity by seeing how much the joint can be distracted (pulled apart). This is done very carefully and to a set standard. These views are used to gauge joint laxity, which can be measured in puppies starting at 16 weeks of age. The joint laxity does not change as the dog ages.

Dogs X-rayed for PennHip measurements are compared only to other dogs of the same breed. Your dog then receives a joint laxity distraction index (DI) number, ranging from 0.0 (perfect) to 1.1 (severely dysplastic). PennHip suggests that only dogs in the top half for their breed with respect to joint laxity be used for breeding. Those dogs who fall into the lower half, which are the ones with the loosest hips, have a greater chance of developing hip dysplasia in the future. In general, dogs with a DI score of .3 or less are unlikely to develop degenerative joint disease.

Finally, the Institute for Genetic Disease Control (GDC) in Animals maintained a separate hip dysplasia registry

Support

Please contact your veterinarian for more information regarding this condition.