According to the criteria established by the Musculoskeletal Infection Society (MSIS), which of the following findings is considered a ‘major’ and absolute definitive criterion for diagnosing a periprosthetic joint infection (PJI)?

Explanation:
The correct option is c. The widely accepted MSIS criteria dictate that an absolute, definitive diagnosis of PJI is made when at least one of two 'major' criteria is met: 1) The presence of a sinus tract communicating with the prosthesis, or 2) Two separate positive periprosthetic cultures yielding phenotypically identical organisms. While elevated CRP, elevated ESR, gross purulence, and elevated synovial WBC are extremely important diagnostic markers, they are classified as 'minor' criteria; multiple minor criteria must be present simultaneously to confirm infection in the absence of a major criterion. Reference: Parvizi J et al. New definition for periprosthetic joint infection: from the Workgroup of the Musculoskeletal Infection Society. Clin Orthop Relat Res.