There are two ligaments inside the knee joint that prevent the bones from moving backwards and forwards against one another. These are known as the cranial (towards the front) and caudal (towards the back) 'cruciate' ligaments, because they cross over. When we talk about cruciate ligament rupture, we are almost always talking about the cranial cruciate ligament.
Rupture of the cranial cruciate ligament is very common in the dog, though it also occurs in cats. In dogs the knee joint is poorly conformed so that there is constant stress on the cranial cruciate ligament. Sometimes the ligament gradually frays over time, or sometimes trauma or a sudden movement can cause it to snap. In cats, cruciate ligament rupture is almost always caused by trauma. Rupture causes instability of the knee joint and can be quite painful. Unless surgery is performed to repair the joint, chronic instability will lead to osteoarthritis.
Since the cruciate ligament prevents the bones from moving backward and forward relative to one another, cruciate ligament rupture will result in instability that we will often be able to feel during consultation. Sometimes it is not that simple, though, since animals that are sore and nervous will often tense their muscles to the point where we can barely move the joint at all! In these cases, we may need to sedate or anaesthetise your pet to get a definitive diagnosis.
The treatment we recommend will depend on the size of your pet. Because cats are small and light and their joints are conformed better than those of dogs, they will often recover well with a course of anti-inflammatory treatment and no repair at all.
Dogs, on the other hand, will invariably need treatment to regain normal function in the leg. In small dogs we recommend a procedure called the DeAngelis repair, where we insert a prosthetic ligament to try to replace the ruptured ligament. At this time, we open the knee joint to remove the ruptured ligament and check for any other damage within the joint.
In larger dogs, the DeAngelis repair is often ineffective in the long term. Many dogs will break the prosthesis, or it will stretch and become non-functional. In these dogs, we recommend a procedure called the Tibial Tuberosity Advancement. This aims to alter the mechanical forces in the joint so that it is stable even without the cranial cruciate ligament.
All animals will initially require some anti-inflammatory treatment for pain relief. After surgery, you will need to confine your dog for up to six weeks, then gradually reintroduce exercise over the next couple of months.
The long-term outcome for most patients is good. You can improve the odds of a good recovery by sticking to the exercise restrictions we recommend, and ensuring that your dog is at an optimal weight. It is important to realise that dogs that have suffered one cruciate ligament rupture are at increased risk of rupturing the ligament in the opposite leg, often within 6 months to 3 years.
Here you can find information and advice about common problems and diseases. Please remember, though, that this information can't replace a visit to the vet!