Osteoarthritis of the knee

osteoarthritis of the knee

Introduction

This booklet aims to help people who have osteoarthritis of the knee, and their families and friends. We first explain how osteoarthritis of the knee develops, how you can recognise the symptoms, and how doctors diagnose and treat it. We then offer hints and advice on living with it more easily, including answers to common questions.

Near the end of the booklet you will find addresses of organisations that can offer further help, including information on how to contact the Arthritis Research Council (arc).

Finally, we have included a brief glossary of medical words (like cartilage). We have put these in italics when they are first used in the booklet.

What is osteoarthritis?

Osteoarthritis is a disease which affects the joints in the body. The surface of the joint is damaged and the surrounding bone grows thicker. ‘Osteo’ means bone and ‘arthritis’ means joint damage and swelling (inflammation). When joints are swollen and damaged, they can be painful. They can also be difficult to move. Some other words are used to describe osteoarthritis, including ‘osteoarthrosis’, ‘arthrosis’ and ‘degenerative joint disease’.

Osteoarthritis of the knee is a very common form of osteoarthritis. Other joints which are often affected include joints in the hands, the spine, the hip joint and the big toe joint. You can find more information on osteoarthritis in arc booklet ‘Osteoarthritis’.

How does osteoarthritis of the knee develop?

To understand how osteoarthritis develops, you need to know how a normal joint works. A joint is where two bones meet. Most of our joints are designed to allow the bones to move in certain directions. The knee is the largest joint in the body, and also one of the most complicated because it has many important jobs to do. It must be strong enough to take our weight and must lock into position so we can stand upright. But it has to act as a hinge too, so we can walk. It must also withstand extreme stresses, twists and turns such as when we run or play sports.

The knee joint is where the thigh bone (femur) and shin bone (tibia) meet. The end of each bone is covered with cartilage which has a very smooth slippery surface. The cartilage allows the ends of the bones to move against each other almost without friction. It also acts as a shock absorber. The knee joint has two extra pieces of cartilage which act as shock absorbers inside the knee (called meniscal cartilages or menisci). A normal knee joint is shown above.

The joint is surrounded by a membrane (the synovium) which produces a small amount of thick fluid (synovial fluid). This fluid helps to nourish the cartilage and keep it slippery. The synovium has a tough outer layer called the capsule which helps hold the joint in place.

The knee cap (patella) is another important part of the knee joint. The underneath of the patella is also covered with cartilage. The patella is attached to the thigh muscles by a very large tendon. The patella is fixed to the bone just below the knee joint at the front of the tibia.

The tendons are strong connecting tissues which attach the muscles to the bones on either side of the joint. They also help to keep the joint in place. When a muscle contracts, it shortens and this pulls the bone and makes the joint move. The diagram shows how the muscles are attached to the bones on either side of the joint.

The knee joint is held in place by four large ligaments. These are thick, strong bands which run within or just outside the capsule. Together with the capsule, the ligaments prevent the bones moving in the wrong direction or dislocating. There is one ligament on each side of the knee joint and two inside. The thigh muscles (quadriceps) also help to hold the knee joint in place.

When a joint develops osteoarthritis, the cartilage gradually roughens and becomes thin. This happens over the main surface of the knee joint or at the cartilage underneath the patella. The surrounding bone reacts by growing thicker. The bone at the edge of the joint grows outwards (this forms osteophytes or bony spurs). This bone growth can affect both the femur and the tibia, as well as the patella.

The synovium swells slightly and may produce extra fluid, which then makes the joint swell. This extra fluid causes what some people call ‘water on the knee’.

The capsule and ligaments slowly thicken and contract, as if they were trying to push the joint back into shape. The muscles that move the joint gradually weaken and become thin or wasted. This can make the knee joint unstable so that it ‘gives way’ when you put weight on it.

When we look at an osteoarthritic joint under a microscope, we see that the joint is trying to repair itself. All the tissues are more active than usual. For example, new tissue is produced to try to repair the damage, such as the osteophytes. In some types of osteoarthritis, especially in the small finger joints, the repair is successful. This explains why many people have osteoarthritis but experience very few problems. Unfortunately, in osteoarthritis of the knee the repair does not usually work. Osteoarthritis may then seriously affect the joint, making it painful and difficult to move.

Osteoarthritis is a slow process that develops over many years. In most cases, there are only small changes which affect only part of the joint. Sometimes, though, osteoarthritis can be more severe and extensive.

