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Periprosthetic infection: where do we stand with regard to Gram stain?

Elie Ghanem1, Constantinos Ketonis, Camilo Restrepo

  • 1Department of Orthopaedic Surgery, Thomas Jefferson University Hospital, Rothman Institute, Philadelphia, PA, USA.

Acta Orthopaedica
|March 21, 2009
PubMed
Abstract

Insights

Gram stain for periprosthetic infection (PPI) diagnosis shows high specificity but low sensitivity. Combining Gram stain results improves accuracy but still has limited value in ruling out PPI, suggesting a need for better diagnostic methods.

Area of Science:

  • Orthopedic Surgery
  • Infectious Diseases
  • Diagnostic Microbiology

Background:

  • Periprosthetic infection (PPI) diagnosis often relies on intraoperative Gram stain.
  • The diagnostic utility of Gram stain in PPI may vary by joint type and sample number.
  • This study evaluates Gram stain performance in a large patient cohort.

Purpose of the Study:

  • To assess the role and effectiveness of Gram stain in diagnosing periprosthetic joint infections (PPI).
  • To determine if Gram stain results differ based on the affected joint (e.g., total hip arthroplasty [THA] vs. total knee arthroplasty [TKA]).
  • To evaluate the impact of combining different Gram stain criteria (organisms vs. neutrophils) on diagnostic accuracy.

Main Methods:

  • Defined positive Gram stain as visualization of bacteria or >5 neutrophils per high-power field.
  • Calculated sensitivity, specificity, and predictive values for individual Gram stain components.
  • Analyzed serial (both positive required) and parallel (both negative required) combinations of Gram stain findings.

Main Results:

  • Individual Gram stain components showed high specificity (98-100%) and positive predictive value (89-100%) for THA and TKA.
  • Sensitivities (30-50%) and negative predictive values (70-79%) were low for both joint types.
  • Serial combination improved specificity to 100% and negative predictive value to 82%, with sensitivity at 43-64%.

Conclusions:

  • Gram stain, even when combined, has limited value in definitively ruling out periprosthetic infection.
  • The diagnostic performance of Gram stain remains suboptimal for PPI.
  • Novel molecular diagnostic methods are needed to replace traditional Gram stain techniques for PPI diagnosis.

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