PURPOSE: To describe the clinical, arthroscopic, and magnetic resonance imaging (MRI) findings of knees with anomalous insertion of the anterior horn of the medial meniscus (AHMM) into the intercondylar notch via an anteromedial meniscofemoral ligament (AMMFL).METHODS: A total of 2,503 arthroscopic knee surgeries performed from July 2003 to October 2016 were reviewed retrospectively to identify knees with an AMMFL. Medical records, arthroscopic photographs, and MRI of identified cases were analyzed. Meniscus width and extrusion were measured on MRI. Fifty patients with a normal meniscus were selected as a control group.RESULTS: A total of 13 (0.52%) patients had an AMMFL with insertion at the intercondylar notch. All cases were diagnosed incidentally during arthroscopy. The characteristics of knee pain were related to surgical pathology. Arthroscopic examination revealed the AMMFL as a band-like structure covering the anterior cruciate ligament. In all cases, the AHMM had no bony attachment to the tibia, and increased mobility was observed on probing of the AHMM. The medial meniscus (MM) was significantly larger than the general size in 8 cases (61.5%). Twelve knees (92.3%) had meniscus tears. On MRI, the AMMFL appeared as a low-signal linear structure arising at the AHMM and coursing superiorly along the anterior cruciate ligament. The mean MM width was greater than that in the control group at the mid-body (P = .030), anterior horn (P = .002), and posterior horn (P = .001).CONCLUSIONS: All cases of AMMFL were found incidentally during arthroscopic surgery, and the AMMFL was a silent lesion. There was no significant meniscal extrusion, although the AHMM had no bony attachment. This is because the AMMFL may act as an anchor for the AHMM. Therefore, the AMMFL should not always be removed. The MM with an AMMFL tended to be larger than the typical MM and may be related to some degree of hypermobility, which raises the risk of meniscal tears.LEVEL OF EVIDENCE: Level IV, retrospective case series.
Adolescent Adult