Your knee joint is somewhat like a hinge and works nicely in a vertical plane. Unfortunately, it is very unforgiving if it's forced to move sideways or is twisted. There are several causes of knee problems. Impact injuries are often due to direct blows in contact sports like basketball. They can also be caused by falls and jumps, sudden twisting, and explosive movements such as a power lift.
Cruciate ligaments cross each other on the inside.
On the outside of the joint you'll find collateral ligaments. Ligaments are tough, fibrous bundles which are strong but only slightly elastic. There's a thin coating called articular cartilage on the end of the femur and tibia that's in contact with the menisci. As well as absorbing shock, cartilage prevents wear because it reduces friction. Your kneecap protects the front of the joint.