Part of Total knee replacement rehab
Problems after a knee replacement: the warning signs, and how fast to act
Warning signs, and when to get help
Get emergency help now
Two of the warning signs below are emergencies, not phone calls. Both are reproduced here word for word so that nobody has to scroll for them. This section is first on the page for one reason: if one of these two is what you are looking at, nothing further down matters tonight.
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.
Read the last clause of that first line twice. A clot in the lung does not wait for the leg to look wrong, and a calf that looks normal is no reassurance at all. The NHS says much the same on its own knee replacement page: leg pain and swelling together with breathlessness or chest pain is the combination that goes to the emergency services or an emergency department, not to a doctor's appointment.
If neither of those two is what you are looking at, the rest of the page sorts everything else by how fast it needs attention, and the full list is at the foot. If you already know what you are seeing and only need to know who to ring and what to have ready, go straight to who to call, when, and what to have ready.
What problems can happen after a knee replacement?
Sort them by speed, not by name: speed is the part that changes what you do tonight. Problems after a knee replacement fall into four groups: the ones that need emergency help in the next few minutes, the ones that need advice the same day, the ones that need a call within a few days instead of a wait for your next appointment, and the ones that belong in a routine review. Almost every mistake I see in clinic is a mistake about which group something belongs in, not about the symptom itself. People who knew perfectly well that a hot leaking wound mattered still waited nine days for a clinic slot.
The list of things that go wrong is shorter than the internet makes it look. A clot, in the leg or in the lung. An infection, at the wound or deeper around the implant, and the deep kind can turn up years later on a knee that had been fine. A break in the bone around the implant, usually after a fall.
Then: a tendon at the front of the knee giving way, so the leg will not straighten. A nerve problem, which most often means numbness or a foot that catches. A knee that stops gaining movement, or starts giving way. And at the far end, pain that returns because the parts of a new joint can loosen or wear over the years.
Every one of those has a line in the warning signs at the foot of this page, grouped by how fast to act, in the same words the rest of this cluster uses. The main knee replacement rehab program carries the same set, and so does every page in the cluster, deliberately, because it is the one thing a reader should meet wherever they land.
One thing comes before all of it. Your surgical team gave you instructions built around your knee and your operation, and where those differ from anything here, theirs are the ones to follow. This page is education, not advice about your knee, and no page can examine a leg.
What are the signs of infection after a knee replacement?
Infection is the thing people ask about most, and it shows up in two quite different ways.
The wound kind is visible. More redness, heat, swelling or pain, leaking or oozing, pus, wound edges starting to come apart, or a temperature and feeling hot, cold and shivery. The NHS sends those signs to an urgent appointment with a doctor, or to NHS 111 if you are in England, and its knee replacement page names oozing or pus from the wound and worsening redness, swelling or pain in the knee among the reasons to ask.
Two details get missed. Redness is harder to see on brown or black skin, so the heat, the pain and the temperature carry more of the weight there. And a wound still leaking in the second week, or one that never stopped at all, counts on its own even when nothing else looks wrong. The exercises for weeks 0 to 2 covers what the wound normally does in that first fortnight.
The deeper kind sits around the implant and shows as a knee that will not settle: redness, warmth, swelling or pain that stays put or worsens, and pain that keeps building when you rest as well as when you move. OrthoInfo lists increasing pain both at rest and with activity among the signs to report, and that is the pattern to watch, because a knee irritated by too much exercise usually quiets down overnight and an infected one does not.
There is a third route in, and it has nothing to do with your knee at all. OrthoInfo says any infection in your body can spread to a joint replacement, and names bacteria that enter the bloodstream during dental procedures, urinary tract infections and skin infections as a common cause of infection after a knee replacement, because those bacteria can lodge around the new joint. The practical version of that: an infection somewhere else gets treated promptly rather than waited out, and whoever treats it is told you have a knee replacement, because it changes how seriously they take it. The same page says that after a knee replacement some people, depending on their own risk factors, need antibiotics before a procedure that could let bacteria into the bloodstream, and that whether you are one of them is a conversation with your surgeon rather than something to assume either way. Worth having before the dental appointment, not in the chair.