In severe osteoarthritis, the cartilage can become so thin that it no longer covers the thickened bone ends. The bone ends touch, rub against each other and start to wear away. The loss of cartilage, the wearing of bone, and the bony overgrowth at the edges all combine to change the shape of the joint. This forces the bones out of their normal position and causes deformity.

A common complication is where chalky deposits of calcium crystals form in the cartilage (a process called calcification or chondrocalcinosis). These calcium crystals can shake loose from the cartilage, irritate the synovium and cause serious inflammation and swelling (pseudogout).

What causes osteoarthritis of the knee?

Many factors seem to increase the risk of osteoarthritis developing in the knee joint. The risk does increase as we get older, but osteoarthritis of the knee joint is not a problem in all elderly people. It is something that runs in some families which shows that there is a gene or genes involved. This may be linked with a gene that affects collagen, one of the main building blocks of cartilage.

Osteoarthritis of the knee is twice as common in women as in men. It mainly occurs in women who are over the age of 50, and is often associated with mild arthritis of the joints at the end of the fingers (causing bony swellings called Heberden’s nodes).

Osteoarthritis of the knee is also more common in some racial groups than others. For example, it is more common in Afro-Caribbean populations. It is also more common in black people in South Africa and America in comparison with white people.

Osteoarthritis of the knee is common in people who are overweight, especially in middle-aged women. Being overweight also increases the chances of osteoarthritis getting worse once it has developed.

Putting regular stress on the knee joint can lead to osteoarthritis. For example, people who go running and jogging for a long time have a slightly increased risk of osteoarthritis of the knee.

Injuries to the knee joint often lead to osteoarthritis in later life. A common cause is a tear of the meniscal cartilage after a twisting injury. This is a common injury in footballers, who can face extra risks. The damaged cartilage can lead to osteoarthritis in later life, and we now know that the operation to remove the torn cartilage substantially increases the risk of osteoarthritis developing after a number of years.

Does osteoarthritis of the knee vary for different people?

Osteoarthritis of the knee affects different people in different ways. Some people have a problem only with one knee, others with both knees. Pain is the main problem for some people while others find their main problem is difficulty in walking. Some people may stay the same for many years while the osteoarthritis in other people keeps getting worse. As a result, it is not very helpful to compare the experience of one person with another as we cannot predict the eventual outcome for anyone with osteoarthritis.

How can I tell if I have osteoarthritis of the knee?

People with osteoarthritis of the knee joint usually complain that the knee is painful or aching. Your knee joint may often feel stiff at certain times. You may have pain all around the joint or just in one particular place, and the pain may be worse after a certain activity. The pain is usually better when you rest. It is unusual to have pain in the knee joint which wakes you up at night, except in severe osteoarthritis. You may feel stiff for a short period after resting and first thing in the morning. Walking for a few minutes usually eases the stiffness.

You will probably find that your pain will vary. There may be good days and bad days or even good and bad months for no apparent reason. Changes in the weather may make a difference. For example, your joints may ache more just before it rains. All joints have nerve endings which are sensitive to pressure. The nerve endings will respond to the drop in atmospheric pressure which occurs before it rains.

If you develop more severe arthritis, your movement will be restricted. Walking any distance or climbing stairs can be a problem. Sometimes your knee joint may give way because of weak thigh muscles or damaged ligaments.

How do doctors diagnose osteoarthritis of the knee?

Your doctor will be looking out for the problems mentioned above. When your joints are examined, your doctor can feel the bony swelling and creaking of the joint and see any restricted movement. Your doctor will also be looking for tenderness over the joint, and any extra fluid.

The thigh muscles are usually thinner and weaker than normal. With very severe osteoarthritis in the knee, the knee joint will tend to give way because of the damaged ligaments. It may even be possible to move the knee from side to side.

What tests can show osteoarthritis?

There is currently no blood test for osteoarthritis, although blood tests are sometimes used to rule out other types of arthritis. The x-ray is the most useful test to confirm osteoarthritis. Often it will show the space between the bones narrowing as the cartilage thins, and changes in the bone such as spurs. Calcification may also show on knee x-rays. Although the x-ray helps the diagnosis, it cannot predict how much trouble you will have. A bad x-ray does not necessarily mean a lot of pain or disability. The diagram opposite shows an example of these changes on an x-ray.

What are the prospects if I have osteoarthritis of the knee?

