Pet Surgery Topics

Canine hip dysplasia is a common developmental orthopedic disease seen in many different breeds of dogs. Both genetic and environmental factors play a role in its origin.

The disease itself is a laxity to the structures that keep the hip joint tight. Although the dog is born with a normal joint, because there is laxity to the structures that hold it together, there is partial luxation of the joint during weight-bearing, termed subluxation of the joint. The consequence of this subluxation is abnormal wearing of the cartilage on the acetabulum and the head of the femur, microfracturing of the acetabulum, inflammation of the joint (synovitis), and progressive osteoarthritis within the joint.

Signalment

Hip dysplasia is typically seen in large breed dogs such as Labrador retrievers, Rottweilers, German Shepherd dogs, Golden retrievers, and many others. It can be seen in smaller dogs and rarely in cats. Dogs with a low incidence of hip dysplasia include greyhounds, borzois, Irish wolfhounds, Afghan hounds, whippets, and salukis which tend to have a high ratio of muscle mass to body fat.

Clinical Signs

Dogs with hip dysplasia can present in two ways, either as a juvenile or as an older patient.

Juvenile Patients

When juvenile patients present they are typically between 5-10 months of age. The signs that the owner can see are a bunny hopping gait, difficulty rising after rest, changes in jumping behavior, exercise intolerance, and popping or clicking noise while walking. A bunny hopping gait refers to the dog using the hind legs together when running so that it looks like a bunny hopping. On examination of these dogs, they typically show pain when the hind leg is pulled back or extended and a positive Ortaloni sign.

An Ortaloni sign is a test whereby pressure is applied dorsally or upwards towards the spine on the femur then the leg is abducted or moved outwards from the body. With a positive Ortaloni sign, when pressure is applied to the femur dorsally, the head of the femur subluxates out of the acetabulum then when the leg is moved outwards from the body, the head of the femur falls back into the acetabulum and a clunk or pop can be felt. Normal dogs will not have a positive Ortaloni sign since their hips cannot subluxate because the structures that keep the joint tight are normal. Lack of a  ositive Ortaloni sign, however, does not guarantee that the dog does not have hip dysplasia. When checking for a positive Ortaloni sign, it usually helps to sedate the dog because it can be mildly painful and unless the dog is cooperative and stays relaxed, contraction of the muscles around the hip joint can give a false negative test result.

When a juvenile dog presents with signs of hip dysplasia it is usually due to the hip joint subluxating causing tearing of the joint capsule and the ligament within the joint. This leads to swelling of the joint termed synovitis. The dog presents for pain secondary to the synovitis within the joint.

Older Patients

The second way that dogs present with hip dysplasia is as an older dog. These patients have had hip dysplasia their whole life but never showed signs to the owner when they were young to say there was a problem. Unless the dog was specifically tested for hip dysplasia as a puppy, the fact that the dog had dysplasia would not have been found.

Owners of older dogs presenting with hip dysplasia typically see the dog is slow to rise in the hind legs, has a stiff or straight-legged gait in the hind legs, exercise intolerance, and has muscle atrophy of the hind legs. On exam, these dogs tend to have pain when the leg is pulled back or extended, reduced range of motion in the hips, and atrophy of the hind leg muscles. Rarely in these dogs can you get a positive Ortaloni sign because scar tissue has formed around the joint preventing it from subluxating.

Older dogs that present with hip dysplasia are showing signs of pain from osteoarthritis within the hip joint. The pain is no longer from the hip subluxating but now is from the changes that have occurred over the years. Over time, the cartilage within the joint wore away because of the subluxation and arthritis developed within the joint and these conditions lead to the pain that the dog shows.

Diagnosis

Ventrodorsal Hip Extended Radiographs

Diagnosis of hip dysplasia is typically made with radiographs.  The dog is laid on its back and both hind legs are extended straight back to give a ventrodorsal hip extended view. Normal hips will have good congruency between the head of the femur and the acetabulum and the dorsal acetabular rim will cover 50% or more of the femoral head. There will also be no signs of new bone formation, osteophytosis, around the joint.

Normal Hip Joint Radiograph

Juvenile Hip Dysplasia Radiograph

In juvenile dogs with hip dysplasia, the head of the femur will be pulled away from the acetabulum and the head of the femur will have less than 50% coverage by the dorsal acetabular rim. Early signs of new bone formation, essentially arthritis within the joint, may also be seen even in dogs less than a year of age.

Adult Hip Dysplasia Radiographs

In adult dogs with hip dysplasia, new bone formation around the joint will be seen as well as flattening of the femoral head, a misshapen appearance to the femoral head, and a shallow appearance to the acetabulum. These are all changes that occur because of the laxity in the joint and at this point, the dog is considered to have end-stage osteoarthritis.

The ventrodorsal hip extended view is a good test to show if a dog that is having lameness has hip dysplasia as the source. It is always indicated to take radiographs to prove if the dog has hip dysplasia and not just assume it does because the signs and breed fit. There are many times when owners are told that their Labrador retriever that is becoming more and more lame in the hind legs has hip dysplasia as the source but in reality, the hips are normal and there is other problems like cruciate ligament tears, OCD of the hocks, or lumbosacral disease. The only way to know for sure that you have the right diagnosis is getting a radiograph and seeing changes to support hip dysplasia.

Because we know that hip dysplasia has a large genetic component, testing to try and identify dogs that have hip dysplasia before they are bred has been important for years. Orthopedic Foundation for Animals (OFA) is an organization that evaluates and grades dogs hips and certifies them as normal or dysplastic and keeps them all in a large database. When considering purchasing a puppy from a breeder, it is a good idea to know if they have been tested by OFA for hip dysplasia. Orthopedic Foundation for Animals uses the same ventrodorsal hip extended radiograph to certify dogs for hip dysplasia. Dogs must be two years of age or older to be certified. The radiographs are graded by a boarded radiologist and classified into one of seven grades. “Normal” hips can be excellent, good, fair, or near normal and “dysplastic” hips can be mild, moderate, or severe.

