Parameniscal cyst formation in the knee is associated with meniscal tear size: An MRI study

Background: The relationship between meniscal tears and parameniscal cyst formation is contentious. We investigated whether the development of a parameniscal cyst is related to the size of the meniscal tear by using magnetic resonance imaging (MRI). Methods: On the basis of a retrospective review of an MRI database, we identified parameniscal cysts in 34 patients with adjacent meniscal tears extending to the meniscocapsular junction. The size of the meniscal tear was measured by dividing the length of the tear along two axes: circumferential and radial. We compared parameters, such as the size of the meniscal tear, the location of the tear, the pattern of each tear, and any associated ligamentous injury and intra-articular lesion, between the 34 patients and the 30 control patients who only had meniscal tears with torn components extending to the meniscocapsular junction. Results: Compared with the controls, patients with parameniscal cysts had significantly larger meniscal tears along the circumferential axis (P< 0.001). A critical size of the meniscal tear along the circumferential axis of 12. mm was associated with the formation of a parameniscal cyst. Conclusions: A larger meniscal tear extending into the meniscocapsular junction is more likely to be associated with the occurrence of a parameniscal cyst. The critical size of the meniscal tear, 12. mm along the circumferential axis as identified using MRI, is a discrimination value for parameniscal cyst formation. Level of Evidence: Level III.