How your knee works

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.


The main symptoms of osteoarthritis of the knee are:

  • pain (particularly when you’re moving your knee or at the end of the day – this usually gets better when you rest)
  • stiffness (especially after rest – this usually eases after a minute or so as you get moving)
  • crepitus, a creaking, crunching, grinding sensation when you move the joint
  • hard swellings (caused by osteophytes)
  • soft swellings (caused by extra fluid in the joint).

Other symptoms can include:

  • your knee giving way because your muscles have become weak or the joint structure is less stable
  • your knee not moving as freely or as far as normal
  • your knees becoming bent and bowed
  • the muscles around your joint looking thin or wasted.

It’s unusual, but some people have pain in their knee that wakes them up at night. This generally only happens with severe osteoarthritis.

You’ll probably find that your pain will vary and that you have good days and bad days, sometimes depending on how active you’ve been but sometimes for no clear reason.

Some people find that changes in the weather (especially damp weather and low pressure) make their pain and stiffness worse. This may be because nerve fibres in the capsule of their knee are sensitive to changes in atmospheric pressure.


Many factors can increase your risk of osteoarthritis of the knee. It’s most common if:

  • you’re in your late 40s or older – this might be because your muscles have become weaker, your body is less able to heal itself or your joints have gradually worn out over time
  • you’re a woman – osteoarthritis is more common and more severe in women
  • you’re overweight – this increases the chances of developing osteoarthritis and of it becoming gradually worse
  • your parents or siblings have had osteoarthritis
  • you’ve had a knee injury, for example a torn meniscus
  • you've had an operation on your knee, for example a meniscectomy (to remove damaged cartilage) or repairs to your cruciate ligaments
  • you do a hard, repetitive activity or a physically demanding job, for example farming or mining
  • you have another type of joint disease which has damaged your joints, for example rheumatoid arthritis or gout.

Versus Arthritis has recently awarded a grant to investigating the use of new drugs to treat early-onset osteoarthritis caused by injury.

How will osteoarthritis of the knee affect me?

Osteoarthritis of the knee affects different people in different ways, so we can’t predict how it’ll progress.

Sometimes it can develop over just a year or two and cause a lot of damage to your joints, which can lead to deformity or disability. But more often it’s a slow process that develops over many years and causes small changes in just part of a joint, although it may still be painful.

Sometimes the condition peaks after a few years and your symptoms remain the same or even get easier.

If you have severe osteoarthritis your cartilage can become so thin that it no longer covers the ends of your bones. They start to rub against each other and eventually wear away. This can alter the shape of your joint, forcing your bones out of their normal position.

In addition, the muscles that move your knee gradually weaken and become thin or wasted. This can make your knee unstable so that it gives way when you put weight on it.

Changing your lifestyle can greatly reduce your risk of your osteoarthritis getting worse. Regular exercise, protecting your knee from further injury and keeping to a healthy weight will all help.

Osteoarthritis doesn’t lead to other types of joint disease and won’t spread through your body. However, deformity caused by osteoarthritis in your knee may mean you put more pressure on your other joints, which could result in osteoarthritis in those joints.


Your doctor will make a diagnosis of osteoarthritis of the knee based on your symptoms and an examination. During the examination, they’ll check for:

  • tenderness over your knee
  • creaking and grating (crepitus)
  • bony swelling
  • excess fluid
  • restricted movement
  • instability of your knee
  • thinning of the muscles that support your knee.

What tests are there for osteoarthritis of the knee?

X-rays are the most useful tests to confirm a diagnosis of osteoarthritis, although they won’t often be needed. X-rays may show changes such as osteophytes, narrowing of the space between bones and calcium deposits within your joint.

X-rays aren’t a good indicator of how much pain or disability you’re likely to have – some people have a lot of pain from minor joint damage but others have little pain from severe damage.

Your doctor may suggest you have a magnetic resonance imaging (MRI) scan on your knee, which will show the soft tissues (e.g. cartilage, tendons, muscles) and changes in the bone that can’t be seen on a standard x-ray. This is quite rare though.

There’s no blood test for osteoarthritis but they can be used to rule out other conditions.


There’s no cure for osteoarthritis as yet, but there are a number of treatments that can help ease symptoms and reduce the chances of your arthritis becoming worse.


Painkillers (analgesics) help with pain and stiffness but they don’t affect the arthritis itself and won’t repair the damage to your joint.

  • Painkillers are best used occasionally when you’re in pain or when you’re likely to be exercising.
  • Paracetamol is usually the best and most well-tolerated painkiller, but make sure you take the right dose because many people take too little – try 1 g (usually 2 tablets) 3 or 4 times a day. You can buy them from your chemist or supermarket.
  • Combined painkillers (e.g. co-codamol, co-dydramol) contain paracetamol and a second codeine-like drug, so they may be helpful for more severe pain. Because they’re stronger than painkillers, they’re more likely to cause side-effects such as dizziness and constipation.

