What is osteoarthritis?

Osteoarthritis is a very common condition. In fact, it is the most common cause of difficulties with mobility and disability in certain age groups. Approximately 30% of the population between 50 and 70 years of age have problems related to osteoarthritis and the percentage increases as age increases.


Younger and middle-aged people can also get osteoarthritis. Approximately 5% of people between 35 and 54 years of age have osteoarthritis. Many of these people have injured their joint earlier in life.


The knee joints are are often affected in osteoarthritis due to the loading that these joints undergo on a regular basis.


Knee osteoarthritis affects affects the whole joint (e.g. bone, ligaments and cartilage) and also the surrounding muscles, however most of all it affects the articular cartilage.


The articular cartilage is the outer coating at the end of bones. In knee osteoarthritis, the articular cartilage becomes thin and fragile. This can be due to:


  •  Healthy cartilage being exposed to heavy loads over a long period of time (for example, very heavy labour over several years), or
  •  Unhealthy cartilage that for some reason cannot handle normal loads.


That being said – the articular cartilage has a complex relationship to loading in that it actually needs loading to stay healthy. This can cause confusion in the rehabilitation process as often people with knee osteoarthritis aren’t sure whether they should be resting or exercising. The information on this website should act as an educational resource to help you better understand knee osteoarthritis and its treatment/management.


If you want to find out more about what constitutes a healthy joint, the changes that osteoarthritis causes in the joint and the joints most affected by osteoarthritis – use the tabs below:

A joint is a connection between two bones. The ends of bones are covered with cartilage, which create a smooth surface for the bones. An articular capsule surrounds the joint. This capsule secures the joint and contains synovial fluid (a lubricant providing nutrition to the cartilage). Muscles and ligaments surround the joint and help to secure it.

The cartilage surface is smooth and lets bones slide easily when moving. Cartilage is solid, but flexible. It absorbs shock and spreads loads over its surface. As far as we know, cartilage has no pain sensors and so it cannot ‘hurt’. The cartilage has no blood vessels. Nutrients are brought to the cartilage by the synovial fluid.



Think of cartilage as a wet sponge; when loads are applied, fluids are pressed out of the sponge. When loads are removed, the sponge sucks the fluids back in. This is what happens with the fluid in and around our cartilage. When we walk for example, loads press down on our cartilage. The cartilage absorbs the shock and fluids squeeze out into the articular capsule. Once loads are removed, the cartilage sucks the fluid back in from the the surrounding area.

This is why loading the joint is needed for cartilage to be healthy. In a healthy joint, there is a balance between degeneration and regeneration of cartilage cells.

You may have heard osteoarthritis described as ‘wear and tear’ of the joint. This statement is incorrect because loads are still needed to keep cartilage healthy. In a healthy joint, there is a balance between the regeneration and degeneration of cartilage. Osteoarthritis occurs when there is more degeneration (breakdown) than regeneration of cartilage. This causes cartilage to thin, crack, and maybe disappear. Bones can then start to rub against each other. However, cartilage needs a certain amount of load to regenerate. This is why healthy loads need to be applied on joints for cartilage recovery.


 You may feel (or hear):

  •  Pain with weight-bearing
  •  Stiff and unstable leg
  •  Knee giving out
  •  Crunching or clicking noises

– It might be hard to walk up and down stairs, or get from sitting to standing

– Occurs with deformities like knock-knees or bowleg


– Pain can be located:

  •  Often outside the hip or deep in the groin
  •  Inside, outside, or down the thigh
  •  Sometimes not in the hip, but instead pain on the inside of the knee

– Hip osteoarthritis often leads to reduced range of motion in the joint. This can lead to trouble getting in and out of a car, putting on socks, picking things up from the floor

– Often, your step length will often get shorter when walking. It may be hard for you to straighten your hips, so you may tend to bend forward when walking.


– Most commonly affects the end of fingers and the base of the thumb

– Fingers may feel stiff or tender. They may look ‘lumpy’ and have minor deformities

– It is common for the muscles in the hands to feel weak. It can be hard to clench your hands into a fist, carry something heavy, write or use scissors

Next – Why you get knee osteoarthritis