Common causes of knee pain

Written by Dr Sean Leo, a consultant orthopaedic surgeon whose clinical focus is the knee, sports injuries and the lower limb.

Last updated: 9 October 2026.

The NHS lists causes of knee pain under two headings: knee pain after an injury, and knee pain with no obvious injury ^[1]. The NHS lists sprains and strains, a torn ligament, tendon or meniscus, cartilage damage and a dislocated kneecap as causes of knee pain after an injury ^[1].

Knee pain can be a symptom of many different conditions ^[1]. A doctor can suggest treatment based on what is causing it ^[1]. This page outlines injuries and joint conditions that can be behind knee pain.

What causes knee pain?

The NHS lists causes of knee pain under two headings: knee pain after an injury, and knee pain with no obvious injury ^[1]. Do not self-diagnose: see a doctor if you are worried ^[1].

What’s covered on this webpage

• What causes knee pain?
• Which injuries can cause knee pain?
• Which joint conditions can be behind knee pain?
• When should knee pain be checked?
• When is urgent help needed?
• What should I do next?

Which injuries can cause knee pain?

The NHS lists sprains and strains, a torn ligament, tendon or meniscus, cartilage damage and a dislocated kneecap as causes of knee pain after an injury ^[1].

A sprain is a torn or twisted ligament (tissue that connects the joints) ^[2]. A strain is an overstretched or torn muscle (also known as a pulled muscle) ^[2]. Tendons connect your muscles to bones in your joints, for example, in your knees, elbows and shoulders ^[3]. The meniscus is the shock-absorbing cartilage in the knee ^[4].

• Sprains and strains. Pain after overstretching, overusing or twisting, often during exercise ^[1].
• A torn ligament, tendon or meniscus, or cartilage damage. The knee may feel unstable, give way when you try to stand, or be unable to straighten, and you may hear a popping sound during injury ^[1].
• A dislocated kneecap. A dislocated kneecap is where your kneecap (patella) moves out of place ^[5]. It is usually caused by an injury to the knee ^[5]. The kneecap changes shape after a collision or sudden change in direction ^[1].

If you think the kneecap has dislocated: A dislocated kneecap often moves back into place by itself ^[5]. Even if it does, you will still need to get it checked by a doctor ^[5]. You will usually need X-rays ^[5]. Do not try to put the kneecap back into place yourself ^[5].

More on the four main ligaments of the knee

The knee joint is located where the end of the thigh bone (femur) meets the top of the shin bone (tibia) ^[4]. Four main ligaments connect these two bones ^[4].

• Medial collateral ligament (MCL) runs along the inside of the knee. It prevents the knee from bending inward ^[4].
• Lateral collateral ligament (LCL) runs along the outside of the knee. It prevents the knee from bending outward ^[4].
• Anterior cruciate ligament (ACL) is in the middle of the knee. It prevents the shin bone from sliding out in front of the thigh bone ^[4].
• Posterior cruciate ligament (PCL) works just opposite to the ACL. It prevents the shin bone from sliding backward under the femur ^[4].

ACL injuries often occur with other injuries ^[4]. For example, an ACL tear often occurs along with tears to the MCL and the shock-absorbing cartilage in the knee (meniscus) ^[4].

Which joint conditions can be behind knee pain?

• Osteoarthritis. Osteoarthritis is a condition that causes joints to become painful and stiff ^[6]. It most often causes problems in the knees, hips and small joints of the hands ^[6]. In osteoarthritis, the protective cartilage on the ends of the bones breaks down, causing pain, swelling and problems moving the joint ^[6].
• Bursitis. Bursitis is when the fluid-filled sacs (bursa) that cushion the joints have become painful and swollen (inflamed) ^[7].
• Rheumatoid arthritis. Rheumatoid arthritis is a long-term condition that causes pain, swelling and stiffness in the joints ^[8]. It is an autoimmune disease: the immune system attacks the cells that line the joints by mistake ^[8].
• Gout. Gout is a type of arthritis that causes sudden, severe joint pain ^[9]. It is caused by having too much uric acid in the blood, which can lead to crystals forming around the joints ^[9]. It is usually in the big toe, but it can be in other joints, including the knees ^[9].

More on osteoarthritis

• The exact cause of osteoarthritis is not known, but several things are thought to increase the risk, including joint injury, age, family history, obesity and being a woman ^[6].
• The condition does not necessarily get any worse over time ^[10]. There are a number of treatments to help relieve the symptoms ^[10].
• Exercise is one of the most important treatments for people with osteoarthritis, whatever your age or level of fitness ^[10]. Discuss any new exercise plan with your doctor or physiotherapist before you start ^[10].

More on rheumatoid arthritis and gout

• Some people with rheumatoid arthritis also experience problems in other parts of the body, or more general symptoms such as tiredness and weight loss ^[8].
• There may be periods where symptoms become worse, known as flare-ups or flares ^[8].
• There is no cure for rheumatoid arthritis ^[8].
• Early diagnosis and appropriate treatment enables many people with the condition to have periods of months or even years between flares ^[8].
• Diagnosing rheumatoid arthritis quickly is important, because early treatment can prevent it getting worse and reduce the risk of joint damage ^[8].
• See a doctor if you think you have symptoms of rheumatoid arthritis, so they can try to identify the underlying cause ^[8].
• See a doctor if you have symptoms of gout for the first time ^[9].

When should knee pain be checked?

Knee pain can often be treated at home ^[1]. For mild knee pain without an injury or the warning signs, the NHS says you should start to feel better in a few days ^[1]. See a doctor if knee pain does not improve within a few weeks ^[1].

When is urgent help needed?

The list below covers the signs that should not wait for a routine appointment.

What should I do next?

If knee pain is not settling, or you are unsure what is causing it, an assessment is a sensible next step. The assessment brings together the patient’s story, an examination and any tests that help, so that the patient and the surgeon can decide together. It looks at the structure involved, the patient as a whole person and the goal they want to return to. An appointment supports an informed decision. It is not a commitment to surgery.

• Read about the Knee Hub.
• Read about ACL reconstruction surgery.
• Read about meniscus repair surgery.
• Read about fractures versus sprains.
• Read about knee swelling and what can cause it.
• Read about when knee pain should be checked.
• Arrange a knee assessment when you are ready.

See also our guide to knee pain during pregnancy.

See also our guide to traveling with knee pain.

References

1. NHS. Knee pain. https://www.nhs.uk/symptoms/knee-pain/
2. NHS. Sprains and strains. https://www.nhs.uk/conditions/sprains-and-strains/
3. NHS. Tendonitis. https://www.nhs.uk/conditions/tendonitis/
4. MedlinePlus. Anterior cruciate ligament (ACL) injury. https://medlineplus.gov/ency/article/001074.htm
5. NHS. Dislocated kneecap. https://www.nhs.uk/conditions/dislocated-kneecap/
6. NHS. Osteoarthritis. https://www.nhs.uk/conditions/osteoarthritis/
7. NHS. Bursitis. https://www.nhs.uk/conditions/bursitis/
8. NHS. Rheumatoid arthritis. https://www.nhs.uk/conditions/rheumatoid-arthritis/
9. NHS. Gout. https://www.nhs.uk/conditions/gout/
10. NHS. Osteoarthritis – Treatment and support. https://www.nhs.uk/conditions/osteoarthritis/treatment/