False-positive Cultures After Native Knee Aspiration: True or False

Area of Science:

• Orthopaedic Surgery
• Infectious Disease Diagnostics
• Microbiology

Background:

• Synovial fluid aspiration is crucial for diagnosing joint infections.
• Positive cultures in low-pretest probability cases may be contaminants, especially skin pathogens.
• The contamination rate in native knee aspirations was previously unevaluated.

Purpose of the Study:

• To determine the frequency of false-positive cultures in native knee aspirations.
• To assess the reliability of knee fluid cultures in diagnosing septic arthritis.

Main Methods:

• A diagnostic study (Level I) analyzed 200 patients undergoing total knee arthroplasty (TKA) for osteoarthritis.
• Knee aspirations were performed under sterile conditions prior to TKA in patients without signs of infection.
• 166 valid knee fluid cultures were analyzed for false-positive results.

Main Results:

• No false-positive cultures were identified in the 166 native knee aspirations.
• The incidence of contamination in native knee aspirations was 0%.

Conclusions:

• Proper sterile technique for knee arthrocentesis yields reliable culture results in native knees.
• Positive cultures from native knee aspirations should be considered strong indicators of bacterial septic arthritis.
• Further research is needed to evaluate false-positive rates in knees with prior TKA.