Both of the kinds above are same-day lines below. Neither is something to save for the six week check-up. Sepsis sits at the end of this road, and the wound line below carries its signs and sends them straight to the emergency services, where they belong.
Here is the awkward part, and pretending otherwise helps nobody: an overdone session and an early joint infection can feel much the same from the inside for a day or two. What separates them is not how bad the pain is. It is your temperature, the state of the wound, and whether the knee is worse again tomorrow morning. Those three work in one direction only, which is the part a surgeon would want said plainly. OrthoInfo's page on infection after a joint replacement says the symptoms vary widely, from mild redness and swelling up to life threatening septic shock, that sometimes there are no symptoms at all, and that fever is no longer considered a sign of an infection after a joint replacement. The same page names wound drainage, usually more than ten days after surgery, and increased pain or stiffness in a joint that had been working well. So a normal temperature is not an all clear, and neither is a knee that has never gone red. A knee that is worse again the next morning is enough on its own to make the call.
Blood clots: the leg signs and the chest signs
One problem, two completely different sets of signs, and the leg set usually comes first.
In the leg, it is a calf or thigh that is newly swollen or swelling further, warm, tender, red or darker than usual, veins that are sore to touch, or a throbbing or cramping pain that does not match what you did. The NHS lists throbbing pain in one leg, swelling in one leg, skin that looks red, blue or darkened, and swollen veins. Muscle soreness after exercise feels earned and settles; this does not.
The third trigger is the one people miss, and it is knee specific. Swelling after this operation is expected and can be moderate to severe in the first days or weeks, and that is exactly what gives an increasing swelling somewhere to hide. How long the swelling lasts sets out the pattern a settling knee follows and what brings it down.
OrthoInfo puts new or increasing swelling in the calf, ankle and foot on its list of clot warning signs, along with increasing calf pain and tenderness or redness above or below the knee, and asks for them to be reported rather than watched. So the question to ask yourself is not whether the leg is swollen. It is whether it is more swollen than it was yesterday.
In the chest, the signs jump straight to the emergency tier, and that is the first line in the section above.
There is a medicine half to this too. If you are on tablets or injections to lower your clot risk, unusual bleeding or bruising is a same-day call, and the line below ends with the instruction that matters most: do not stop the medicine on your own. Bang your head while you are taking one and you need urgent advice even when you feel fine. The prevention side of all this, the stockings, the ankle exercises and the ice, belongs to the main program and is not repeated here.
After a fall or a knock, even a small one
The serious half of this is the emergency line above. The half that gets skipped is the smaller knock: a stumble into a door frame, a slide off a step, a knee that caught the edge of the bath. If a knock like that leaves the knee newly painful, swollen or bruised, it gets checked the same day even though you walked away from it. The line above says why: a break in the bone around a new knee is not always obvious at first.
OrthoInfo's page on fracture after total knee replacement describes the same picture from the surgeon's side: pain and swelling around the thigh or knee, not being able to bear weight, a leg that looks shortened or deformed, and a fall or a higher energy injury such as a car crash behind it. On its knee replacement page it puts the stakes plainly. A fall in the early weeks can damage the new joint, and it may take another operation to put right.
Two details from that fracture page are worth holding on to for longer than the early weeks. The first is timing: these breaks can happen at any point after a knee replacement, not only while the knee is new, so a fall three years on gets the same thought as a fall in week three. The second is who they happen to. OrthoInfo names a condition that weakens bone, such as osteoporosis, and the things that make a fall likelier in the first place, muscle weakness, poor vision and poor balance, among what raises the risk. If any of those describes you, the leg gets checked after a fall rather than watched, and it is worth asking your own doctor about your bone health instead of waiting for a break to raise the subject.
Then there is the fall that hurt nothing, which is the one worth a call precisely because nothing happened. The line below asks for an appointment within a few days and for a falls assessment after a single fall, and the NHS falls page itself says to see a doctor if you have had one. A knee replacement leaves most people walking differently for months, and that is the window in which a second fall is most likely and most expensive. Balance and falls prevention is the program for the strength and balance side, and how long you use a walker covers hanging on to the aid for longer, which is the side to err on. Things to avoid after a knee replacement sets out the rest of the early precautions, including how long each one lasts and the ones people keep up far longer than they need to.
