The meniscus is a C-shaped piece of cartilage that acts as a shock absorber between the femur (thigh bone) and the tibia (shin bone) in the knee joint. It's not composed of just cartilage, but of fibrocartilage.

Here's a breakdown of what makes up the meniscus:

* Fibrocartilage: This is a type of cartilage that's stronger and more flexible than hyaline cartilage, the type found in other joints. It's made up of dense collagen fibers that are arranged in a way that allows for both strength and flexibility.

* Water: The meniscus is about 70% water, which helps it to cushion the joint and absorb shock.

* Cells: The meniscus also contains cells called chondrocytes, which are responsible for maintaining the structure of the cartilage.

The meniscus is vital for maintaining the stability and function of the knee joint. It helps to:

* Distribute weight evenly across the knee joint.

* Absorb shock during activities like running and jumping.

* Prevent excessive movement of the knee joint.

* Provide lubrication to the joint.

If the meniscus is injured, it can lead to pain, swelling, and instability in the knee.