If there is injury to the knee, it is possible that more than one of these structures may be injured at the same time.
Collateral ligaments exist on the inside and on the outside of the knee joint.
A collateral ligament can be partially torn apart and yet the knee may still remain fairly stable. This is because a collateral ligament is not a single, thin ligament, but consists of many minor ligaments in different directions and layers, which mesh together into one single strong ligament. A ligament injury may occur when the knee is strained from the inside, but more often than not, it will be caused by a strain from the outside. For example, while playing football, the outside of the knee may be hit or kicked with great force by an opponent. As the knee is pressed together on the outside and forced apart on the inside, the ligaments on the inside of the knee will be injured.