A swollen knee can be an uncomfortable and sometimes painful experience. By ‘swollen’, we don’t really mean a small bump to the kneecap; when doctors talk about swollen knees, they tend to mean quite extensive inflammation around the joint: front, sides, even the back. So… what could be going on?
First of all, this kind of swelling usually means that an excess of fluid is collecting around the joint. We call this an effusion. That fluid, a mixture of white and red blood cells and other lubricants, is basically the body’s way of protecting the joint. But it can cause the whole knee to become quite stiff, sore, hard to move, or painful. If the swelling happens very quickly after an injury (typically within four hours or so), the fluid may be mainly blood, and this will need urgent medical attention.
There are several possible reasons for knee swelling of this kind. The following list includes some of the common ones. While you shouldn’t use it to self-diagnose a problem, it may help you to understand some of the potential background to knee pain and swelling.
Infection
While infection is a relatively rare reason for a swollen knee, it’s potentially serious and needs to be excluded from any diagnosis. Infections aren’t just caused by scratches or cuts on the knee itself; they can track to the joint from other areas of the body. When an infection happens, the skin around the knee can become red and may feel hot to touch. You might run a temperature and feel unwell. If these symptoms occur, see a doctor straight away.
Trauma
If your knee swells after an accident, the root cause is often pretty obvious – a fall, a twist, a blow to the kneecap. An injury to parts of the knee like the ligaments, tendons, bursae, cartilage or meniscus can trigger swelling in the joint. Minor injuries can be treated at home with an ice pack to reduce the swelling. If the knee is locked, ie it doesn’t move, if it gives way under you, or it is very swollen and painful, you’ll need to see a doctor.
Overuse
Knee swelling isn’t only caused by accident-related injuries. It can also be provoked by what we call “microtraumas”. This is where a repeated action – say a long run, a hike, a gardening or DIY task with lots of kneeling – causes irritation or damage to the underlying tissues. Stopping the activity and resting the knee are, obviously, the first port of call here; ice treatment may also help to reduce the swelling in the first instance.
Degeneration
Osteoarthritis, where the joint surfaces lose their protective covering of cartilage, is another common cause of knee swelling because it often results in overproduction of joint fluid. You might expect that this would only happen in longstanding arthritis cases, but in fact it’s sometimes the point at which people realise they have the condition in the first place. Gout, pseudogout and rheumatoid arthritis are other forms of arthritis that can cause swelling.
Another underlying condition
Two other relatively common conditions that can cause knee swelling are bursitis and Baker’s cyst. Bursitis is what happens when the cushioning sac within the knee becomes irritated and fills with excess fluid. This can happen after an injury or a repetitive stress (such as kneeling). You can find out more about this condition on the blog here. A Baker’s cyst is when fluid from the joint causes a lump to form at the back of the knee. It can be brought on by a number of things, including injury or arthritis. You can find out more about how it’s diagnosed and treated in this article.
As you’ve probably noticed, the potential triggers for knee swelling are quite wide-ranging, so it’s good to be armed with a diagnosis. If you need more information or help around swollen knee conditions, we’ll be happy to see you. You can book an appointment on the website, or by calling Mr Bailey’s secretary Cheryl on 01962 826107.
