Synovial fluid leukocyte cell count before versus after administration of antibiotics in patients with septic arthritis of a native joint

Arthroscopy or arthrotomy for native knee septic arthritis: A systematic review

Purpose

Septic arthritis of any joint is an orthopaedic emergency which requires prompt diagnosis and treatment. The knee is the commonest joint afflicted, and the primary objective of any treatment is complete source control. This commonly takes the form of antibiotic therapy and a washout of the infected joint by means of arthroscopy or arthrotomy. The primary aim of this review is to investigate if arthroscopic washout for native knee septic arthritis confers a lower risk of repeat procedure than arthrotomy.

Methods

A systematic review and meta-analysis was conducted of the MEDLINE, SCOPUS and the Cochrane Library data bases. The primary outcome of interest was requirement for repeat washout with all-cause complications, length of inpatient stay and mortality secondary outcomes.

Results

A total of 17,140 subjects were included for analysis of the primary outcome, and the overall rate of repeat procedure was 14.6%. No statistical difference was found between arthroscopy and arthrotomy for repeat washout (risk ratio 0.86 [95% confidence interval, CI: 0.72-1.02], I 2 = 36%). Eligible studies found in favour of arthroscopy for all-cause complication rate (risk ratio 0.75 [95% CI: 0.6-0.93], I 2 = 84%) and length of stay in hospital (mean difference -1.98 days [95% CI: -3.43 to -0.53], I 2 = 84%). No statistical difference was found for the mortality rate (risk ratio 1.17 [95% CI: 0.52-2.63], I 2 = 57%).

Conclusion

Our analysis found arthroscopy and open arthrotomy to be equivocal for repeat surgical washout in native knee septic arthritis. All-cause complication rate and length of inpatient stay were favourable for arthroscopy with no difference noted between mortality rates.

Level of Evidence

Level III.

Effect of Antibiotic Administration Before Joint Aspiration on Synovial Fluid White Blood Cell Count in Native Joint Septic Arthritis

Background

This study was performed to assess the impact of preaspiration antibiotics on synovial fluid analysis and timing of operative treatment in native-joint septic arthritis.

Methods

We performed a retrospective record review of adult patients from an urban level 1 trauma center with native joint septic arthritis in 2015-2019, identified by means of codes from the International Classification of Diseases (Ninth Revision and Tenth Revision). Univariate and multivariate analyses were performed to determine whether antibiotics were associated with lower synovial fluid white blood cell counts (WBCs), the percentage of polymorphonuclear neutrophil (PMNs), and rate of culture positivity. Secondary analysis included time elapsed from aspiration to surgery.

Results

Of the 126 patients with septic joints included, nearly two-thirds (n = 80 [63.5%]) received antibiotics before joint aspiration. The synovial fluid WBC count, percentage of PMNs, and rate of culture positivity were significantly lower in patients who received preaspiration antibiotics than in those who did not (mean WBC count, 51 379.1/μL [standard deviation, 52 576.3/μL] vs 92 162.7/μL [59 330.6/μL], respectively [P < .001]; PMN percentage, 83.6% [20.5%] vs 91.9% [6.0%; P = .01]; and culture positivity, 32.5% vs 59.1% [P = .008]). Multivariable analyses revealed that these associations remained after controlling for potential confounders (change in PMNs, -42 784.60/μL [95% confidence interval, -65 355/μL to -20 213.90/μL [P < .001]; change in PMNs, -7.8% [-13.7% to -1.8%] [P = .01]; odds ratio, 0.39 [.18-.87; P = .02). Patients with a synovial fluid WBC count ≤50 000/μL experienced significant delay in time from joint aspiration to operative intervention (mean [standard deviation], 10.5 [11.3] vs 17.9 [17.2] hours; P = .02).

Conclusions

The administration of antibiotics before joint aspiration for suspected septic arthritis appears to decrease the synovial fluid WBC count, the percentage of PMNs, and the rate of culture positivity. Efforts to limit antibiotic administration before joint aspiration are important to minimize diagnostic dilemmas and circumvent treatment delays.

Optimal Synovial Fluid Leukocyte Count Cutoff for Diagnosing Native Joint Septic Arthritis After Antibiotics: A Receiver Operating Characteristic Analysis of Accuracy

INTRODUCTION

Urgent treatment of septic arthritis is key in preventing devastating morbidity or mortality. Accurate diagnosis is critical, and the standard diagnostic cutoff of 50,000 synovial leukocytes may be altered by previous administration of antibiotics. Our objective was to identify and compare a cutoff synovial leukocyte count with a high sensitivity and specificity for diagnosis of septic arthritis in patients who received antibiotics and those who had not. A receiver operating characteristic (ROC) curve was used to provide a discriminate cutoff value for diagnosing septic arthritis.

METHODS

A retrospective chart review of 383 patients was done over a 13-year period including those who had arthrocentesis of any joint. Two groups were created, those who had not been given antibiotics within 2 weeks (control) and those who received intravenous or oral antibiotics within 2 weeks before arthrocentesis. Relevant data included synovial leukocyte count and differential cell count. Additional metrics included temperature, erythrocyte sedimentation rate, and C-reactive protein. A ROC curve determined the optimal synovial white blood cell cutoff for diagnosing septic arthritis in native joints for each group.

RESULTS

The ROC curve determined that patients who received antibiotics had an optimal cutoff of >16,000 cells (sensitivity = 82%, specificity = 76%), and a neutrophil percentage cutoff of >90% (sensitivity = 73%, specificity = 74%). The control group had an optimal synovial leukocyte cutoff of >33,000 cells (sensitivity = 96%, specificity = 95%). The optimal neutrophil percentage cutoff in the control group was >83% neutrophils (sensitivity = 89%, specificity = 79%).

CONCLUSION

When a patient is given antibiotics before arthrocentesis, a diagnostic value of >16,000 synovial leukocytes should be used to guide treatment of septic arthritis. A diagnostic value of >33,000 synovial leukocytes yields the highest accuracy for diagnosis of septic arthritis in patients who have not been given antibiotics before arthrocentesis.

LEVEL OF EVIDENCE

III.