Your meniscus is a tough, rubbery wedge of cartilage that acts as your knee’s built-in shock absorber, load distributor, and stabilizer. You have two in each knee, one on the inner side (medial) and one on the outer side (lateral), and together they handle the majority of the force that passes through your knee joint with every step. Without them, the smooth cartilage covering your bones wears down far faster, which is why losing meniscus tissue dramatically raises the risk of arthritis.
How It Absorbs and Spreads Force
The most important job of your menisci is distributing weight across the knee so no single spot on the cartilage takes too much pressure. When you stand, walk, or land from a jump, force travels from your thighbone (femur) down into your shinbone (tibia). The menisci sit between these two bones and spread that force over a wider area, protecting the thin layer of cartilage on each bone’s surface.
The numbers are striking. In a straight leg, the medial meniscus carries about 50% of the load on the inner side of the knee, while the lateral meniscus handles roughly 70% on the outer side. Bend your knee to 90 degrees and those figures jump to 85% and 90%, respectively. In other words, the deeper you bend, the more work your menisci do. Research on intact knees shows the medial meniscus alone bears about 61% of the total medial contact force, leaving only 39% for the tibial cartilage to handle directly.
This load-sharing ability comes from the meniscus’s unique shape and fiber structure. When compressed, the wedge-shaped tissue converts downward force into outward “hoop stress” along its circular fibers, much like squeezing a rubber ring between your palms pushes it outward rather than collapsing it flat. This mechanism is what makes the meniscus so effective at cushioning impact.
Keeping Your Knee Stable
Beyond cushioning, the menisci help hold your knee in proper alignment. The bottom of your thighbone is rounded, while the top of your shinbone is relatively flat. That’s a mismatch that could allow the bones to slide around. The menisci fill the gaps, deepening the shallow surface of the tibia and increasing the contact area between the two bones. This added congruity makes the joint mechanically more stable.
The medial and lateral menisci contribute to stability in different ways. The medial meniscus, particularly its rear (posterior) horn, is a critical backup restraint against the shinbone sliding forward. This is especially important if the anterior cruciate ligament (ACL) is damaged. The lateral meniscus, by contrast, plays a bigger role in controlling rotational movement. It helps restrain the twisting and pivoting motions that stress the knee during cutting, turning, or changing direction. This division of labor means that a tear in one meniscus can create a very different pattern of instability than a tear in the other.
Lubrication and Cartilage Nutrition
Your knee joint is bathed in synovial fluid, a slippery liquid that reduces friction and delivers nutrients to the cartilage (which has no direct blood supply of its own). The menisci help distribute this fluid across the joint surfaces during movement. Each time you bend and straighten your knee, the menisci compress and release, pushing synovial fluid into areas that need it. Without this pumping action, cartilage can become malnourished and break down over time.
Position Sensing and Reflexes
Your menisci contain tiny sensory receptors that detect pressure, stretch, and vibration inside the joint. These receptors send signals to your brain about where your knee is in space, how fast it’s moving, and how much force is passing through it. This feedback loop, called proprioception, is what lets you walk on uneven ground, adjust your footing mid-stride, or land a jump without consciously thinking about knee position.
Several types of these receptors exist in knee structures. Some respond to slow, sustained stretching and help your brain track joint position. Others detect rapid vibrations or sudden changes in force, triggering protective reflexes. When joint tissues degenerate, the number of these receptors drops, which may partly explain why people with knee arthritis often feel less steady on their feet.
What Happens When a Meniscus Tears
A torn meniscus can no longer distribute force evenly, and the consequences depend on the type and location of the tear. Traumatic tears, common in younger, active people, tend to be vertical or radial and can produce a loose flap of tissue that moves in and out of position. This displaced fragment causes the hallmark mechanical symptoms: catching, clicking, and locking. A locked knee gets stuck in a bent position because the torn piece has wedged itself where it doesn’t belong. Some people can unlock it by gently twisting and bending the knee, but sometimes it stays stuck for days.
Degenerative tears, more common after age 40, are usually horizontal and split the meniscus into upper and lower layers that stay in place. These tears are less likely to cause locking but still compromise load distribution. Pain along the joint line, swelling, and a sensation of the knee “giving way” are typical. That giving-way feeling often happens because pain signals cause the brain to briefly shut off the quadriceps muscle, making the leg buckle.
A displaced fragment that keeps catching can also grind against the smooth cartilage surfaces nearby, accelerating wear and increasing the risk of arthritis in that compartment.
Why Meniscus Loss Leads to Arthritis
Removing part or all of a meniscus (meniscectomy) relieves mechanical symptoms but eliminates the tissue that was protecting the cartilage. Without that cushion, contact stress on the remaining cartilage spikes, and the joint begins to break down. Data from the Osteoarthritis Initiative found that people who had arthroscopic meniscectomy were three times more likely to eventually need a knee replacement compared to matched individuals who did not have the surgery, with risk estimates ranging from about two to nearly five times higher depending on the analysis.
This is why surgeons now try to repair meniscus tears whenever possible rather than trimming or removing tissue. Repair success depends heavily on where the tear is located. The outer third of the meniscus has a rich blood supply (often called the “red zone”), and tears there can heal well because blood delivers the oxygen and nutrients needed for tissue repair. The inner two-thirds has little to no blood flow (the “white zone”), making healing much less likely without intervention. Tears at the border between these regions have an intermediate chance of recovery.
How the Meniscus Changes With Age
In younger adults, the meniscus is tough and resilient, able to withstand the repetitive loading of running and jumping. Over time, the tissue gradually dries out, stiffens, and develops small internal cracks. This is why degenerative meniscus tears can happen during ordinary activities like squatting or stepping off a curb, with no obvious injury. The blood supply to the inner portions also diminishes with age, further reducing the tissue’s ability to repair itself. Maintaining leg strength, particularly in the quadriceps and hamstrings, helps compensate by improving how force is distributed across the joint and reducing the load the meniscus has to handle alone.