There are many structures involved in making a joint move freely while remaining stable and supported. Careful diagnosis is needed to find out which structures are involved after injury.
Some injuries are due to trauma, some overuse, wear and tear or postural related.
The capsule, which is the lining of the joint, can become inflamed causing pain and stiffness known as frozen shoulder. Overuse injuries can cause degeneration of tendons like tennis elbow or nerves can get compressed such as carpel tunnel syndrome at the wrist. Other conditions of joints may be due to an imbalance or stiffness of muscles causing anterior knee pain or a twisting injury can cause cartilage or ligament damage in the knee.
These are just a few examples that can be treated by physiotherapy. Our bodies are so finely tuned that when one part goes wrong it often sets up other aches and pains else where in the body. While limping with a bad knee, if left it could go on to cause hip, back or ankle pain .It is always best to get treatment early.