Ring-Shaped Lateral Meniscus – Rise Awareness and Avoid Unnecessary Surgery: A Case Report

There are numerous meniscal anatomical variants, particularly prevalent in the East Asian population. These variants typically involve the lateral meniscus and are often asymptomatic. The ring-shaped meniscus is a relatively rare variant, with an incidence of 0.9 to 2.4% in the Asian populations. Magnetic resonance imaging (MRI) has a pivotal role in diagnosing meniscal and ligament injuries of the knee. Still, it has been difficult to distinguish a ring-shaped meniscus from a bucket-handle tear of a lateral meniscus or a central tear of a discoid lateral meniscus.

The subject was a woman in her 20s, reporting pain in her left knee after a mild sprain. The first MRI showed a small mediopatellar plica with a fissure of lateral femoral cartilage posteriorly and a massive bucket-handle rupture of the lateral meniscus with intercondylar incarceration of the fragment. During arthroscopic knee surgery, an intercondylar lateral meniscus fragment was visualized. The fragment could not be reponed due to a massive fibrous band attaching it to the joint capsule posteromedially. A congenital condition was suspected. Later, a follow-up bilateral MRI was performed, showing a symmetrical condition and confirming the presence of bilateral ring-shaped lateral menisci. The radiologist, however, still interpreted the finding as a bilateral incarcerated bucket-handle lateral meniscus tear.

Our case highlights the importance of knowing the plethora of meniscal variants to avoid unnecessary surgery.