BACKGROUND:
Antibiotics have been shown to affect the accuracy of cultures; so antibiotics are held prior to obtaining cultures intra-operatively. No study has evaluated the effects of antibiotics on synovial fluid leukocyte cell count. The purpose of the current study is to compare the leukocyte cell count of native joints with septic arthritis when antibiotics have been given before aspiration and when no antibiotics have been given prior to aspiration.

METHODS:
This study was performed at a community hospital and a level 1 urban trauma hospital after IRB approval from both institutions from July 2007 to July 2017. Inclusion criteria comprised of a diagnosis of septic arthritis with positive cultures and a recorded arthrocentesis with cell count performed. Patients with septic arthritis were identified using ICD-9 codes 711.00-711.99 and ICD-10 codes M00 - M02. A retrospective chart review was performed and data was collected. Patients were placed into one of two groups. Group 1 received no antibiotics for two weeks prior to arthrocentesis, group 2 received antibiotics within 24 h prior to arthrocentesis. Demographic information, cell count number and differential, and blood lab values were collected. Timing data was also collected on timing of admission, antibiotics, joint irrigation, and discharge from the inpatient setting.

RESULTS:
There were 81 patients meeting final inclusion criteria. The average cell count for the group which received antibiotics (n = 30) was 40,408 ± 29,433 while the average cell count for the group receiving no antibiotics (n = 51) was 93,824 ± 73,875 (p <  .0001). The average length of stay was not significantly different between the antibiotic group versus no antibiotic group (14.0 days vs 12.1 days p = .4). The time from admission to arthrocentesis and admission to washout was longer for the antibiotic group versus no antibiotic group (p = .004 and p = .002, respectively).

CONCLUSION:
When antibiotics are given prior to arthrocentesis of a septic joint, there is an associated lower synovial fluid leukocyte count compared to when no antibiotics are given prior.

LEVEL OF EVIDENCE:
Level III.



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