Knee Replacement Infection

@ejstocker - I’m sorry to hear about the swelling and discomfort you’re experiencing with your knee—it’s understandable to feel worried, especially with the timing and inability to reach your surgeon.

Infections in an artificial knee (prosthetic joint infections, or PJIs) are diagnosed through a combination of symptoms, physical examination, lab tests, and imaging. PJIs can occur at any time after surgery, including years later (late-onset, >3 months post-surgery). Here’s how they’re typically identified:
Symptoms:
Pain: Persistent or worsening pain in the knee, often with movement or weight-bearing, that doesn’t resolve with rest. Late infections may present with a dull ache or stiffness rather than acute pain.
Swelling: Localized or diffuse swelling around the knee, often with warmth or redness. Rapid or unexplained swelling is concerning.
Reduced Mobility: Difficulty bending or moving the knee due to stiffness or pain, as you’re experiencing
Have you also experienced fever chills or night sweats?
Does This Sound Like a PJI?

Your symptoms—rapidly worsening swelling and inability to bend the knee—are concerning for a possible late-onset PJI, though other causes are possible. Here’s an analysis:
Swelling and Limited Mobility:
Rapid, severe swelling that restricts knee movement is a red flag for infection, especially in a replaced knee. Swelling alone can occur with other issues (e.g., bursitis, blood clot, or mechanical issues), but the intensity and progression you describe align with PJI symptoms.
The “outer side” localization could suggest a specific issue (e.g., prepatellar bursitis or localized infection), but PJI often causes diffuse swelling.
No Fever:
The absence of fever is reassuring but doesn’t rule out PJI. Chronic or low-grade late infections may lack systemic symptoms, presenting only with local signs like swelling and stiffness.
Sinus Infection as a Source:
Your concern that the sinus infection “settled” in your knee is valid. Hematogenous spread from a distant infection (e.g., sinusitis, urinary tract infection, or dental work) can seed bacteria in an artificial joint. Staphylococcus aureus (common in skin and sinus infections) is a frequent culprit in PJIs.
However, sinus infections are typically viral or caused by bacteria (e.g., Streptococcus pneumoniae) less likely to cause PJI. If your urgent care prescribed antibiotics, this might reduce the risk of spread, but it’s not guaranteed.

Hopefully this does not get worse over the weekend and you can reach your doctor early Monday. Does this help address some of your concerns?

Thank you for the detailed reply. My knee doesn't really hurt other than the stiffness, so that gives me hope that it is something else. I also wondered if it could be something like bursitis. I've had no fever, chills, or night sweats. I do have swelling on the kneecap and the upper right as well. Urgent care prescribed Cefdinir as an antibiotic which I started this morning (it was too late to get it filled last night). I will reach out to the doctor who did my knee replacement first thing Monday and will report back, though it may take a few days to get in to see him. Thank you again for your response!

I replied above, but swelling seems to be getting worse quickly. Would it be prudent to go to an emergency room at the local hospital, or best wait until Monday when I can talk to my surgeon?

It's good news that you do not have redness, or fever.....I'm not a doctor but those symptoms would be more of a predictor for infections. Cefdinir is effective against many bacterial infections, but some bacteria may be resistant, reducing its efficacy, and thats an issue for PJI since a "biofilm" can form on the surfaces and are tough to deal with once they firm and some of these can be resistant to antibiotics. You're doing a great job in watching it closely. Hope you can see your doctor soon

I just saw this after my other message to you. I cannot offer medical advice, but I think most would say redness, swelling AND fever would suggest an ER visit.....can you check your temp? I know it's difficult because many thoughts are running through your mind right now

Just a little more info for your doctor visit....Cefdinir, a third-generation cephalosporin, is not typically recommended as a first-line treatment for PJI due to several limitations:
Spectrum of Activity:
Cefdinir is effective against some PJI pathogens like methicillin-sensitive S. aureus (MSSA) and certain streptococci.

However, it is ineffective against MRSA, methicillin-resistant coagulase-negative staphylococci, and Pseudomonas aeruginosa, which are common in PJI.

It has variable activity against Gram-negative bacteria and is not reliable for biofilm-associated infections.

Biofilm Penetration:
PJIs often involve bacterial biofilms, which are notoriously difficult to treat. Cefdinir has poor biofilm penetration, reducing its efficacy in eradicating infections on prosthetic surfaces.

Guidelines and Evidence:
Per the Infectious Diseases Society of America (IDSA) and other guidelines, PJI treatment typically involves antibiotics with better activity against resistant organisms and biofilms, such as vancomycin, daptomycin, or rifampin (often in combination).

Cefdinir is not mentioned in standard PJI treatment protocols due to its limited role in deep-seated or hardware-associated infections.

The antibiotic was for a sinus infection. The knee issue came about after the appointment for a sinus infection that’s. But I appreciate all the information! Thank you again.

Please let us know how you are doing ejs and all the best.

Since having my knees replaced, I have to take four "horse-pill-like" amoxicillin an hour before the procedure. I don't know if the risk of infection lowers over time. The metal in my prostheses actually bonds with the edge of the bone that was cut, further integrating the prostheses with the living bone. I'm not a professional, but I would think the risk of infection in the joint goes down overtime. Some TKRs are done with cement, when osteoporosis is present and that may cause a problem later. But I don't know any of this for a fact, so best to ask your Dr.

And I'd play it safe and get to an ER. Take care of yourself and all the best.

Joe

@ejstocker
Until you can get in with your doctor, you may want to take ibuprofen or other NSAID for inflammation or you can get Voltaren gel and apply topically.

@ejstocker
Did you hyperextend, twist or injure your knee recently? Could you have injured soft tissues in your knee? Your symptoms seemed to come on suddenly. You may have irritated a nerve/blood vessel and surrounding tissues.

I once was dancing and felt a crunch in my knee and ended up with significant swelling, couldn’t bend my knee, pain, etc. and ended up having inflamed plica tissue. I couldn’t walk on my leg for a while.