Introduction: Previous work has shown that fixation of meniscus tears supports healing by preventing tears from gapping. However, an anterior cruciate ligament (ACL) insufficiency might increase the loads especially on the posterior horns of the meniscus. The aim of this study was to test an ACL tear results in wider gaps of longitudinal meniscal tears.

Methods: 3 cm longitudinal tears were artificially set in the posterior horn of the medial menisci in 10 human cadaver knee joints. The medial plateau of the joints was replaced by a translucent copy, under which an arthroscope was positioned to observe the gapping phenomenon of the meniscal tears. The knee specimens were flexed and extended in a motion and loading simulator allowing for all degrees of freedom. The maximum gap width occurring during a flexion-extension cycle was registered.

Results: Longitudinal meniscal tears showed significantly wider gaps after cutting the ACL (p< 0.01). However, refixation of the tears with suture anchors significantly reduced the gap width to much lower values (p< 0.01), still higher then with intact ACL.

Conclusion: The results indicate that medial meniscal tears in the posterior horn are exposed to higher loads in case of an ACL insufficiency. A missing ACL leads to increased anterior instability, which obviously results in wider tear gaps also in case of tear fixation with an implant. This confirms from a biomechanical point of view the clinical finding that meniscus repair is significantly enhanced when combined with ACL reconstruction.