A knee that gives way, or a leg that will not straighten
Two events get confused here, and they sit on different rungs.
Giving way is the common one. The knee buckles slightly as you put weight on it, usually on a step or when you turn, and most of the time that is the thigh muscle not switching on quickly enough, not anything structural. It still gets reported: the line below puts it at a call within a few days, with the walking aid and a rail used every time until somebody has watched you walk. The NHS names instability when standing or walking among the longer term problems after this operation, so it is a known thing to raise rather than a strange one.
The other event is not that, and it is time sensitive. A sudden loss of being able to straighten the knee or lift the leg straight when you could before, often after a pop, a tearing feeling or a stumble, sometimes with a dip you can feel just above or below the kneecap. OrthoInfo's patellar tendon tear page describes an indentation at the bottom of the kneecap and not being able to straighten the knee, and says that people who need surgery do better when the repair happens soon after the injury. That is why the line below says to keep your weight off it and contact your surgical team the same day, with an emergency department as the route if you cannot reach them.
Which matters, because the same page lists two more things a torn tendon does, and both of them look at first like the common problem rather than the serious one: difficulty walking because the knee buckles or gives way, and a kneecap that has moved up into the thigh because it is no longer anchored to the shin bone. So sort them by what came with the giving way, not by the giving way itself. A knee that has quietly buckled now and then for weeks is the within a few days line. A knee that gave way suddenly, with a pop or a tearing feeling, or with a dip at the kneecap, or with a kneecap that looks or feels as though it has ridden up the leg, or alongside any new difficulty straightening the knee or lifting the leg straight, is the same-day line instead: keep your weight off it and ring the surgical team that day. If you are not sure which of the two you are looking at, treat it as the same-day one.
One check separates them at home and it takes a minute. Lie down and have somebody straighten the leg for you. If the knee goes straight while they move it, but you cannot then lift the straight leg off the bed yourself or hold the knee straight against gravity, the mechanism that does that job is no longer pulling on the shin the way it was. That is the same-day line rather than a stiff knee, and it is the most useful thing you can say on the phone.
A systematic review of the injury after first-time and revision knee replacements reports the published incidence as 0.1 to 2.5 percent of operations, and found that direct repair of the tendon failed in about a third of quadriceps cases and nearly two thirds of patellar tendon cases (Rajgopal and colleagues, 2025). Rare, then, and hard to put right, which is the reason the call is worth making the same day rather than at the next clinic.
Nerve symptoms, numbness and a foot that drags
Some numbness is part of this operation. OrthoInfo says most people have some numbness in the skin around the incisions, and that patch beside the scar can stay for a long time. It is worth knowing for one practical reason: numb skin cannot tell you an ice pack has been on too long.
What is not that: new numbness, tingling or burning further down, in the lower leg or foot, beyond the numb patch. And a foot that drags, catches on the ground or slaps down as you walk. Both are same-day lines below. The foot drop line also tells you to use the walking aid and hold a rail in the meantime, and that instruction is doing real work, not being cautious for the sake of it: a foot that catches is how people fall, and a fall onto a new knee is the thing this whole page is trying to prevent. Both lines carry an escalation inside them as well, for a foot or toes turning cold, pale, blue or gray, and for weakness that is getting worse by the hour.
A knee that has stopped improving or is getting stiffer
Being as stiff as last week and being stiffer than last week are two different observations, and only one of them is patience.
Movement after a knee replacement tends to come in uneven steps with flat spells in between, and a flat spell on its own is not an alarm. What needs raising is movement going backward, or a knee that has not gained anything in either direction for several weeks running. The NHS lists ongoing stiffness and difficulty bending the knee among the problems that can persist after this operation, so it is a recognized conversation rather than a complaint about nothing.
The line below puts this at a call within a few days instead of a wait, and it carries the timing and the source for why the date you raise it matters. That is the whole point of it: the treatments for a stiff new knee are not equally good at every stage, so this is the one slow problem on the page with a clock attached. How to improve the bend covers the daily work on the range itself, including the straightening most people let slide. If the hold-up is getting hold of a physiotherapist and not the knee, NHS physio self-referral sets out the route for readers in the UK, and your surgical team can usually shortcut it.
