What are the next steps for managing pricking pain at the joint 35 days after total knee replacement (TKR)?

Management of Pricking Pain 35 Days After Total Knee Replacement

Obtain plain radiographs of the knee immediately, followed by joint aspiration if infection cannot be excluded clinically, as this represents the most critical diagnostic pathway at 5 weeks post-TKR. 1, 2

Initial Diagnostic Approach

At 35 days post-TKR, you must systematically exclude periprosthetic infection—the most serious complication occurring in 0.8-1.9% of cases. 2 The American College of Radiology provides clear guidance for this exact clinical scenario:

First-Line Imaging

• Plain radiographs (X-ray) of the knee are rated 8/9 ("usually appropriate") and must be obtained before any other intervention. 1, 2 Look specifically for component positioning, alignment, periprosthetic lucency, or early signs of loosening. 2, 3

Infection Exclusion Protocol

• Joint aspiration is rated 9/9 ("usually appropriate") after reviewing the X-ray when infection cannot be excluded. 1, 2 This is performed after—not before—radiographic evaluation. 1

• Clinical red flags for infection at this timeframe include:

  • Night pain or pain at rest (highly suggestive of infection) 2, 3
  • Warmth, erythema, or systemic signs 2
  • Pain that is constant rather than activity-related 3

• Pain with weight-bearing alone is more characteristic of mechanical issues (loosening, malposition) rather than infection. 2, 3

Laboratory Testing

While the guidelines focus on imaging, obtain ESR and CRP if infection is suspected. 3 CRP >13.5 mg/L has 73-91% sensitivity and 81-86% specificity for prosthetic infection. 3 However, do not delay aspiration waiting for lab results if clinical suspicion is moderate to high. 3

Management Based on Findings

If Aspiration Cultures Are Positive

• Immediate surgical consultation for source control 2
• Collaborative management with orthopedic surgery and infectious disease 2
• MRI without and with IV contrast (rated 5/9 "may be appropriate") can help define extent of infection after diagnosis is confirmed 1

If Aspiration Is Negative or Equivocal

• Repeat aspiration is rated 9/9 if infection remains suspected despite negative initial culture. 1
• Consider Indium-111 WBC scan with Tc-99m sulfur colloid (rated 6/9 "may be appropriate") for equivocal cases 1

If Infection Is Excluded

• Fluoroscopy (rated 4/9) may supplement radiography to detect occult periprosthetic loosening 1
• CT without IV contrast for suspected periprosthetic fracture or component rotation issues 2
• Referral back to orthopedic surgeon for persistent pain despite negative workup 2

Pain Management During Workup

While diagnostic evaluation proceeds, multimodal analgesia is appropriate. 1 However, avoid masking symptoms that could indicate infection—do not aggressively treat pain until infection is definitively excluded. 1

Critical Pitfalls to Avoid

• Never perform joint aspiration before obtaining plain radiographs. 1 The X-ray must be reviewed first to guide aspiration technique and assess for other complications.

• Do not assume normal peripheral WBC count excludes infection—chronic prosthetic infections typically present with normal leukocyte counts. 3

• Fever within 48 hours post-surgery is usually non-infectious, but at 35 days post-op, fever strongly suggests infection. 4

• Do not rely on ESR alone—it can be elevated in uninfected patients with loosening. 3 Use combined ESR + CRP per AAOS guidelines. 3

• Ultrasound (rated 3/9 "usually not appropriate") and MRI without contrast (rated 2/9 "usually not appropriate") are not appropriate for initial evaluation of post-TKR pain when infection cannot be excluded. 1