PennHIP Distraction Technique

Ventrodorsal, Neutral, Distraction Radiographs

There have also been newer tests that have come about  o try and test dogs at younger ages to see if they are dysplastic.  Penn HIP (Hip Improvement Program) is a test that uses a means of applying distraction to the hip joints. Radiographs are taken in neutral position and in distracted position and a distraction index is calculated. The test is submitted to the University of Pennsylvania Penn HIP program where a database of pretty much all breeds is kept and the distraction index is compared to other dogs within that breed because there is some variation from breed to breed. The nice thing with the Penn Hip test is that it has been shown to be accurate as early as four months of age. Penn HIP radiographs must be taken by a veterinarian certified by the program to take them but there are many people doing them so finding someone usually is not difficult.

Another radiographic test that is sometimes done is the dorsolateral subluxation score. This test is similar to Penn HIP test in which radiographs are taken in neutral and when weight-bearing is simulated. It has also been shown to be accurate in younger dogs but is less commonly done. Other tests like CT scans or MRIs can also be performed but because of cost are less often done.

Although it is important to know if breeding dogs have normal or dysplastic hips, it does not guarantee that dogs with radiographically normal hips when bred will not have dysplastic puppies. Dogs can be a carrier for hip dysplasia and not show signs of the disease.  Unfortunately, if two dogs who are carriers for the disease are mated then they can have offspring that has clinical hip dysplasia. So, unfortunately, even if dogs have OFA certification that their hips are excellent, they have a chance of producing hip dysplastic puppies. By testing not only the parents but all offspring for hip dysplasia and continuing to test for multiple generations is the only current way to feel comfortable that the disease is out of a line of dogs. Currently, one place having success with this is Guide Dogs for the Blind which does test all puppies and has made great strides to eliminating hip dysplasia from its dogs.

Another important note is that studies have shown that there is a poor correlation between clinical signs of hip dysplasia and radiographic findings. In one study, 86% of dogs with severe radiographic signs of hip dysplasia showed only mild signs at one year of age. This means that many dogs can have hip dysplasia on radiographs but never show signs of a problem. This is important when considering whether or not to treat a dog that shows signs of hip dysplasia on radiographs.

Canine hip dysplasia is a common developmental orthopedic disease that affects many breeds and usually both hips. The underlying disease is an instability within the hip joint that leads to subluxation and secondary degenerative joint disease. Hip dysplasia in dogs has a strong genetic determination but is also influenced by environmental factors such as nutrition and exercise.

The hip joint, or coxofemoral joint, in the dog is made up of the head of the femur and the acetabulum of the pelvis. Hip dysplasia puppies are born with normal hips. As they develop, the ligaments and joint capsule that keep the joint together become too lax and lead to the two bones being able to pull apart. This is the underlying disease of hip dysplasia in dogs.

Normal Hip Joint

When the head of the femur pulls away from the acetabulum, it partially luxates the joint, a condition we term subluxation. When the dog bears weight on the affected leg, subluxation occurs within the joint.  This subluxation causes the head of the femur to put excessive pressure on the edge of the top part of the acetabulum called the dorsal acetabular rim.  This dorsal acetabular rim is not used to having this excessive pressure and with time starts to develop microfractures and starts to wear down.  The  subluxation also leads to tearing of the ligaments that hold the joint together and the joint capsule which leads to swelling within the hip joint called synovitis. It is typically the synovitis which leads to the lameness that owners see when the dog is a puppy.

Canine Hip Dysplasia

As the hip dysplasia dog continues to bear weight on the leg and the hip joint keeps subluxating, the dorsal acetabular rim continues to break down.  This leads to the cartilage on the dorsal acetabular rim and on the head of the femur getting worn away which leads to secondary arthritis formation within the joint. Over time, the hip dysplasia dog is left with minimal cartilage on the two bones and an arthritic joint which becomes the source of pain in the mature dog.

Radiographs Hip Dysplasia

Hip dysplasia in dogs is a multifactorial disease. It is caused by both hereditary factors as well as environmental factors.  Hereditary factors are the primary determining factors in the disease. Meaning that dogs with any signs of hip dysplasia should not be used for breeding since they will likely pass the hip dysplasia onto the offspring. It also means that even if a dog does not show signs of bad hips, they can have the genetic make-up to produce offspring with hip dysplasia if bred to the wrong dog. This unfortunately, is why even with screening for hip dysplasia in dogs, occasionally a mating of two dogs that appear normal produces puppies that are affected with hip dysplasia.

Hip dysplasia in dogs is also influenced by environmental factors as possibly dysplastic puppies are growing. One big factor that has been shown to shorten the time to first appearance and increase the severity of canine hip dysplasia is abundant food consumption as a puppy.  While overfeeding itself doesn’t cause hip dysplasia, it does maximize the trait expression in genetically susceptible dogs. The mechanism of how this works is not known but in multiple studies, dogs that were limited in their food consumption from 6 weeks to 1 year of age had a markedly reduced incidence and severity of canine hip dysplasia.

To try and prevent dogs from having hip dysplasia, it is recommended to screen both parents before breeding and to screen all offspring of a breeding to see if any of the dogs have the disease. In this way, a breeder can eliminate any dogs from breeding that are carriers of the disease.  Also, in any puppy that is suspected to have a genetic predisposition for canine hip dysplasia to limit food consumption during the first year of life.  Currently, I recommend in any high risk breed to feed 25% less than what you would normally give. This should result in the puppy appearing a little thin which is the desired body condition score we are hoping for.