Osteoarthritis does not always get worse. Most people with osteoarthritis carry on a normal life and do not become severely disabled. For many people, osteoarthritis reaches a peak a few years after the symptoms start and then either stays the same or gets a little easier. However, osteoarthritis of the knee can often worsen as the years go by, and it may become painful and disabling.

Sometimes osteoarthritis gets better on its own, but this is unusual. Doctors cannot predict the outcome for individuals. However, there are a number of treatments that can improve symptoms, and certain changes in lifestyle can greatly reduce the risks of osteoarthritis progressing. Regular appropriate exercise, protecting the joints from further injury, and maintaining an ideal weight through healthy eating will all help. So, to a certain extent, the person with osteoarthritis is in control of the outcome in their own case.

How can osteoarthritis of the knee be treated?

There are no cures for osteoarthritis. But there are many treatments. Treatment can help to:

  • relieve the discomfort and pain
  • reduce the stiffness
  • stop any further damage to the joint.

Can drugs help?

At the moment, there are no drugs which affect how osteoarthritis develops. But some drugs can help you deal with the symptoms. Pain relievers (such as paracetamol) and anti-inflammatory creams to rub into the knee can help pain and stiffness. Some people find them more helpful than others. (See arc leaflet ‘Drugs and Arthritis’.)

Anti-inflammatory drugs (NSAIDs) help some people more than paracetamol but they can cause stomach ulcers. Discuss this with your doctor.

Sometimes an injection may help, either into a tender spot around the knee, or even into the joint itself. Hospital doctors occasionally ‘wash out’ the knee by removing any fluid in it and flushing it through with a sterile solution. This is not done very often.

Can surgery help?

Most people with osteoarthritis of the knee will never need surgery. But operations are sometimes used for badly damaged joints. These include joint replacement. Doctors will consider this for someone who is barely able to walk and who is in constant pain. (See arc booklet ‘A New Knee Joint‘.)

Are there any other measures which can help?

Many other measures are now being researched to help people with osteoarthritis of the knee, such as exploring new drugs to help the joint heal and using electrical nerve stimulation (a TENS machine) to relieve pain.

Beware of ‘miracle cures’ and special diets. Sadly, there are no miracles for most people with osteoarthritis.

What can I do to help myself?

You can make a major difference to your arthritis of the knees in two ways:

(1) Lose weight (if overweight). Many people with osteoarthritis of the knee are overweight. Studies have shown that people who can lose weight have less knee problems in the future than those who cannot. There is no special osteoarthritis diet but it is always good to eat a healthy diet containing lots of fruit and vegetables as well as white meat and fish, and to avoid high calorie foods.

(2) Quadriceps (thigh muscle) exercises. The quadriceps muscles become weaker in everyone with arthritis in the knees, because the normal nerve supply to the muscles is reduced. To overcome this it is essential to carry out quadriceps muscle exercises as often as possible (see below). It has been proved that strengthening these muscles not only improves your mobility but also reduces pain.

Which exercises are the best?

  • Straight-leg raise – sitting The most important thing is to choose exercises which you can do regularly. The easiest one to do is when sitting down in a chair. Get into the habit of doing this every time you sit down. Sit well back in the chair with a good posture. Straighten and raise the leg, hold it for a slow count to ten, then slowly lower it. Repeat this several times with each leg at least ten times with each. If this can be done easily, repeat the exercises with a weight on the ankle (buy ankle weights from a sports shop or improvise with a tin of e.g. peas in a carrier bag wrapped around the ankle).
  • Straight-leg raise lying Get into the habit of doing straight-leg exercises in the morning and at night whilst lying in bed. With one leg bent at the knee, hold the other leg straight and lift the foot just off the bed. Hold for a slow count of five then lower. Repeat with each leg five times every morning and evening.
  • Muscle stretch At least once a day when lying down, do the following exercise. Firstly, place a rolled-up towel under the ankle of the leg to be exercised. Then bend the other leg at the knee. In the leg to be exercised, use your leg muscles to push the back of the knee firmly towards the bed or the floor. Hold for a slow count of five. Repeat with each leg five times. Not only does this exercise help to strengthen the quadriceps muscles, but it also prevents the knee from becoming permanently bent.
  • Clenching exercises During the day, get into the habit of clenching and releasing the quadriceps muscles. By constantly stimulating the muscles, they become stronger.

What else can I do?

