Part of Total knee replacement rehab

Pain at night after a knee replacement: why it happens and what helps

Pain at night after a knee replacement is usually at its worst in the first few weeks, and the reasons are mechanical rather than sinister. A knee that has been held still for hours stiffens into whatever position it was left in. The day's swelling is still in the leg when you stop moving. Nothing is happening to take your attention off the knee. And the night is the longest stretch any dose of pain relief has to cover. OrthoInfo describes pain at night, along with pain on activity, as common for several weeks after this operation, so a knee that keeps you awake in week two is doing what most new knees do. This page is the why, the how long and the medication question. It gives no sleeping positions, because positions, pillows and getting in and out of bed have a page of their own in this series. Your surgical team's plan comes before anything written here, and the timing of prescribed pain relief is a decision for whoever prescribed it. Two things come before any comfort advice. Sudden breathlessness or chest pain in the night is a call to emergency services, even if your leg looks normal. And night pain that climbs week by week instead of easing, pain that keeps building while you rest, a knee that is hot or red, a temperature, or a wound that is leaking all need your surgical team the same day.

Warning signs, and when to get help

Why does your knee hurt more at night after a knee replacement?

Because of what the night does to the knee, not because of anything you did wrong in it. Several things stack up, and none of them is a mistake on your part.

If you are reading this in the dark and what you want is something to do rather than an explanation, go straight to what to do when you wake at 3 in the morning. The rest of this will keep until daylight.

Stillness is the big one. A new knee stiffens quickly when nothing moves it, and it stiffens into whatever position it has been left in for the last three hours. Morning stiffness comes from the same mechanism, so the nights and the mornings are one story after this operation and not two. The NHS gives one specific night instruction, not to sleep with a pillow under your knee, and otherwise says you do not need to sleep in a special position.

Then the swelling the day has left in the leg. The NHS asks you to keep the leg raised as much as you can manage to bring the swelling down, and not to stand for long stretches, which it says can make your ankles swell. A day spent mostly upright comes to bed with you, and plenty of people put the result as a throb that only shows itself once they lie still. How long the swelling lasts has the pattern a settling knee follows and what brings an evening leg down.

Nothing is competing for your attention either. Through the day the knee shares the stage with a visit, a meal, a television program and the walk to the bathroom. At two in the morning it has the stage to itself, and the same pain is louder for it.

The gap between doses matters too. Whatever you take before bed has to cover the longest unbroken stretch of the day, and the small hours are usually furthest from a dose. Whether your schedule can be arranged differently is a question for your prescriber, and there is a section on it below.

One more surprises people: the pain of this operation is not only in the knee. South Tees lists aching, a bruised feeling, tenderness and sharp pains among the common symptoms, along with swelling down the leg and into the calf, and a leg that feels heavy and weak. So an ache in the thigh or the shin at night is not automatically a new problem. The calf is the exception that is never waved away, and it has its own line in the warnings at the foot of this page.

Is night pain normal, and how long does it last?

Take the exceptions first, because a tired reader needs those before anything else. Pain that is climbing week by week instead of easing, pain that keeps building while you are resting as well as when you move, a knee that is hot or red, a temperature, or a wound that is leaking are not the subject of this section. They need your surgical team the same day, at the level the warning signs below set out.

With that said: yes. OrthoInfo describes pain at night, along with pain on activity, as common for several weeks after this operation. Several weeks is the only timeframe a source we trust puts on it, and it describes the usual course. It is not a promise about your knee. Nobody can tell you the night it stops, and we will not offer you a figure that no source produced.

Watch the direction, not the level. OrthoInfo asks you to speak to your doctor if the pain has not started to improve within a few days of the operation. A knee that hurts a great deal at night and is slowly hurting less each week is behaving. A knee whose nights are getting worse is a knee to report, however early in the recovery you are.

If what you actually want is the whole arc, the recovery timeline week by week sets out what each source says about each stage, and the exercises for weeks 0 to 2 covers the fortnight when the nights are usually at their worst.

