How is the knee structured?
How does a normal knee work?
Your knee joint is where your thigh bone (femur) and your shin bone (tibia) meet. It allows the bones to move freely but within limits.
Your knee is the largest joint in the body and also one of the most complicated. It needs to be strong enough to take our weight and must lock into position so we can stand upright. But it also has to act as a hinge so we can walk, and it must withstand extreme stresses, twists and turns, such as when we run or play sports.
What happens to a knee with osteoarthritis?
When your knee has osteoarthritis its surfaces become damaged and it doesn’t move as well as it should do. The following happens:
- The cartilage becomes rough and thin – this can happen over the main surface of your knee joint and in the cartilage underneath your kneecap.
- The bone underneath the cartilage reacts by growing thicker and becoming broader.
- All the tissues in your joint become more active than normal, as if your body is trying to repair the damage.
- The bone at the edge of your joint grows outwards, forming bony spurs called osteophytes.
- The synovium may swell and produce extra fluid, causing the joint to swell – this is called an effusion or sometimes water on the knee.
- The capsule and ligaments slowly thicken and contract.
These changes in and around your joint are partly the result of the inflammatory process and partly an attempt by your body to repair the damage. In many cases your body’s repairs are quite successful and the changes inside your joint won’t cause much pain or, if there is pain, it’ll be mild and may come and go.
However, in other cases the repair doesn’t work as well and your knee is damaged. This leads to instability and more weight being put onto other parts of the joint. This can cause symptoms to become gradually worse and more persistent over time.