As the name suggest its tearing, stripping, split of this essential disc in your knee. There’s classifications for these tears, but what you must understand is that this cushioning discs are vital to keep the bones tracking on each other.
There are different degrees, severity and ways How the meniscus can tear. Grade I meniscus tears happen when the two bones hooking on a part of the cartilage and then shear it off its anchor position. With a Grade I there is no displacement of the meniscus or dislodging of its pieces. There is a physical tear in the cartilage, but everything stays in place. However, this is still very painful and can cause locking and sharp pain in your knee joint only at certain angles.
With any injury to the meniscus greater than a Grade I, the part of the meniscus that tears could even come loose and fold over, doubling and twisting inside the joint split. Some pieces may even tear off their anchor site completely. These loose pieces of cartilage are pinched between the Tibia and the Femur, which causes pain and a locking/stuck feeling deep inside the joint.
You’ll notice there’s a difference between standing on the knee, or when moving it when sitting down. When weight is put through your knee, these discs are compressed. The normal slide and glide action of the Femur on the Tibia is blocked and you will find it very painful to straighten or bend your knee.