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Pathogenesis
Canine Hip Dysplasia (CHD) literally means an abnormal development of the hips (dys = abnormal, plasia = development). CHD is a multifactorial developmental disease. All dogs are born with normal hips, but those who are genetically coded for CHD will develop abnormally as they grow. Environmental influences do not cause CHD, but they can have an impact on the severity of the disease.
Dogs who are genetically coded for good hips will develop good hips. Dogs who are coded for bad hips will develop bad hips... there is nothing we can do to change the course of this development. However, dogs who are coded for marginal hips may be more susceptible to environmental influences.
The most important environmental influence is proper nutrition. It is important for dogs who are susceptible to CHD to grow at a normal rate. Many people feel that they should supplement their puppy's diet with extra protein and fat and calcium to help them grow. This is actually detrimental to their health, as it can cause them to grow too quickly. This rapid growth results in abnormal pressures on developing hips and can lead to a worsening of hip dysplasia. There are a few companies today who have developed puppy food for large breed dogs which allows for a normal growth rate and we strongly recommend these diets in susceptible dogs.
Knowing the genetic background of a puppy and feeding diets that result in normal growth and development are the best steps you can take to reduce the risk of hip dysplasia. No dogs at risk of hip dysplasia should be bred without having the hips evaluated in both dogs involved in breeding.
Diagnosis
There are two radiographic methods which are primarily used to identify hip dysplasia. The first, a subjective evaluation by the Orthopedic Foundation for Animals (OFA) has been the primary means of diagnosing hip dysplasia since 1966. The second, an objective evaluation by the Pennsylvania Hip Improvement Project (PennHIP) is a newer, but very promising means of diagnosis. The following discussion should help you decide which technique may be best for your pet.
OFA1
The Orthopedic Foundation for Animals was developed in 1966 with the purpose of providing a standardized evaluation for hip dysplasia and to serve as a database for control of hip dysplasia through selective breeding. To date the OFA maintains the world's largest data base on hip conformation.
The OFA requires a single radiograph (x-ray) taken in a consistent manner with a number of specific technique requirements. These radiographs are not required to be taken under anesthesia, but anesthesia is recommended in order to obtain the best view in a relaxed position. The radiograph is then sent, along with a registration form, to the OFA, where it will be screened immediately for proper positioning techinique. If the radiograph is not diagnostic, it is returned to the veterinarian. Acceptable radiographs are then evaluated independently by 3 board certified veterinary radiologistst and a consensus is derived. The hips are evaluated for subluxation (looseness of hip joint), shallow acetabulum (the "socket" of the ball-and-socket hip joint) and signs of degenerative joint disease (arthritis). This evaluation is most often completed within 3 weeks.
Once evaluated, the hips are reported to be in one of these three categories: Normal, Borderline or Dysplastic.
Normal - Normal hips are further categorized as "Excellent", "Good", or "Fair". All dogs over 24 months of age with normal hips will be assigned a breed registry number and will periodically be reported to the parent breed club and the AKC.
Borderline - OFA recommends a repeat study in 6-8 months.
Dysplastic - Dysplastic hips are further categorized as "Mild", "Moderate, or "Severe". No OFA number is assigned. Abnormal findings are only reported to the veterinarian and the owner of record.
A dog must be 24 months old to receive an OFA number. However, preliminary studies can be done between 4 and 23 months of age. These preliminary studies are reportedly 90% accurate when compared to the follow-up studies done at 24 months of age.
Some female dogs show subluxation when radiographed around a heat cycle. This subluxation will not be present when the dog is no longer in a heat cycle. For this reason, the OFA recommends radiographs be performed no closer than 3-4 weeks before or after a heat cycle.
PennHIP2
PennHIP is a scientific method to evaluate a dog for Hip Dysplasia. In 1983, Dr. Gail Smith from the University of Pennsylvania School of Veterinary Medicine began to actively research and develop a new scientific method for the early diagnosis of Canine Hip Dysplasia. This research resulted in a diagnostic method capable of estimating the susceptibility of CHD in dogs as young as sixteen weeks.
