The purposes of the knee meniscus (menisci for plural because there are two in each knee joint) is to disperse the stresses of weight across a large area of the knee in an attempt to keep the joint cartilage healthy. The menisci also serve as shock absorbers in the knee as well as stabilizers of the joint during most activities. They are crescent-shaped and have a tapered appearance.
Because the meniscus is composed of a tough rubber-like cartilage, it tends to not heal when torn. In turn, the knee can exhibit certain particular signs and symptoms indicating a torn meniscus.
Pain
If the injury is recent enough, there may be pain, ranging from mild soreness to severe disabling pain. This occurs primarily because there are pain nerve endings in the outer zones of the cartilage, as well as pain receptors located within the joint cartilage cells. When weight is applied, or motion exerted, on the knee joint, pain receptors fire to warn the host of a problem within the knee.
Excessive Fluid Production in the Knee (Effusion)
In cases of a torn meniscus, the tear pattern can be such that a portion of the meniscus can displace into the knee joint, creating a mechanical blockage or irritant. If this happens, the body only knows one way to battle against the irritation that is caused by the meniscal tear, and that is to produce additional joint fluid. This is done as the body's effort to increase lubrication to reduce the local mechanical irritation. This is called "joint effusion."
Limited Range of Motion
Meniscal tears, especially with the added problem of extra fluid buildup in the joint, can easily translate into altered range of motion of the knee. The mere presence of excess fluid can cause hydraulic pressure to be exerted when there is an attempt to bend the knee, effectively blocking full motion.
Additionally, the torn meniscus can, and usually does, play an important role in altered mobility of the joint, particularly if the meniscus has been damaged to the point of mobile flasp that flip in and out of the knee, causing a "catching" sensation.
Popping Sensation
A torn cartilage can often "flip" in and out of the joint, getting "stuck" and then releasing back to its near-normal position and shape. The catching is frequently referred to as a "popping" in the knee and is one of the most common complaints.
