This study defines optimal diagnostic cutoffs for early periprosthetic joint infection (within 6 weeks) after primary THA. It addresses a critical gap: standard chronic PJI thresholds are unreliable in the postoperative period because inflammation and serologic markers are physiologically elevated after surgery. The authors analyzed 73 patients who underwent reoperation from a cohort of 6033 consecutive THAs.
Before this paper, no established diagnostic thresholds existed for PJI in the early postoperative period after THA. Clinicians were forced to apply chronic PJI cutoffs (synovial WBC >4,200 cells/μL, CRP >10 mg/L) — thresholds that are physiologically exceeded by normal postoperative inflammation in many uninfected patients.
In practice: use serum CRP as your first-line screen. Any patient within 6 weeks of THA with CRP approaching 93 mg/L, or with fever, purulent drainage, or high clinical suspicion, warrants joint aspiration.
When you aspirate, the number that matters most is the synovial WBC count. A value above 12,800 cells/μL in the first 6 weeks after THA is your threshold for diagnosing infection. If the WBC is borderline, a PMN differential above 89% supports infection.
Do not anchor to the ESR in this setting. Its poor specificity (53%) means a positive result adds little, and you should not withhold aspiration based on a normal ESR alone.
This study defines optimal diagnostic cutoffs for early periprosthetic joint infection (within 6 weeks) after primary THA. It addresses a critical gap: standard chronic PJI thresholds are unreliable in the postoperative period because inflammation and serologic markers are physiologically elevated after surgery. The authors analyzed 73 patients who underwent reoperation from a cohort of 6033 consecutive THAs.
Before this paper, no established diagnostic thresholds existed for PJI in the early postoperative period after THA. Clinicians were forced to apply chronic PJI cutoffs (synovial WBC >4,200 cells/μL, CRP >10 mg/L) — thresholds that are physiologically exceeded by normal postoperative inflammation in many uninfected patients.
In practice: use serum CRP as your first-line screen. Any patient within 6 weeks of THA with CRP approaching 93 mg/L, or with fever, purulent drainage, or high clinical suspicion, warrants joint aspiration.
When you aspirate, the number that matters most is the synovial WBC count. A value above 12,800 cells/μL in the first 6 weeks after THA is your threshold for diagnosing infection. If the WBC is borderline, a PMN differential above 89% supports infection.
Do not anchor to the ESR in this setting. Its poor specificity (53%) means a positive result adds little, and you should not withhold aspiration based on a normal ESR alone.