The ring-shaped meniscus: a case series demonstrating the variation of imaging appearances on MRI

Area of Science:

• Orthopedic Surgery
• Radiology
• Anatomical Variants

Background:

• The ring-shaped meniscus (RSM) is a rare meniscal anomaly characterized by an intermeniscal bridge.
• It is more frequently observed in the lateral meniscus than the medial meniscus.
• Distinguishing RSM from a bucket handle tear (BHT) with a displaced fragment can be diagnostically challenging.

Purpose of the Study:

• To describe the imaging features of RSM on MRI.
• To differentiate RSM from BHTs.
• To report rare presentations of RSM, including medial and bilateral lateral involvement, and associated anomalies.

Main Methods:

• Retrospective review of six patients diagnosed with RSM via MRI.
• Detailed description of MRI findings for each case.
• Comparison of imaging features between RSM and BHTs.

Main Results:

• The study presents six cases of RSM, including two medial RSM and one bilateral lateral RSM, diagnosed via MRI.
• Key imaging characteristics that differentiate RSM from BHTs are detailed.
• Associated anomalies such as hypoplastic ACL and anomalous popliteus tendon insertion were observed.

Conclusions:

• MRI is crucial for diagnosing RSM and differentiating it from BHTs.
• RSM can present with medial or bilateral involvement, which are rare findings.
• Associated musculoskeletal anomalies may occur with RSM, requiring careful radiological assessment.