CANINE HIP DYSPLASIA
Peter H. Laverty, BVSc, MACVSc, Dip. ACVS Simon T. Kudnig, BVSc, MVS, MS, FACVSc, Dip. ACVS Specialist Small Animal Surgeons
Canine hip dysplasia (CHD) was first described by Schnelle in the mid-1930s and at that time it was thought to be a rare condition. By the 1960s it was recognised to be a very common problem in large breed dogs and is still extremely common today. The simplest definition of hip dysplasia is a literal translation from its Latin roots: “Faulty development of the hip.” A practical definition is: A varying degree of laxity of the hip joint permitting subluxation (partial dislocation) during early life which results in varying degrees of remodeling and degenerative joint disease (arthritis) at a later age. Canine hp dysplasia can affect all breeds of dogs; however, it is most common in large and giant breeds. Prevalence varies by breed. The Orthopaedic Foundation for Animals (OFA) has estimated the prevalence of CHD at between 10 and 48% based on X-ray diagnosis. There figures are probably conservative, since X-rays of obviously poor quality hips are less likely to be sent to the OFA for evaluation and certification. Other less biased estimates of the prevalence of radiographic diagnosis approach 50 to 70% in some popular breeds of dogs (Golden Retriever, Rottweiler).
CHD are the result of many factors. A genetic predisposition has been documented. The prevailing thought at this time is that CHD has a polygenic mode of inheritance. However, the “clinical” expression of the disease is determined by the interaction between the dog’s genetics and environmental or non-genetic factors. Some of the non-genetic factors include body size, growth rate, nutrition and exercise activity. It is important to realise that hip dysplasia does not equal arthritis. CHD is a laxity of the hip joint that develops in juvenile dogs between birth and skeletal maturity. Dogs with CHD may be born with normal conformation of their coxofemoral (hip) joints. The growth /development of the acetabulum and the femoral head is synchronised and dependent upon good mechanical function, lubrication, full congruity and neutral or balanced forces for continued normal growth. With CHD the joint laxity allows the femoral head to subluxate. As a result of subluxation the normal weight bearing surface area between the femoral head and acetabulum is reduced. This causes an increase in the compressive forces per unit of surface area and results in degenerative joint disease.
Factors proposed to influence the biomechanics of the coxofemoral joint and the development of hip dysplasia include:
1. Degree of joint laxity, (looseness versus tightness) this appears to have a genetic basis.
2. Joint fluid volume
3. Abnormal pelvic muscle development
4. Abnormal femoral and/or acetabular conformation
5. The rate of growth
Two separate age groups are typically seen. There are the younger animals, usually less than one year of age that has clinical signs due to the presence of laxity and incongruency of the hip joint. Some of these young dogs with a milder disease may compensate to some extent for the joint laxity and clinical signs either resolve or are not apparent until the development of secondary arthritis. This older group of dogs may present any time after about one year of age.
Initial clinical signs may include:
Difficulty rising, walking, running and stair climbing
‘Bunny hopping’ (hind legs staying together while running) or a waddling gait
An audible click may be heard as the dogs walks
Unilateral or bilateral pelvic limb lameness exacerbated by exercise
Apparent weakness in pelvic limbs
Dog may prefer to sit rather than stand, and they may shift their weight to their forelimbs.
Physical examination may reveal:
Varying degree of pelvic limb muscle atrophy and well developed forelimb musculature
Decreased range of motion (ROM) of the hips with pain particularly on extension
Demonstration of hip joint laxity using one of several techniques. This is best performed with the dog sedated.
A tentative diagnosis of CHD is made on the basis of age, breed, history, clinical signs and physical examination. Definitive diagnosis required radiographic evaluation.
A diagnosis of CHD is made if there is radiographic evidence of hip joint subluxation, arthritis or both.
X-rays may demonstrate:
Subluxation, 60% or more of the femoral head should be covered by the acetabulum
Rough irregular bone formation around the hip joint.
Malformation of the femoral head and neck
Filling of the acetabulum (“hip cup”) with bone with a resultant shallow acetabulum
All available treatment options are aimed at slowing the natural progression of the disease and ameliorating the clinical signs. Options can be divided into conservative surgical methods.
Dogs with no/minimal hip arthritis
Many young dogs treated medically may overcome the initial lameness and discomfort associated with excessive laxity and early arthritis and may not need subsequent surgical treatment. The primary goals of conservative therapy are to promote muscle mass, eliminate obesity, and alleviate discomfort. Conservative therapy consists of controlled exercise, body weight management and the use of chondroprotectants (joint supplements such as glucosamine etc), and non-steroidal anti-inflammatory medications.
1.- Exercise: The goal of controlled exercise is to enhance muscle mass. The exercise should be low impact, for example walking or swimming. The rational for controlled exercise is to minimize irritation of the inflamed hip joint tissue and to avoid further mechanical trauma to the hip joint. Joint movement also is important in maintaining cartilage nutrition and health. I recommend daily exercise in the form of leash walking or swimming.