Non-steroidal anti-inflammatory drugs (NSAIDs), for example ibuprofen or naproxen, may be recommended if inflammation is contributing to your pain and stiffness.

  • NSAIDs can sometimes have side-effects, but your doctor will take precautions to reduce the risk of these. They may suggest the lowest effective dose for the shortest possible time and prescribe another drug called a proton pump inhibitor to help protect your stomach from digestive problems.
  • NSAIDs also carry a slightly increased risk of a heart attack or stroke, so your doctor will be cautious about prescribing them if there are other factors that increase your overall risk (e.g. you smoke or you have circulation problems, diabetes, high blood pressure or high cholesterol).

Non-steroidal anti-inflammatory creams and gels are a good option if you have trouble taking NSAID tablets.

  • Creams and gels can be applied directly onto painful joints three times a day and there’s no need to rub them in – they absorb through your skin on their own.
  • They’re extremely well tolerated because very little is absorbed into your bloodstream.
  • You can tell within a few days whether they’ll help with your pain.

Capsaicin cream is made from the pepper plant (capsicum) and is an effective and well-tolerated painkiller.

  • Capsaicin cream is only available on prescription and needs to be applied three times a day.
  • Most people feel a warming or burning sensation when they first use it, but this generally wears off after several days.
  • The pain relief starts after a few days and you should try it for at least two weeks before deciding if it’s helped.

Stronger painkillers, for example opioids/anti-inflammatories, may be prescribed if you have severe pain and other medications don’t work well enough.

  • Stronger painkillers are more likely to have side-effects, especially nausea, dizziness and confusion, so you’ll need to see your doctor regularly and report any problems.
  • Some opioids can be given as a plaster patch to wear on your skin, which can give pain relief for a number of days.
  • Stronger painkillers are only available on prescription.

Because these treatments work in different ways, you can combine them for greater pain relief. Ask your chemist or doctor for advice on safe combinations.

If you have trouble opening childproof containers, ask the pharmacist to put your drugs in a more suitable container. You can also order a child-resistant closure card.

Steroid injections are sometimes given directly into a particularly painful knee joint.

  • The injections can start working within a day or so and may improve pain for several weeks or months.
  • They’re mainly used for very painful osteoarthritis, for sudden attacks caused by shedding calcium crystals and to help you through important events (such as a family wedding).

Versus Arthritis has awarded a grant for the PROMOTE trial, a study into whether methotrexate, a drug commonly used to treat rheumatoid arthritis, can be used to treat osteoarthritis of the knee. Another trial is looking into whether a drug called spironolactone is an effective treatment.

Managing your symptoms

There’s no cure for osteoarthritis as yet, but there’s a lot that you can do to improve your symptoms and reduce the chances of your arthritis becoming worse.


It’s very important to be active and to keep your joints moving if you have osteoarthritis of the knee.

There are many important benefits of regular exercise, and some of the main ones are:

  • keeping the muscles in your legs strong, as this will provide extra support. This can greatly reduce the pain, stiffness and swelling in your joints
  • helping you to stay at a healthy weight, as this will mean less pressure on your knees
  • helping the knees to maintain a normal range of movement
  • boosting energy levels
  • helping you get a good night’s sleep
  • making you feel better about yourself.

There are many types of good physical activity. The key is to find something you enjoy and to keep doing it.

You may worry that being active will make the pain in your knee or the arthritis itself worse. In fact, the right exercise for you will improve your symptoms and strengthen your knee. Taking painkillers, such as paracetamol, and non-steroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen, before you exercise can help you be active.

Not doing enough physical activity will make your knees more painful and stiff.

Try to aim to do at least some physical activity every day. You could start off gently, and try to gradually increase what you do – both in terms of the length of time you exercise and the effort levels you feel able to put in. This gradual increase will help your body get used to doing that little bit more, and should really help improve your health, fitness and symptoms.

Swimming is a fantastic all-round exercise. Your body will be supported by the water, and swimming improves strength, stamina and flexibility. Water aerobics, which is exercising to music in a class in a swimming pool led by an instructor, is a good alternative to swimming. Hydrotherapy has also helped a lot of people with knee osteoarthritis. This is a form of exercising in warm water under the supervision of a physiotherapist.

It’s important to keep the muscles around your knees strong, but also to strengthen muscles all over the legs and hips. This will mean your knees are well supported and protected.

Brisk walking and cycling are good at strengthening leg muscles. With cycling you might need to start off gently and gradually increase the amount you do. Take note if your knees do start to hurt, and in which case you might need to try a different exercise at least for a while. Testing out how you get on with cycling on a machine in the gym first might be a good move.

Yoga, T’ai Chi and Pilates can be great exercises for people with knee osteoarthritis.

