Meniscus tears happen in two main ways: a sudden twist or pivot on a weight-bearing knee, or a slow breakdown of the cartilage over years of wear. The first type is common in athletes and younger adults. The second is so widespread that about 31% of people aged 50 to 90 have a meniscus tear, often without knowing it.
Your knee has two menisci, C-shaped pads of tough, rubbery cartilage that sit between your thighbone and shinbone. They absorb shock, distribute load, and keep the joint stable. The medial meniscus (on the inner side of the knee) carries roughly 61% of the total load on that side of the joint, meaning the bone surface beneath it only handles the remaining 39%. When a meniscus tears, that load distribution shifts dramatically, putting more stress on the cartilage covering the bone itself.
Traumatic Tears From Twisting and Pivoting
The classic mechanism is straightforward: your foot stays planted while your body rotates over it, forcing the knee to twist under load. This is why meniscus tears are so common in sports that involve cutting, pivoting, and sudden direction changes, like soccer, basketball, football, and tennis. The meniscus gets trapped between the rotating bones and splits under the shearing force.
You don’t need to be on a field for this to happen. Forceful deep squats, heavy lifting, or simply catching your foot on an uneven surface while walking can generate enough torque to tear the tissue. The key ingredients are weight on the leg and a rotational force through the knee at the same time. A sudden stop-and-turn movement is especially risky because the knee absorbs both a deceleration force and a twisting force simultaneously.
Traumatic tears tend to be vertical or longitudinal, running along the length of the meniscus. A severe version of this is a bucket-handle tear, where a long vertical strip flips into the center of the joint like the handle of a bucket. This type can physically block the knee from straightening, a symptom called mechanical locking.
Degenerative Tears From Aging and Wear
Not all meniscus tears involve a memorable injury. Degenerative tears develop gradually in people typically over 35, often without any specific trauma. Over time, the meniscus loses cells and becomes more brittle. Studies of older meniscus tissue show decreased cell density, abnormal cell clusters, and a general breakdown in the tissue’s architecture. This weakened cartilage can tear from something as minor as standing up from a chair or stepping off a curb.
Degenerative tears usually take a horizontal pattern, splitting the meniscus into upper and lower layers rather than tearing it from front to back. They’re strongly linked to early osteoarthritis, and in many cases, the tear and the arthritis develop together as part of the same process. Among people aged 18 to 39, only about 5.6% have a meniscus tear on imaging. By ages 50 to 90, that number jumps to 31%, and many of those people have no knee pain at all.
Why the Medial Meniscus Tears More Often
The inner (medial) meniscus is more commonly torn than the outer (lateral) one, and the reason is largely anatomical. The medial meniscus is more firmly attached to the joint capsule and surrounding ligaments, which makes it less mobile. When the knee twists, the lateral meniscus can slide out of the way slightly, but the medial meniscus is anchored in place and absorbs more of the force. Think of it like a rope tied tightly at both ends versus one with some slack: the taut rope is more likely to snap.
The ACL Connection
Meniscus tears frequently happen alongside tears of the anterior cruciate ligament (ACL). In one study of adolescents with ACL ruptures, 58% had additional damage inside the joint, and meniscus tears were the most common finding. The lateral meniscus was involved in 27% of cases, the medial meniscus in 19%, and both menisci in about 12%.
The relationship works in the other direction too. In a knee with a torn ACL, the medial meniscus takes on extra work as a stabilizer, helping resist the shinbone from sliding forward. This added stress means that delaying ACL surgery increases the odds of developing a secondary medial meniscus tear over time. Each month of waiting slightly raises the risk, likely because the unstable knee accumulates small amounts of damage with everyday activity.
Body Weight as a Risk Factor
Carrying extra weight significantly increases the forces passing through the menisci with every step, and the numbers are striking. Compared to people at a normal weight, men with a BMI of 30 to 32 are nearly five times as likely to need meniscus surgery. For women in the same BMI range, the odds are also about five times higher. At a BMI of 40 or above, the risk jumps to 15 times higher for men and 25 times higher for women. These are among the strongest weight-related risk increases seen for any orthopedic condition.
The mechanism is partly mechanical: more body weight means more compressive and shearing force on the meniscus during walking, climbing stairs, and squatting. But excess weight also contributes to low-grade inflammation throughout the body, which may accelerate the degenerative changes that weaken meniscal tissue over time.
Types of Tears and What They Mean
The shape and location of a tear matter because they influence symptoms, healing potential, and treatment options.
- Longitudinal and bucket-handle tears run along the length of the meniscus. Bucket-handle tears can displace into the center of the joint, causing the knee to lock in a bent position. These are more common in younger patients after acute injuries.
- Radial tears cut across the meniscus from the inner edge outward. When a radial tear extends all the way to the outer wall, it disrupts the meniscus’s ability to distribute load almost as completely as if the meniscus were missing entirely.
- Horizontal tears split the meniscus into top and bottom halves. These are the signature pattern of degenerative wear and are more common in older adults. They can sometimes produce fluid-filled cysts along the joint line.
- Oblique (flap) tears create a loose flap of tissue that can catch between the bones during movement, producing a clicking or catching sensation.
How Tears Are Identified
Most meniscus tears are diagnosed with a combination of physical examination and MRI. During an exam, pressing along the joint line while rotating the knee typically reproduces pain at the site of the tear. MRI is highly accurate for confirming the diagnosis, with a sensitivity of 96% and specificity of 97%, meaning it catches nearly all tears and rarely flags one that isn’t there.
That said, MRI findings don’t always match symptoms. Because degenerative tears are so common in middle-aged and older adults, an MRI may reveal a tear that isn’t actually causing your pain. This is why the physical exam and your specific symptoms, particularly mechanical catching, locking, or pain with twisting, are just as important as what the scan shows.
What a Tear Feels Like
Traumatic tears usually announce themselves with a pop or sharp pain at the moment of injury, followed by swelling over the next several hours. You can often still walk, which leads many people to assume the injury isn’t serious. Over the following days, the knee may feel stiff, swell further, and catch or click during movement.
Degenerative tears are subtler. You might notice a gradual onset of inner knee pain, mild swelling that comes and goes, or a sensation that the knee isn’t quite trustworthy on stairs or uneven ground. Some people only become aware of a tear when the knee suddenly locks or gives way during an ordinary activity, weeks or months after the tissue first started to fail.