Improvement in the medial meniscus posterior shift following anterior cruciate ligament reconstruction

Purpose Anterior cruciate ligament (ACL) reconstruction can reduce the risk of developing osteoarthritic knees. The goals of ACL reconstruction are to restore knee stability and reduce post-traumatic meniscal tears and cartilage degradation. A chronic ACL insufficiency frequently results in medial meniscus (MM) injury at the posterior segment. How ACL reconstruction can reduce the deformation of the MM posterior segment remains unclear. In this study, we evaluated the form of the MM posterior segment and anterior tibial translation before and after ACL reconstruction using open magnetic resonance imaging (MRI). Methods Seventeen patients who underwent ACL reconstructions without MM injuries were included in this study. MM deformation was evaluated using open MRI before surgery and 3 months after surgery. We measured medial meniscal length (MML), medial meniscal height (MMH), medial meniscal posterior body width (MPBW), MM-femoral condyle contact width (M-FCW) and posterior tibiofemoral distance (PTFD) at knee flexion angles of 10 degrees and 90 degrees. Results There were no significant pre-and postoperative differences during a flexion angle of 10 degrees. At a flexion angle of 90 degrees, MML decreased from 43.7 +/- 4.5 to 41.4 +/- 4.5 mm (P < 0.001), MMH from 7.5 +/- 1.4 to 6.9 +/- 1.4 mm (P = 0.006), MPBW from 13.1 +/- 2.0 to 12.2 +/- 1.9 mm (P < 0.001) and M-FCW from 10.0 +/- 1.5 to 8.5 +/- 1.5 mm (P < 0.001) after ACL reconstruction. The PTFD increased from 2.1 +/- 2.8 to 2.7 +/- 2.4 mm after ACL reconstruction (P = 0.015). Conclusions ACL reconstruction affects the contact pattern between the MM posterior segment and medial femoral condyle and can reduce the deformation of the MM posterior segment in the knee-flexed position by reducing abnormal anterior tibial translation. It possibly prevents secondary injury to the MM posterior segment and cartilage that progresses to knee osteoarthritis.