In this clinical scenario, meniscal tear would be near the top of the differential diagnoses list. Other differential diagnoses include infection, implant failure, bone failure, and patellar luxation.
The reported rate of medial meniscal tears associated with an unstable CrCL rupture is approximately 50%.1-3 The rate of meniscal tears in dogs with a stable partial CrCL tear is not well described but is likely less than unstable joints.1,4 Despite the meniscus appearing normal at the time of TTA, it is possible that the clinical signs relate to a meniscal tear. Presence of a palpable or audible click is reported to increase the likelihood that meniscal pathology is present by a factor of 11.3 and has a positive predictive value of 85%.5,6
A meniscal tear noted on revision surgery may either be a subsequent meniscal tear that occurred sometime after TTA stabilization or was present during the original TTA procedure but missed during joint examination (ie, a latent tear). Regardless of the cause, the occurrence rate of meniscal tears is estimated to be 12% to 28% following TTA and 2% to 12% after tibial-plateauleveling osteotomy (TPLO).1,2,7,8
A key step in any cruciate surgery is to obtain adequate exposure for a thorough visual examination of the joint. Several instruments (eg, self-retaining Gelpi retractors, stifle distractors, small [1.5-mm] meniscal probes) can be useful in this approach.
Stifle arthroscopy, although limited to select practices and associated with a steep learning curve, also provides magnification and illumination and is particularly useful in the stifle joint. Probing the menisci, in addition to using arthroscopy, increases the sensitivity of tear detection by 1.5 to 2 times as compared with arthrotomy alone.9 Tears are almost exclusively confined to the caudal horn of the medial meniscus because of its firm attachment on the tibial plateau. The most common tear pattern is a displaced vertical longitudinal or bucket-handle tear, which accounts for the palpable click as the torn meniscus flips caudal-to-cranial in the joint.
Lateral meniscus tears are rare because robust caudal meniscofemoral attachments allow the meniscus to move with the femur during active range of motion. The original descriptions of both TPLO and TTA procedures advocated for a meniscal release at time of stabilization to prevent late tears.
A meniscal release involves cutting through the meniscus. The meniscus drops to the back of the joint and reduces the potential for a subsequent tear after stabilization. This can be done at the meniscotibial ligament (via craniomedial approach) or midbody just caudal to the medial collateral ligament (more often via a blind caudomedial approach). In a cadaveric model, the efficacy of release was only 56% to 81%, depending on the approach used.10 Surgeon skill and experience likely impacted this result, so it is important to confirm by visual examination once complete. Meniscal release is effectively the same as meniscal excision; therefore, the decision should be based on individual case selection and scientific evidence.11