The ring-shaped meniscus (RSM) is a rare meniscal variant in which there is an intermeniscal bridge between the anterior and posterior horns of the meniscus, thus forming a complete ring. The lateral meniscus is more commonly involved than the medial meniscus. Distinguishing an RSM from a bucket handle tear (BHT) with a displaced fragment in the intercondylar notch is challenging and there are reports of negative arthroscopies for suspected BHTs. There are many reports of symptomatic and asymptomatic lateral RSMs diagnosed on MRI in the literature. We report a series of RSMs in six patients, which includes MRI descriptions of two cases of medial RSM and a case of bilateral lateral RSM, which were diagnosed on MRI and have never previously been reported. This study will also describe the various imaging features of a RSM that distinguish it from a displaced BHT. We will also discuss associated rare malformations encountered in our study, such as hypoplastic anterior cruciate ligament and the anomalous insertion of the popliteus tendon onto the posterior horn of a lateral RSM.

中文翻译：

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环形半月板：一个病例系列，展示了MRI成像外观的变化

环形半月板（RSM）是一种罕见的半月板变体，其中半月板的前角和后角之间存在桥间桥，从而形成完整的环。外侧半月板比内侧半月板更常见。从桶柄撕裂（BHT）的con突间凹口中有移位的碎片中区分出RSM是具有挑战性的，并且有报道称可疑BHT的关节镜阴性。文献中有许多关于在MRI上诊断出有症状和无症状的外侧RSM的报道。我们报告了一系列6例患者的RSM，其中包括2例内侧RSM和1例双侧外侧RSM的MRI描述，这些病例是在MRI上诊断出来的，以前从未报道过。这项研究还将描述RSM的各种成像特征，以区别于置换后的BHT。我们还将讨论在我们的研究中遇到的相关罕见畸形，例如发育不良的前十字韧带以及the肌腱在侧向RSM的后角上的异常插入。