Canine hip dysplasia is a common developmental disease which tends to occur in large breed dogs. The disease usually occurs in both hind legs and is caused by both genetic and environmental factors. The underlying condition is a laxity in the structures that hold the hip joint together. In this article, I will discuss the clinical signs that dogs show with hip dysplasia and how the diagnosis of hip dysplasia is made.
Dogs with hip dysplasia tend to present in one of two ways, either as a young dog or as an older patient. The young dogs present typically between 5-10 months of age with signs of difficulty rising in the hind legs especially after rest, reluctance to jump, a bunny-hopping gait when running, exercise intolerance, and popping that can be heard or felt around the hips when walking. When examined, these dogs tend to show pain when the hips are pulled straight back and laxity in the hip joint can usually be demonstrated by a procedure called an Ortaloni test. This test involves partially luxating the joint manually then feeling it pop back into place again. Young dogs present with pain because the structures that are holding the hip together are too loose and as the dog bears weight on the leg, the two bones keep pulling apart from each other causing the ligaments and joint capsule to stretch and tear resulting in swelling within the joint.
Older dogs present usually after 8-10 years of age and show signs of difficulty rising in the hind legs, a stiff or stilted gait when walking, and muscle atrophy in the rear legs. On examination, they are painful when the hind leg is pulled straight back and have a decreased range of motion in the hip joint. Most older dogs do not have a positive Ortaloni test since the joint has developed scar tissue preventing this from happening. Older dogs present with pain in the hips because over time, the two bones pulling apart have resulted in loss of the cartilage on the bone surface and progressive arthritis formation within the joint. These dogs are said to have end-stage osteoarthritis within the joints.
Diagnosis of hip dysplasia is usually made with radiographs. Typically, a ventrodorsal hip extended view is taken which is done by laying the dog on their back and pulling both hind legs straight back. In the young dog, the main sign seen on the radiograph is separation of the head of the femur from the acetabulum. Occasionally early bone formation within the joint, termed osteophytosis, may also be seen. The older the dog gets with this disease, the more bone change or remodeling, will be seen. Typically the femoral head changes from being round to flattened and the acetabulum becomes more shallow. Visible new bone formation within the joint, termed osteophytes, will be seen on the acetabulum and on the head of the femur also.
For purposes of determining if a dogs lameness is due to hip dysplasia, the routine ventrodorsal hip extended radiographs work well. It is always indicated to take radiographs to verify that the dog has dysplasia, even if the symptoms all fit, because there are many other diseases with similar symptoms such as cruciate disease, lumbosacral disease, and hock OCD. These diseases can be treated and the dog may return to normal function. Unfortunately, some dogs are assumed to have hip dysplasia when they do not or they have hip dysplasia but it is one of these other conditions that are really causing the pain but radiographs never get taken to prove one way or the other.
Another important consideration when it comes to diagnosing hip dysplasia is that just because a young dogs hips show some signs of dysplasia does not guarantee that the dog will have problems with the disease. It has been shown in studies that there is poor correlation between clinical signs and radiographic findings. Meaning, many dogs can have significantly dysplastic hips on radiographs but show no clinical signs related to it. This is important when trying to decide if treating a young dog with dysplasia is appropriate.
For purposes of screening breeding dogs to ensure that they do not have hip dysplasia, other radiographic tests have been developed which studies have shown to be more accurate in detecting hip dysplasia. These tests are necessary because you want to know that the breeding dogs have no signs of hip dysplasia at all. These tests include the PennHIP (University of Pennsylvania Hip Improvement Program) technique and the dorsolateral subuluxation score. Both of these techniques use distraction to determine the degree of laxity within the hips. The other benefit of these tests is that they have been shown to be accurate as early as 4 months of age. Other tests such as CT scans and MRI of the hips have been looked at in research settings but are rarely used in clinical practice.
Screening breeding dogs for hip dysplasia before mating is important but does not guarantee that the puppies will not have hip dysplasia. Some dogs may be carriers for the genes for hip dysplasia but not show overt signs of the disease. When two dogs that are carriers are bred, they can have a litter of puppies that have overt signs of hip dysplasia. The only current way to reduce this possibility is by screening not only the parents but all offspring for multiple generations proving that none of the generations of puppies ever showed overt signs of hip dysplasia which is rarely, if ever done. In the near future, genetic analysis for hip dysplasia should be available which will be a much easier and accurate way of screening potential breeding dogs.
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