The burning, nerve-like and numb feelings at night

People search for this at three in the morning almost as often as they search for the ache, and hardly anywhere answers it. They were warned about the ache. Nobody mentioned the burning, buzzing, electric or oddly numb feeling across the front of the knee.

Part of it is expected, and documented. OrthoInfo says most people feel some numbness in the skin around their incisions, and that patch of skin is not the same as the joint underneath it. It matters for a practical reason as well: numb skin cannot tell you an ice pack has been on too long, so check that area with your eyes.

We have no figure to give you for how many people notice a burning quality at night, and this page does not put a name on it. Naming it would mean handing you a diagnosis that only the person examining your knee can make, and nerve-related pain after surgery gets managed differently depending on what is found. Describe it to your team in your own words at your next contact. Tell them the time of day it is worst, which is a detail they can use.

One version of it is not something to describe at the next appointment. New numbness, tingling or burning in your lower leg or foot, beyond the numb patch around the scar, is a same day call, and the line below says what to do if the foot also turns cold, pale, blue or gray.

What to do when you wake at 3 in the morning

Everything below is for an ordinary bad night. If you are awake because the pain has changed rather than because it is bad, read the warning signs at the foot of this page before anything here.

Move the knee. Lying there waiting for it to settle is the one thing that reliably does not work, because a knee that has been still for hours is stiff, and stiffness is the half of night pain you can do something about at the time. The exercises you already have are the ones to use: ankle pumps for the calf and the circulation, heel slides for bending, and quad sets and the knee extension stretch for the thigh and for straightening. Each of those pages carries its own starting dose and your physio will adjust this, and the dose at three in the morning is not a bigger one than the dose at three in the afternoon.

Nobody wants four links at that hour, so here are the numbers those pages give, as one round. Around 10 to 20 ankle pumps on each foot. About 10 quad sets, holding each for roughly 5 seconds. Ten to fifteen slow heel slides, kept inside the bend you already have rather than reaching for more. Your own physio's numbers come first if they differ. Then lie still again and give it several minutes, because that is when it usually eases.

One round, not round after round until the knee feels normal. A knee worked over and over at two in the morning is sorer by six, and the next day's exercises are the ones that matter. If a second round is what gets you back to sleep an hour later, that is reasonable; chasing it all night is not.

Do not invent anything at that hour. A new stretch, a harder repetition or a test to see whether the knee has got worse all belong in daylight, with your team's list in front of you. The same goes for the knee you are tempted to push into a bend to prove it still bends.

Have the telephone numbers to hand before the night you need them. Anyone doing their rehabilitation on their own at home should have been given clear goals and a point of contact for advice and support, which is what NICE asks of the service looking after you (NICE NG157). If you were not given one, or you cannot find it, ask at your next contact and write it down somewhere you can read it half asleep.

Positions, pillows, the mattress and the business of turning over are not on this page by design. They have a page of their own, how to sleep after a knee replacement. Look there if what you want tonight is a set-up and not an explanation.

Pain relief and the night: the timing question, and who answers it

The timing of your pain relief against the hour you go to bed is the single most useful thing to ask about, and it is not ours to answer. Whoever prescribed it can look at what you are taking, when you are taking it and how the night is going. A page cannot do any of that. Never stop or change a prescribed medicine on your own.

Before you ring, two things are worth knowing. South Tees says patients leave hospital with only a week of pain relief and asks you to contact your family doctor in good time if you need more, so the call to make is the one before you run out. The same leaflet makes the point that effective pain relief in the early stages is what allows you to move and exercise comfortably. That puts it inside the rehabilitation, not beside it. A night you cannot sleep through is a rehabilitation problem as much as a comfort problem.

On the stronger painkillers, OrthoInfo is direct: use opioids only as your doctor directs, and stop them as soon as your pain begins to improve. Ask your prescriber how to come off them rather than stopping on your own.