Pain that has come back months or years later
Two things look alike here, and what separates them is the pace and the company they keep.
Pain that had settled and has crept back, or pain that is worse month by month, is a review rather than an emergency. The parts of a new joint can loosen or wear over the years, and the routine line below asks for that review, because loosening is found by examining and scanning the knee rather than by waiting to see what happens.
There is a version of this that arrives before any pain does. OrthoInfo asks you to see your orthopedic surgeon periodically for routine follow-up examinations and X-rays, and says your surgeon will tell you how often and when. Those appointments are how wear and early loosening turn up on a film while the knee still feels more or less fine, which is a good deal earlier than symptoms arrive. A review skipped because nothing hurts is the one worth keeping.
The same line carries an escalation that is the half to read twice. If the knee also turns hot, red or swollen, if you have a temperature or feel hot, cold and shivery, or if the pain is building week by week rather than month by month, that is a same-day call instead. A replaced joint can become infected years after the operation, and in the first days the two can be hard to tell apart from the outside. That is also why one of the lines below has no time limit at all: new pain in the new knee plus a temperature is a same-day matter whether you are six weeks or six years out. New pain without a temperature is still worth a review rather than nothing. OrthoInfo names increased pain or stiffness in a joint that had been working well among the signs of an infection around a new joint, says the signs can be as little as mild redness and swelling, and says fever is no longer considered a sign of one.
What is ordinary in this recovery, and what is not?
This comes after the ladder on purpose. Most people reading a warning page are looking at something ordinary, and reassurance is worth nothing if it arrives ahead of the signs that are not.
Start with the findings that frighten people and are expected after a knee replacement. Clicking, which OrthoInfo says most people feel or hear from the metal and plastic as the knee bends or as they walk, and calls normal. The clicking it calls normal is painless, and that word is doing work: a new clunk or click that arrives with pain, with swelling, or with the knee giving way under you is not on the normal list and belongs with the instability line below. A numb patch of skin beside the scar. Bruising and swelling that run down the leg into the calf and ankle instead of staying at the knee, which is gravity doing what gravity does, and the reason the NHS tells you to keep the leg raised as much as possible and not to stand for long periods. What is not that: swelling that increases from day to day instead of settling, and a calf that becomes warm, tender or more swollen than it was yesterday. Get medical advice the same day for either, and the warning list below gives the full set of signs.
Then pain at night and pain with activity. OrthoInfo describes it in one line worth quoting, that some pain with activity and at night is common for several weeks after surgery, and pain at night after a knee replacement goes into why it happens and what helps at three in the morning. A knee that is stiff first thing and loosens as the day goes on belongs on this list too. OrthoInfo expects most normal daily activities to be back within 3 to 6 weeks, which for a lot of people is faster than their knee feels. The recovery timeline carries the sourced figures and the reasons one recovery runs slower than another.
The shape that should make you pick up the phone is different, and it is a direction rather than a level. Something getting worse week on week instead of better. A temperature. A wound still leaking past the first week.
A movement you had and have suddenly lost. A calf that has become tender or swollen. Anything new after a fall.
Every one of those is in the list below with its own urgency attached, and that is the part worth carrying away.
If you have had both joints replaced, warning signs after a hip replacement covers the hip's own set. It is not the same set. A hip can dislocate and a knee does not do that, so each joint has warnings the other has no use for.
Who to call, when, and what to have ready
In the first weeks, the team that operated is the right first call for anything to do with the wound, the knee itself, or a fall. Their number is usually on the discharge letter that came home with you, and it is worth putting on the fridge today instead of hunting for it at nine in the evening. Out of hours, the hospital where you had the operation still has a route to the ward or to the on-call team, and that route exists for exactly this.
If you cannot reach anybody, do not let that turn a same-day sign into a tomorrow-morning sign. Use whichever urgent advice service your country runs, below, and if you cannot get advice from anyone at all, go to an urgent care service or an emergency department the same day rather than waiting for the office to open. That matters most if you live alone, because there is nobody in the house to notice that the leg looks worse than it did at teatime.
