A discoid meniscus occurs from an anomaly during development in utero. There is no further development after birth and many cases patients with a discoid meniscus are asymptomatic their entire life. Incidence rate is difficult to estimate secondary to many individuals being asymptomatic. Studies indicate an incident rate between .03 to 17%.
There are three types of discoid meniscus:
Incomplete- The lateral meniscus is a bit thicker and wider than that of a normal meniscus
Complete- The tibia is completely covered by the meniscus
Hypermobile Wrisberg- There is no posterior attachment to the tibia
Discoid Meniscus is often referred to as popping knee syndrome as a visible snap or pop may occur during the last 10-20 degrees of terminal knee extension. Vague knee pain may be reported with swelling and potential knee locking. If symptomatic it is typically present in the younger population and discoid meniscuses are more prone to typical meniscus injuries such as meniscal tears.
Historically treatment for stable or unstable discoid meniscus is a meniscectomy. Recently partial meniscectomy to reshape the meniscus have demonstrated positive short term and long-term outcomes as it preserves the meniscus. Discoid meniscus with no symptoms should not be treated surgically.