Sleep medicines, supplements and alcohol belong in that same conversation, with your prescriber or your pharmacist and not with a web page. One reason for it is worth knowing tonight. The NHS lists feeling sleepy or tired among the common side effects of codeine, and says it is best not to drink alcohol with it because that raises the risk of side effects. Put a drink or an over-the-counter sleep aid on top of a prescribed painkiller and the walk to the bathroom at four in the morning is being made on a leg that is not reliable yet, by someone less steady than they feel. Ask before you add anything, herbal remedies and vitamins included, which the NHS also asks you to mention to a pharmacist or doctor.

Getting out of bed in the dark deserves one extra caution of its own, whatever you are taking. Stand up slowly with a hand on something solid, because a fall in these first weeks can damage the new knee and may lead to further surgery (OrthoInfo), and the dizziness line in the warnings below covers the version of that which needs reporting.

The sleep itself, which can lag behind the pain

Almost nobody is told this, and it explains a worry that sends people back to their surgeon. Your pain can be improving while your sleep is not, and the second is not evidence against the first.

Two small studies have followed sleep after this operation. In the first, 34 people having a planned first replacement of one knee were measured before surgery and up to six months after it. Sleep quality got worse over the first six weeks and then improved by the three month and six month checks, while pain fell throughout, and sleep quality did not track the pain (Chen and colleagues, 2016). In the second, 67 people were followed for three months after a first knee replacement: pain fell steadily, while sleep was at its worst at around one month and then gradually recovered (Fatah and colleagues, 2020).

Thirty-four people in the United States and sixty-seven in Iraq are a narrow base, so take the shape from them and leave the numbers. That shape is the useful part: broken sleep peaking somewhere between the first weeks and the first month, lagging behind the pain instead of mirroring it, is a documented pattern and not a sign your knee is going backward.

If the nights are wrecking your days to the point where the exercises are not happening, say so. Do not push on alone. NICE recommends supervised rehabilitation as an outpatient, in a group or one to one, for people who are having difficulty with daily activities, who have an ongoing functional problem with specific needs, or who are not meeting their goals on their own (NICE NG157). Not managing the program because you have not slept for a fortnight is that conversation, not a failure to own up to.

What makes the nights worse without anyone noticing

A few things usually turn out to be behind it, and they are all invisible from inside the night they ruin.

The afternoon that felt fine. The commonest version is a good day, a longer walk or a visit, nothing much at the time, and the bill arriving at one in the morning. The knee is a slow reporter. If your nights are suddenly worse, look at what the previous day asked of the leg before you look for anything else. The pain monitoring model is written for physiotherapists and not for patients, and it judges a session by the next morning instead of by the moment it happened. That is a sound way to read a bad night too.

The evening the knee spends bent. Hours in a chair with the knee held at the same angle, or an evening with the leg propped so the knee sits bent, sets up exactly the stiffness that wakes you later. That is the same instruction as the NHS one about the pillow under the knee, and it is as easy to break on a sofa at eight in the evening as it is in bed. Where the leg is up to bring the swelling down, nothing goes under the knee itself.

Stopping the exercises after a bad night. It is the most understandable decision in the recovery and it makes the following night worse, because the stiffness that drives night pain gets its way. The dose on the main knee replacement rehab program is the one to go back to, and if the knee is not bending or straightening any further from week to week, that is on the warning list below as something to raise within a few days rather than to work through. The daytime work on the bend and on the last part of the straightening is on how to improve the bend.

One more belongs here because the night is when it happens. Getting up in the dark, half asleep, on a leg that is not reliable yet is how people fall after this operation, and OrthoInfo is blunt about what a fall in the first few weeks can cost. Keep the aid within reach of the bed, keep a light on the route to the bathroom, and keep the phone within reach of the bed rather than across the room on a charger, because the fall you would need help after is the one that leaves you on the floor away from it. If you live alone, that is the most useful thing on this page. How long you use a walker, frame or stick covers how long that lasts and why handing it back early is the expensive mistake.

When night pain is a warning sign, and how quickly to act

On this one subject the ordinary answer and the serious one feel the same at two in the morning, so the test is the pattern and not how much it hurts.

Sudden breathlessness, chest pain or coughing up blood in the night is a call to emergency services, even if your leg looks normal and even if you feel foolish about it.

