The knee joint is complex, and a range of factors can lead to damage and pain.
When the components of the knee are not working properly, pain, inflammation, and other symptoms can occur. Problems can result from trauma or a medical condition.
Read on to find out more about the causes of knee pain and what people can do to relieve it.
The knee joint
Chronic knee pain can have a variety of causes, including accidents and some health conditions.
To understand what causes knee pain, it may help to know what makes up the knee joint.
The knee is the joint where the thighbone, shinbone, and kneecap (patella) connect. It also involves cartilage, ligaments, menisci, and tendons.
Cartilage is a slippery substance on the ends of the bones in the knee. It lets the bones rub or pass smoothly over one another as the leg bends and straightens.
The menisci act as cushions between the femur and tibia that also act as shock absorbers.
Ligaments hold the bones together and give the knee its stability. Damage to the ligaments can result from overuse, as in sports, or from a traumatic injury.
Tendons are the connective tissues that attach the muscles in the leg to the bones they control.
When all these pieces work together, the knee functions as it should, and the person can move around freely.
Falling from a height, receiving a direct blow to the knee, making a sudden change in direction, or making repetitive movements during sports training are all causes of traumatic knee injuries.
These can lead to:
- dislocation of the kneecap
- a fracture of the kneecap, femur, or tibia
- torn ligament
- meniscus tear
Injuries can happen if a person:
- does not warm up before or after exercise or works too hard in an activity
- participates in some sports, especially without using protective equipment
- has a road traffic accident or a fall
Accidents, falls, and physical activities are common causes of traumatic knee injury. They can put the knee under extreme strain. If the knee does not heal properly, chronic pain can result.
Common problems include bone fractures, dislocated kneecaps, and torn ligaments.
Knee pain can be the long-term result of an accident, or it can stem from a medical condition, such as arthritis.
Medical conditions that lead to knee pain include the following:
- degenerative tissue disorders, such as osteoarthritis
- auto-inflammatory disease, such as rheumatoid arthritis
- tendinitis, an inflammation of a tendon, leading to pain when walking upstairs
- bursitis, an inflammation resulting from overuse
- chondromalacia patella, or damage to the cartilage below the kneecap
- gout, a type of arthritis
- a Baker's cyst, when fluid builds up behind the knee
- a tumor, either benign or malignant in the knee
Read on for more detail on some of these conditions.
Obesity and excess weight are major contributors to chronic knee pain.
Between 1971 and 2004, the incidence of knee pain rose by 65 percent in the United States, according to a study published in 2011 in the Annals of Internal Medicine. The researchers say this is mostly due to a rise in obesity.
Gout is a metabolic disorder. People with gout may experience knee pain, because gout causes uric acid crystals to build up in the joints. The result can be painful inflammation.This can also affect how the knee moves.
Degenerative tissue disorders
Osteoarthritis (OA) is a common chronic condition of the joints. It is a degenerative disease, caused by the "wear and tear" of the joints over time.
Common symptoms are pain and stiffness after long periods of rest. The knees may also become swollen after extended activity.
Osteoporosis is another common disorder. The bone becomes thinner, resulting in damage in the cartilage and connecting tissues in the knee. This can make a fracture more likely.
Bacterial infections — such as cellulitis — can cause sudden knee pain. Cellulitis occurs when bacteria that are normally on the surface of the skin make their way underneath the skin's protective surface.
Without treatment, cellulitis around the knee can cause infection in the joint, resulting in redness, swelling, pain, and stiffness.
In time, chronic knee pain can develop.
Rheumatoid arthritis (RA) is the most common connective tissue disorder that causes knee pain.
It is an auto-inflammatory disease, in which the body's immune system attacks its own tissues. In the case of knee pain, RA attacks the tissues of the knee.
Some lifestyle factors can increase the risk of knee pain.
Trauma: Starting physical activity without stretching properly first can increase the risk if a traumatic knee injury. People who play intense sports, such as basketball and football, have a higher risk of traumatic injury.
Gout: Disorders like gout may be caused by lifestyle choices or genetics. Excessive alcohol use, obesity, and dietary factors may contribute.
Degenerative disorders: These often happen with ageing, although there are other factors. The risk of osteoporosis increases with age, specific genes, lack of exercise, and dietary factors.
Obesity: This increases the risk of OA, especially in the large joints such as the knees. Excess weight can put strain on the knees, resulting in pain and inflammation.
Bacterial infections: Cellulitis can occur in a person who has a weakened immune system, skin conditions, long-term swelling in the arms and legs, and obesity, or if they use drugs that require needles.
Connective tissue disorders: Risk factors for RA include a family history of RA, being over 40, smoking, and obesity. Women are also more likely to develop RA than men.
Other possible factors for knee pain include age, overuse of the joints, and genetic factors.
Exercising and following a healthful diet throughout life can help reduce the risk of many of these problems.
Depending on the cause of the problem, the doctor may recommend:
- pain relief medication or other drugs
- an exercise plan, which may include low-stress exercise
- resting the knee
- a knee support
Pain-relief medications include anti-inflammatory drugs that will reduce the pain and swelling.
Taking care of the body and making healthful lifestyle choices can often help reduce the risk of chronic knee pain.
Tips for reducing the risk of chronic knee pain and improving the outlook for existing knee problems include:
- reducing alcohol intake
- quitting smoking
- maintaining a healthy weight
Obesity is a risk factor for many of the disorders that cause chronic knee pain. Keeping body weight in check can greatly reduce the risk of chronic knee pain.
Regular moderate exercise can reduce the risk, but warming up is essential.
Activities that strengthen the knees can help reduce the symptoms of knee pain if OA develops.
Low-stress exercises that may help improve or prevent knee pain include:
Depending on the cause of the knee pain and the health status of the individual, a doctor can advise on what type of exercise will help, and how intense the exercise should be.
Some types of pain — for example, OA — can be worse at night. Tips for getting a better night's sleep include:
- finding a comfortable position, possibly with a pillow between the legs
- using a long-lasting anti-inflammatory, for example, one that is effective for 12 hours
- avoiding alcohol and caffeine, as these can disrupt sleep
- maintaining good sleep hygiene, with regular times for going to bed and getting up
- avoiding sleeping aids as people need a higher dose if they use them regularly
- doing low-impact exercise to help with both pain and sleep
- using a firm mattress, possibly with a foam pad on top to help distribute your weight
As well as knee pain, a person may also have:
- weakness of the knee and an inability to stand properly or fully lengthen out the knee
- popping sounds as the knee flexes or straightens
- swelling and stiffness around the knee
- redness or warmth throughout the knee
These will depend on the cause.
Since many causes of knee pain can lead to the same symptoms, anyone who has knee pain that does not go away or who has severe pain should see a doctor.
Knee pain can occur for a wide variety of reasons. Anyone who is experiencing persistent knee pain should see a doctor.
The doctor will ask about the symptoms, carry out a physical examination, and they may also suggest imaging tests such as an X-ray or MRI scan. After diagnosing the cause, they will discuss the treatment options.
Suitable treatment may prevent a sudden or short-term knee problem from becoming long-term, or chronic.