Mechanical problems
Some common examples of mechanical problems that can lead to knee pain and other symptoms include:
Loose body
Sometimes degeneration of bone or injury can cause a piece of cartilage or bone to break off and glide in the joint space. In some cases, this may not generate any problems unless the body starts interfering the knee joint movement. However, in most cases, the loose body causes something like a piece of wood caught in a door hinge and leads to pain.