Meniscus tear

Lore & Background

The menisci are nourished by small blood vessels but have a large avascular central area, which presents a problem for healing after injury. Traumatic tears are usually radial or vertical and more likely to produce a moveable fragment that can catch in the knee, often requiring surgical treatment. Degenerative tears are usually horizontal and less likely to produce mechanical symptoms of catching or locking.

A meniscal tear commonly follows a trauma involving rotation of the knee while it was slightly bent. 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 in younger, more active patients can lead to displaced tears causing mechanical symptoms such as clicking, catching, or locking during motion of the joint.

Signs and symptoms include knee pain along the joint line, swelling, joint locking, a clicking feeling, and a sensation that the knee gives way. The unhappy triad—a tear of the medial meniscus together with a tear of the anterior cruciate ligament and medial collateral ligament—is seen in sports such as football when the player is hit on the outside of the knee.

Reader's Guide

Meniscal tears are significant because they affect the knee's ability to distribute force and protect articular cartilage. The menisci contain 70% type I collagen and are oriented in a circumferential pattern; when a compressive force is applied, a tensile force is transmitted to the menisci. A lesion in the peripheral rim disrupts normal mechanics, allowing the meniscus to spread under load and distributing force directly to the articular cartilage, increasing the risk of developing arthritis.

Diagnosis involves noting symptoms and performing clinical tests to determine if pain is caused by compression and impingement of a torn meniscus. Treatment considerations depend on the type and location of the tear, as avascular areas tend not to heal without the essential nutrients supplied by blood vessels. Preserving the peripheral rim during partial meniscectomy is essential to avoid irreversible disruption of the structure's hoop tension capability.

Risk factors include rapid rate of loading and repetitive loading, as seen in athletes (e.g., soccer, rugby) and people over 60 with working conditions involving squatting and kneeling. Increasing time between ACL injury and ACL reconstruction also increases the chance of meniscus tears, with rates of 50–70% depending on delay.

Did You Know?

• The menisci are made of tough fibrocartilage and contain 70% type I collagen.
• A tear of the medial meniscus can occur as part of the 'unhappy triad' with tears of the anterior cruciate ligament and medial collateral ligament.
• Degenerative meniscal tears are most common from age 40 upward and are usually horizontal, producing upper and lower segments that do not typically move out of place.
• Lateral meniscal root tears occur in approximately 7% of ACL-injured knees.

Anatomy and the Healing Paradox

The knee houses two crescent-shaped pads of dense fibrocartilage known as the menisci, positioned between the rounded ends of the femur and the flat surfaces of the tibia. Unlike the thin hyaline cartilage that coats bone ends, these strips are built from a tougher, viscoelastic material that molds itself to the contours of the bones they bridge. One pad sits on the inner (medial) tibial plateau, the other on the outer (lateral) plateau. Despite their robust construction, the menisci face a fundamental biological limitation: they receive nourishment only from a network of small blood vessels at their periphery, while a broad central zone remains entirely avascular. This means that when a tear occurs in that inner region, the body simply cannot deliver the nutrients and cells needed for repair. The result is that many meniscal injuries, particularly those in the avascular zone, resist natural healing and may ultimately demand surgical intervention to restore the joint's function.

Mechanisms of Injury

Meniscal tears arise from two broad pathways: acute traumatic events and gradual degeneration. The traumatic variety, most prevalent among active individuals between the ages of ten and forty-five, typically results from rotational or shear forces applied to a knee that is bent and bearing weight. Pivoting, sudden changes of direction, and deep squatting all generate these dangerous loading patterns. A valgus force combined with internal rotation of the femur tends to rupture the medial meniscus, while a varus force with external rotation targets the lateral side. These acute tears often run radially or vertically, creating a loose fragment that can migrate and wedge itself into the joint, producing mechanical symptoms and frequently necessitating surgery. In contrast, degenerative tears—most common after age forty and linked to the progressive breakdown of collagen fibers—tend to split the meniscus horizontally into upper and lower layers. Because these segments generally stay in place, they are less prone to causing catching or locking, though they still produce pain and swelling.

What Patients Feel

The clinical picture of a meniscal tear is often recognizable to both patient and physician. The hallmark complaint is pain localized along the joint line, accompanied by swelling that intensifies whenever the knee carries more load—running being a classic aggravator. Many individuals report a distinct episode of joint locking, in which the leg simply refuses to extend fully, as though a fragment of torn cartilage has jammed the mechanism. A clicking or catching sensation during movement is another frequent descriptor, and some patients describe the unsettling feeling that the knee is about to buckle or give way. Notably, a significant number of people can pinpoint the exact moment of injury, often recalling a twisting motion while the knee was slightly bent. Everyday actions that involve that same rotational pattern—such as rising from a car seat—can reproduce the pain. In younger, more active patients, displaced fragments are more likely to create these mechanical disturbances, whereas older patients with degenerative tears may experience a more diffuse ache without the dramatic locking episode.

The Unhappy Triad and Risk Landscape

A meniscal tear rarely exists in isolation. In contact sports such as football, a blow to the outer aspect of the knee can simultaneously rupture the medial meniscus, the anterior cruciate ligament, and the medial collateral ligament—a devastating combination clinicians call the unhappy triad. Research further shows that an ACL injury dramatically elevates the odds of a concurrent meniscal problem: depending on how long reconstruction is delayed, meniscal tears appear in fifty to seventy percent of cases. Meniscal ramp lesions at the posterior horn of the medial meniscus affect roughly a quarter of ACL-injured knees, while lateral meniscal root tears are present in about seven percent. Beyond sports, risk factors span the lifespan. People over sixty whose occupations demand frequent squatting and kneeling face heightened degenerative risk, as do obese individuals of any age. Athletes in high-loading disciplines like soccer and rugby are perpetually exposed to the rapid and repetitive forces that the viscoelastic meniscal tissue is least equipped to absorb.