What is a joint and how does it work?
A joint is where two or more bones meet and is made up of a number of different parts that all work together so that we can bend, stretch, twist and turn easily – but within certain limits. Most of our joints are designed to allow bones to move only in certain directions.
The ends of your bones are covered in a thin layer of cartilage. This cushions the joint and helps to spread the load evenly when you put pressure on it. Its smooth, slippery surface allows your bones to move freely, without friction.
Surrounding the joint is a tough, fibrous sleeve called the capsule, which stops your bones from moving too much. The inner surface of the joint capsule (the synovium) produces a thick fluid that nourishes the cartilage and lubricates the joint.
Within or just outside the joint capsule are ligaments that help to hold the joint together and prevent it dislocating. The bursa helps to reduce friction in the joint.
At either side of the joint, your muscles are attached to the bones by tendons. As your muscles contract, they pull on the bones to make the joint bend, straighten or rotate.