Sonographic Diagnosis of Medial Meniscocapsular Separation of the Knee

Medial meniscocapsular separation (MCS) is an uncommon knee injury. No dedicated sonographic study on medial MCS has been reported thus far. This article retrospectively analyzes the sonogram of two patients with medial MCS confirmed by either magnetic resonance imaging (MRI) or surgery. Both patients are in their 30s with sports-related medial knee injuries. Sonograms of their medial knees displayed similar features of fluid collection between the medial meniscus and the deep portion of the medial collateral ligament (MCL), and an unsmooth outer surface of the meniscus. Meniscal tear and MCL injury were also found in both of these patients. Sonographic diagnostic criteria for the medial MCS are proposed based on the two patient cases. The differentiation of medial MCS from other cystic lesions in the medial parameniscal area is also discussed.