The same day list is the one to know by heart. A calf or thigh that is newly swollen or getting more swollen, warm or tender. A leg that is swelling further from day to day instead of settling, including swelling spreading into the calf, ankle or foot. A wound that is more red, hot or painful, is leaking, or has edges coming apart. A temperature, or feeling hot, cold and shivery. A knee whose redness, warmth, swelling or pain is not getting better or is getting worse, including pain that keeps building while you rest as well as when you move, which is the pattern that points at infection around the new joint rather than at a long night. New numbness, tingling or burning below the knee, beyond the numb patch around the scar. And new pain in the joint at any time afterward, even years later, with a temperature or a hot, red, swollen knee.

None of those needs the others for company. OrthoInfo asks you to tell your doctor immediately about any one of its infection warning signs, and increasing knee pain with both activity and rest is on that list in its own right. A knee that looks normal from the outside, feels cool to the hand and comes with no temperature does not buy you time, because that climbing pain is itself one of the signs OrthoInfo wants reported. A normal temperature is not an all clear either: OrthoInfo's page on infection after a joint replacement says fever is no longer considered a sign of an infection after a joint replacement, and that the signs can be as little as mild redness and swelling. Whether anything is growing around the implant is a question for the people who can test the joint, and not one you can settle by looking at your knee at two in the morning. Pain is the part you can feel. It is enough on its own to make the call.

Two are slower, and they are the two people wrongly save for an appointment that is weeks away. Pain that has not started to ease in the first days, or pain that was settling and starts climbing again day by day, goes to your team within a few days. So does a knee that is not bending or straightening any further from week to week or is getting stiffer.

One route into a late infection has nothing to do with the knee, and it is the one patients never connect. OrthoInfo says any infection in your body can spread to a joint replacement, and names bacteria entering the bloodstream during dental procedures, urinary tract infections and skin infections among the common causes. So if new night pain in a knee that had been comfortable follows an infection somewhere else, a tooth, a chest, a water infection, a break in the skin, say that when you ring rather than leaving them to find it. And get the infection elsewhere treated promptly instead of waiting it out.

One more belongs to the reader whose operation was years ago, not weeks. Pain in the new knee that had settled and has come back, or that is getting worse month by month, is a review to ask for rather than an emergency, because the parts of a new joint can loosen or wear over the years. It changes level if the knee is also hot, red or swollen, if there is a temperature, or if the pain is building week by week rather than month by month, because an infected joint and a worn one can feel similar at first.

The warning signs at the foot of this page give all of these with the urgency attached to each, and problems after a knee replacement sorts the whole set by how fast each one needs answering and says who to ring where you live. If you cannot tell at three in the morning which one you are looking at, make the call anyway. No surgical team would rather hear about this in week six.

Related exercise programs

Total knee replacement rehab

Warning signs

Get emergency help now

Emergency: since your operation, you suddenly become short of breath, you get chest pain or pain in your upper back that may be worse when you breathe in, you cough up blood, your heart is beating very fast, or you faint. Call emergency services straight away, even if your leg looks normal. These can be signs of a blood clot in the lungs (pulmonary embolism).
Emergency: after a fall or a knock, you cannot put weight on the leg, your knee or thigh is very painful, or the leg looks out of shape or shorter than the other. Go to an emergency department straight away, and do not drive yourself. If you cannot get up, call emergency services. A broken bone around a knee replacement is rare, but it needs treatment in hospital. If a smaller fall or knock leaves the knee newly painful, swollen or bruised, even if you can still walk on it and the leg looks normal, stop the exercises, go back to your crutches or sticks and keep your full weight off that leg, and get it checked by your surgical team the same day. A break in the bone around a new knee is not always obvious at first, and walking normally on one can move the broken ends apart.

