As the name suggests, the meniscus should be “half-moon shaped”. If a meniscus has to be large and thick, like a disk, then it is only a “discoid meniscus”, which can be called a “full moon”. The latter is the type of meniscus that lacks stability and is most likely to cause a “popping knee”. Discoid meniscus is most often seen on the lateral side and is rarely seen on the medial side in Asians. It is very rare to find a discoid meniscus in the same knee, both medial and lateral, and it is said that not many cases have been reported worldwide. Is a discoid meniscus harmful? Anatomical variation, obviously, cannot be called “normal” and may be harmful. For example, congenitally missing a kidney, or missing a gene. Many people have two toenail caps on the little toe (the outer one is small, or a split toenail cap), and you can say that is not “normal”? Discoid meniscus is not very common (and certainly not rare), so it is somewhat abnormal. In fact, this type of meniscus is not only larger and thicker, but also has a different inner cellular structure than a normal meniscus, so it is a “hidden” meniscus that is more likely to tear during sports than a normal meniscus. How is it diagnosed? The basic diagnosis is made by imaging, x-ray, MR, etc. Arthroscopy is the ultimate diagnosis. As for the doctor’s examination to diagnose the disc meniscus, it is not reliable, not for me anyway. X-rays: widening of the lateral space of the knee, dysplasia and flattening of the lateral femoral condyle, and dysplasia of the anterior tibial spine. This is due to extrusion of the thick meniscus. MR: In the sagittal plane, the anterior and posterior angles of the meniscus are connected at more than 3+ levels to form a “bow tie”-like change; the width of the narrowest part of the meniscus in the coronal plane is greater than 15mm or more than half of the joint surface of the medial (lateral) tibial plateau (more than 20% of the entire tibial plateau); the height of the lateral meniscus is higher than the opposite side by more than 2mm. Do I need treatment? Changes in the shape of the body often require surgical treatment, and surgery is the only best means of changing the shape. Common sense dictates that trimming a discoid meniscus to a “half-moon” shape is better for the joint, but treatment of the discoid meniscus has always been controversial, because after all, a person is born with a discoid meniscus and has probably adapted to this shape over decades of movement. However, the disc meniscus is prone to tearing, and a tear obviously requires surgery because its torn pieces are generally large and fully destructive to the joint. Therefore, for an intact disc meniscus, if there is no discomfort or only occasional discomfort, it should not be a candidate for surgical consideration. However, if there is significant discomfort, it is still important to seek early professional treatment.