Partial Rupture of Cranial Cruciate Ligament
A surprising number of cases of stifle lameness are caused by partial rupture of the cranial cruciate ligament. The veterinarian needs only to explore joints in the face of minimal physical findings to verify this.
An increasing number of dogs (especially Labrador retrievers and Rottweilers) sustain partial tears at a young age (6 to 24 months). Often, tears are bilateral and mimic hip dysplasia clinically, which may also be a concurrent problem.
It is our experience that cruciate problems cause more clinical signs than hip dysplasia and should be addressed first before it is deemed necessary to perform any surgical procedure on the hips.
Clinical signs and history mimic those of complete rupture but are not as dramatic, and secondary arthrosis is much slower in developing, probably because the meniscus is not damaged as often as in complete ligament rupture.
Degenerative changes can be extensive given enough time. The cranial cruciate ligament functionally is composed of two parts: the small craniomedial band (CrMB) and the larger caudolateral band (CdLB). The CrMB is taut in both flexion and extension, whereas the CdLB is taut only in extension.
The ability to diagnose these injuries by examination for drawer motion depends on which part of the ligament is damaged. If the injury is caused by hyperextension, it is most likely to damage the CdLB, and no drawer motion will be present because the CrMB is intact.
An injury caused by rotation or twisting with flexion is more likely to injure the CrMB. Under these circumstances, there is a small amount of drawer motion in flexion (the CdLB is relaxed) but no motion in extension (the CdLB is taut).
Pain on full extension of a stable stifle with effusion or the “fat pad sign” is also highly suggestive of a partial cranial cruciate ligament tear.
the incidence of partial tears of the cranial cruciate ligament is not insignificant and should be carefully considered as a cause of lameness in midsize to large breeds with pain in the stifle region and minimal or no drawer motion.
Radiographs demonstrating the “fat pad sign” or osteophytes are truly significant.
When repairing these injuries, the surgeon should approach them as if they were complete ruptures, since the ligament is no longer functional.
if there is osteoarthrosis (and no indication of inflammatory joint disease) of the stifle without overt causes, such as osteochondritis dissecans, luxating patella, the rare instance of isolated meniscal damage, or synovial cell sarcoma, then the cruciate ligament is suspect.
Careful probing to detect tears of the caudal side of the ligament and observing the color and reflectivity of the ligament are warranted. Arthroscopic evaluation, magnetic resonance imaging (MRI), or ultrasound may have identified these unusual cases before open surgery