Get help today

Same day: a calf or thigh that is newly swollen or getting more swollen, warm, tender, red or darker than usual, has swollen veins that are sore to touch, or has a throbbing or cramping pain that does not fit your injury or condition, or that feels different from normal muscle soreness after exercise. This can be a sign of a blood clot (deep vein thrombosis), especially after surgery, an injury, time in a cast or boot, a long trip or a spell of being much less mobile than usual. Get medical advice the same day. If you are also short of breath or have chest pain, call emergency services.
Same day: swelling in the operated leg that is increasing from day to day instead of settling, including swelling spreading into your calf, ankle or foot, pain in your leg or calf away from the wound, increasing pain in your calf, or tenderness or redness above or below your knee. Get medical advice the same day. Swelling is expected after this operation, and it can be moderate to severe in the first days or weeks, but OrthoInfo asks you to tell your doctor about new or severe swelling because it can be the warning sign of a blood clot, and increasing swelling of the calf, ankle and foot, increasing calf pain, and tenderness or redness above or below the knee are all on its list of clot signs. Your clot risk does not end on the day your tablets or injections do. If you are also short of breath or have chest pain, call emergency services.
Same day: you are taking tablets or having injections to lower your risk of a blood clot and you notice blood in your urine, black or bloody stools, bleeding gums, a nosebleed that goes on and on, bruising far beyond what the knock would explain, or you are being sick or coughing up blood. Get medical advice the same day, and do not stop the medicine on your own. Bleeding more easily is the known trade-off of these medicines (NHS), and the dose or the type may need looking at. Go to an emergency department if the bleeding will not stop, you feel faint, or you bang your head while you are taking it, even if you feel fine, because the NHS advises getting urgent advice after a head injury on medicine that thins your blood and only a hospital can scan for a bleed inside the head.
Same day: your wound becomes more red, hot, swollen or painful, starts to leak or ooze, is still leaking in the second week or has never stopped, has pus coming out of it or its edges start to come apart, or you have a high temperature or feel hot, cold or shivery. Contact your surgical team or get medical advice the same day. Redness can be harder to see on brown or black skin. If you feel very unwell, go to an emergency department. If you have a very high or very low temperature, shivering you cannot control, you are breathing very fast or finding it hard to breathe, you are confused or your speech is slurred, your skin, lips or tongue look blue, gray, pale or blotchy (on brown or black skin this can be easier to see on the palms of the hands or soles of the feet), or you have a rash that does not fade when you press it, call emergency services, as this can be sepsis.
Same day: in the days or weeks after your operation you are getting more and more tired, breathless doing everyday things such as walking to the toilet or getting dressed, dizzy or lightheaded, your heart is racing, or your skin looks paler than usual. Contact your surgical team or get medical advice the same day. Tiredness and breathlessness that build up like this are not part of the usual recovery. Blood loss during and after a knee replacement can leave you short of red blood cells (anemia), which is treatable, and a slow bleed or an infection can show up the same way. If breathlessness comes on suddenly, or you get chest pain, call emergency services, as the emergency line above explains.
Same day: since your operation, the redness, warmth, swelling or pain in your knee is not getting better or is getting worse, for example the knee pain keeps building both when you move and when you rest. Contact your surgical team or get medical advice the same day, as this can be a sign of infection around the new joint. If you feel very unwell, go to an emergency department.
Same day: at any time after your operation, even years later, new pain in your new knee along with a high temperature or feeling hot, cold or shivery, or a knee that becomes hot, red or swollen, which counts on its own, with or without pain and with or without a temperature. Contact your surgical team or get medical advice the same day. A new joint can become infected long after the operation, and that needs treating quickly. A normal temperature is not an all clear: OrthoInfo says fever is no longer considered a sign of an infection after a joint replacement, that the signs can be as little as mild redness and swelling and sometimes there are none at all, and that increased pain or stiffness in a joint that had been working well is one of them. So do not wait for a temperature before you report new or increasing pain in your new knee to your surgical team.
Same day: you suddenly cannot straighten your knee or lift your leg straight when you could before, often after a pop, a tearing feeling or a stumble, or you notice a dip just above or below your kneecap, or you suddenly cannot put weight on the leg, even without a fall. Keep your weight off it and contact your surgical team the same day. If you cannot reach them that day, go to an emergency department. A tendon at the front of the knee may have torn, and a repair works better when it is done soon.
Same day: a leg or foot that is getting weaker, for example your foot drags, catches on the ground or slaps down when you walk (foot drop). Get medical advice the same day. Until it has been checked, use your walking aid, hold a rail on stairs and keep off uneven ground, because a foot that catches trips you and a fall onto a new knee can damage it. If the weakness is getting worse by the hour, go to an emergency department.
Same day: new numbness, tingling or burning in your lower leg or foot, beyond the numb patch of skin around your scar. Contact your surgical team or get medical advice the same day. If it started after a fall or an injury, or your foot or toes turn cold, pale, blue or gray, call emergency services or go to an emergency department straight away, and do not drive yourself.
Same day: dizziness, lightheadedness, blurred vision or feeling faint when you stand up that is new for you, does not pass within a minute or two, keeps happening, or has made you fall. Sit or lie down, and get medical advice the same day. This can be a drop in blood pressure on standing (postural hypotension), a type of low blood pressure, which the NHS lists among the causes of falls, and your doctor can check it. Tell them about your medicines, because some can cause it. If it does not settle within a few minutes of sitting or lying still, call emergency services. If you faint, call emergency services, even if you come round quickly, because the NHS says to call them when someone faints while exercising or is badly hurt, and a fall onto a new knee can damage it.
Same day: dizziness or feeling faint during or after exercise, other than the brief lightheadedness as you stand up covered in the line above, without any of the emergency signs above. Stop the exercises and get medical advice the same day. If you faint, it does not settle within a few minutes of sitting still, or you cannot stand or walk steadily, call emergency services.

