A meniscus tear is a knee injury. This type of injury is caused by turning the knee quickly or twisting it with the foot planted and the knee bent, according to WebMD. Meniscus tears are common, especially in weight lifters, athletes and older individuals.
The meniscus is a C-shaped, rubbery disc in the knee. Each knee has two menisci that cushion the knee joint and distribute weight evenly across the knee. When a meniscus is torn, the knee fails to work properly. Symptoms of a torn meniscus include pain, swelling, stiffness, cracking, popping and an inability to straighten the knee, according to WebMD.