Knee pain

The knee is a big weight-bearing joint, held steady by ligaments, padded inside by two wedge-shaped cartilages, the menisci, and ringed by tendons and small fluid-filled sacs, the bursae; pain can come from any of them. The usual causes group like this:

• Strains, sprains and tears. Sport, a twisting movement or a fall are the usual setting, although you do not need to play sport to hurt one. A torn ligament or meniscus usually follows an injury, sometimes only a minor twist, and may leave the knee swollen, locking or giving way; from middle age on a meniscus can also tear through wear, with no injury at all.
• Tendons and the kneecap. Overuse or a knock can leave a tendon sore and puffy. An ache behind or around the kneecap that stairs and long sitting typically make worse is known as patellofemoral pain.
• Wear. Osteoarthritis, the most frequent kind of arthritis, often settles in the knee, mostly after 50: an ache that mounts with use, and morning stiffness that passes within half an hour. It has a guide of its own.
• Crystal arthritis. Gout and pseudogout bring on sudden attacks in which the joint turns hot, red and extremely painful; pseudogout in particular picks on the knee.
• Inflammatory arthritis. Rheumatoid arthritis, psoriatic arthritis and their relatives can start in the knee, typically with swelling and morning stiffness and, often, other joints joining in; our joint swelling guide follows that picture.
• Around the joint. Bursitis causes a tender, puffy patch, typically after much kneeling, and a Baker's cyst, a fluid-filled swelling at the back of the knee, is covered in its own guide.
• Infection. Rarely, infection gets into the knee (septic arthritis), leaving it hot and swollen whether or not a fever comes with it, and the lists under "When to seek help" route it.

These patterns give hints, but a knee that is swollen, or has hurt for a while, is not one to work out on your own: several causes look much alike and need quite different treatment.

What the knee does matters as much as where it hurts:

• An ache that mounts with activity and fades with rest, and stiffness that passes within half an hour of getting going: wear
• Stiffness every morning that takes more than half an hour to ease, with swelling and other sore joints: an inflammatory cause
• A sudden, severe attack in a knee that is hot and red: crystals, or an infection, which the lists below route
• Pain that started with a twist or a knock, along with swelling, locking or the knee giving way: a ligament or a meniscus
• A small, tender swelling in one spot, often after kneeling: a bursa
• Tightness, or a swelling you can feel behind the knee: a Baker's cyst

Clicking that does not hurt is normal and harmless; clicking with pain, or a knee that locks or gives way, is another matter, and the lists below give its route.

Often the history and a careful look at the knee are enough, with no scan at all. When a test would add something, it is picked to answer a particular question.

At the appointment, ultrasound shows fluid in the joint, a Baker's cyst and the ligaments near the surface in real time. Point-of-care ultrasound is part of the consultation with Dr Borukhson, so in most cases the knee is scanned during that first appointment; the ultrasound clinic page explains more. For a suspected tear of a meniscus or a cruciate ligament deep in the knee, MRI is often the better test, and she arranges a referral for it.

If a knee is swollen and its cause still unclear, taking off some of the fluid (joint aspiration) can settle the matter: the sample is examined for gout and pseudogout crystals and, if infection is possible, for bacteria. Guided by ultrasound, this can usually be done at that same appointment.

The plan depends on the cause. Most ordinary strains need little more than sensible care and get better over days to a few weeks. A physiotherapist's exercises and strength work help a wide range of knee problems, kneecap pain and wear among them, and often form the core of treatment. When inflammation, a bursa or an arthritis flare is behind the pain, an ultrasound-guided injection, placed precisely with the scan, can calm it, though an injection is seldom a cure on its own; draining fluid from a tight, swollen knee can ease it. The gout and pseudogout guides describe how crystal arthritis is treated. An inflammatory arthritis needs a rheumatologist's care, and a ligament or meniscus tear that needs mending goes to a knee surgeon. You and Dr Borukhson settle the plan together.

