Pathophysiology Literally, hip dysplasia (CHD), means”badly formed hip”. In order to understand this complex problem it is first necessary to understand the anatomy of the canine hip. This ball and socket joint consists of two basic parts – the acetabulum and the femur. The femur, or thigh bone, consists of the head (the ball) and the neck (the part of the femur that joins the long shaft of the bone to the head). The acetabulum forms the socket part of the joint and it is into this socket that the head of the femur rests.
In unaffected dogs there is a good fit between ball and socket. An easy way to think about it is to imagine a tennis ball and a cup. If you put the ball into the cup there is a good fit. If you put the ball into a saucer, it will roll around loosely.
This poor fit between femoral head and acetabulum is characteristic of dysplastic dogs. CHD can also be diagnosed if the femoral neck is shortened or if there is an improper angle between the femoral head and the long axis of the femoral neck (Cargill and Thorpe-Vargus, 11/95).
The hip joint is strengthened by a ligament going directly from the femoral head into and attaching to the acetabulum. The joint is surrounded by the joint capsule – a thick band of connective tissue. (Foster and Smith)
Dogs are not born with CHD. As puppies grow, laxity of the muscles and ligaments surrounding the joint and the poor fit between the bones produces excess movement of the acetabulum. The separation between the bones is called subluxation, and at its most severe it can become a total dislocation (the head of the femur leaves the acetabulum). The surfaces of the bones start out completely smooth, but with CHD there begin to be changes (remodeling). Bone rubbing against bone causes an irritation which results in irregular bone growth and wear on the articular surfaces. These irregular surfaces result in Osteoarthritis which can cause significant pain. As the bone of the acetabular rim is ground away, it becomes shallower and it is now more difficult to keep the head of the femur properly seated.
Outward signs of hip dysplasia can range from none to severe pain. Gait (movement) may or may not be affected. Some outward signs that MAY be seen in affected dogs are:
Difficulty getting up from a lying or sitting position or in climbing stairs.
A bunny hop gait (moving both rear legs together).
A painful reaction to extension of the rear legs.
Pushing on the rump may cause the pelvis to drop.
When rolled over, some affected dogs will resist having their legs spread into a frog-leg position.
A side to side sway of the croup
Dogs may resist jumping
Lameness may be seen especially after strenuous exercise.
It is very important to understand that the only way to accurately diagnose CHD is through X-rays. The above symptoms may also be seen in dogs with normal hips and affected dogs may display none of these symptoms at all.
As stated above, the only way to conclusively diagnose CHD is through x-rays of the hip joint. Positioning of the dog is very important if the films are to be read correctly. It is wise to find a practitioner who is experienced in correct positioning when seeking evaluation. The are currently two main methods for evaluating hips in use in the U.S. It is beyond the scope of this article to evaluate the merits and drawbacks of these methods, so only a brief description will be given.. Anyone planning to begin a breeding program, or wishing to improve hips in a current program, is encouraged to study both in more depth.
The Orthopedic Foundation of Animals (OFA) is a non-profit organization which uses board certified radiologists to evaluate submitted x-rays. After the age of two years, dogs whose films do not, in the view of at least two of the three evaluators, indicate the presence of CHD are assigned an OFA number and rated either excellent, good or fair. Hips felt to be dysplastic are rated mild, moderate or severe. There is also an
option for the evaluator to state that the films are inconclusive at this time. Preliminary ratings are given for dogs under the age of two. These plates are read by only one evaluator (Carricato, 1992).
The OFA number consists of several parts. A typical number might look like this:
The “GR” is the OFA abbreviation for Golden Retriever. The number 37961 means that this dog is the 37961th G.R. to be given a number. The “G” stands for a rating of Good (E would mean excellent, F- fair). T he 24 is the age, in months, at the time of x-ray. The “F” means female and the “-T” indicates the dog was tattooed.
Positioning for an OFA x-ray requires that the dog must be flat on its back with the femurs extended parallel to each other and the knees rotated slightly inward. Dogs can be restrained chemically (anesthesia or sedation) or mechanically (strapped down). The average OFA x-ray costs around $80- $100. The registration fee to the OFA is now $25.00
The second type of evaluation currently being used is the PennHip® method of measuring passive hip laxity, thought to be a predicting factor for CHD. This method uses a technique called “compression/distraction” In this procedure the hips are compressed to determine where the center of the femoral head and the acetabulum coincide. The hips are then distracted using a special device and the distance that the head can be moved away from the center is measured. This measurement is called the distraction index or DI. The DI will range from 0 to 1. Through research, PennHip® developers have postulated that a DI of .03 or lower indicates that the animal is negative for CHD. A DI of .07 or above is associated with a greater incidence of degenerative hip disease. Between .03 and .07 is a gray area. It is also important to consider the average for the breed when making breeding decisions using this method. Breeding animals with DI€™s below the breed average will, according to PennHip® proponents, gradually decrease the hip laxity of the bred and with it, the incidence of CHD.
Although this new method shows promise, an OFA number is still considered the standard clearance. Responsible breeders will obtain an OFA number before breeding an animal. Some breeders will also, as availability permits, obtain a DI before breeding. A Penn-Hip® procedure is usually more costly that an OFA x-ray (approx. $150.00).
CHD is a inherited trait that is influenced by several genes (polygenic). It is not caused by any environmental factors, but environment can influence the expression of the disease (Corley, Willis, Cargill/Thorpe-Vargeson, Carricato). In other words, how you raise your puppy won€™t determine whether or not he is dysplastic, but it can affect when and perhaps if, he begins to develop symptoms. Some common factors which have been proposed to worsen, but not cause, CHD are:
Rough play, jumping, climbing stairs or slick floors.
excess weight gain or rapid growth.
calcium supplementation (may increase the bone remodeling).