Three radiographs are typically taken in a PennHip evaluation and in order to obtain diagnostic radiographs, anesthesia is required. In addition to the traditional "hip extended" radiograph, both a compression and distraction radiograph of the hips are taken. This procedure allows the dog's "passive hip laxity" to be measured. This is essentially a measurement of the looseness of the hips. Research has shown that the degree of passive hip laxity is an important factor in determining susceptibility to development of degenerative joint disease (arthritis) later in life.
A PennHIP evaluation results in a confidential report to the owner indicating the dog's distraction index or DI. The DI is a measure of passive hip laxity and is expressed as a number between 0 and 1, with 0 being very tight hips and 1 being very loose hips. Multiple investigations have confirmed that dogs with tighter hips are less likely to develop joint disease than dogs with loose hips. PennHIP data provides a profile for each individual breed of dog. Over 165 breeds are represented in the PennHIP database. PennHIP evaluations are currently recognized by the American Kennel Club and in the future, DI information will be included in the AKC's Information and Health Database.
The PennHIP method can be performed on dogs as young as sixteen weeks.
Comparison of OFA and PennHIP3
So, what should you do if you are concerned about hip dysplasia in your pet? We have listed our perception of the advantages and disadvantages of each method as a guide to help you make decisions for your pet.
OFA Features PennHIP One # of radiographs Three Strongly Recommended Anesthesia Required Subjective Evaluation Method Objective No Breed Specific Yes 24 Months Age 16 Weeks The most important features are the evaluation method and the age. Let's take a closer look at each of these.
Evaluation method: The OFA evaluation method is subjective. This means that it is based on the opinions of the evaluators. The conclusions reached on an individual radiograph could vary based on different opinions of the evaluator. OFA radiographs are evaluated by board-certified veterinary radiologists, so these opinions are indeed "expert opinions" but there still exists room for error with any subjective method of evaluation. For instance, what specific signs are required to be present or absent in order for hips to be considered "excellent" instead of "good"? All normal hips receive an OFA certification number, but these normal hips can range from fair to excellent. How does a person make good breeding recommendations based on these results? We know that different breeds have different levels of hip quality, but OFA evaluation does not specifically say how a single dog compares to other dogs within its own breed.
The PennHIP method is objective. This means that it is based on a specific factual measurement which is not influenced by the opinion of the person evaluating the hips. The Distraction Index (DI) is a specific, measured evaluation. However, in order to obtain consistency, only veterinarians specifically trained in the PennHIP technique can take the radiographs that are sent in for evaluation. The results of the PennHIP evaluation are specific for each breed. Instead of reporting a subjective analysis such as "good" or "fair", the PennHIP results are reported as a specific number (DI) which is ranked against all other dogs of the same breed which have been previously evaluated by PennHIP. Therefore, you will receive a report telling you how loose your dog's hips are compared to all other dogs of the same breed. This information is extremely valuable when trying to make breeding recommendations.
Age: The age at which we evaluate hips is important for two reasons. The earlier a breeder knows which dogs in a litter have good or bad hips, the sooner they can decide which dogs to keep as breeding stock and which to sell as companion animals. In addition, there are solid medical reasons to spay female dogs prior to their first heat (see Spay/Neuter information) and this cannot be done if the dog cannot be certified until 24 months of age. Preliminary studies can be done prior to 2 years but the predictability for breeding is not as good this early with OFA as it is with PennHIP.
Conclusion
At North Shore Veterinary Hospital, we offer both the OFA and the PennHIP methods of evaluation for Canine Hip Dysplasia. Dr. Anderson is currently one of only a few veterinarians in the state of Minnesota who have been certified for PennHIP evaluation. We strongly recommend that intended breeding dogs of all breeds at risk for Hip Dysplasia (particularly medium to giant size breeds) be evaluated by one of these methods as a tool in selecting appropriate breeding animals.
