A
Elevated serum CRP (>10 mg/L) and ESR (>30 mm/hr)
B
Elevated synovial fluid white blood cell count (>3000 cells/uL)
C
Two positive periprosthetic cultures yielding phenotypically identical organisms
D
Purulence in the affected joint space as documented visually by the surgeon
Explanation:Correct Option: C. According to the MSIS and subsequent International Consensus Meeting (ICM) criteria, there are only two definitive 'major' criteria for PJI: 1) a sinus tract communicating with the prosthesis, or 2) two positive periprosthetic tissue or fluid cultures yielding the exact same organism. Purulence alone is considered a minor criterion due to subjective interpretation and non-infectious causes of metallosis/inflammation. (Ref: Parvizi et al., J Arthroplasty, 2011/2018)