Summary A discoid meniscus is the abnormal development of the meniscus leading to a hypertrophic and discoid shaped meniscus. Diagnosis can be suspected on radiographs with (squaring of lateral condyle with cupping of lateral tibial plateau) but require MRI for confirmation (3 or more 5mm sagittal images with meniscal continuity). Treatment is generally observation for patients who are asymptomatic. Arthroscopic meniscectomy and saucerization may be indicated for patients with continued pain and mechanical symptoms. Epidemiology Incidence common present in 3-5% of population Anatomic location usually lateral meniscus involved 25% bilateral Etiology Pathophysiology failure of apoptosis in utero Classification Watanabe Classification Type I Complete Type II Incomplete Type III Wrisberg (lack of posterior meniscotibial attachment to tibia) Presentation Symptoms pain, clicking, mechanical locking often becomes symptomatic in adolescence Physical exam mechanical symptoms most pronounced in extension Imaging Radiographs recommended views AP and lateral of knee findings widened joint space (up to 11mm) squaring of lateral condyle cupping of lateral tibial plateau hypoplastic lateral intercondylar spine MRI indications study of choice for suspected symptomatic meniscal pathology findings diagnosis can be made with 3 or more 5mm sagittal images with meniscal continuity ("bow-tie sign") sagittal MRI will show abnormally thick and flat meniscus coronal MRI will show thick and flat meniscal tissue extending across entire lateral compartment Symptomatic cases may reveal underlying meniscus tear Treatment Nonoperative observation indications asymptomatic discoid meniscus without tears Operative partial meniscectomy and saucerization indications pain and mechanical symptoms meniscal tear or meniscal detachment technique obtain anatomic looking meniscus with debridement repair meniscus if detached (Wrisberg variant) meniscal instability is frequently present recent literature suggest anterior horn instability is most common