One sentence to say wherever you end up, and it is the most useful thing you can tell anybody: that you have had a knee replacement, and when. A hot, painful replaced knee is assessed differently from a hot, painful ordinary one, and the team that put the implant in is the team that decides what happens to it, so if you are seen somewhere else, ask them to contact the hospital that operated rather than leaving that to chance.
After that, where you live decides the rest. In the UK, an urgent appointment with your GP, and NHS 111 in England as the service that will tell you where to go when your doctor's office is closed. In the United States and Canada, your surgeon's office, which usually has an after-hours or on-call arrangement, and the hospital that did the operation; many Canadian provinces also run a telephone health advice line. In Australia, healthdirect is a free service, available at any hour, where you can speak to a nurse or a doctor about whether what you are seeing needs to be seen. In New Zealand, Healthline is the free telephone service staffed by registered nurses, running 24 hours a day.
No phone number appears anywhere on this page, because they differ by country and a wrong one costs minutes. For anything in the emergency group above, the instruction is the same everywhere: call emergency services or go to an emergency department.
Before you dial, two minutes of preparation changes the call. Have the date of the operation and which knee it was. The hospital and the surgeon's name. Your medicines, including anything you take to lower your clot risk and when the last dose was. Your temperature, if you can take it.
Then the history. How long this has been going on and whether it is worse than yesterday. A photograph of the wound taken in daylight, which beats any description of the color. And whether you have had a fall, including the one you did not mention to anybody.
What happens next if you do call
Expect questions before anything else, usually about your temperature, the wound, the calf, your breathing, and when things changed. Then, quite often, a request to come in and be looked at.
That request is not a verdict. A suspected clot and a suspected joint infection are both settled by examining and testing, never by a description down a phone line, so being asked to come in is a normal answer and not a frightening one. If you are told to go to an emergency department, the lines below say what I would say in the room: do not drive yourself.
Two things keep people from calling, and both deserve an answer. Nobody keeps a tally of calls that turned out to be nothing, and the people on the other end would much rather see a knee that had simply done too much than hear about a hot one a fortnight late. The second is the arithmetic. These two mistakes are not the same size: waiting costs more than calling, every time. That is why the page is ordered the way it is.
Related exercise programs
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 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
What are the signs of infection after a knee replacement?
They come in two shapes. The wound kind shows on the outside: more redness, heat, swelling or pain, leaking or oozing, pus, wound edges starting to part, or a temperature and feeling hot, cold and shivery. The NHS sends those to an urgent appointment with a doctor, or to NHS 111 if you are in England, and its own knee replacement page names oozing or pus and worsening redness, swelling or pain in the knee. The deeper kind sits around the new joint and shows as a knee that is not settling, with pain that keeps building both when you move it and when you rest it, which OrthoInfo also lists. Redness is harder to see on brown or black skin, so the heat, the pain and the temperature carry more of the weight there. Both are same-day matters, and both are in the warning signs on this page with what to do.
When should I call my surgeon after a knee replacement?
Sooner than most people do. In the first weeks the team that operated is the right first call for anything to do with the wound, the knee itself or a fall, and their number is usually on the discharge letter you came home with. Out of hours, the hospital that did the operation still has a route to the ward or to the on-call team, and in England NHS 111 can also tell you where to go. What you do not need is a reason good enough to justify the call. A hot wound, a temperature, a calf that has become tender or a knee that suddenly will not straighten are all things they would rather hear about on the day than a fortnight later at a clinic appointment.
Is this pain normal, or is something wrong?
Pain alone is a poor signal after this operation, because there is so much of it to start with. OrthoInfo says some pain with activity and at night is common for several weeks after surgery. What carries information is the direction and the company it keeps. Pain that is easing week on week, even slowly, is the usual pattern. Pain that is climbing week on week, pain that keeps building at rest as well as on the move, pain with a temperature, and pain in the calf rather than the knee are the patterns that need a call, and each one is in the warning signs on this page at its own urgency. An honest difficulty worth knowing about: a session you overdid and an early joint infection can feel much the same from the inside for a day or two, which is why the temperature, the wound and what tomorrow morning looks like matter more than how bad today feels. Those point one way and not the other. A normal temperature does not rule it out, because OrthoInfo says fever is no longer considered a sign of an infection after a joint replacement, so pain that keeps climbing is reason enough to ring.
