There are several structures that make up the knee joint: bones, muscles and tendons, ligaments and the meniscus. The meniscus is sometimes called the cartilage. It is gristle like structure that is composed of both a medial and a lateral meniscus. This is the inner and outer parts of the joint. The meniscus sits on top of the tibia and when we walk or stand it helps give support and cushioning between the femur and the tibia. You can think of the meniscus like the cushion or insole of your shoes.
If you injure the meniscus during an activity it can tear. Most tears are small and not symptomatic. However, if the tear is large enough it can cause the meniscus to flip over onto itself. This can then cause pain or locking of the knee. If this happens then it is probably going to require surgery to repair the tear.
Most tears are degenerative and occur over a period of time. The tear can start with some fraying and then over time it may increase in size. Usually these tears do not require treatment as they are part of arthritis in the knee joint. In rare cases they can become symptomatic enough that a knee arthroscopy is necessary.
A torn meniscus in a young patient is less common, but requires attention. These tears if left untreated can lead to a larger tear that may not be repairable. It is important to see an orthopedic surgeon and get it checked out. In my practice I have seen meniscus tears as young as 7 years of age. These patients almost always need surgical repair.
In conclusion if your knee starts catching, popping, clicking or locks up and you have pain then you may have a torn meniscus. Go see an orthopedic surgeon to get it checked out.