Bones are hard structures and cannot be bent. But, we can still bend our elbow, knee, etc. How is this possible?

Due to the presence of different types of joints between the bones we are able to bend our body parts such as elbow, knee, back etc.

Elbow and knee are not made up of a single bone but two or more bones which are joined to each other by hinge joint. This joint along with the muscles help us to bend the elbow and knee.