Anybody who follows sports will know that athletes, particularly football players, will sometimes injure their ACL, the anterior cruciate ligament, putting them out of action for weeks or months.
Your dog can suffer a similar injury — Cruciate Ligament Rupture, or CLR. It’s a painful, acute or chronic degenerative injury, usually of the anterior cruciate ligament, that results in partial or complete instability of the knee joint.
There are two cruciate ligaments — the anterior and the posterior — in the dog’s knee, or the stifle. As they pass between the two main bones of the leg, the femur and tibia, they cross, hence the ‘anterior’ and ‘posterior names. If the knee is subjected to twisting when under load the anterior cruciate ligament can tear, destabilising the knee joint. The tear may be partial or complete.
As with athletes, the cause may be trauma related but that is not actually a common cause in dogs. More often, cruciate ligament rupture is a gradual process, resulting from chronic inflammation in the knee joint. Obesity, age-related changes, poor conformation and immune-mediated diseases — where the body’s defense mechanism starts attacking the body instead of protecting it — are some of the more common causes of CLR in dogs.
The type of cruciate ligament injury that shows as an inability to bear weight on a leg, with the animal holding the affected limb off the ground, is generally caused by athletic or traumatic events.
Signs of degenerative types of cruciate ligament injuries are much more subtle, showing as marked intermittent lameness that continues for weeks or months. Bilateral cruciate disease, where both knee joints are affected, is also common.
In some cases degenerative changes in the ligaments may predispose a dog to injury, resulting in partial ligament tears that, in time, can progress to full tears, so there is a chance that the opposite knee joint may have a similar type injury in the future. The underlying reason for these degenerative changes is not fully understood.
How is a torn cruciate ligament diagnosed?
An initial physical examination can often reveal a suspected cruciate ligament rupture. With the stabilising action of the anterior cruciate ligament ‘out of action,’ the femur and tibia will move in an abnormal fashion in relation to each other, demonstrating instability. This kind of physical exam can sometimes be done when the dog is conscious but, besides being painful, the muscles of the dog’s joint will probably be in spasm, making diagnosis difficult. Usually the dog requires sedation or general anaesthesia to allow proper examination of the joint.
While an x-ray will not detect the damaged ligaments in your pet when they occur, they will pick up arthritic changes as they later develop in the unstable joint.
We may also use ultrasound to help confirm a diagnosis, or, in some cases, insert an arthroscope into the joint, allowing us to see if the cruciate ligament is torn or the meniscal cartilage is damaged, and the full extent of the damage.
A CLR can be treated either by medical management or by surgery.
Medical management is most suited for smaller, lighter dogs but larger breeds can show improvement as well.
A conservative medical management program essentially lets nature take its course, with a little help from us. It uses a planned regime of rest, restriction of strenuous exercise, planned diet and weight loss programs, hydrotherapy and anti-inflammatory medications, and time. Around two thirds of dogs weighing under 10 kg will show marked improvement within six months. Most dogs will show some degree of improvement with this regime, but few will return to full knee function.
Other possible treatments include cryotherapy, laser therapy and neuromuscular electrical stimulation — all treatments commonly used in sports and rehabilitative human medicine but still very rare in veterinary medicine, and with few documented case studies.
The difficulty with this type of conservative management of a CLR is that it is not fixing the underlying problem and, if instability of the knee remains, it will normally lead to arthritic changes in of the joint, which cannot be reversed.
Surgery to repair the ligament and stabilise the knee joint is the other option for CLR treatment. There are a number of different surgical techniques available to help repair the knees of pets suffering a torn cruciate ligament.
Intra-capsular techniques insert devices used to stabilise the knee and require opening the joint. Extra-capsular techniques are designed to add strength to the structures surrounding the joint to compensate for the torn cruciate.
There are other surgical techniques, with new procedures continually being developed. In all cases there is no guarantee that surgery can ensure the affected joint will function normally. Arthritis can still develop in the affected joint following surgery, but will normally be to a significantly lesser extent than if no surgery were performed.
There is some debate about the long term effectiveness of surgery for the repair of cruciate ligament ruptures. At least one study has found that the number of dogs who return to full normal leg function after surgery is little more than those who recover with conservative medical management.
We use both treatments and our experience at Alpine Animal Doctors has been that our surgical patients, in most cases, experience a better long term outcome than those treated without surgery. Significantly, dogs who have undergone surgery for CLR appear to be far less likely to go on to develop arthritis in the affected knee, and suffer less long term pain.
We will discuss with you the various treatment options available, and fully explain the pros and cons of each but, in the end, the decision on treatment options is always left to the pet owner.
It’s worth noting that overweight and obese dogs are much more prone to cruciate ligament tears. The best way to prevent a CLR in your dog is to ensure their diet is matched to their size and level of exercise.