It is important to understand the anatomy of the knee joint. The knee is the junction of two bones, the femur (thighbone) and the tibia (shinbone). The menisci (cartilage) lie over the surface of the tibia and function as a shock absorber by keeping the two bones from rubbing directly on each other. Both muscles and ligaments help to stabilize this joint by connecting these two bones.
Ligaments are very strong bands of collagen with elastic properties, which allow them to stretch slightly. On the inside and outside of your knee, the medial and lateral collateral ligaments prevent movement side to side.
The anterior (ACL) and posterior (PCL) cruciate ligaments are in the middle of the knee and cross each other. The ACL runs from the anterior tibia to the posterior surface of the femur; the PCL joins the posterior tibia to the anterior femur. The ACL prevents the tibia from sliding forward from the femur; the PCL, conversely, prevents the tibia from sliding backwards on the femur. The quadriceps and hamstring muscles also play a very important role in keeping the knee joint stable.
How do injuries happen?