Arthroscopic, histological and imaging studies of rare abnormal insertion points in the anterior root of the medial meniscus / 中华骨科杂志

ABSTRACT

Objective:To investigate the characteristics of an abnormal attachment point of the anterior horn of the medial meniscus (AHMM) by methods of arthroscopy, radiological imaging, and pathology.Methods:A total of seven cases of a rare abnormal attachment (anteromedial meniscofemoral ligament, AML) connecting the AHMM and anterior cruciate ligament (ACL) were identified in the more than six thousand arthroscopic procedures from January 2018 to April 2021. During the procedures, subtotal meniscal resection or meniscal repair was performed in all cases. Tissue removed intraoperatively was used for pathologic examination. For this study, the preoperative MRI films of these patients were retrospectively examined.Results:Finally, seven cases with diagnosed meniscal tears were included in this study, including 4 males and 3 females with a mean age of 37.85±7.70 years (range, 27-50 years). The AML, which extends outward and upward and is anterior to the ACL, begins at the AHMM and ends anterior to the femoral attachment of the ACL. The histological staining showed that the AML was a bundle of collagen fibers, whereas the ACL was a bundle of dense fibrous collagen. The AML could be clearly identified in the proton-weighted image of sagittal MRI preoperatively and showed a low signaling similar to the signal intensity of the ACL. AML was easily identified on sagittal MRI but not on axial and coronal MRI. In three patients who underwent bilateral MRI, the AML structure was found in both knees.Conclusion:The incidence of rare anatomic variation between the AHMM and the lateral condyle of the femur is 0.1%, usually occurring in both knees simultaneously. In cases with this variation, there is no bony attachment in the AHMM connected to the ACL via the AML. After transection of the AML, the annular fibrous structure and mechanical properties of the meniscus are damaged, as consequently the AML should be carefully protected in clinical practice.