Determining Diagnostic Thresholds for Acute Postoperative Periprosthetic Joint Infection

Area of Science:

• Orthopedic Surgery
• Infectious Diseases
• Diagnostic Medicine

Background:

• Diagnosing early postoperative periprosthetic joint infection (PJI) is challenging.
• Existing serum C-reactive protein (CRP) and synovial fluid markers may lack sensitivity.
• Optimal diagnostic thresholds for acute PJI require re-evaluation.

Purpose of the Study:

• To evaluate serum CRP, ESR, synovial fluid WBC count, and PMN percentage for PJI diagnosis.
• To identify optimal cutoff values for these markers in acute postoperative PJI.
• To compare new thresholds with existing Musculoskeletal Infection Society (MSIS) guidelines.

Main Methods:

• Multicenter study of 197 patients investigated for PJI within 90 days of arthroplasty.
• Included 123 patients with confirmed PJI and 74 non-infected controls.
• Utilized receiver operating characteristic (ROC) curve analysis to determine optimal cutoff values.

Main Results:

• Optimal cutoffs: synovial fluid WBC 6,130 cells/μL (91% sensitivity), serum CRP 39.8 mg/L (91% sensitivity), ESR 39.5 mm/hr (76% sensitivity), PMN 79.5% (95% sensitivity).
• Thresholds were generally lower than current MSIS guidelines.
• Synovial fluid WBC cutoff increased significantly when using a 30-day vs. 90-day definition.

Conclusions:

• Established PJI diagnostic cutoffs are likely too high and lack sensitivity.
• The study's calculated thresholds offer improved diagnostic accuracy for acute PJI.
• Diagnostic thresholds may need adjustment based on time elapsed since index arthroplasty.