While the OFA evaluation method has the advantage of history and public awareness, we believe that PennHIP evaluation gives more conclusive findings which can more directly be used to assist in breeding. If you are not intending to breed your dog, but desire to know the status of your dog's hips, it is not necessary for you to proceed with either of these evaluation methods. All of our doctors are capable of evaluating your dog's radiographs and if necessary, we can send the radiographs to a board-certified veterinarian for further evaluation.
This information is intended to introduce you to the methods used to diagnose Hip Dysplasia, but for specific recommendations about your pet and it's health, or specific breeding recommendations for your pet, please contact us for further information.
1All comments in the "OFA" section are taken directly from the pamphlet "Orthopedic Foundation for Animals".
2All comments in the "PennHIP section are taken directly from the PennHIP pamphlet produced by the Synbiotics Corporation, 3/98.
3All comments in this section are the opinions of the doctors and staff of North Shore Veterinary Hospital.
Treatment*
Before discussing treatment, it is important to distinguish between Canine Hip Dysplasia (CHD) and Degenerative Joint Disease (DJD). Hip Dysplasia is the abnormal development of the hips which results in an increased amount of looseness in the hip joint. Degenerative Joint Disease (arthritis) is the changes within the joint which occur as a result of this increased looseness. Pain can result from either of these problems. The young dog with hip dysplasia can be painful without having degenerative joint disease, and dogs with chronic DJD do not always have hip dysplasia.
Therefore, our treatment methods are different depending on which particular problem we are trying to treat.
Treatment methods are divided into two categories: Medical and Surgical
Medical Therapies
Young Animals With Hip Dysplasia
Pain relief and clinical improvement associated with conservative treatment are derived from strenthening the joint capsule and preventing further capsular sprain.
Initially, painful dogs should be treated for acute sprain. Complete rest is mandatory for 2 weeks. Physical therapy during this time can be performed to maintain good range of motion. However, resuming normal activity early can predispose to further injury, pain, and prolonged recovery. According to one source, approximately 60% of young patients treated conservatively return to acceptable clinical function with maturity.
Mature Animals With Chronic DJD
Medical therapies for chronic degenerative joint disease can be subdivided into 3 areas - weight control, proper exercise, and anti-inflammatories.
Weight Control: Regardless of whether or not a dog has hip dysplasia, they will be at higher risk for joint disease if they are overweight. The further they are from their ideal weight, the more likely they will be to have orthopedic problems such as arthritis, intervertebral disk disease and cruciate ligament disease. Dogs who have hip dysplasia and are overweight are at extremely high risk for chronic arthritis in the hips. Proper weight control should be obtained through proper exercise and dietary management. If your pet is overweight, please discuss proper weight control with us to minimize these risks.
Proper Exercise: If your dog has hip dysplasia you should limit him or her to moderate exercise such as swimming and long walks. High-intensity activity should be of short duration and should only be allowed after an adequate warm-up period.
Anti-inflammatories: There are a number of anti-inflammatory medications on the market which are available for use in dogs. We will not make any specific drug recommendations here, as all drug therapy should be specifically discussed with your veterinarian. However, there are some general comments which are useful in understanding treatment with anti-inflammatories.
There are many nonsteroidal anti-inflammatory medications (NSAIDs) available for use in dogs. However, all of these medications must be used with caution, as the pharmacokinetics are largely unknown and overdosage may result in severe gastrointestinal ulceration. NSAIDs should never be given without the specific recommendation of a veterinarian. Most NSAIDs interfere with glycosaminoglycan synthesis in the joint fluid and therefore should not be used for extended periods of time. In general, NSAIDs should be reserved for acute flare-ups of pain, but should not be used for long term management due to the potential for gastrointestinal side effects and continued joint breakdown.