Can a knee replacement get infected years later?
Yes. A replaced joint can become infected long after the operation, which is why one of the warning signs on this page has no time limit on it at all. The combination to watch for is new pain in the new knee together with a temperature or feeling hot, cold and shivery, or a knee that turns hot, red or swollen. That is a same-day call to your surgical team or for medical advice, not something to raise at a routine review, and it is also why pain that has come back after years is worth having looked at rather than lived with. A normal temperature does not rule it out, because OrthoInfo says fever is no longer considered a sign of an infection after a joint replacement. New pain without a temperature is still worth a review rather than nothing. The route in is often somewhere else entirely: 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 treat an infection elsewhere promptly, tell whoever treats it that you have a knee replacement, and ask your surgeon whether your own risk factors mean you need antibiotics before dental work.
What happens if I call and it turns out to be nothing?
Nothing bad, and nobody keeps score. Expect questions first, usually about your temperature, the wound, the calf, your breathing and when things changed, and then quite often a request to come in. That request is not a sign they think it is serious; a suspected clot and a suspected joint infection are both settled by examining and testing rather than by description over the phone. The two possible mistakes here do not cost the same. A call that turns out to be a knee that did too much costs you an hour. A clot or an infection left for a fortnight costs a great deal more, and that asymmetry is the whole reason this page exists.
References
- NHS. Complications of a knee replacement. Page last reviewed 9 September 2026. https://www.nhs.uk/tests-and-treatments/knee-replacement/complications/
- NHS. Recovering from a knee replacement. Page last reviewed 9 September 2026. https://www.nhs.uk/tests-and-treatments/knee-replacement/recovery/
- NHS. Deep vein thrombosis (DVT). Page last reviewed 30 April 2026. https://www.nhs.uk/conditions/deep-vein-thrombosis-dvt/
- NHS. Pulmonary embolism. Page last reviewed 25 May 2023. https://www.nhs.uk/conditions/pulmonary-embolism/
- NHS. Sepsis. Page last reviewed 14 May 2026. https://www.nhs.uk/conditions/sepsis/
- NHS. Anticoagulant medicines. Page last reviewed 9 September 2024. https://www.nhs.uk/conditions/anticoagulant-medicines/
- NHS. Falls. https://www.nhs.uk/conditions/falls/
- NHS. Low blood pressure (hypotension). Page last reviewed 11 July 2023. https://www.nhs.uk/conditions/low-blood-pressure-hypotension/
- NHS. Fainting. https://www.nhs.uk/symptoms/fainting/
- American Academy of Orthopaedic Surgeons. Total knee replacement. OrthoInfo. https://www.orthoinfo.org/en/treatment/total-knee-replacement/
- American Academy of Orthopaedic Surgeons. Activities after total knee replacement. OrthoInfo. https://www.orthoinfo.org/en/recovery/activities-after-knee-replacement/
- American Academy of Orthopaedic Surgeons. Fracture after total knee replacement. OrthoInfo. https://www.orthoinfo.org/en/diseases--conditions/fracture-after-total-knee-replacement/
- American Academy of Orthopaedic Surgeons. Patellar tendon tear. OrthoInfo. https://www.orthoinfo.org/en/diseases--conditions/patellar-tendon-tear/
- American Academy of Orthopaedic Surgeons. Infection after joint replacement. OrthoInfo. https://www.orthoinfo.org/en/diseases--conditions/joint-replacement-infection/
- Rajgopal A, Aggarwal K, Tripathi S. Extensor mechanism disruption following primary and revision total knee arthroplasty: a systematic review and meta-analysis. Archives of Orthopaedic and Trauma Surgery. 2025;145(1):371. https://doi.org/10.1007/s00402-025-05991-w
- Hosanee S, Elebo N, Sikhauli N, Pietrzak JRT. Reluctant knee: understanding and managing stiffness after total knee arthroplasty. International Orthopaedics. 2026;50(9):2337-2346. https://doi.org/10.1007/s00264-026-06905-0
- Healthdirect Australia. healthdirect. https://www.healthdirect.gov.au/
- New Zealand Government. Healthline. https://www.govt.nz/organisations/healthline/
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.