@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?