The cause of knee pain depends on age and on whether the pain began after an injury: pain around the kneecap stands out in young people, osteoarthritis over the age of 50, and ligament and meniscus damage after an injury [1][2][3]. It often starts to ease within a few days with measures taken at home; if it has not improved within a few weeks, you should see a doctor [1]. Do not wait if you cannot put weight on the knee, if it locks, is badly swollen, or if redness comes with a fever [1].
What causes knee pain and what can it be a sign of?
Knee pain affects approximately 25% of adults [2]. It has no single cause: it can be a sign of many conditions, from a sprain to a ligament or meniscus tear, from pain around the kneecap to osteoarthritis, and from bursitis to gout and joint infection [1][2].
Knee pain that starts after an injury
The timing of the swelling is a useful guide: swelling that develops within minutes to a few hours of an injury suggests a ligament rupture, a fracture inside the joint or a dislocated kneecap; swelling that appears within hours to a few days suggests a meniscus tear [2]. The main possibilities are [1]:
- Sprains and strains: pain after overstretching, overusing or twisting the knee, often during exercise
- Tendonitis: pain between the kneecap and the shin, often linked to repetitive running or jumping
- A torn ligament, tendon or meniscus, or cartilage damage: the knee gives way or cannot be straightened; a popping sound may be heard at the time of injury
- Dislocated kneecap: the kneecap changes shape after a collision or a sudden change of direction
Knee pain that starts without an injury
Over the age of 50, long-standing, diffuse knee pain is commonly due to osteoarthritis, particularly when the pain is worse at the end of the day, is aggravated by weight-bearing and is relieved by rest [2].
Bursitis and pain around the kneecap are among the conditions that come to mind when pain appears in positions where you kneel and the knee is bent deeply, as in kneeling for prayer: kneeling and bending the knee make the pain and swelling of bursitis worse [1]; pain around the kneecap can also make kneeling and squatting difficult [3]. The main possibilities are:
- Osteoarthritis: pain and stiffness in both knees with mild swelling; more common in older people [1]
- Bursitis (inflammation of a sac around the knee): warmth, redness and swelling of the knee [1]
- Gout or joint infection (septic arthritis): a hot, red knee with sudden attacks of very bad pain [1]
- Bleeding into the joint: swelling, warmth and bruising; more likely in people taking blood-thinning medicines [1]
- A cyst behind the knee (Baker's cyst): may be the cause of pain at the back of the knee, which is less common [2]
Knee pain at a young age and kneecap pain
A common picture in teenagers and young adults is pain felt at the front of the knee, around or underneath the kneecap (patellofemoral pain syndrome, 'runner's knee') [3][4]. It is common in people who take part in sport, especially women and young adults, but it can also occur in people who do not [3].
The pain is dull and aching and begins gradually; climbing stairs, running, jumping, squatting and sitting for a long time with the knees bent make it worse [3][4]. In adolescents this pain is not usually caused by a structural abnormality in the knee [4].
It is usually fully relieved with simple measures or physiotherapy [3][4]. Surgery is very rarely needed; the pain may come back if the training routine is not adjusted [3].
In growing teenagers, pain and swelling below the kneecap suggest Osgood-Schlatter disease; it comes on gradually during periods of rapid growth, together with overuse [1][2].
What do swelling, clicking and catching in the knee mean?
Painless clicking from the knee is normal [1]. In pain around the kneecap, popping or crackling may be heard when climbing stairs or when standing up after sitting for a long time [3]. Painful clicking, locking, catching or giving way, on the other hand, points to a mechanical problem inside the joint; it can be seen with a meniscus or ligament tear and needs to be assessed by a doctor [1][2][4].
Mild swelling can be seen in osteoarthritis; a hot, red and very painful knee suggests gout or a joint infection [1]. Anterior knee pain in adolescents does not usually cause swelling [4].
What helps knee pain at home?
Knee pain can often be treated at home and starts to ease within a few days [1]. If a painkiller is needed, it can be used as tablets or as a gel [1]; ask your pharmacist or doctor which one is suitable for you.
The sources this article is based on make no recommendation for herbal mixtures or other popular home remedies [1][3]. The measures they do recommend are listed below; the last three are reported for pain around the kneecap:
- Putting as little weight as possible on the knee; for example, not standing for a long time [1]
- An ice pack wrapped in a towel on the knee for up to 20 minutes every 2 to 3 hours [1]
- Stopping the activities that bring on the pain; switching to activities that put less load on the knee, such as a stationary bike or swimming [3]
- Losing weight if you are overweight; this reduces the load on the knee [3]
- Exercises that strengthen the thigh and hip muscles [3]
Do knee braces and creams work?