Forced running for any distance, especially on tarmac, asphalt or other hard surfaces.
Therefore it makes sense to keep puppies lean, avoid any type of forced exercise or very rough play and provide surfaces that allow for good traction.
The OFA recommends the following guidelines to decrease the incidence of CHD in a breeding program:
1. Breed normal to normal
2. Breed normals with normal ancestry
3. Breed normals from litters with low incidence of CHD
4. Select sire that produces a low incidence of CHD
When deciding to breed or to purchase a puppy it is wise to look at the hip clearances of not only the parents, but the brothers and sisters, grandparents and other offspring of the parents. Having mostly OFA clear relatives on both sides is thought to increase the chances of the litter having clear hips.
Non-surgical treatment attempts to improve function and reduce pain and inflammation. Drugs that can produce these results are aspirin, phenylbutazone (“bute”), NSAIDS (non-steroidal anti-inflamatories) and steroids. Be aware that all three drugs can produce significant side effects and should be used with caution, if at all, under the supervision of a veterinarian. Other products that have shown promising results are glycoaminoglycans such as Adequan, Cosequin and Glycoflex. Adequan is an injectable drug. Glycoflex and Cosequin are both given orally. Vitamin C can also be effective in reducing inflammation (Corley). Some people have also reported success with herbal medicines. Exercise restriction is also sometimes
recommended (Carricato). An ideal type of exercise for dysplastic dogs is swimming which allows exercise without stressing the joints.
Several surgical procedures exist to treat CHD. Each procedure has pros and cons associated with it. Furthermore, different surgeons may have more experience and therefore be more skilled with a particular type of surgery. A second opinion before surgery may be helpful.
Surgery is indicated when:
non-surgical management has failed to reduce pain or restore function.
surgery will correct current problems
surgery will prevent or slow the progress of further problems (Cargill, Thorpe-Vargeson)
Factors that will be considered in selecting a type of surgery to be performed should include:
- Age and weight of the animal
- Complicating factors such as extensive bone remodeling or osteoarthritis
- Function of the dog (i.e. is the dog a working dog, required to perform strenuous activity or is he primarily a sedentary pet).
Types of Surgery:
Before advanced remodeling of the joint has taken place the most often recommended surgical treatment for CHD is the triple pelvic ostomy or TPO. This procedure must be done before the acetabulum has been worn down and therefore us usually recommended for young dogs (under 9 months of age) who have clinically diagnosed subluxations. The surgery involves cutting the pelvis in three places and then tilting the bone to a more favorable angle to keep the femoral head in place. A somewhat similar option is the inter- trochanteric osteotomy, which changes the length and angle of the femoral head. Both procedures are aimed at improving the fit between femur and acetabulum (Cargill, Thorpe-Vargas). Approximate costs for these procedures average around $800.00 to $1000.00 per hip. After a TPO the dog must be kept on crate rest for several weeks to allow the healing process to occur.
If there is already extensive damage to the joint other options include the shelf arthroplasty or BOP procedure, the femoral head and neck excision or a total hip replacement. The shelf procedure seeks to extend the rim of the joint, thus improving stability. This option has been criticized because it does not halt the progression of a rthritic changes, thus the animal may continue to have worsening pain (Cargill, Thorp-Vargas).
The femoral head and neck excision involves removing both the head and neck of the femur. A “sling” of muscles are then used to support and cushion the femoral shaft. This procedure has the best chance for success in dogs weighing less than 50 lbs. Because the bone is shortened, the gait will be affected. This should be considered an end-stage salvage procedure, but costs are usually much lower than other types of surgery.
A total hip replacement involves replacing the head and neck of the femur and the acetabulum with prosthetics. Indications for this radical type of surgery are:
- Osteoarthritis associated with CHD
- Failed head and neck excisions
- Irreparable head and neck fractures
- Non-reducible chronic hip luxations
- avascular necrosis of the femoral head
- and repair of a failed total hip arthroplasty (Cargill, Thorpe-Vargas)
The procedure should be done after the dog has reached adult growth. It is quite costly (averaging around $1500.00 per hip), but the prosthesis can be expected to last for the life of the dog and the dog can bear weight very soon after the surgery. As with any orthopedic surgery, infection can pose a serious threat to the recovery and usually antibiotics are prescribed during convalescence.
In conclusion, if you suspect your dog may have dysplastic hips or you are planning to breed, arrange for an x-ray to be taken. If CHD is diagnosed YOUR PET SHOULD BE SPAYED OR NEUTERED!!! You should also notify the breeder of your dog so that he/she can use that information to take steps to improve the breeding program that produced the problem.
Cargill, J.C. & Thorpe-Vargas, S.” Predicting the abnormal hip”, Dog World. September, 1995. 26-31.
Cargill, J.C. & Thorpe-Vargas, S. “Surgical Management of Canine Hip Dysplasia” Dog World. November, 1995. 20-25
Cargill, J.C. & Thorpe-Vargas, S. “Operations: Two viable options”, Dog World. December, 1995. 22-25.
Carricato, A. M. (1992). Veterinary Notes for Dog Breeders. Howell Book House, New York.
Corley, E.A. OFA seminar, 9/95.
Foster, R. & Smith, M. “Hip dysplasia”. Pet Pause. 1996. Dr€™s Foster & Smith Inc.1-3.
Willis, M.B. 1989. Genetics of the Dog. Howell Book House, New York.
A special thanks to Ann Greenbank, DVM for reviewing this article.
Any mistakes or inaccuracies are entirely my own.