Your veterinarian will perform three tests to determine whether or not your dog has a ruptured cruciate ligament.
Tests to Diagnose Ruptured or Torn Cruciate Ligament:
- Physical exam
- Manual instability tests.
Your vet will look for the following during the physical exam:
- Positive Sit Test: Dogs normally sit with the stifle fully flexed under the pelvis. Dogs with cranial cruciate ligament injury will frequently sit with the entire leg out to the side. Sitting with “the entire leg out” is referred to as a “positive sit” test.
- Medial Buttress: By palpating the inside of your dog’s stifle, your veterinarian will be able to discern the presence of a medial buttress. A medial buttress is a swelling on the inside of the stifle developing in an attempt to control the instability. Swellings appear as early as one month after cruciate injury.
- Stifle swelling called effusion: Swelling inside a joint is termed effusion. Effusion develops as a reaction to the torn fibers. It presents as a swollen knee. Your veterinarian will be able to easily discern the presence of effusion during the physical exam. When effusion exists, damage to the cruciate ligament is confirmed.
Your veterinarian will most likely take x-rays to positively diagnose cruciate disease.
X-rays of the stifle joint can determine the presence of joint effusion or arthritis.
Both disorders are diagnostic of cruciate damage.
Manual Testing for Instability
The first test is cranial drawer.
During the cranial drawer test, your vet will stabilize your dog’s femur with one hand and at the same time manipulate your dog’s tibia with the other hand.
If your dog’s tibia moves forward, the result is a positive drawer.
When the cruciate ligament is ruptured, the tibia moves similar to a drawer being opened.
If the rupture happened a while ago, the side of the leg facing the opposite leg will be swollen.
Swelling on a leg facing the opposite leg indicates arthritis and is called medial buttress.
The majority of dogs with cranial drawer sign can be palpated and examined with the dog awake.
However, if any uncertainty exists, palpation of the dog under sedation or anesthesia is necessary.
Dogs with partial tears of the cranial cruciate ligament and dogs with chronic cranial cruciate ligament injury will tend to have less cranial drawer than the “normal” dog with a cranial cruciate injury.
It is imperative to compare the drawer of one stifle to the opposite stifle. The second manual test is termed cranial tibial thrust.
The cranial tibial thrust test is another manually applied force to test the stability or lack of stability of the stifle joint.
So, all of the above tests should give your veterinarian a good idea of whether or not a ligament injury is causing your dog’s lameness.
Due to the progressive nature of ligament injury, dogs present to the veterinarian with either a partial or complete tear.
Diagnosing a Partial Tear
A partial tear occurs when individual fibers of the ligament tear, not the entire ligament. Imagine your daughter’s ponytail.
The entire ponytail represents the entire cranial cruciate ligament, and every single hair in the ponytail represents an individual fiber in the cruciate ligament.
When individual fibers tear and lameness occurs, the situation is described as a partial tear.
Partial tears lead to lameness and swelling but rarely lead to gross instability of the joint.
Some dogs adapt to partial tears and no surgery is necessary.
Diagnosing a Full Tear or Rupture
Occasionally, a full tear is the result of trauma much like the tear seen in football players.
However, as mentioned earlier, partial tears frequently escalate to full tears.
Full tears lead directly to joint instability and generally require costly surgery to correct.
Cost can vary depending on the surgeon and the surgical technique employed.
The treatment for each type of tear will depend on a variety of factors including the size and weight of your dog, your dog’s age, other concurrent diseases, your veterinarian’s experience and more.
Diagnosing a cranial cruciate ligament injury usually requires fairly straightforward tests such as a complete physical exam and x-rays.
Unfortunately, the treatment may be much more complex.