[Pathogenesis of cysts of the external meniscus]

A classification of cysts of the menisci into three groups is proposed. The first is secondary to dystrophy of the meniscus. The second is secondary to traumatic lesions of the meniscus. Third is related to degenerative changes in the meniscus. The authors have studied 7 cases in the first group, 23 in the second group and 15 in the third group. They emphasize the role of a horizontal defect in the meniscus with subsequent formation of a cyst. They consider that, in monopodal weight-bearing, intra-articular pressure forces synovial fluid into the defect to initiate the formation of a cyst. The authors propose that the cyst and the damaged meniscus should be systematically removed to avoid recurrence.