Book an appointment

Within a few days: your pain has not started to ease within the first few days after the operation, or pain that was settling starts climbing again day by day. This is not an emergency, but tell your surgical team or your doctor rather than waiting for your next routine appointment, because OrthoInfo says to speak to your doctor when pain has not begun improving a few days after surgery. Get medical advice the same day instead if the knee is also hot or red, if you have a temperature or feel hot, cold or shivery, or if the pain keeps building while you are resting as well as when you move, as the lines above explain.
Within a few days: your knee is not bending or straightening any further from week to week, is getting stiffer, or feels unstable or gives way when you stand or walk. This is not an emergency, but contact your physio or surgical team within the next few days rather than waiting for your next routine appointment, and keep using your walking aid until they have checked it. A stiff knee is easier to free up early than late: where it has to be freed up under anesthetic, doing that earlier, generally within about 6 to 12 weeks of the operation, is associated with regaining more movement than doing it later, although how much any one knee gains also depends on how stiff it was to begin with, on who is suitable and on the rehabilitation afterward. So the date you raise it matters (Hosanee and colleagues, 2026). If the knee has given way and let you fall, or it gives way on stairs, hold a rail and use your walking aid every time, and stay off stairs on your own until you have been seen.
Within a few days: you have had a fall, even if you were not hurt, or you keep tripping, stumbling or feeling that your legs might give way. Book an appointment with your doctor within a few days and ask about a falls assessment. Tell them about every fall, even the ones where you were not hurt.
Routine: pain in your new knee that had settled and has come back, or pain that is getting worse month by month, for example pain that starts as soon as you stand up and begin to walk. This is not an emergency, but ask your surgical team for a review, as the parts of a new joint can loosen or wear over the years. Get medical advice the same day instead, not a routine appointment, if the knee also becomes hot, red or swollen, or you have a high temperature or feel hot, cold or shivery, or the pain is building week by week rather than month by month. A new joint can become infected years after the operation, and the two can feel similar at first.

Common questions

Why does my knee hurt more at night after a knee replacement?

Mostly because of what the night does to a new knee, not because anything has gone wrong in it. The knee is held still for hours and stiffens in whatever position it was left in. The swelling the day put into the leg is still there once you stop moving. There is no television, no visitor and no walk to the kitchen competing for your attention. And the overnight stretch is the longest gap any dose of pain relief has to cover. OrthoInfo describes pain at night, along with pain on activity, as common for several weeks after this operation. What is not that: pain climbing week by week rather than easing, pain that keeps building while you rest, a hot or red knee, a temperature, or a wound that is leaking. Those need your surgical team the same day, and sudden breathlessness or chest pain in the night is a call to emergency services.