Another option for medical therapy is the use of a nutritional supplement called Cosequin. Cosequin is made up of the raw materials which are the building blocks for cartilage and joint fluid. We have found that extended use of this product is very safe and provides pain relief in a high percentage of patients. In addition, it theoretically helps to reduce the breakdown of the joint which is better for the long-term prognosis for your pet. More information about Cosequin can be found at the following website: www.cosequin.com/veterinary/cosequin.htm
Surgical Therapies
Young Animals With Hip Dysplasia
Pectineal Myectomy: This procedure is designed to relieve tension produced by the pectineus muscle which is transmitted to the hip joint. Studies have indicated that there is no effect in preventing dysplasia as a result of pectineal resection. However, symptomatic improvement does result in many dogs for a varialbe lenght of time following pectineal resection and this procedure has the advantage of being significantly less expensive than TPO. Surgical recovery is rapid.
Pectineal resection does not affect the radiographic changes associated with hip dysplasia. Degenerative changes continue and pain usually returns after a variable period of time ranging from a few months to years. There is no reliable way of predicting how long the effects of the surgery will be beneficial.
Triple Pelvic Osteotomy(TPO): TPO is indicated in young animals leading athletic lives (i.e., working breeds). The purpose of this procedure is to arrest or slow the progress of osteoarthritis. The most favorable prognosis is in patients with radiographic evidence hip dysplasia with minimal DJD. Patients are usually 5-10 months of age. This operation is designed to redirect the acetabulum (the "socket" of the hip) to stabilize the head of the femur (the "ball"). This procedure must be performed early in order to take advantage of the remodeling capability of immature bone.
Three cuts are made in the pelvis. The freed section is rotated by a predetermined amount and screwed in place with a metal plate. This rotation helps to capture the head of the femur (not pictured) which helps to slow the degeneration of the joint.
The prognosis after TPO is largely determined by case selection. Best results are obtained in those dogs with little to no degenerative changes. Long-term function is good to excellent. Although degenerative changes are radiographically evident after this procedure, they are less than what would be expected without surgery.
Mature Animals With Chronic DJD
Femoral Head and Neck Excision (excision arthroplasty): In this procedure, the head and neck of the femur are excised and a fibrous false joint is formed. Pain is relieved by elimination of bony contact between the femur and the pelvis as scar tissue interposes. This procedure is a nonreversible procedure which is mainly considered a salvage operation. However, it is a valuable technique to eliminate pain and improve the quality of life.
The femoral head and neck are excised, leaving no bone-to-bone contact. A fibrous false joint is formed and the pain associated with the degenerative joint disease is eliminated.
The prognosis depends on a number of factors, primarily the degree of joint disease prior to surgery. Dogs with long-term history of joint disease often have decreased muscle mass and strength in the affected limbs and recovery is longer. There will be some change in the gait, particularly in larger dogs. In large patients 50% of animals have good or excellent function and the remainder have varying degrees of lameness, but function is usually improved when compared with the preoperative status. Medium and small patients usually have good or excellent limb function.
Total Hip Replacement: This procedure is similar to the head and neck excision, but following the removal of the femoral head and neck, a plastic acetabular cup and a stainless stell femoral head component are implanted. This procedure offers all of the benefits of the head and neck excision (elimination of pain and increased quality of life), but adds the structural stability that is lost with the head and neck excision. The total hip replacement is considered the "gold standard" for relief of chronic DJD.
This is a radiograph of a hip after receiving a total hip replacement. There is no more pain, because the affected bone has been removed, but full function is maintained because of the stability provided by the implant.
This procedure is most commonly used in mature patients when conservative therapy is not effective. The success rate is good to excellent return to normal function.
*Most of the information contained on this page was obtained from the chapter "Management of Joint Disease" in Small Animal Surgery by Theresa Fossum, et al, copyright 1997 and "Handbook of Small Animal Orthopedics and Fracture Treatment" by Brinker, Piermattei, and Flo.