A Cochrane review of knee braces, sleeves and bandages for pain around the kneecap found very low-quality evidence that, in adults who were also exercising, a brace did not reduce pain or improve function in the short term (under three months) [6]. In knee osteoarthritis, too, the evidence on the benefit of a brace for pain, stiffness and function was inconclusive [7].
According to a Cochrane review of creams and gels that contain an anti-inflammatory painkiller (NSAID), in studies lasting 6 to 12 weeks, carried out mostly in people with knee osteoarthritis, some of these reduced pain more than a gel without the medicine; however, this additional benefit was seen in a minority of people [5]. There is no evidence for chronic painful conditions other than osteoarthritis [5].
Which specialty sees knee pain and how is it assessed?
Knee pain is seen by orthopaedics and traumatology. The assessment begins with the history: age, the location, onset and duration of the pain, accompanying symptoms, swelling and earlier injuries; the knee is then examined, and range of movement, muscle strength, the ligaments and the menisci are assessed with special tests [2].
Not every painful knee needs imaging: an X-ray is requested for pain that has lasted more than six weeks or, after an injury, when certain criteria are met, for example being unable to bear weight for four steps [2]. MRI generally comes up when surgery is being considered or when pain continues despite adequate non-surgical treatment [2]. If an infection or an inflammatory disease is suspected, blood tests may be requested and a sample of joint fluid may be taken [2].
Treatment depends on the cause: the doctor may suggest medicine or physiotherapy, and may refer you for further imaging or for treatment such as surgery [1]. The common causes are described in separate articles in this guide: the treatment of knee osteoarthritis, the choice between exercise and arthroscopy in a meniscus tear, the decision about surgery in an anterior cruciate ligament tear, and knee replacement surgery.
When not to wait
See a doctor if the pain has not improved within a few weeks; in the following situations seek care without waiting [1][2]:
- The knee is very painful, cannot be moved or cannot take any weight
- The knee is badly swollen or has changed shape
- Swelling developed straight after an injury, within minutes to a few hours
- The knee locks, gives way or clicks painfully
- There is redness or heat around the knee together with a very high temperature and shivering (this can be a sign of infection)
- In an adolescent, the pain persists at rest or gets worse at night (other causes, including a tumour, are looked for)
Frequently asked questions
- Which doctor should I see for knee pain?
- An orthopaedics and traumatology specialist. The assessment begins with the history and examination; X-rays and MRI are not needed for every painful knee and are requested in specific situations [2].
- How does knee pain go away?
- It often starts to ease within a few days with putting less weight on the knee, applying ice and, if needed, taking a painkiller [1]. See a doctor if it has not improved within a few weeks [1].
- Why won't my knee pain go away?
- Knee pain that has not improved within a few weeks needs to be assessed by a doctor [1]. Over the age of 50, long-standing pain is commonly due to osteoarthritis [2]; pain around the kneecap may come back if the training routine is not adjusted [3].
This article is a general summary; diagnosis and treatment decisions are made by the doctor who examines you.
Sources
- Knee pain. NHS (nhs.uk), 2023. nhs.uk
- Knee Pain in Adults and Adolescents: The Initial Evaluation. American Family Physician (Bunt CW, et al.), 2018. pubmed.ncbi.nlm.nih.gov
- Patellofemoral Pain Syndrome. American Academy of Orthopaedic Surgeons (OrthoInfo), n.d.. orthoinfo.org
- Adolescent Anterior Knee Pain. American Academy of Orthopaedic Surgeons (OrthoInfo), n.d.. orthoinfo.org
- Topical NSAIDs for chronic musculoskeletal pain in adults. Cochrane Database of Systematic Reviews (Derry S, et al.), 2016. pubmed.ncbi.nlm.nih.gov
- Knee orthoses for treating patellofemoral pain syndrome. Cochrane Database of Systematic Reviews (Smith TO, et al.), 2015. pubmed.ncbi.nlm.nih.gov
- Braces and orthoses for treating osteoarthritis of the knee. Cochrane Database of Systematic Reviews (Duivenvoorden T, et al.), 2015. pubmed.ncbi.nlm.nih.gov
This article is general information and does not replace an examination or imaging. If you have symptoms, see a doctor.
More in this area
- Anterior cruciate ligament tear: is surgery always needed?
- Baker's cyst: what causes a swelling behind the knee and how does it settle?
- Cartilage damage in the knee: does cartilage heal, and how is it treated?
- Knee injections: what do cortisone, hyaluronic acid, PRP and stem cells do?
- Knee osteoarthritis: exercise, weight, injections and replacement, what and when?
- Knee replacement surgery: who is it for and what is recovery like?
- Meniscus tear: exercise or arthroscopy?
- Kneecap pain and chondromalacia patella: what causes it and how does it settle?