Diagnosing cranial cruciate ligament pathology - Veterinary Medicine
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Diagnosing cranial cruciate ligament pathology
Not all dogs with cranial cruciate ligament pathology have palpable stifle instability. Here are a few examination skills and diagnostic tools to help you make an early diagnosis.



Figure 4 Assess the dog's response to full stifle extension, and compare it to full extension of the contralateral stifle.
The purpose of the standing examination is to begin to localize the source of the lameness by detecting muscle mass asymmetry, joint swelling, tissue warmth, decreased joint range of motion, and joint instability. Stand behind the dog and encourage it to assume a symmetric stance while you simultaneously palpate each limb to compare muscle mass and determine whether periarticular fibrosis, stifle and tarsal joint effusion, and warmth are present (Figure 3). Closing your eyes may help you focus all sensory input to your fingers. Specifically note the presence or absence of fibrosis and swelling at the medial aspect of the stifle, often called a medial buttress. A normal stifle does not have a palpable medial buttress. A normal stifle has a discretely palpable patellar ligament that feels similar to a pencil with small indentations on each side that have a consistency similar to a bruise on an apple. Palpable loss of the indentations and discrete patellar ligament indicates joint effusion, periarticular fibrosis, or both. If the cranial cruciate ligament is completely ruptured, you may also note a cranial shift of the tibia. Finally, evaluate the patient for a pain response to full stifle extension by placing one hand around the cranial surface of the distal thigh while pushing the other hand forward on the distal tibia or foot (Figure 4). Compare the dog's response to full stifle extension with a similar maneuver performed on the contralateral stifle.

Figure 5A To perform the tibial compression test on the left stifle, place your right index finger on the tibial tuberosity, and squeeze toward the right thumb, which is secured behind the lateral fabella. This maneuver shifts the tibia of the cranial cruciate ligament-deficient stifle caudally into its normal anatomic position under the femur. With your right hand, hold the stifle in a standing angle (neither fully flexed nor fully extended) while you flex the hock with your left hand to simulate weightbearing. This maneuver tenses the gastrocnemius muscle, creating cranial tibial thrust force. In a cranial cruciate ligament-deficient stifle this cranially directed shear force palpably shifts the tibia cranial relative to the femur.
Some dogs are more relaxed in the standing position than when restrained in lateral recumbency. For this reason, I prefer to perform a tibial compression test to evaluate for cranial tibial thrust instability at the conclusion of my standing examination (Figures 5A & 5B).15 With practice, the tibial compression test is a reliable method to test for gross stifle instability, especially in larger breeds in which the cranial drawer test is difficult because of muscular strength or sheer size.


Figure 5B A dog undergoing a tibial compression test.
The purpose of the recumbent examination is to continue localizing lameness by detecting a pain response, joint swelling, a limited range of motion, or joint instability. Some form of sedation may be needed in anxious or tense dogs, but heavy sedation may abolish responses to painful stimuli.

Examine the unaffected pelvic limb first to establish a baseline, and palpate from the digits toward the pelvis. Examine the upper-most limb of the laterally recumbent patient. Evaluate patellar stability, and perform tibial compression and cranial drawer tests, all stifle-specific procedures. For example, imagine you are evaluating the left pelvic limb of a dog in right lateral recumbency. Position yourself behind your patient's pelvic limbs. To test lateral patellar stability of the left stifle, apply firm lateral pressure on the patella with your right hand while holding the extended stifle in external rotation with your left hand, and then slowly flex the stifle. Conversely, to test medial patellar stability, apply firm medial pressure on the patella with your right hand while holding the extended stifle in internal rotation with your left hand, and then slowly flex the stifle. Luxation is detected as a popping or snapping sensation of the patella. Bony crepitus and an indistinct transition between luxation and reduction may indicate a loss of articular cartilage and subchondral bone suggestive of chronicity. Perform the tibial compression test as described previously.


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