Anomalous insertion of the medial meniscus: Case series of a rare meniscal anatomical variant with literature review

Medial meniscal anomalies are rare and predominantly affect the anterior horn. Under normal circumstances, this segment attaches anteriorly to the tibial intercondylar eminence, just ahead of the anterior cruciate ligament (ACL). A range of embryological and structural variations in the medial meniscus has been reported across cadaveric, anatomical, and clinical studies. These include the discoid morphology, agenesis, underdevelopment of the anterior horn, and the uncommon anomalous insertion of the medial meniscus (AIMM) into the ACL. Among these, the discoid form appears most frequently, with an incidence between 3% and 5%, whereas AIMM is exceptionally rare, with a reported occurrence of 1.2–2.3%. The prevalence is imaging based. We found this variant in nine patients undergoing magnetic resonance imaging (MRI) of the knee for various indications. The goal of this review is to detail the MRI features of AIMM and explore existing literature and clinical impact. Through radiologic evaluation and clinical insights, this article seeks to strengthen diagnostic confidence and inform treatment decisions in orthopedic practice.