There are simple exercises you can do throughout the day at home, that will help you keep moving and strengthen your leg muscles. These could include:

  • standing up from a chair, sitting down and repeating. Do this without using your arms
  • doing step-ups on the first step of the stairs.

You could start with a number you can manage easily, and do two or three sets a day. Then every few days you could see if you could do one more than the previous day.

It’s normal for your muscles to feel a bit sore when exercising, especially if you are new to exercise or if you haven’t exercised for a while. However, if you’re in a lot of pain during or after exercising and the pain won’t go away, see a GP.

A physiotherapist or a personal fitness trainer qualified to level two or above will be able to offer you expert advice as well as specific exercises and programmes for you.

We have examples of exercises you can do in your home every day to improve the flexibility and strength of your knees. This should greatly improve your symptoms. These exercises can be found at the back of the Osteoarthritis of the knee booklet .

Living with osteoarthritis of the knee

Learn more about living with osteoarthritis of the knee.

Dealing with stress

Living with a long-term condition like osteoarthritis can lower your morale and may affect your sleep. It’s important to tackle problems like these as they could lead to depression and make the osteoarthritis more difficult to cope with. It often helps to talk about negative feelings – speak to your healthcare team, family or friends. Your doctor may also be able to tell you about local support groups.

Possible complications

There can sometimes be rarer complications with osteoarthritis of the knee, including deposits of calcium crystals in your cartilage and cysts forming at the back of your knee.

Osteoarthritis with crystals

Chalky deposits of calcium crystals can form in your cartilage. This is called calcification or chondrocalcinosis. The crystals show up in x-rays and can be seen under a microscope in samples of fluid taken from your joint.

Osteoarthritis tends to become more severe more quickly when crystals have formed. Sometimes the crystals can shake loose, causing a sudden attack of very painful swelling called acute calcium pyrophosphate crystal arthritis (acute CPP crystal arthritis), which has previously been called 'pseudogout'.

Baker’s cysts (popliteal cysts)

Baker’s cysts can form when extra joint fluid is being produced by the joint and some of it becomes trapped in a pouch (hernia) sticking out of the joint lining. They’re often painless, but you may be able to feel a soft-to-firm lump at the back of your knee. Sometimes a cyst can cause aching or tenderness when you’re exercising.

Occasionally a cyst can press on a blood vessel, which can lead to swelling in your leg, or the cyst may burst (rupture) and release joint fluid into your calf muscle, which can be very painful.

A cyst may not need treatment, but if it does the extra fluid can be drawn from your knee using a syringe (this is called aspiration) and a steroid solution can be injected into it.

Exercises to manage knee pain

Knee pain has a number of different causes. Whatever the cause, exercise and keeping to a healthy weight can reduce symptoms.

Try these exercises to help ease pain and prevent future symptoms.


  • Knee pain can be caused by a number of different things. Whatever the cause, exercise and keeping to a healthy weight can reduce symptoms.
  • You can take painkillers to ease pain. Taking them before exercise can help you stay active without causing extra pain.
  • Try the exercises suggested here to help ease pain and prevent future symptoms.

Straight-leg raise (lying)

Bend one leg at the knee. Hold the other leg straight and lift the foot just off the bed. Hold for a slow count of 5, then lower. Repeat 5 times with each leg. Try doing it in the morning and at night while lying in bed.

Step ups

Step onto the bottom step of stairs with the right foot. Bring up the left foot, then step down with the right foot, followed by the left foot. Repeat with each leg until you get short of breath. Hold on to the bannister if necessary. As you improve, try to increase the number of steps you can do in 1 minute and the height of the step.

Knee squats

Hold onto a chair or work surface for support. Squat down until your kneecap covers your big toe. Return to standing. Repeat at least 10 times. As you improve, try to squat a little further. Don't bend your knees beyond a right angle.

Leg cross

Sit on the edge of a table or bed. Cross your ankles over. Push your front leg backwards and back leg forwards against each other until the thigh muscles become tense. Hold for 10 seconds, then relax. Switch legs and repeat. Do 4 sets with each leg.

Leg stretch

Sit on the floor with your legs stretched out in front. Keeping your foot to the floor, slowly bend one knee until you feel it being comfortably stretched. Hold for 5 seconds. Straighten your leg as far as you can and hold for 5 seconds. repeat 10 times with each leg.

Straight-leg raise (sitting)

Sit will back in the chair with good posture. Straighten and raise one leg. Hold for a slow count to 10, then slowly lower your leg. If you can do this easily, try it with light weights on your ankles and with your toes pointing towards you. Try doing this every time you sit down.


Sit on a chair. Without using your hands for support, stand up and then sit back down. Make sure each movement is slow and controlled. Repeat for 1 minute. As you improve, try to increase the number of sit/stands you can do in 1 minute and try the exercise from lower chairs or the bottom two steps of a staircase.