Meniscal injury in dogs and cats primarily occurs secondary to stifle instability resulting from cranial cruciate ligament (CCL) rupture.7-18 Isolated meniscal tears are rare and may be more likely to occur secondary to trauma or in canine athletes; a limited number of these cases have been reported.8,10-12 CCL rupture is the most common cause of pelvic limb lameness in dogs, and ≥85% of dogs—and 67% of cats—with CCL rupture have been reported to have meniscal tears diagnosed at the time of surgery.12,13 Postoperatively, meniscal tears can also occur secondary to persistent stifle instability and have been reported in 0.7% to 27.8% of dogs, with the lowest rates generally following tibial plateau leveling osteotomy (TPLO) surgery and the highest rates generally following tibial tuberosity advancement surgery.15-18
Spayed/neutered, older, and obese dogs, as well as certain breeds (eg, rottweilers, Newfoundlands, Staffordshire terriers), have been shown to have a higher risk for CCL rupture.19,20 Specific risk factors for the development of meniscal tears after CCL rupture include increased stifle instability, increased duration of lameness, increased weight, and older age.21-23
Although there are 2 menisci in the stifle joint, >96% of meniscal tears occur in the medial meniscus alone.1,2,4,13,15,16,24 This is secondary to anatomic differences between the medial and lateral menisci. Both menisci are attached cranially to the tibia, but the medial meniscus is more closely associated with the tibial plateau because of its firm attachment at the medial collateral ligament, peripheral attachment to the joint capsule, and primary caudal attachment to the tibia at the meniscotibial ligament. The lateral meniscus lacks an attachment at the collateral ligament, has looser capsular attachments, and has its primary caudal attachment on the femur versus the tibia. When the CCL is ruptured (Figure 1), the femoral condyles translate caudally during weight-bearing, leading the lateral meniscus to translate caudally with the lateral femoral condyle. The medial meniscus, which is more firmly attached to the tibia, is then crushed by the medial femoral condyle when it translates caudally. Excessive rotational forces in the stifle, either from CCL rupture or supraphysiologic loads, can also lead to meniscal injury.8,25,26 Tears may be partial or full thickness through the meniscus.