Sudden meniscal tears often happen during sports. Players may squat and twist the knee, causing a tear. Direct contact, like a tackle, is sometimes involved.
Older people are more likely to have degenerative meniscal tears. Cartilage weakens and wears thin over time. Aged, worn tissue is more prone to tears. Just an awkward twist when getting up from a chair may be enough to cause a tear, if the menisci have weakened with age.