Schinsky and colleagues measured how well serum markers, hip aspirate cell counts, frozen section and culture identified infection in hips undergoing revision.
Prospectively evaluated series of 235 painful hips in 220 patients reoperated by two surgeons under one protocol (August 2003 to March 2007), 201 analyzed.
Key Findings
When both ESR and CRP were elevated (79 hips), an aspirate count above 3000 WBC/mL had 90% sensitivity, 91% specificity and 90% accuracy.
When only one of the two markers was elevated (60 hips), the optimal cut‑point rose to 9000 WBC/mL, with 83% sensitivity and 100% specificity.
No hip with both ESR below 30 mm/hr and CRP below 10 mg/dL was infected. The authors recommend the pair, with history and examination, as a low‑cost screen.
Alone, the serum markers were sensitive but not specific: ESR 97% sensitive and 39% specific, CRP 94% and 71%.
Across all 201 hips, the best single aspirate cut‑points were 4200 WBC/mL (84% sensitive, 93% specific) and 80% PMN (84% sensitive, 82% specific).
Frozen section was 73% sensitive and 94% specific. Culture grew organisms in 12 of 146 noninfected hips, an 8% false‑positive rate.
Board pearl
The authors propose 3000 WBC/mL when ESR and CRP are both elevated and 9000 when only one is. Hip infection WBC cut‑points are far below older thresholds of 25,000 to 80,000 in earlier lower‑extremity reports.
Authors' conclusion
A synovial fluid cell count of >3000 white blood cells/mL was the most predictive perioperative testing modality in our study for determining the presence of periprosthetic infection when combined with an elevated preoperative erythrocyte sedimentation rate and C-reactive protein level in patients undergoing revision total hip arthroplasty.
Schinsky and colleagues measured how well serum markers, hip aspirate cell counts, frozen section and culture identified infection in hips undergoing revision.
Prospectively evaluated series of 235 painful hips in 220 patients reoperated by two surgeons under one protocol (August 2003 to March 2007), 201 analyzed.
Key Findings
When both ESR and CRP were elevated (79 hips), an aspirate count above 3000 WBC/mL had 90% sensitivity, 91% specificity and 90% accuracy.
When only one of the two markers was elevated (60 hips), the optimal cut‑point rose to 9000 WBC/mL, with 83% sensitivity and 100% specificity.
No hip with both ESR below 30 mm/hr and CRP below 10 mg/dL was infected. The authors recommend the pair, with history and examination, as a low‑cost screen.
Alone, the serum markers were sensitive but not specific: ESR 97% sensitive and 39% specific, CRP 94% and 71%.
Across all 201 hips, the best single aspirate cut‑points were 4200 WBC/mL (84% sensitive, 93% specific) and 80% PMN (84% sensitive, 82% specific).
Frozen section was 73% sensitive and 94% specific. Culture grew organisms in 12 of 146 noninfected hips, an 8% false‑positive rate.
Board pearl
The authors propose 3000 WBC/mL when ESR and CRP are both elevated and 9000 when only one is. Hip infection WBC cut‑points are far below older thresholds of 25,000 to 80,000 in earlier lower‑extremity reports.
Authors' conclusion
A synovial fluid cell count of >3000 white blood cells/mL was the most predictive perioperative testing modality in our study for determining the presence of periprosthetic infection when combined with an elevated preoperative erythrocyte sedimentation rate and C-reactive protein level in patients undergoing revision total hip arthroplasty.