Evidence brief
The 2018 Definition of Periprosthetic Hip and Knee Infection
Major criteria: Two positive cultures OR sinus tract communicating with joint
Minor criteria: Elevated CRP, ESR, synovial WBC, synovial PMN%, alpha-defensin
Scoring system: ≥6 points = infected
Improved sensitivity and specificity over previous definitions
Alpha-defensin provides high specificity
The MSIS criteria provide a standardized, evidence-based framework for diagnosing periprosthetic joint infection. This guides treatment decisions and allows comparison between studies.
Must know MSIS criteria cold. Major criteria (definitively infected): 2+ cultures same organism, sinus tract. Minor criteria and scoring: CRP>10, ESR>30, synovial WBC>3000, PMN>80%, alpha-defensin positive. Score ≥6 = infected, 2-5 = possibly infected, <2 = not infected.
Level I
Systematic review of RCTs or high-quality RCT