2.-Nutrition: Proper nutrition is important. Young, puppies should be “limit fed” adult dog or large breed puppy foods and should not be allowed to grow too quickly.
3.- Medical therapy: Medical treatment is perhaps the least important part of the conservative therapy. However, hip pain may prohibit exercise. If analgesia is necessary we prefer to use NSAID’s. (Rimadyl, Metacam or Zubrin)
1.- TPO- Triple pelvic osteotomy is a procedure where as the name suggests. Three osteotomies (bone cuts) are made in the pelvis to permit the acetabulum (hip cup) to be rotated over the femoral head. Rotation of the acetabular segment results in better coverage of the femoral head improves joint congruency, stability and slows the progression of arthritis. The ideal candidate for a TPO is a dog 4-12 months of age with clinical signs of CHD (we don’t consider laxity alone an indication for TPO). Manipulation of the hip joint under sedation allows us to determine if the hip is suitable for a TPO. Hip X-rays must reveal no to minimal degenerative changes. A definite window of opportunity exists for this procedure so it is important to intervene promptly if a TPO is considered a possibility. Contraindications for a TPO include moderate/severe osteoarthritis or a severely damaged/eroded dorsal acetabular rim.
Dogs with significant hip arthritis
Conservative therapy in these dogs is aimed at the management of the osteoarthritis secondary to CHD.
Obesity prevention and correction
Specific feeding instructions detailing quality and quantity of food to be fed will be made. It is essential to achieve weight reduction and optimal body condition.
The goal of exercise control in cases of CHD with significant DJD is to minimize joint damage. Complete rest is recommended in cases with an acute lameness. In cases with a more chronic history of lameness, moderate self regulated activity (leash walking and swimming) is recommended.
Keeping your dog in a warm environment or applying heat in the form of a warm compress may help alleviate pain associated with CHD.
4.-Medical Therapy to alleviate arthritic pain.
NSAID’s are typically used as the mainstay of medical therapy.
“Rimadyl” has become the most widely used of this class of drug in recent times. It is safe and effective. Potential side effects of the NSAID group of drugs include gastroduodenal irritation/ulceration and liver damage. Other drugs that may be indicated include “Metacam” or “Zubrin”. Why some patients respond to one NSAID but not to another is not understood. It is sometimes necessary to trial several different drugs to determine the best drug for your dog.
Nutraceuticals are a family of drugs that includes Cartrophen and Cosequin
There are no contraindications to concurrent use of NSAID’s and nutraceuticals. Reported benefits of nutraceuticals include pain relief and chondroprotective properties. There is extreme variation in response to these medications between dogs. Some may respond well, others not at all!
FHNE- Femoral head and neck excision is a salvage procedure that is indicated when the window of opportunity for a TPO has been missed, conservative therapy has failed, or a THR is not possible. Ideally dogs should weigh less than 15-20kg, but satisfactory results can also be obtained in larger dogs. Dogs with a typical ‘household pet’ lifestyle do very well with FHNE. This procedure involves the removal of the head and neck of the femur. This eliminates the pain associated with two “rough” bone surfaces moving over each other. Contraindications for FHNE include animals with severe muscle atrophy as these animals will be more difficult to rehabilitate. Larger, heavier dogs, working dogs or dogs with concurrent forelimb problems tend not to do so well. We favor a total hip replacement in these dogs.
Hip denervation procedure
This surgery involves the transection of the sensory nerve supply to the hip joint. This technique is a palliative procedure that can relieve the discomfort of hip dysplasia.
It is a minimally invasive technique that does not preclude total hip replacement or other hip surgeries.
We consider the indications for this technique to be as a preliminary procedure in any case of hip dysplasia or geriatric animals in which an invasive procedure such as a total hip replacement is considered to carry an unacceptable risk.
Total hip replacement is considered the “gold” standard for the treatment of moderate to severe arthritis secondary to hip dysplasia. Arthritic pain is the result of inflammation of the joint capsule, joint capsule distension and bone on bone contact as the hip moves through its range of motion. THR involves the removal of these painful components and replaces them with a polyethylene acetabular (hip cup) and cobalt chrome femoral component.
THR results in a successful outcome in 90-95% of cases in established total hip replacement programs. These patients have pain free function, increased muscle mass, no limping and increased activity. Dr’s Laverty and Kudnig have been involved in hip replacement surgery since 1997.
Contraindications for this procedure include the absence of lameness and/or pain regardless of radiographic appearance, pre-existing infection anywhere in the body! This is the reason why an extensive evaluation and workup is performed prior to surgery.
As you can see CHD is a complex disorder. For best results a thorough evaluation of your dog and the formulation of a customized treatment plan is required. Both medical and surgical treatments play a role in alleviating your dogs discomfort and improving their quality of life. Dr’s Laverty and Kudnig are happy to discuss any questions that you may have after reading this information sheet.