There are a number of factors which contribute to the development of hip dysplasia in the dog, some of which are better understood than others. These factors include genetic influences, nutritional factors, and certain hormones within the milk of the dam. Other unidentified factors are likely to be responsible. No single factor alone can be implicated in the development of hip dysplasia. Restriction of food intake has been shown to reduce the expression of the condition in genetically predisposed animals.
Diagnosis of hip dysplasia is generally made after signs of discomfort in the hind limbs are noticed. These can include difficulty or slowness rising, limping on one or both hind legs, reluctance to walk or play, or “bunny hopping” in the hind limbs. The diagnosis is sometimes made at a young age when the problem primarily consists of looseness of the hip, or sometimes at an older age when the looseness has resulted in arthritic changes in the joint.
The diagnosis is in part made by feeling the joint for pain and performing special maneuvers to feel any looseness in the joint. In addition, radiographs (x-rays) are used in the diagnosis.
There are a number of x-ray techniques that are used for diagnosis including OFA (Orthopedic Foundation for Animals) views, PennHIP views, and the dorsolateral subluxation score.
OFA views are the most standard and allow evaluation of the hip for any arthritic changes and will often demonstrate any looseness of the hip. However, sometimes the looseness of the hip can go unseen or be under appreciated on these views because there is no standard force pulling the hips out of their sockets.
The PennHIP views place a standard force on the hips to distract them, or pull then out of the socket. This allows calculation of a distraction index which is a measure of the looseness of the hips. This calculation is primarily used in the selection of breeding animals.
The dorsolateral subluxation score is figured by measuring the looseness in the hips from x-rays taken while the animal is in a weight-bearing position and sedated.
It is important that hip dysplasia can be mimicked closely by other orthopedic problems such as disk protrusion in the lower back or rupture of the cranial cruciate ligament in the knee.
Medical treatment of hip dysplasia consists of management of the arthritis. As the term implies, this is not a cure, but rather management of the symptoms of arthritis. There are three aspects of medical management. They include weight control, the use of anti-inflammatory medications, and exercise adjustment.
Weight control is extremely important. By reducing the weight of an animal, we can significantly reduce the stress seen by individual joints. This in turn will reduce the discomfort experienced by the dog. Studies have shown that weight reduction alone was successful in improving the comfort level of dogs with hip arthritis.
Medications are also an important part of arthritis management. The most commonly used medications are non-steroidal anti-inflammatory drugs (NSAIDs). These include aspirin, carprofen, deracoxib, etodalac, and meloxicam. They are effective in reducing the pain and inflammation associated with osteoarthritis. However, it is important to note that they do not affect the underlying disorder, they are merely symptomatic treatments.
Nutritional supplements for joint health are also used. The most common of these is Glucosamine and Chondritin Sulfate. The anti-inflammatory properties and pain reducing effects of these supplements have been fairly well documented in clinical studies. This is some evidence that they may also have a cartilage protective effect. However, the degree to which this is clinically important is still up for some debate. Other supplements include SAMe, Vitamin C, and a number of others.
The last part of medical management is exercise adjustment. This is different than exercise reduction. It is important to retain muscle mass in hip arthritis and so it is still important to have exercise. Low impact activities are ideal such as walking and swimming for dogs. Activities which are not ideal are activities such as playing with other dogs and fetch which include twisting, turning, starting, and stopping. For some dogs, these activities will be an important part of their quality of life. If they are, surgical intervention may be needed to allow them to return to these activities.
Surgical treatment can be broken down into two categories: procedures performed at a young age and procedures performed on severely arthritic joints.
The procedures performed at a young age are designed to help prevent the development of osteoarthritis in hips that are loose (preventative procedures). Procedures performed on severely arthritic joints are designed to relieve discomfort associated with the arthritis (salvage procedures). Juvenile Pubic Symphysiodesis and Triple Pelvic Osteotomy are two preventative procedures discussed. There are a number of other preventative procedures, but they are rarely used and some are considered inappropriate.
The two salvage procedures are Femoral Head and Neck Ostectomy and Total Hip Replacement.
Triple Pelvic Osteotomy (TPO)
TPO is a procedure performed to try and prevent the progression of arthritis in dysplastic hips by changing the anatomy of the hip to prevent subluxation (partial dislocation) during weight bearing. This should prevent abnormal wear of the cartilage and help prevent arthritis.