There are a number of things you can do:

  • Make sure that you do not keep your leg bent in the same position for long periods. For example, do not put pillows under your knee at night. This may ease your pain for a while but, if you do it regularly, it will affect the muscles and may leave your leg permanently bent. Even if the pain is severe, always fully straighten the knee several times a day.
  • Wear cushioned training shoes as much as possible to act as a shock absorber for the knee.
  • Keep using your knee, but rest it when it becomes painful and start again later.
  • Use a stick to take the weight off the joint if you need to, but keep moving!
  • Use a hand-rail for support when climbing stairs. Go upstairs one at a time with your good leg first. Come downstairs with your bad leg first followed by good, always using a rail for support.
  • Keep the knee warm. It can help relieve pain and stiffness. Hot baths, hot-water bottles, a heat lamp or a rub with a suitable cream can all bring relief. It does not cause any harm to use heat even during a flare-up.

Who else can help?

As well as doctors, other health care professionals can help. Physiotherapists, occupational therapists and others can advise on exercise, heat and other treatment. If you have trouble in activities at home, such as bathing, stairs or getting in and out of bed, they can advise on equipment to help you. Your GP or hospital doctor can refer you to one of these services for an assessment if necessary. Friends and family can help with shopping and domestic tasks, but remember to keep as mobile and independent as possible. (See arc booklet ‘Your Home and Arthritis’ and leaflets ‘Physiotherapy and Arthritis’ and ‘Occupational Therapy and Arthritis‘.)

Are there any likely complications with osteoarthritis of the knee?

Most people do not suffer any complications. The problem often settles down to be a nuisance rather than a major problem. However, complications do occur occasionally in some people.

Rapid deterioration

This is more likely to affect older people with a severe form of the disease. The pain can increase with a reduction in mobility within a few weeks or months. This is rare and occurs in less than one in 20 people with osteoarthritis of the knee.

Loss of stability

If the ligaments are damaged or the muscles have weakened, the knee joint can give way if weight is put upon it. You should be able to prevent this if you take regular exercise to move the knee joint.

Sudden flare-ups of pain

It is quite common to have mild flare-ups. Sometimes they can be more severe and last longer. The joint may swell markedly. In some people, this is caused by chalky crystals forming in the cartilage. The crystals make the lining of the joint (synovium) inflamed, which causes a large amount of fluid to develop in the knee joint. This extra fluid is not good for the joint. Your doctor will usually attempt to drain off the fluid and give a steroid injection at the same time to prevent it happening again.

Questions and answers

Can any special diet help?

A large amount of research is being done on diet, nutrition and osteoarthritis. Many books, articles and advertisements claim benefits for diets and natural food products. At the moment, we have no evidence that any particular food, vitamin or supplement has a real effect on osteoarthritis, either for better or for worse.

However, there is ample evidence that being overweight increases the risk of developing osteoarthritis, especially of the knee. Being overweight also increases the risk of osteoarthritis progressing. Therefore, you should eat a balanced, healthy diet and keep your weight as close as possible to the ideal for your height and age. (See ‘What can I do to help myself?’ and also the separate arc booklet ‘Diet and Arthritis‘.)

Will rest or exercise help?

Joints do not wear out with normal use. In general, it is much better to use them than not to! However, you must strike a sensible balance between too much activity and too much rest. Most people with osteoarthritis find that while too much exercise worsens their pain, their joints stiffen up if kept still for too long.

For most people with osteoarthritis, the best advice is little and often: a little rest, followed by a little exercise. For example, do the housework or gardening in short spells interrupted by short rests. Avoid sitting in one place for too long – get up and stretch the joints from time to time. Break up a long car journey with frequent stops to walk around.

Activities which cause severe pain afterwards are probably best avoided. If for some special reason you do need to do a lot extra, it can help to take a painkiller before you start. Don’t worry, even if it causes extra pain. You are unlikely to damage the joint but your doctor or therapist will advise you.

Can swimming or pool treatment help?

Swimming can be a very good way of exercising and keeping fit as it causes little pain. Water supports the body’s weight so that little force goes through the joints as you exercise. Also, warm water relaxes muscles and joints and is very soothing, allowing joints to move more freely.

Prescribed exercises in a hydrotherapy pool can help get muscles and joints working better, without undue pain. Supervised swimming in natural spa waters is an ancient treatment it is the exercise that helps rather than any healing properties of the water itself! (See arc leaflet ‘Hydrotherapy and Arthritis‘.)

Does the weather really affect osteoarthritis?

