A tear of a meniscus is a rupturing of one or more of the fibrocartilage strips in the knee called menisci. When doctors and patients refer to "torn cartilage" in the knee, they actually may be referring to an injury to a meniscus at the top of one of the tibiae. Menisci can be torn during innocuous activities such as walking or squatting. They can also be torn by traumatic force encountered in sports or other forms of physical exertion. The traumatic action is most often a twisting movement at the knee while the leg is bent. In older adults, the meniscus can be damaged following prolonged 'wear and tear'. Especially acute injuries (typically in younger, more active patients) can lead to displaced tears which can cause mechanical symptoms such as clicking, catching, or locking during motion of the joint. A tear of the medial meniscus can occur as part of the unhappy triad, together with a tear of the anterior cruciate ligament and medial collateral ligament.
Signs and symptoms The common signs and symptoms of a torn meniscus are knee pain, particularly along the joint line, and swelling. These are worse when the knee bears more weight (for example, when running). Another typical complaint is joint locking, when the affected person is unable to straighten the leg fully. This can be accompanied by a clicking feeling. Sometimes, a meniscal tear also causes a sensation that the knee gives way. A person with a torn meniscus can sometimes remember a specific activity during which the injury was sustained. A tear of the meniscus commonly follows a trauma that involves rotation of the knee while it was slightly bent. These maneuvers also exacerbate the pain after the injury; for example, getting out of a car is often reported as painful.
Causes There are two menisci in the knee. They sit between the thigh bone (femur) and the shin bone (tibia). While the ends of the thigh bone and the shin bone have a thin covering of soft hyaline cartilage, the menisci are made of tough fibrocartilage and conform to the surfaces of the bones they rest on. One meniscus rests on the medial tibial plateau; this is the medial meniscus. The other meniscus rests on the lateral tibial plateau; this is the lateral meniscus. The menisci are nourished by small blood vessels but have a large area in the center with no direct blood supply (avascular). This presents a problem when there is an injury to the meniscus, as the avascular areas tend not to heal. Without the essential nutrients supplied by blood vessels, healing cannot take place. The two most common causes of a meniscal tear are traumatic injury (often seen in athletes) and degenerative processes, which are the most common tear seen in all ages of patients. Meniscal tears can occur in all age groups. Traumatic tears are most common in active people aged 10–45. Traumatic tears are usually radial or vertical in the meniscus and more likely to produce a moveable fragment that can catch in the knee and therefore require surgical treatment. A meniscus can tear due to an internally or externally rotated knee in a flexed position, with the foot in a flexed position. It is not uncommon for a meniscal tear to occur along with injuries to the anterior cruciate ligament ACL and the medial collateral ligament MCL — these three problems occurring together are known as the "unhappy triad," which is seen in sports such as football when the player is hit on the outside of the knee. Individuals who experience a meniscal tear usually experience pain and swelling as their primary symptoms. Another common complaint is joint locking, or the inability to completely straighten the joint. This is due to a piece of the torn cartilage preventing the normal functioning of the knee joint. Degenerative tears are most common in people from age 40 upward but can be found at any age, especially with obesity. Degenerative meniscal tears are thought to occur as part of the aging process when the collagen fibers within the meniscus start to break down and lend less support to the structure of the meniscus. Degenerative tears are usually horizontal, producing both an upper and a lower segment of the meniscus. These segments do not usually move out of place and are therefore less likely to produce mechanical symptoms of catching or locking. Meniscal tears typically occur due to rotational or shear forces across the knee joint, especially when the knee is flexed and weight bearing. These forces are commonly seen in activities involving pivoting, rapid changes in direction, or deep squatting.
Risk factors The meniscus is made of cartilage, a viscoelastic material, which makes it more susceptible to rate of loading injuries. Repetitive loading can also lead to injury. Recent studies have shown people who experience rapid rate of loading and/or repetitive loading to be the most susceptible to meniscus tears. People over the age of 60 who have working conditions in which squatting and kneeling are common are more susceptible to degenerative meniscal tears. Athletes who constantly experience a high rate of loading (e.g. soccer, rugby) are also susceptible to meniscus tears. Studies have also shown with increasing time between ACL injury and ACL reconstruction, there is an increasing chance of meniscus tears. This study showed meniscus tears occurring at a rate of 50–70% depending on how long after the ACL injury the surgery occurred. Meniscal ramp lesions (tears of the medial meniscus posterior horn at the menisco-capsular junction) occur in approximately 25% of ACL-injured knees. Lateral meniscal root tears occur in approximately 7% of ACL injured knees.
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