Classic history and presentation: Unstable discoid menisci present as atraumatic and nonpainful knee snapping / popping at a young age (patients aged 3-5 years) that progresses to painful snapping / popping over a couple of years (patients aged 8-10 years). Stable discoid menisci present in older children with mechanical symptoms suggesting a meniscal tear. Acute traumatic tears can occur at any age and are most often related to athletic activity.
Prevalence: Of the general US population, 3%-5% are affected. Asian populations have a prevalence as high as 15%.
- Age – Presents in children in the first or second decade of life. Symptoms of snapping (if present) can begin as early as age 3.
- Sex / gender – Equal prevalence.
Pathophysiology: Discoid meniscus is a congenital abnormality that results from failed absorption of the central part of the meniscus during embryonic development. The result is a meniscus that is larger and "discoid" shaped (as opposed to the "C" shape of a normal meniscus), which occupies a greater surface area of the tibial plateau. Discoid menisci are more prone to tearing than normal menisci due to their shape and abnormal vascularity.
Grade / classification system:
- Type I – Stable, complete; discoid menisci with intact peripheral attachments covering the entire lateral plateau.
- Type II – Stable, incomplete; discoid menisci with intact peripheral attachments covering only a portion of the lateral plateau.
- Type III – Unstable; discoid menisci (complete or incomplete) that lack posterior capsular attachments, with the exception of the posterior meniscofemoral ligament (ligament of Wrisberg).