A break or rupture in the crescent shaped pad of cartilage, called the meniscus, located in the knee where the ends of the thighbone and lower leg bone meet to form the knee joint. An impact injury or a rapid twisting motion from a squatting position are the usual causes of meniscal tears. A slight swelling typically occurs within several hours of the injury. There may be episodic, recurrent swelling, an inability to fully extend the knee (“locking”), and an instability of the knee causing it to give way.