Discoid lateral meniscus: importance, diagnosis, and treatment

Discoid lateral meniscus (DLM) is a common anatomic variant in the knee typically presented in young populations, with a greater incidence in the Asian population than in other populations. As DLM is a congenital anomaly, the ultrastructural features and morphology differ from those of the normal meniscus, potentially leading to meniscal tears. Snapping and pain are common symptoms, with occasional limitations of extension, in patients with DLM. Examination of the contralateral knee is necessary as DLM affects both knees. While simple radiographs may provide indirect signs of a DLM, magnetic resonance imaging (MRI) is essential for diagnosis and treatment planning. Although DLM was traditionally classified into three categories, namely, complete, incomplete, and Wrisberg DLM, a recent MRI classification provides useful information for surgical planning because the MRI classification was based on the peripheral detachment in patients with DLM, as follows: no shift, anterocentral shift, posterocentral shift, and central shift. Asymptomatic patients require close follow-up without surgical treatment, while patients with symptoms often require surgery. Total or subtotal meniscectomy, which has been traditionally performed, leads to an increased risk of degenerative arthritis; thus, partial meniscectomy is currently considered the treatment of choice for DLM. In addition to partial meniscectomy, meniscal repair of peripheral detachment is recommended for stabilization in patients with DLM to preserve the function of the meniscus. Previous studies have reported that partial meniscectomy with or without meniscal repair is effective and shows superior clinical and radiological outcomes to those of total or subtotal meniscectomy during the short- to long-term follow-up. Our preferred principle for DLM treatment is reduction, followed by reshaping with reference to the midbody of the medial meniscus and repair as firm as possible.