A Discoid Meniscus (DM) is an abnormal development of the meniscus which leads to a hypertropic meniscus that is larger than a typical one
It may or may not be “unstable,” meaning that when these menisci are probed in the operating room they don’t have typical stable peripheral attachments to the tibia.
The other important difference between DM and a typical meniscus is its ultrastructure.DM have decreased collagen and a heterogenous course of fibers. The reason why the ultrastructure matters is that it makes it more prone to tearing.
Photo Credit: Atay et al. AJSM.2007 Mar35(3):475-8.
On exam, individuals may have asymptomatic snapping, but with increasing age, children more commonly experience pain. Older adolescents may present with more acute, mechanical or traditional meniscal-type symptoms. A lateral joint line bulge may be present and, if it is an unstable subluxing lateral DM, a clunk may be noted during McMurray testing. X-rays may show some features of DM, such as widening of the lateral joint space, a squared off appearance of the lateral femoral condyle, and/or tibial eminence flattening. MRI are helpful to assess for tearing or other co-existing pathology.
Treatment is determined based on individual factors, including symptoms, duration of symptoms, age and imaging findings. If symptoms such as pain, locking, giving way or instability persist, then surgical management is often the next step. Partial meniscectomy (saucerization) with preservation of a stable peripheral rim of meniscus (with or without meniscal repair) is the current standard of care.
After saucerization alone (no meniscal repair), they can be weight bearing as tolerated. Progression to return to sport or recreational activity begins once full knee range of motion and strength is achieved.