Ruptured Anterior Cruciate Ligament
Holly Frisby, DVM
Veterinary Services Department, Drs. Foster & Smith, Inc.
The knee is prone to a number of injuries as any football player will tell
you. One of the most common knee injuries in dogs is a ruptured cruciate
ligament.
Knee Anatomy
The knee is a joint that is formed by three bones: Femur (the long bone
extending down from the hip); Tibia (the bone between the knee and ankle);
and Patella (the kneecap). These bones are joined together by a number of
ligaments, which are tough fibrous bands of tissue. Two ligaments crisscross
in the joint from the femur to the tibia and are called cruciate ligaments
(cruciate means cross). The one towards the front of the leg is called the
anterior cruciate ligament and the one crossing behind it is the posterior
cruciate ligament. These ligaments prevent the ends of the femur and tibia
from moving back and forth across each other.
A rupture of the anterior cruciate ligament
When the anterior cruciate ligament ruptures (is torn), the joint becomes
unstable and the femur and tibia can move back and forth across each other.
The anterior cruciate ligament is most commonly torn when the dog twists
on his hind leg. The twisting motion puts too much tension on the ligament
and it tears. This often occurs if the dog slips on a slippery surface, makes
a sudden turn while running, or is hit by a car. Obesity puts too much weight
on the knee and overweight dogs tend to have more occurrences of ruptured
cruciate ligaments.
Symptoms of a ruptured cruciate ligament
Dogs who have ruptured their cruciate ligament will appear suddenly lame,
and usually hold the foot of the affected leg off the ground. The knee may
become swollen. In time, the dog may start to use the leg again, but often
lameness returns.
Diagnosis of a ruptured cruciate ligament
The diagnosis of a ruptured cruciate ligament is made through observing abnormal
movement of the joint. A veterinarian will place one hand around the femur
and one around the tibia in a precise manner. By applying pressure on the
knee, the veterinarian will feel the bones move abnormally in what is called
a 'drawer sign.' It is called that because the movement of the femur in relation
to the tibia is similar to pulling and pushing in the drawer of a cabinet.
If an animal is in a lot of pain, or very nervous, the muscles near the knee
may be so tense that they prevent the drawer movement from occurring. If
a veterinarian suspects a ruptured cruciate ligament in a dog but cannot
elicit the drawer sign, the dog may be heavily sedated to relax the muscles
and then re-examined for the drawer sign.
A device, called the 'DGY2000', has been developed by the University of Wisconsin
School of Veterinary Medicine to detect stretched or partially torn ACLs.
In these conditions there is often insufficient joint laxity to detect using
the procedure described above. The DGY2000 consists of a platform with two
moving pieces. The dog's leg is strapped onto the platform and the femur
is held in place while a small force is applied to the front and then the
back of the tibia while radiographs ( x-rays) are taken. An exact measurement
of the amount of laxity in the joint can then be determined from the two
radiographs. Earlier diagnosis and a chance to stabilize the joint before
total rupture of the ligament occurs has the potential to help prevent pain
and arthritis in dogs.
Treatment of a ruptured cruciate ligament
If the ligament is completely torn, the dog (especially a large dog) is generally
treated with surgery. There are several different methods used to repair
the knee joint when an anterior ligament is torn. They all entail using synthetic
suture material, or a portion of adjacent fibrous tissue to basically re-create
the ligament. The suture or tissue is made to extend from the outside lower
portion of the femur to the inside upper portion of the tibia. After the
surgery, the dog must be strictly confined for 2 weeks. By day 10 after surgery,
most dogs touch the toe of the affected leg to the ground and will start
bearing minimal weight on the leg. Once the dog has reached this point, it
is often very difficult to keep the dog quiet until complete healing has
taken place. The dog generally has to be restricted to only leash walking
for a minimum of 4-6 more weeks; the exact amount of time depends upon the
extent of the injury and the corrective procedure performed. This exercise
is extremely important to prevent the surgical correction from tearing. The
veterinarian's instructions regarding exercise during the recovery period
should be followed very carefully.
In some instances, if the cruciate ligament is only partially torn, the animal
is older, has medical conditions which could affect healing, or the owners
will not be able to keep the dog quiet for a number of weeks after surgery,
medical treatment is used. This basically consists of controlling the dog's
activity for 8-12 weeks. Swimming and low-impact exercise (walking) may be
done on a controlled basis, as instructed by a veterinarian, to keep up muscle
strength. If overweight, the dog should be placed on a reduced-calorie diet.
Buffered aspirin or other medications are often used to reduce inflammation
in the joint and relieve pain. (Do NOT give your cat aspirin unless prescribed
by your veterinarian.)
If a dog with a ruptured cruciate is not treated, severe degenerative joint
disease (arthritis) usually occurs. In addition, because the dog favors the
affected leg, he will generally put more weight on the unaffected leg. It
is not unusual for the dog to rupture the anterior cruciate ligament on that
leg as well because of the increased stress on the leg.
Prognosis
If the dog's exercise is restricted as instructed, and overweight dogs return
to normal body weight, the prognosis is good. Depending on the amount of
injury to the knee and length of time between the injury and correction of
the problem, degenerative joint disease may occur as the pet ages.
