Introduction
Hip dysplasia is, generally, a hereditary disease that, in its most severe form, can eventually cause crippling lameness and painful arthritis. It is caused by a combination of genetic and environmental factors. It can be found in many animals, but is most commonly associated with dogs, and is most prevalent in larger breeds of dogs.
Normal Hips vs. Dysplastic Hips
In the normal anatomy of the hip joint, the femur (thigh bone) is connected to the pelvis at the hip joint. While bones provide the strength necessary to support body weight, cartilage ensures a smooth fit and a wide range of motion.
In hips suffering from dysplasia there are two primary abnormalities. First, instead of a deep tight fit, the femur fits into the pelvis loosely or partially. Secondly, abnormalities in the shapes of the bones cause wear and tear within the joint as it moves.
Causes of Hip Dysplasia
Prevalent in some breeds of dogs, there is considerable evidence that genetics plays a large role in the development of this defect. Several genetic factors can contribute to the problem including a femur that does not fit correctly into the pelvic socket, or poorly developed muscles in the pelvic area. Symptoms almost always appear by the time the dog is 18 months old and the defect can range anywhere from mild to severely crippling.
Hip Dysplasia occurs most frequently in medium-to-large pure breeds of dogs including German Shepherds, Labrador and Golden retrievers, Rottweilers and Mastiffs. However, the condition also occurs in some smaller dogs in the long list of dog breeds as well as in cats.
Symptoms of Hip Dysplasia
It is important for owners to recognize the clinical signs of hip dysplasia so that effective treatment options can be pursued as early in the course of the disease as possible. This can be difficult, however, because the signs of hip dysplasia often mimic those of other degenerative disorders.
Hip dysplasia is one of the most common skeletal disorders seen clinically in dogs. Large and giant-breed dogs have the highest incidence of hip dysplasia, including St. Bernhards, German shepherds, Labrador retrievers, Golden retrievers and Rottweilers. Small breeds can also be affected but are less likely to exhibit clinical signs of the disease. Both sexes are affected equally, and clinical signs tend to show up early, usually between 4 and 12 months of age, although signs of osteoarthritis can first present in more mature animals.
The main effect of hip dysplasia is rear leg lameness characterized by a “bunny-hopping” or swaying gait, pain or weakness in one or both hind legs, difficulty rising, exercise intolerance, reluctance to run or jump (into cars, onto furniture, etc), and sometimes an audible “clicking” sound coming from the hips when rising or walking (called “crepitus”). Other signs include a narrow hind-end stance, poor pelvic limb conformation and musculature, hypertrophy (enlargement) of the shoulder muscles and sometimes an arched appearance of the spine caused by the shifting of weight to the forelimbs. These signs may be intermittent or persistent and tend to worsen after exercise. Affected dogs may seem fine most of the time, but be stiff in the morning or after a nap. Obesity or rapid weight gain can exacerbate the lameness and pain associated with this disease.
If left untreated, hip dysplasia will progress and the symptoms will become more obvious to owners. Owners should be especially aware of signs in young, rapidly-growing large and giant breed dogs in the first year of their life, and in aging dogs. Medical and surgical treatments are available that can greatly reduce the discomfort caused by hip dysplasia, allowing affected dogs to remain active lead normal lives.
Diagnosing Hip Dysplasia
Diagnosing hip dysplasia in dogs can be difficult because a number of other diseases cause similar clinical signs and therefore must be ruled out before a definitive diagnosis of hip dysplasia can be made.
If a dog presents with unilateral or bilateral hind end lameness – especially if it is a young, rapidly-growing large or giant breed puppy between 4 and 12 months of age – the initial veterinary database normally will include blood work (complete blood count and serum chemistry panel run on fresh blood samples), a urinalysis, palpation of the hip joints (which may require sedation or even general anesthesia because of pain) and pelvic radiographs (x-rays). Very specific positioning of the dog for hip radiographs is essential to an accurate diagnosis of hip dysplasia and can be determinative even if the dog is not showing clinical signs of the disease.
Responsible breeders often have their dogs tested for hip dysplasia radiographically before breeding them. There currently are two procedures for this screening. The older and still more common method is recommended by the Orthopedic Foundation for Animals (the OFA). The dog’s veterinarian will take radiographs of the hips with the dog in a particular position – on its back, with its hind legs being stretched and slightly rotated – and will submit those films to the OFA. There, specialized veterinary radiologists will analyze the radiographs and compare them to a large computerized database of hip x-rays of other dogs to determine whether hip laxity exists and, if it does, how severe it is at that point. While this can be done in young dogs, official certification by the OFA (excellent, good, fair, borderline or dysplastic) must be done on radiographs taken after the dog is 2 years of age.
