Considered a normal anatomic variant, the discoid meniscus is the most common congenital difference of the knee and is found almost exclusively in the lateral tibiofemoral compartment. Discoid menisci are, by definition, wider from medial to lateral. There is a spectrum of morphologic differences ranging from widened “incomplete” discoid menisci that retain the characteristic C-shape of the meniscus to “complete” discoid menisci that cover 90%-100% of the lateral tibial plateau. Discoid menisci also have less-organized collagen structure and decreased vascularity, predisposing them to tears.1, 2, 3 Meniscocapsular and meniscotibial attachments may also be deficient and lead to instability.

The incidence of discoid lateral meniscus (DLM) is estimated at 5% in the United States population. Ethnic variation has been reported, with up to 16.6% prevalence in patients of Japanese heritage.4, 5, 6 Bilateral discoid lateral menisci have been reported in 5% to 25% of cases, and caregivers should have a low threshold to image the contralateral knee in the setting of even mild contralateral signs or symptoms. The incidence of discoid medial meniscus is much rarer, with an incidence of 0.06% to 0.3%.1,7,8 The true prevalence of discoid meniscus is unknown, however, as they may be asymptomatic in some patients.5,9

Due to the altered shape and increased tissue volume, a discoid meniscus can change the biomechanics and contact area of the lateral tibiofemoral compartment and may increase the risk of chondral damage, given the association between osteochondritis dissecans (OCD) in the lateral femoral condyle and a DLM.10, 11, 12

Historically, discoid menisci were empirically treated with partial, sub-total, or total meniscectomy, which led to high rates of arthritis and disappointing long-term outcomes.6,13 Management of DLM has evolved to focus on preserving and reshaping meniscus tissue to recreate the normal contact relationships between the tibia, femur, and meniscus. In addition to recontouring the meniscus, repairing tears within the zone of the typical meniscus shape and stabilizing the meniscus in the setting of hypermobility due to inadequate meniscocapsular or meniscotibial attachments have been advocated. This review explores modern operative techniques to manage symptomatic, torn, or unstable discoid menisci and provides strategies to help surgeons optimize patient outcomes.