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The Drawer Sign
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Cranial Drawer Test
This is when the Vet stabilizes the distal femur with one hand and
attenpts to move the proximal tibia. If there is movement cranially
this is termed as a positive cranial drawer sign. The diagnosis of a ruptured
cruciate ligament is made through observing abnormal movement of the
joint. Your
veterinarian may suspect cruciate ligament rupture after an
examination.
Without the stabilizing action of the anterior cruciate ligament, the
femur
and tibia move in an abnormal fashion in relation to each other. This
instability
can be demonstrated by eliciting the ‘drawer sign’. A negative
drawer
sign means the ACL is doing it's job and preventing the femur from
sliding
forward on the tibia. A positive drawer sign means that the ACL is not
functioning
properly and the femur is sliding forward on the tibia. The sliding is
what
is referred to as the instability in the knee. In the majority of cases
a positive drawer sign is pretty indicative of a dog needing surgery to
stabilize the knee. There are varying degrees of a
positive
drawer sign and this helps a surgeon determine the extent of the
tear.
A positive drawer sign doesn't necessarily mean that the ACL is
torn.
It could be stretched too and sometimes surgery is unnecessary.
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 not possible for a normal knee to show this 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. The veterinarian
stabilizes the position of the
femur with one hand and manipulates the tibia with the other hand. If
the
tibia moves forward (like a drawer being opened), the cruciate ligament
is
ruptured.
Cranial Thrust Test
Another test that can be
used is the "Cranial
Thrust Test" or
“Tibial Compression test” where the veterinarian stabilizes the femur
with one hand and flexes the ankle
with the other hand. The Vet is looking for Cranial motion of the
proximal tibia.
If the ligament is ruptured, again the
tibia moves abnormally forward.
If the rupture occurred some
time ago, there will be swelling on side of the knee joint that faces
the other leg. This is called a “medial buttress” and is a sign that
arthritis is well along.
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. It can
sometimes be demonstrated when the dog is conscious, but in many cases,
the dog requires sedation or general anaesthesia to allow proper
examination of the joint. This is especially true with larger
dogs.
Radiographs
The Vet is looking for joint effusion . If the injury is chronic and
the knee unstable for a period of time there likely will be evidence of
arthritis. X-rays
assist in identifying arthritic changes within and around the knee
joint. Since arthritis can set in relatively quickly after a
cruciate ligament rupture, radiographs to assess arthritis are a good
idea. Another reason for radiographs is that occasionally when the
cruciate ligament tears, a piece of bone where the ligament attaches to
the tibia breaks off as well. This will require repair and the surgeon
will need to know about it before beginning surgery.
Many dogs have to be sedated to get an accurate diagnosis. Please be
sure that your Orthovet does all three tests to determine an ACL tear.