The other recognized method, called PennHip, was devised by doctors at the University of Pennsylvania. The radiographs for this method are taken at several specific angles and require the joint to be at its most relaxed, so general anesthesia normally is necessary. A mathematical formula is applied to the angles of bones evident on the radiographs to quantitate the degree of laxity in each hip joint. This formula yields a number which represents whether or not hip dysplasia is present.
Confirmatory testing might include additional x-rays taken at different views, and possibly computed tomography (CT or CAT scan).
Treating Hip Dysplasia in Dogs
While there is no cure for hip dysplasia in dogs, there are treatments available to help alleviate the animal's pain and manage its quality of life. The overall goals of therapy are to relieve pain and stabilize the hip joint to return the dog to normal or nearly-normal function. Depending upon the severity of the condition, the veterinarian will recommend a treatment plan that may contain both surgical and non-surgical options.
Non-Surgical Options for Treating Canine Hip Dysplasia
Dogs with mild cases of hip dysplasia may respond well to conservative medical (non-surgical) management on an outpatient basis. Of course, which treatment protocol to adopt depends on the patient’s age, size and intended function (companion, hunting, show, etc), the severity of joint laxity, the existence and degree of osteoarthritis, the veterinarian’s personal treatment preferences and the financial considerations of the owners. Non-surgical options include physical therapy, swimming, dietary weight control, exercise restriction and use of oral anti-inflammatory and pain management medications. Corticosteroids normally are not recommended as part of a treatment plan for dogs with hip dysplasia, because despite their beneficial anti-inflammatory effects they also can cause cartilage damage with long-term use. A number of oral supplements are available to help protect and lubricate the cartilage in the hip joint as well. In many cases, weight loss alone can dramatically reduce the pain and clinical signs associated with hip dysplasia in overweight dogs. Reasonable and regulated exercise can stimulate cartilage growth and reduce degeneration, while long controlled walks in early or mild cases of dysplasia may help prevent loss of muscle mass.
Surgical Options for Treating Canine Hip Dysplasia
There are a number of surgical options for treating hip dysplasia, if less intrusive methods do not accomplish acceptable results. Depending on the severity of the condition in a given dog, the veterinarian may attempt to modify the existing hip joint, or instead may opt for a total hip replacement.
Hip Modification
Hip modification surgery can be effective but may not be adequate for older or heavier animals. Hip modification surgeries include:
- Juvenile pubic symphysiodesis – electrocautery is used to fuse the pubic symphasis in immature dogs (3 - 4 months of age), causing the head of the femur to be more completely covered by the “hip socket.” This is not a complicated procedure and is very effective if done in very young dogs.
- DAR arthoplasty – a technique available in young dogs to augment the outer rim of the hip socket.
- Excision arthroplasty, also called femoral head and neck ostectomy (FHO) - the head and neck of the femur (the long bone in the upper thigh that joins with the hip socket to create the hip joint) are removed to alleviate joint pain. The resulting scar tissue essentially replaces the hip joint. Following this surgery, the dog’s weight must be managed throughout its life in order to maintain mobility, and a total hip replacement cannot thereafter be done. This is primarily a salvage procedure for dogs whose dysplasia has deteriorated to severe osteoarthritis, when medical management cannot control the pain or when a total hip replacement is financially unavailable. Excision arthroplasty is most successful in small, light dogs with good pelvic muscle development. However, it can lead to complete freedom from pain and return to almost-normal function even in giant breed dogs (some minor gait abnormalities may exist and owners will often see muscle atrophy in the pelvic area post-operatively).
- Triple pelvic osteotomy (TPO) – a corrective procedure involving surgical rotation of the pelvis to improve coverage of the head of the femur. It is best done in young animals (6 – 12 months of age), before degenerative joint disease develops.
- Intertrochanteric osteotomy (ITO) – possible in immature dogs with abnormal femoral neck angles, but not commonly performed.
Total Hip Replacement (THR)
Total hip replacement, while expensive, has the highest surgical success rate especially in large or severely-dysplastic mature dogs that do not respond adequately to medical therapy. Pain-free hip joint function is reported in more than 90% of cases; even replacing only one hip joint can restore pain-free mobility.