Posterior horn instability of the medial meniscus a sign of posterior meniscotibial ligament insufficiency

Purpose In longstanding chronic anterior cruciate ligament (ACL) insufficiency, we identified an abnormal movement of the posterior medial meniscal horn, likely due to insufficiency of the posteromedial meniscotibial ligament. Passing from extension to flexion or vice versa, the medial posterior horn slides below the posterior rim of the tibia exposing the tibial plateau. Fixation with suture anchors of the meniscotibial ligament through a posteromedial portal restored normal meniscotibial tension and reduced instability of the meniscal posterior horn. The purpose of the present study was to present the arthroscopic features of posterior medial meniscus instability and to report results following arthroscopic repair. Methods During the two-year study period, from 2007 through 2008, this arthroscopic feature was detected in 12 patients, 5 patients had failure of a previous ACL reconstruction and 7 patients had delay in ligamentous reconstruction for various reasons. All patients were affected by severe anterior–posterior translation with 11.3 ± 4.3 mm of side-to-side difference at KT-2000 and by associated rotatory laxity with grade 3 of pivot shift. Results At follow-up of 1 year, the combined ACL reconstruction and fixation of the posteromedial horn showed a reduction in the rotatory and anteroposterior laxity. Conclusions This study suggests the importance of a proper arthroscopic evaluation of the posterior medial capsule in patients with chronic ACL insufficiency and highlights the potential presence of an unstable posterior horn of the medial meniscus as an indirect arthroscopic sign of peripheral laxity. Level of evidence Retrospective chart review, Level IV.