Knee Pain: Causes, Treatment and When to Seek Help

01A symptom

Knee pain as a symptom

Knee pain is not a diagnosis but a symptom of many different conditions. The knee is a complex joint: bones, cartilage, ligaments, tendons and small fluid-filled sacs called bursae all work together, and any of them can be the source of pain.

Mayo Clinic notes that the location and severity of pain vary with the cause, and that knee pain may come with swelling and stiffness, redness and warmth, weakness or instability, popping or crunching noises, or an inability to fully straighten the knee. Many types of minor knee pain respond well to self-care, while some need physiotherapy, other treatment or, in some cases, surgery.

02How it started

Pain after an injury or without one

The first useful distinction is whether the pain started with an injury. The NHS separates knee pain after an injury, such as a twist, a collision or overuse during exercise, from knee pain with no obvious injury, which is more often linked to arthritis, bursitis or other medical conditions.

Neither list is a self-diagnosis tool: the NHS stresses not to self-diagnose and to see a doctor if you are worried. But knowing how the pain started, how quickly it appeared and what you were doing helps the professional narrow down the cause.

03Injuries

Common injury and overuse patterns

Mayo Clinic and the NHS describe these common causes after an injury or repeated strain:

• sprains and strains, after overstretching, overusing or twisting the knee, often during exercise
• tendinitis, with pain between the kneecap and the shin, often from repetitive running or jumping; see our guide on patellar tendonitis
• a torn ligament, such as the anterior cruciate ligament (ACL), common in sports with sudden stops, pivots or changes in direction; the knee may feel unstable, give way or be hard to straighten, and a pop may be heard at the time of injury
• a torn meniscus, the rubbery cartilage that cushions the joint, which can tear when the knee twists while bearing weight; see our guide on a meniscus tear
• a fracture after a fall or accident, or sometimes after a simple misstep in people with bones weakened by osteoporosis
• a dislocated kneecap, which can visibly change the shape of the knee after a collision or sudden change in direction

Mayo Clinic also describes mechanical problems, such as a loose piece of bone or cartilage in the joint, tightness of the band on the outer thigh in runners and cyclists, and knee pain caused by changing the way you walk because of hip or foot pain.

04Medical causes

Arthritis and other medical causes

Knee pain without an obvious injury has several possible causes, according to the two sources:

• osteoarthritis, the most common type of arthritis, with pain and stiffness often in both knees and mild swelling, more common in older people
• rheumatoid arthritis, an autoimmune condition that can affect the knees and vary in severity
• bursitis, in which a bursa becomes inflamed, with warmth and redness and pain made worse by kneeling or bending
• gout and pseudogout, caused by crystals in the joint, with sudden attacks of very bad pain and a hot, red knee
• septic arthritis, an infection of the joint with swelling, pain and redness, often with fever and usually no previous injury
• bleeding into the joint, with swelling, warmth and bruising, more likely in people taking anticoagulant medicines
• pain around or behind the kneecap, common in athletes and young adults, and in older adults often related to arthritis of the kneecap

Mayo Clinic lists risk factors such as excess weight, lack of muscle strength or flexibility, sports and jobs that put repeated stress on the knees, and a previous knee injury. Pain does not mean the knee is inevitably wearing out: many causes are treatable.

05Location

Why location alone cannot give a diagnosis

It is tempting to match the place that hurts with a cause, but the sources do not support diagnosing knee pain by location alone. Different problems can hurt in the same area, the same problem can cause pain in different places, and pain from the hip or foot can change the way you walk and load the knee.

The NHS tables combine several features: how it started, which part of the knee is involved, swelling, warmth, redness, instability, age and medicines. Even then, they only suggest possible causes. If your pain is on the inner side of the knee, our guide on inner knee pain gives more detail, but a professional examination is what confirms the cause.

07Assessment

Clinical assessment and selected imaging

The NHS explains that a doctor can suggest treatment based on the cause, and may prescribe medicine or physiotherapy or refer you to hospital for a scan or specialist treatment, such as surgery. In other words, imaging is selected according to what the history and examination suggest; the sources do not describe a scan as necessary for every painful knee.

Before the appointment, it helps to note how and when the pain started, what makes it better or worse, whether the knee swells, locks or gives way, any fever, previous injuries, and the medicines you take, especially anticoagulants.

08Early care

Safe early care and adapted loading

For knee pain without warning signs, the NHS suggests trying these first steps, after which you should start to feel better within a few days:

• putting as little weight as possible on the knee at first, for example avoiding standing for long periods
• using an ice pack, or ice wrapped in a cloth, on the knee for up to 20 minutes every 2 to 3 hours, never directly on the skin
• using simple pain relief from a pharmacy, such as a painkiller or anti-inflammatory gel, following the instructions on the packet

Reducing load does not mean stopping all movement for long. Mayo Clinic notes that people with osteoarthritis, chronic knee pain or recurring injuries may need to change the way they exercise, for example by switching to swimming or other low-impact activities some days of the week, or simply limiting high-impact activities. The NHS advises seeing a doctor if the pain does not improve within a few weeks. Our guide on ice or heat for knee pain explains when each is used.

09Sources

Where the sources differ

The sources set different thresholds for seeking help. The NHS suggests self-care first, expects improvement within a few days and advises seeing a doctor if pain does not improve within a few weeks, with urgent advice for specific warning signs. Mayo Clinic lists signs that should prompt a call to the doctor but gives no time frame for pain without them. Read together, warning signs mean acting the same day, and persistent pain without them still deserves an appointment.

Mayo Clinic emphasizes prevention through a healthy weight, conditioning, strength and flexibility, while the NHS focuses on first steps and recognizing urgent signs. Weight management may help some people, but it is not a universal treatment for every cause of knee pain.

Both pages are relatively old: the Mayo Clinic page is dated January 2023 and the NHS page was last reviewed in December 2023, so details of treatment may have evolved. The urgent advice numbers on the NHS page apply to the UK; elsewhere, use your local health service or emergency number.

10Summary

In summary

Knee pain can come from injuries, overuse, mechanical problems, arthritis, gout, bursitis or infection, and the location of the pain alone cannot tell you which. Minor pain often improves with less weight-bearing at first, ice wrapped in a cloth and simple pain relief, followed by adapted activity rather than complete rest.

Get same-day advice if the knee is very painful, cannot bear weight or move, is badly swollen or deformed, locks or gives way, or is hot and red with fever. Treatment depends on the cause and may include medicines, physiotherapy or, in selected cases, surgery. For adults who have been assessed and have no warning signs, our physiotherapy practice in Bilbao offers rehabilitation adapted to the cause (consultations are in Spanish). Recording pain, swelling, walking distance, stairs and sleep each week helps review progress.