As mentioned earlier, painful joints are often sensitive to the weather. They tend to feel worse when the atmospheric pressure is falling, such as just before it rains. This helps to explain how people with osteoarthritis can predict rain, and why joint pains seem linked with the damp.

However, there is no evidence that different climates have any long-term effect on osteoarthritis or its outcome. The weather may temporarily affect symptoms but not the arthritis itself. There is no point in moving to a different area in the hope of curing osteoarthritis. Osteoarthritis occurs all over the world, in all types of climate.

Can heat or other remedies help?

Warmth or other remedies applied to the affected area often relieves the pain and stiffness of osteoarthritis. Heat lamps are popular, but you can get a similar effect more cheaply with hot-water bottles (be careful, though, it is easy to burn yourself with either). There are also many creams, available at the chemist, that can cause localised heat.

These measures make no long-term difference to the disease, but they can give you temporary relief. Used carefully, they are safe and soothing. We have no proof that copper bracelets or other such measures can affect osteoarthritis, but faith in them seems to help some people.

Who should I listen to?

Many well-meaning people offer advice. Magazines and the media are full of articles on arthritis and its treatment. Some offer new hope, others offer a special diet or medicine with miracle properties. Unfortunately, there are no miracle cures or easy answers. Discuss things with your doctor and think about the advice in this booklet before spending money on new ideas.

How important is it to keep my spirits up?

Depression, low morale, and poor sleep can all make pain worse they can lower your threshold to pain.

If you become depressed, your pain may feel worse. You might go to the doctor and be given bigger doses of tablets to relieve the pain. But sometimes what you really need is help for the depression and the demoralising effect of arthritis. If the depression is lifted, the pain becomes less.

A positive and hopeful approach is half the battle, though this is easier said than done. Make every effort to make life fuller and more interesting than before. Your morale will drop after too much rest and inactivity, whereas hobbies and interests take your mind off your problems. Sleep is important it is best not to take naps during the day but to save all your sleep for night-time, taking a painkiller last thing if necessary. If you have enjoyed vigorous activity and sport, you may have to develop less active pastimes, but there is no reason to let osteoarthritis get you down or stop you doing most everyday activities.

What does research mean for the future?

We do not yet know the causes or the cure for osteoarthritis. However, recent research, much of it sponsored by arc, is uncovering the mechanisms which lead to joint damage as well as the factors which control the healing response. For example, we now know some of the chemicals which thin out the cartilage in osteoarthritis, and we are now testing new drugs that inhibit these chemicals.

Doctors and research workers have changed their attitude a great deal in recent years. They now see real possibilities of understanding and controlling osteoarthritis in the future. They no longer see osteoarthritis as an inevitable part of ageing or a wear and tear disease, but more as a major challenge and an important problem which they can solve.

Glossary

Calcification deposits of calcium crystals in ‘soft tissues’ such as cartilage.

Capsule the tough, fibrous sleeve around a joint; its inner layer is the synovium.

Cartilage strong, tough material on the bone ends that acts as a shock absorber; its slippery surface allows smooth movement between bones.

Chondrocalcinosis calcification of cartilage.

Collagen the building material of tissues.

Deformity abnormal angulation or swelling of a joint.

Femur the upper-leg or thigh bone the longest bone in the body.

Heberden’s nodes firm, bony swellings of the end joints of fingers, often painless when fully formed the hallmark of nodal osteoarthritis.

Ligament tough, fibrous bands which hold two bones together in a joint.

Menisci free rings of cartilage, like washers, lying between the cartilage-covered bones in the knee, acting as extra shock absorbers. Each knee has an inside (medial) and outside (lateral) meniscus.

Nodal osteoarthritis a form of osteoarthritis that often runs in families, characterised by knobbly finger swellings (Heberden’s nodes) and a tendency to get osteoarthritis at several sites (especially knees, big toes).

Osteophytes overgrowth of new bone around the sides of osteoarthritic joints, also known as ‘spurs’.

Patella the kneecap, a small bone that helps the front thigh muscles work the knee.

Pseudogout a painful, sudden attack of a hot, very swollen, red joint, caused by calcium crystals in the joint (mainly the knee).

Synovial fluid the fluid produced by synovium to nourish and lubricate the joint.

Synovium the inner layer of the capsule that produces synovial fluid.

Tendon strong fibrous guiders that connect muscles to bones.

Tibia the lower-leg or shin bone the second largest bone in the body.

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