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Ruptured Anterior Cruciate Ligament
(ACL) |
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Veterinary
Services Department, Drs.
Foster & Smith, Inc. |
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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.
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 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. It appears that in most
dogs with the problem, the ACL slowly degenerates
and becomes weaker until it ruptures, without any
sudden injury. Certain breeds appear to be at
increased risk of ACL degeneration and include the
Newfoundland, Labrador Retriever, Rottweiler, Bichon
Frise, St. Bernard, and others. Many dogs with a
degenerating ACL will have the condition in both
knees. In small breed dogs, a
luxating patella may predispose them to a
ruptured anterior cruciate ligament.
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. Dogs with
a degenerating ACL may also show some pain, and
there may be some swelling in the joint.
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. Many dogs with a ruptured cruciate ligament
will have swelling on the inside aspect of the knee,
and this is called a medial buttress. Radiographs
are commonly performed to better assess the amount
of arthritis that may be present.
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. Some 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 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.
Another surgery that may be performed is the
tibial plateau leveling osteotomy (TPLO). In this
procedure, a portion of the tibia is cut, moved, and
reattached to a different portion of the tibia using
plates and screws. By changing the conformation of
the tibia, the joint is stabilized. This is a
technically difficult surgery but it has shown to
produce excellent results, often with less
arthritis. This surgery is especially recommended
for dogs over 50 pounds in weight. The recovery
period is similar to that with the other surgical
procedures.
The third procedure that may be used is the
tibial tuberosity advancement (TTA). This is another
surgery in which a different portion of the tibia is
cut, and allowed to heal at a different angle to
change the mechanical stresses on the joint. As with
the TPLO, this surgery is more complex and it
requires special equipment and training.
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. Nonsteroidal anti-inflammatory
drugs (NSAIDS) such as carprofen, etodolac,
meloxicam, deracoxib, 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.) Products
containing glucosamine, chondroitin, perna mussel,
polysulfated glycosaminoglycans, and other
chondroprotective agents are often recommended, as
well.
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