How long does pain at night after a knee replacement last?

Nobody can give you a date, and no source we would trust gives one. The nearest thing to a figure comes from OrthoInfo, which describes pain at night as common for several weeks after surgery, and it describes the usual course without setting a deadline. The direction of travel is the part worth watching. OrthoInfo asks you to speak to your doctor when the pain has not started to improve within a few days of the operation, so pain that is easing slowly is a different thing from pain that is going the wrong way. Sleep can take longer to recover than the pain does, which is normal and is covered on this page.

Why does it burn or feel nerve-like at night?

A burning or electric quality in the skin at the front of the knee is something people describe often, and it frightens them more than a deep ache does. One part of it is expected: OrthoInfo says most people feel some numbness in the skin around their incisions, and that patch can take months to change. We have no figure to give you for how many people get a burning quality with it, and this page does not label it, because that is a job for the person examining your knee and not for a web page. What does need reporting rather than tolerating: new numbness, tingling or burning in your lower leg or foot, beyond the numb patch around the scar, is a same day call to your surgical team, and sooner if your foot or toes turn cold, pale, blue or gray.

Should I take my painkillers before bed?

That is a question for whoever prescribed them, and it is a reasonable one to ask, because the timing of a dose against the hour you go to bed is something a prescriber can change. Never stop or change a prescribed medicine on your own. Two practical points from an NHS hospital leaflet are worth knowing before you ring: South Tees says patients are given only a week of pain relief when they leave hospital and asks you to contact your family doctor in good time if you need more, and it makes the point that pain relief in the early stages is what lets you move and exercise comfortably rather than being something separate from the rehabilitation.

When does night pain mean an infection or a clot?

When the pattern changes, not when the level is high. Pain that keeps building while you rest as well as when you move is one of the things OrthoInfo links to infection around the new joint, along with a knee that is hot, red or swollen, a temperature, chills, or a wound that is leaking. OrthoInfo asks you to tell your doctor immediately about any one of those signs, so rest pain that is climbing counts on its own: a knee that looks normal, feels cool and comes with no temperature does not cancel it out. A calf or thigh that is newly swollen or getting more swollen, warm or tender needs advice the same day too, whatever the knee is doing, and sudden breathlessness or chest pain is a call to emergency services even if the leg looks normal. New pain in the joint months or years later, with a temperature or a hot red knee, is also a same day call, because a new joint can become infected long after the operation. The warning signs at the foot of this page give the full set with the urgency attached to each.

References

American Academy of Orthopaedic Surgeons. Total knee replacement. OrthoInfo. https://www.orthoinfo.org/en/treatment/total-knee-replacement/
American Academy of Orthopaedic Surgeons. Infection after joint replacement. OrthoInfo. https://www.orthoinfo.org/en/diseases--conditions/joint-replacement-infection/
American Academy of Orthopaedic Surgeons. Activities after total knee replacement. OrthoInfo. https://www.orthoinfo.org/en/recovery/activities-after-knee-replacement/
NHS. Recovering from a knee replacement. Page last reviewed 9 September 2026. https://www.nhs.uk/tests-and-treatments/knee-replacement/recovery/
NHS. Low blood pressure (hypotension). Page last reviewed 11 July 2023. https://www.nhs.uk/conditions/low-blood-pressure-hypotension/
NHS. Codeine. Page last reviewed 9 June 2026. https://www.nhs.uk/medicines/codeine/
South Tees Hospitals NHS Foundation Trust. Post total knee replacement management. Patient information, 26 February 2025. https://www.southtees.nhs.uk/resources/post-total-knee-replacement-management/
National Institute for Health and Care Excellence. Joint replacement (primary): hip, knee and shoulder. NICE guideline NG157. Published 4 June 2020. https://www.nice.org.uk/guidance/ng157
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Written and checked by the PocketPhysio editorial team. Last updated 2026-10-17.

This page is general education, not a diagnosis or a personal treatment plan. See a physiotherapist or doctor for advice about your own situation.