When a knee has started to hurt after a strain or a spell of overuse:

• Go easy on it for a day or two: keep weight off the knee as far as is practical, and avoid long stretches on your feet
• Use cold: a bag of frozen peas or an ice pack in a tea towel, held on the knee for 20 minutes or less, with two or three hours between goes
• Pharmacy pain relief: paracetamol, or ibuprofen as a gel or, where needed and safe for you, as tablets. Any fabric that ibuprofen gel touches burns more easily, so do not smoke, and stay away from open flames, for as long as you are using it
• After that, keep it moving: gentle use, then a stepwise return to your usual activities, helps the knee more than long rest

Over time, strengthening the muscles that support the knee, those around the hip among them, guards it best, and bringing your weight down, where there is extra, lightens what the knee carries with each stride. Our arthritis and exercise guide explains how to build up gradually and when to ease back.

A sore knee can usually be looked after at home to begin with. For the few pictures that need more, the lists below say where to go: an injured knee that may be broken or out of place, an infected joint, which can become sepsis, a knee that locks or swells badly, and a clot in the leg.

Treat any of these as a 999 or A&E emergency: call 999 and do not drive yourself to A&E.

• Severe illness with suspected sepsis: a high fever with shaking, confusion, rapid breathing, or feeling dramatically worse over hours
• With a fever or feeling unwell, a rash that does not fade when you press it, a stiff neck with eyes that cannot bear bright light, or skin, lips or tongue turning blue, grey, pale or blotchy, since these can be signs of meningitis or sepsis, as can a very bad headache, confusion or a first seizure with a fever or feeling unwell; on black or brown skin the rash and the change of colour may be easier to see on the palms of the hands or the soles of the feet
• A joint you cannot put weight on or move, or that has moved out of place, or, after a fall or injury, very bad pain or any tingling or numbness
• After an injury, a crack heard as it happened, or skin around it that has turned blue, grey or cold, since these can be signs of a broken bone
• After a knee injury, a knee that has changed shape, swells up very quickly, gave a pop or a snap, shows bone through the skin, or is bleeding heavily, since the kneecap may have dislocated, or a bone or ligament may be broken or torn
• Lips, mouth, throat or tongue that suddenly swell, a throat that feels tight, very fast breathing or a struggle to breathe or to swallow, skin, tongue or lips turning blue, grey or pale (on black or brown skin this may be easier to see on the palms of the hands or the soles of the feet), becoming suddenly very confused, drowsy or dizzy, or fainting and not being able to be woken, since this can be a severe allergic reaction, anaphylaxis, which can follow a dose of any medicine

Any of these needs an assessment that is urgent, on the same day, from your GP or NHS 111:

• A joint that is hot and swollen, with a fever or feeling unwell, since an infected joint has to be ruled out at once, at A&E or through NHS 111
• A joint that has become hot and very swollen suddenly, or is worsening quickly, even without a fever, since an infected joint does not always announce itself with one
• Joint pain with a fever, or feeling hot, cold or shivery, or generally unwell, since an infection in or around a joint has to be found the same day
• A knee that is badly swollen, that is very painful with no fall or injury, or that locks, gives way or clicks painfully so that you cannot carry on as normal, since the cause has to be found without waiting; NHS 111 can say where to be seen, and a knee you cannot put weight on or move belongs to the first list instead
• After a knee injury, short of the signs in the first list, pain that keeps getting worse, a swelling or bruise that is large or still growing, or a kneecap that slipped out of place and went back on its own, since a ligament, the cartilage or a bone may be damaged; NHS 111 can say where to go, and an urgent treatment centre can sometimes X-ray it
• A calf that is swollen, hot or painful, or a limb that is painful, swollen or discoloured, which can mean a clot; with breathlessness, chest pain, palpitations or feeling faint, this is a 999 or A&E emergency: call 999 and do not drive yourself to A&E

