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Published on: December 3, 2017
Gram stains have limited application in the diagnosis of infected total knee arthroplasty
Michael G Zywiel1, D Alex Stroh, Aaron J Johnson
1Rubin Institute for Advanced Orthopedics, Center for Joint Preservation and Replacement, Sinai Hospital of Baltimore, West Belvedere Avenue, Baltimore, MD 21215, USA.
Background:
The diagnosis of periprosthetic knee infections can present a challenge to surgeons, especially in the case of chronic presentation. Gram stains are regularly performed as part of the microbiological evaluation of suspected infected total knee arthroplasties. Recently, the utility of this test in diagnosing infections has been questioned. The purpose of this study was to assess the effectiveness of Gram stains performed from surgical site samples by comparing their results to the final diagnosis of infection.
Methods:
The results of 347 Gram stains performed at a single center at the time of revision total knee arthroplasty for both septic and aseptic reasons were compared to the final diagnosis based on intra-operative findings and histological evaluation.
Results:
Gram staining demonstrated a low sensitivity of 7% (95% confidence interval 4-12%), a specificity of 99% (95% confidence interval 97-100%), and positive and negative predictive values of 92% and 57%, respectively.
Conclusions:
This study confirmed previous findings of the poor utility of this test for the diagnosis of periprosthetic knee infections. The authors recommend that Gram staining no longer be performed at the time of suspected periprosthetic knee arthroplasty infection.
Insights
Gram stains are ineffective for diagnosing periprosthetic knee infections, showing low sensitivity. This study suggests discontinuing Gram staining for suspected knee joint infections.
Area of Science:
- Orthopedic Surgery
- Infectious Disease Diagnostics
- Microbiology
Background:
- Diagnosing periprosthetic knee infections, particularly chronic cases, poses a significant challenge for surgeons.
- Gram stains are a standard microbiological test for suspected infected total knee arthroplasties.
- Recent evidence questions the diagnostic value of Gram stains in these cases.
Purpose of the Study:
- To evaluate the effectiveness of Gram stains in diagnosing periprosthetic knee infections.
- To compare Gram stain results from surgical samples against the definitive diagnosis of infection.
Main Methods:
- A retrospective analysis of 347 Gram stains performed during revision total knee arthroplasty at a single center.
- Comparison of Gram stain results with final diagnoses determined by intra-operative findings and histological evaluation.
Main Results:
- Gram staining exhibited low sensitivity (7%) and high specificity (99%).
- Positive predictive value was 92%, while negative predictive value was 57%.
- These results indicate limited utility in diagnosing periprosthetic knee infections.
Conclusions:
- The study confirms the poor utility of Gram stains for diagnosing periprosthetic knee infections.
- Gram staining is not recommended for suspected periprosthetic knee arthroplasty infections.
- Alternative diagnostic methods should be prioritized.
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