This is the one article on this site we hope you never need. Most joint replacement recoveries move along without serious trouble — but every patient should be able to recognize the signs of infection after knee replacement or hip replacement, the signs of a blood clot, and the handful of symptoms that mean emergency care, not a phone call. Hospitals and public health agencies teach these warning signs to every surgical patient, and this guide collects them in one place from two of those sources: the CDC and an NHS hospital trust (CDC; Chelsea and Westminster NHS).
One rule covers everything on this page
Before the lists, the rule: every warning sign below leads to the same action. Contact your surgical team now, or go to the emergency room / call 911 if it feels urgent or you feel very unwell. This article will not tell you whether a symptom is serious or safe to watch — no article can. If something feels wrong, trust that feeling and reach out for care rather than waiting to see what happens.
That framing matters because playing the odds is exactly the wrong strategy here. According to the CDC, about half of people with a deep vein blood clot have no symptoms at all (CDC). You cannot reliably grade these problems from your recliner — and the good news is you don't have to. Recognize, call, done.
Signs of infection after knee replacement (and hip replacement)
Surgical-site infections are one of the complications your team watches for most closely, and the warning signs are the same whether your new joint is a knee or a hip. Watch your incision and how you feel overall for these signs (CDC; Chelsea and Westminster NHS):
- Redness around the wound that is spreading or getting worse
- Increasing swelling around the surgery site
- New or increasing pain, or pain that feels worse than before
- Fluid or pus draining from the wound — especially if it's thick, yellow, or has a bad smell
- The wound feels hot or tender to the touch
- The wound isn't healing, or it opens back up
- Fever or chills
- Sweating that isn't normal for you
- Feeling very unwell, confused, drowsy, or faint
- A fast heartbeat or rapid breathing
What to do: call your surgical team immediately. If you feel very unwell, confused, or faint, go to the emergency room or call 911 (CDC).
Signs of a blood clot (DVT) in your leg
A clot in a deep vein — deep vein thrombosis, or DVT — can form after joint replacement surgery. The CDC lists these leg signs (CDC):
- New swelling in your leg
- Pain or tenderness, especially in your calf
- Warmth in one area of your leg
- Redness or skin color changes
What to do: contact your surgical team right away, or seek emergency care. Do not wait to see if it gets better on its own (CDC). And because so many clots are silent, keep following your team's instructions for moving, walking, and any prescribed medication even when you feel fine.
Signs of a pulmonary embolism — call 911
A pulmonary embolism (PE) happens when part of a clot breaks loose and travels to the lungs. This is a medical emergency, and it can occur without any leg symptoms first (CDC). Warning signs:
- Sudden trouble breathing
- A fast or irregular heartbeat
- Chest pain or discomfort, especially if it worsens when you breathe deeply or cough
- Coughing, including coughing up blood
- Feeling very lightheaded, dizzy, or fainting
What to do: call 911 or go to the emergency room immediately. This is one of the few situations where you should not call your surgical team first — get emergency help right away (CDC).
The whole page in one table
| Category | Examples | Action |
|---|---|---|
| Possible infection | Spreading redness, increasing swelling or pain, drainage or pus, hot or reopening wound, fever, chills | Call your surgical team immediately |
| Possible blood clot (DVT) | New leg swelling, calf pain or tenderness, warmth, redness or color change | Contact your team right away, or seek emergency care |
| Possible pulmonary embolism | Sudden trouble breathing, chest pain, fast or irregular heartbeat, coughing up blood, fainting | Call 911 / emergency room now |
| Feeling very unwell | Confusion, drowsiness, faintness, rapid breathing | Emergency room or 911 |
Notice what the third column never says: "wait and see," "monitor it," or "probably fine." Every row ends in a call.
Set this up before surgery, not during a scare
The worst time to hunt for your surgeon's after-hours number is at 2 a.m. with a swollen calf. Before surgery day, write down your surgical team's daytime and after-hours contact numbers and put them somewhere everyone in the house can find — on the fridge, and in your phone. Make sure whoever is helping you recover knows this list of warning signs too, since the person who spots a change is often not the patient.
That prep step is part of our free home prep checklist, alongside the practical setup — clear walking paths, bathroom safety, and the supplies worth having ready before you leave for the hospital.
Put the phone numbers on the fridge this week
The free JointPrep home-prep checklist covers the safety setup most patients wish they'd done sooner — emergency contacts included. No payment, no subscription. We'll email you the PDF.
Where this fits in your recovery
Warning signs are the exception; most days of recovery are about steady, unglamorous progress. For what a typical recovery arc looks like, see the knee replacement recovery timeline or the hip replacement recovery timeline. And if your surgery is still ahead of you, the knee prehab guide covers how to use the weeks before it.
Frequently asked questions
What are the signs of infection after knee replacement?
Per CDC and NHS patient guidance: spreading redness around the wound, increasing swelling, new or worsening pain, fluid or pus draining from the incision, a wound that feels hot or is not healing, fever or chills, unusual sweating, or feeling very unwell, confused, or faint. Any of these means contact your surgical team immediately.
How do I know if my pain is normal or a warning sign?
This guide cannot make that call, and neither should you have to. If pain is new, increasing, or feels worse than before — or if anything about your recovery worries you — contact your surgical team and let them decide. Calling about something that turns out to be minor is a good outcome, not a wasted call.
When should I call 911 instead of my surgeon?
CDC guidance treats possible pulmonary embolism as a medical emergency: sudden trouble breathing, chest pain or discomfort that worsens with a deep breath or cough, a fast or irregular heartbeat, coughing (including coughing up blood), or feeling very lightheaded or fainting. For those signs, get emergency help immediately rather than calling your surgical team first. The same applies if you feel very unwell, confused, or faint.
Can you have a blood clot with no symptoms?
Yes. According to the CDC, about half of people with a deep vein thrombosis have no symptoms at all. That is why following your team's instructions for moving, walking, and any prescribed medication matters even when you feel fine.
Do these warning signs apply after hip replacement too?
Yes. The CDC guidance on blood clots and surgical-site infections applies across major surgery, and the NHS leaflet this article draws on was written for both hip and knee replacement patients. The signs and the action — contact your team now — are the same.
The bottom line
You don't need to memorize every item on this page. You need three habits: glance at your incision and your leg each day, take "I feel really off" seriously, and keep your surgical team's number where you can reach it. The signs above come straight from CDC and NHS patient education — the same lists hospitals hand to every joint replacement patient — and they all point to one move: make the call (CDC; Chelsea and Westminster NHS).
Sources
- CDC. About Venous Thromboembolism (Blood Clots). https://www.cdc.gov/blood-clots/about/index.html
- CDC. Surgical Site Infections (SSI) Basics. 2024. https://www.cdc.gov/surgical-site-infections/about/index.html
- Chelsea and Westminster Hospital NHS Foundation Trust. How to look out for infection after your Hip or Knee Replacement. https://www.chelwest.nhs.uk/your-visit/patient-leaflets/surgery-services/how-to-look-out-for-infection-after-your-hip-or-knee-replacement
Ready for the calmer half of preparation?
Warning signs are the emergency page. The rest of getting ready is practical: set up your home, learn the exercises, know what each week may look like. Start with the free checklist — we'll send the PDF to your inbox.