Carpal instability and arthrodesis in dogs and cats
Today we want to tell you about a problem in dogs and cats that often goes unnoticed in time – instability of the wrist joint (subluxation). The wrist joint is made up of many small bones, which are stabilised by even more ligaments. It is the disruption of these ligaments that causes instability of the wrist joint.
Why does instability of the wrist occur? Since the front legs of an animal have to bear 60% of its body weight and the carpal joint is involved in virtually all (90%) of the movements performed by the front leg, it is subjected to enormous loads when the animal runs, brakes, jumps and turns.
It is micro-trauma, partial or complete tears of the ligament, that is the main cause of carpal joint problems. Another cause of damage to the carpal joints is impaired bone development, where the bones and articular surfaces of the carpal joints develop irregularly as the puppy or kitten grows (Figure 1).
This puts extra strain on the ligaments in the joint and can cause them to tear. In older dogs, degeneration of the ligaments develops (especially in the Collie breed) and they become less elastic and no longer fulfil their function.
Why is instability bad? When a joint is unstable, the bones start to move more than they should. This movement causes swelling and inflammation of the surrounding tissues (joint capsule, tendons, muscles). This causes discomfort and pain in the animal, which leads to lameness. If the problem persists for a prolonged period of time, chronic inflammation and osteoarthritis begin to develop. Osteophytes (bone growths) form at the site of the lesion and come into contact with the surrounding tissue as the animal walks. This leads to further pain and joint dysfunction (Figure 2).
How to diagnose wrist problems early? At the veterinary clinic, instability of the wrist joint is evaluated during the examination using special tests. X-rays are also taken to determine the size of the gaps between the joints and the maximum wrist extension angle. In the early phase of the lesion, the animal does not always walk with a limp, but if you notice that the animal holds its leg up more often or that the carpal area of one leg is thicker than that of the other, we recommend that you see your vet.
How is wrist instability treated? Conservative treatment is used when wrist instability is minimal and noticed early, before damage to the articular surfaces or bones has developed. The wrist joint is fixed with an elastic bandage or a special splint and supplements are given to promote ligament regeneration. When the wrist is unstable or shows signs of osteoarthritis, surgical treatment, such as partial or total arthrodesis, is applied. During these procedures, the wrist joint is fixed with titanium plates and screws to prevent it from bending. Partial arthrodesis does not fix all the joints of the wrist, so the partial function of the wrist is maintained. After full arthrodesis (Fig. 3), the wrist cannot flex and the other joints take over its function.
So we have a great example of how a simple procedure can significantly improve the quality of life of animals. A couple of months ago, a 6-year-old cat was brought to the clinic with no support on its front leg. This condition had been going on for about a year. The cat had been on painkillers, but was limping. In our clinic, this cat was diagnosed with osteoarthritis of the wrist joint and underwent a total wrist arthrodesis. One week after the operation, the cat is now trying to support her leg. Now, for the first time, she is no longer in pain and is not taking any painkillers.