Healthy shaped menisci are in the shape of a crescent moon. However, some people are born with an abnormally shaped meniscus; some abnormalities appear as a half moon or complete circle. This abnormality will usually occur on the outside portion of the knee (lateral meniscus); discoid medial meniscus is quite rare. A discoid meniscus is defined as an abnormally shaped meniscus in the knee. While it is more prone to injury than a normally shaped meniscus, many people with the abnormality may go through life without ever experiencing any problems. However, the majority of individuals with a discoid lateral meniscus will have issues, especially athletes. This condition is seen in about 2% of the population, and 20% of all discoid meniscus cases will affect both knees. Your physician will treat the discoid meniscus using arthroscopic surgery, to reshape the meniscus, and to repair any tears.