Spontaneously reduced extrusion of lateral meniscus following lateral meniscal repair and anterior cruciate ligament reconstruction: a case report

Introduction and importance: Anterior cruciate ligament (ACL) injuries are frequently accompanied by meniscal tears and extrusion. While meniscal repair is commonly performed concurrently with ACL reconstruction (ACLR), persistent postoperative extrusion can occur, and its clinical significance remains uncertain. The spontaneous reduction of such extrusion is a potentially important but underreported outcome. Case presentation: We report a case of multi-ligament knee injury involving a complete ACL rupture, medial collateral ligament (MCL) tear, and a lateral meniscal tear with significant extrusion. The patient underwent arthroscopic double-bundle ACLR, inside-out repair of the lateral meniscus, and suture anchor repair of the MCL. A 3-month postoperative MRI confirmed persistent lateral meniscal extrusion. However, subsequent MRI at 6 months showed evident reduction, with near-complete anatomical restoration achieved by 12 months. Clinical discussion: This case demonstrated that early residual extrusion following meniscal repair may not necessarily indicate surgical failure. The observed delayed, spontaneous reduction suggests that restored knee stability (via ligament reconstruction) and optimal load distribution may allow the healed meniscus to progressively regain functional integrity. This process may be facilitated by the gradual restoration of circumferential collagen fibers and hoop stresses, rather than representing an immediate postoperative outcome. Conclusion: Early postoperative meniscal extrusion may not definitively indicate repair failure and could be monitored over time. Restored knee stability and optimal load distribution may facilitate spontaneous reduction, likely through the gradual restoration of circumferential fiber integrity and hoop stress.