Is the present classification of discoid meniscus sufficient?
Introduction: Although uncommon, the discoid meniscus is quite prone to injury due to its abnormal shape and abnormal histology. The weak or absent peripheral attachment of the discoid meniscus causes instability even after partial meniscectomy. Therefore, recently, after resection of the central part of the meniscus, in which tears develop most frequently, the remnant of the meniscus is preferred to repair. In that time, the Watanabe classification, which classifies the discoid meniscuses in three groups, is used to plan treatment. However, discoid meniscus can develop in the different forms from these three main shapes. In the present study we aimed to analyse the discoid meniscuses, which we encountered during arthroscopic procedures in the knee, according to Watanabe classification. Patients and methods: The lateral discoid meniscuses in the 36 knees of 35 patients, who were operated on because of meniscus tear of either the discoid lateral meniscus itself or the normal medial meniscus, were classified according to Watanabe classification. Results: While the lateral discoid meniscuses were classified as “complete” in 13, “incomplete” in 15 knees, the meniscuses were very thin or absent in the central (one knee) or in the postero-lateral regions (seven knees) of discoid meniscus ( Figure 1 ). In this series this opening was next to the popliteus tendon except in one case. In these cases, the continuity of the meniscus between middle and posterior horn frequently was not possible after central partial meniscectomy (CPM). On the other hand, posterior horn has stable peripheral attachment unlike the Wrisberg type discoid meniscus. Of the 36 discoid meniscuses, CPM was performed in 21 knees, CPM with anterior horn repair in three, CPM with posterior horn repair in one and anterior horn repair without meniscectomy in two patients. In nine patients the lateral discoid meniscus was left alone. [Figure: see text] Discussion and conclusion: When meniscus sparing methods are intended to perform, both to decide the amount of resection and repair of the remnant, besides the shape of meniscus tear, the stability of discoid meniscus is crucial. This study shows that the Watanabe classification cannot be sufficient to include some specific type of lateral discoid meniscus. We believe that to add the discoid meniscuses, with opening in postero-lateral region next to the popliteus tendon, to the Watanabe classification might be useful to decide the amount of resection or repair of the discoid lateral meniscus.