Immediate Evaluation for Possible Infection Required
You need urgent medical evaluation within 24 hours to rule out prosthetic joint infection, which presents with exactly these symptoms—pain, warmth, and swelling—and represents a serious complication requiring immediate intervention. 1
Why This Is Urgent
Infection after knee surgery occurs in 0.8% to 1.9% of total knee arthroplasties and is increasing in frequency 1. The triad of pain, warmth, and swelling are classic signs of acute infection, though these symptoms can also indicate other complications. In acute infection, pain, swelling, warmth, erythema, and fever are common presenting features 1.
What Your Doctor Should Do Immediately
Clinical Assessment
Your physician should specifically evaluate for:
- Fever or systemic signs of infection
- Erythema (redness) around the surgical site
- Wound drainage or sinus tract formation
- Character of pain: Night pain or pain at rest is characteristic of infection, whereas pain only with weightbearing suggests mechanical issues 1
- Pulsatile mass: Though rare, vascular complications like pseudoaneurysms can present with pain and swelling 2, 3, 4
Laboratory Testing
Your doctor should order blood tests including:
- C-reactive protein (CRP): Sensitivity 73-91%, specificity 81-86% when cutoff is 13.5 mg/L 1
- Erythrocyte sedimentation rate (ESR): Cutoff 27 mm/h 1
- Combined testing: When at least 2 of 3 tests are abnormal (CRP >0.93 mg/L, ESR >27 mm/h, fibrinogen >432 mg/dL), diagnostic accuracy reaches 97% 1
Note that peripheral white blood cell counts are often normal even with infection, so don't be falsely reassured by a normal WBC 1.
Imaging Studies
Initial radiographs (X-rays) of the knee should be obtained first 1. If infection is suspected based on clinical findings and laboratory results, joint aspiration is the most useful diagnostic tool alongside CRP 1.
Timeline Matters
If your surgery was within the past 2 months, CRP can be elevated normally during healing 1. However, your symptoms of warmth and swelling still warrant investigation. If symptoms appeared more than 3 months after surgery, this would be classified as delayed infection 1.
Other Possible Causes (Less Urgent but Still Important)
While infection must be ruled out first, other causes of your symptoms include:
- Normal postoperative swelling: Common after knee surgery and can be managed with various interventions 5
- Hemarthrosis (bleeding into joint): Can occur 10+ days after surgery 2
- Pseudoaneurysm: Rare (0.03-0.2% incidence) but presents with pain, swelling, and sometimes a pulsatile mass 3, 4
Critical Pitfall to Avoid
Do not dismiss persistent or worsening pain as "normal postoperative discomfort." Infection was not obvious preoperatively in 53% of knees requiring revision surgery for infection 1. The combination of warmth and swelling with pain should trigger immediate evaluation, as delayed diagnosis of infection leads to worse outcomes and may require multiple surgeries or long-term antibiotic suppression 6.
Contact your surgeon or go to an emergency department today for evaluation.