PURPOSE: The purpose of this study was to investigate the matrix collagen network of the discoid lateral meniscus in comparison with normal lateral meniscus.METHODS: Discoid meniscus samples obtained arthroscopically from 10 patients with a diagnosis of intact complete-type discoid lateral meniscus by a technique of excision in 1 piece were examined histomorphologically regarding the integrity of both main collagen fiber systems, radial and circular, because they have been described in the structure of normal knee meniscus. As a control group, intact lateral menisci excised during knee arthroplasty procedures were used.RESULTS: Histomorphologic scoring showed statistically significant disorganization of the circular collagen network in the discoid meniscus group compared with the normal meniscus group, especially along the posterior third of the specimen (P < .001). In addition, a heterogeneous course of the circumferentially arranged collagen fibers was shown in the discoid meniscus structure.CONCLUSIONS: Findings of discontinuity and inhomogeneity of the circumferential collagen network in the discoid meniscus in comparison with normal meniscus indicate that the discoid lesion represents a structural lesion rather than a morphologic variant.CLINICAL RELEVANCE: Disorganization of the circular collagen fiber system in the discoid meniscus matrix may contribute to the pathogenesis of the high tear and degenerative lesion rate observed among menisci with discoid configuration.