See a GP within days if the knee stays stiff for more than half an hour after waking, which our joint pain without swelling guide covers, or if it has stayed soft and swollen for a week or two with no injury to explain it, which our joint swelling guide takes further, since an inflammatory arthritis may start like this; the same pace holds if the knee keeps hurting at rest or at night in a way that using it does not explain, if you have lost weight without trying, if you have had cancer, or if a hard lump has appeared beside the knee or is growing. See a GP if, after two weeks of care at home, the knee is no better, if the pain is getting worse or keeps returning, or if it is stopping your normal activities or affecting your sleep. After an injury, a knee or leg left at an odd angle or out of shape is a 999 or A&E emergency. No referral is needed to be seen here; next-working-day appointments can almost always be arranged, and same-day appointments are sometimes possible. If you cannot tell how urgent something is, asking is never a mistake.

A painful knee has many possible explanations, and one specialist visit can test them in turn: an examination, ultrasound of the joint and the tissues around it, a fluid sample where the diagnosis depends on it, and treatment there and then where it fits. If your knee keeps hurting, or the pain comes and goes, a specialist can pin down the cause and set a plan in motion instead of letting it drag on.

My knee hurts: when is it time to see someone?

A knee you cannot move or put weight on, or one that has moved out of place and stayed there, is a 999 or A&E emergency, injured or not; so, after an injury, is a knee that looks the wrong shape, swells up fast, pops or snaps, or shows bone. Call 999 and do not drive yourself to A&E. A hot, swollen knee needs to be seen the same day: at A&E or through NHS 111 if you also have a fever or feel unwell; if it has become hot and very swollen suddenly or is worsening quickly without a fever, through an urgent GP appointment, NHS 111 or a specialist clinic that can see you that day. A badly swollen knee, very bad pain with no injury, and a knee that locks, gives way or clicks painfully so that you cannot carry on as normal need your GP or NHS 111 the same day. After an injury short of those signs, growing swelling or bruising, or a kneecap that slipped out and went back on its own, is for NHS 111 the same day. Otherwise plain knee pain often gets better over a few days of rest, cold and pain relief at home; book a GP appointment if a fortnight of that has not helped, if it is worsening or coming back, or if it is getting in the way of everyday life or your sleep. The lists under when to seek help give the detail.

What do the different kinds of knee pain point to?

The way the pain behaves is a guide: pain that grows with activity and settles with rest suggests wear; stiffness in the mornings with swelling suggests inflammation; a sudden, hot, intensely painful attack suggests a crystal attack such as gout or pseudogout, or an infection, which looks the same and which the lists under when to seek help route; and pain that began with a twist or a knock suggests a strain or an injury inside the joint. These are pointers, not answers, and a swollen knee should not be self-diagnosed; examining it, with ultrasound where useful, gives a far more dependable answer.

A hot, red knee that suddenly hurts a lot: what is it?

It may be a crystal attack, gout or pseudogout, each covered in its own guide, or an infected joint, which can look exactly the same from the outside. A knee you cannot put weight on or move is a 999 or A&E emergency, fever or no fever. If the hot, red knee can still move and take weight and you have a fever or feel unwell, it needs to be seen the same day at A&E or through NHS 111; without those, it still needs seeing that day, through an urgent GP appointment, NHS 111 or a specialist clinic that can see you that day, so the cause can be pinned down.

How is the cause of knee pain found?

Mostly by listening to the story and examining the knee carefully. When that leaves questions, ultrasound can show fluid in the joint, a Baker's cyst and the ligaments near the surface. Point-of-care ultrasound is part of the consultation with Dr Borukhson, so the scan usually happens at the same appointment; if a tear of the cartilage or of a ligament deep inside the knee is suspected, she arranges an MRI, which is often the better test for those.

Can treatment start at the first appointment?

Often, yes. With ultrasound in the room, treatment can begin there and then once the cause is clear and you have agreed the plan: a guided injection when inflammation or a bursa is to blame, or draining fluid from a swollen knee, which can relieve the pressure and lets the fluid be checked for crystals and infection. When something else is the right next step, such as physiotherapy or a surgical opinion, a referral is arranged instead.