This is accomplished by externally rotating the cup of the hip joint so that it sits more over the top of the ball of the femur. To accomplish this, three cuts are made in the bone of the pelvis, the section containing the cup of the hip is rotated, and then held in place by a plate so that it will heal permanently in that position.
It is important to note that although the procedure appears to be effective, it should not be performed on every young dog with loose hips.
It has been shown that many dogs in which laxity of the hips can be demonstrated, either by x-rays or feeling, will not have problems with arthritis in the future. Therefore, most surgeons will agree that the procedure should only be performed on young dogs who are showing clinical discomfort associated with loose hips.
Also, the procedure will not be effective if significant damage to the cartilage of the hip has already occurred. Because of this, most surgeons will perform the procedure only on dogs less than one year of age that show no signs of arthritic changes on x-rays.
Juvenile Pubic Symphysiodesis
This is a new procedure in which the growth plate in the middle of the pelvis is surgically closed at a young age. This changes the way in which the pelvis grows and results in changes in the hip joint which are very similar to those caused by a TPO procedure.
The advantage is that this procedure is significantly less invasive than a TPO. Unfortunately, in order to be effective, the procedure must be performed between 4-6 months of age, younger than most dogs show clinical signs of hip arthritis.
Some surgeons have recommended that routine x-rays be taken of young animals and the procedure should be performed on any animal with loose hips regardless of clinical signs. Whether or not this is necessary is a topic of debate among surgeons at this point in time.
Femoral Head and Neck Ostectomy (FHO)
When an FHO is performed, the ball and neck portion of the hip joint are removed.
After the procedure, a false or fibrous joint will form between the pieces of remaining bone. This joint is not anatomically normal, but since there is no longer any bone on bone contact, the pain associated with the arthritis is generally relieved. As long as postoperative use of the leg is good and physical therapy is performed, the use of the limb and range of motion can be relatively good.
This procedure is very effective and successful in smaller dogs and cats. However, as the size and activity level of the dog increases, the procedure becomes less desirable.
There are many large dogs which have had good results with the FHO procedure, however the possibility of discomfort and poor use of the limb seems to increase as the size of the animal increases.
If there is poor use of the limb after the FHO and physical therapy has been unsuccessful, there is generally little that can be done to improve the outcome. The primary advantage of FHO over a total hip replacement is that the cost is significantly lower.
Total Hip Replacement (THR)
Caine Total hip replacement is considered by most surgeons to be the gold standard for treatment of severe hip arthritis in larger dogs. Generally, dogs greater than 40lbs will be sufficiently large to allow implantation of the hip replacement systems currently available.
A hip replacement provides an anatomically and functionally normal hip and will relieve the discomfort associated with arthritis of the hip joint. The expectation with hip replacement is to return to 100% normal function with no restrictions on exercise. Although the possibility of complications exists as with any surgery, overall success with hip replacement is estimated between 92 and 95%.
There are two major types of hip replacement systems: cemented and cementless hips.
Cemented systems were the original hip replacement systems used. In these systems, the implants (cup and stem) are held to the bone with a type of cement. Cementless systems are temporarily held stable while the surrounding bone grows into the porous surface of the implant. In the long-term, the bone is what holds the implants stable.
The type of hip replacement system which is best will be determined in part by the details of the individual case and also in large part by the surgeon’s preference. Each system has advantages and disadvantages.
Cemented systems have been in use for a long time and are well proven, but can have problems with infection in the cement or loosening of the cement over time.
Cementless systems are presumably less susceptible to infection, and once bony ingrowth occurs, they are less likely to loosen. However, cementless systems may have more problems with movement of the implants in the early post operative period.
The most common cemented system in use is the biomedtrix CFX system. Currently there are two cementless systems in common usage. The Kyon, or Zurich cementless hip system, is system that is held in place by screws as the bony ingrowth occurs. The biomedtrix BFX is a cementless system based on an earlier experimental system which is held in place by a press fit and has recently been introduced for clinical use.
Selected Websites for Further Information:
http://www.biomedtrix.com for Total Hip Replacement information
http://kyon.ch/ for Total Hip Replacement information
http://www.pennhip.org/ for general information and information on the PennHip method