Review Question - QID 213141

Based on the 2018 revised Musculoskeletal Infection Sociecty (MSIS) criteria, the elevated ESR, serum CRP, positive alpha defensin, and elevated PMNs convey a score of 1, 2, 3, and 2, respectively, for a combined score >6. This is diagnostic of a chronic prosthetic joint infection (PJI), for the most supported management strategy is two-stage revision arthroplasty with intravenous (IV) antibiotic therapy for 4-6 weeks.

PJI after TKA is estimated to be 2.5%. The chronicity of the infection determines management. Non-MRSA PJI within 4 weeks of surgery is considered acute and may be treated with irrigation, debridement, polyethylene exchange, component retention, and IV antibiotics, as the organism has purportedly had too little time to form a robust biofilm. PJI occurring more than 4 weeks after TKA is considered chronic and, due to a high likelihood of biofilm formation, requires two-stage revision arthroplasty with IV antibiotic therapy.

Ting et al. reviewed an algorithm-based approach for diagnosis of PJI. They reported that the diagnosis of PJI is made in 90% of patients by ESR and CRP, followed by arthrocentesis if the results are high, with a focus on synovial WBC count, differential, and cultures.

Everhart et al. developed and validated a preoperative surgical site infection (SSI) risk score for primary or revision TKA and hip arthroplasty (THA). They reported that patient comorbidities composing the risk significantly influence SSI risk for primary or revision TKA and THA. They concluded that preoperative SSI risk can be objectively determined by the proposed SSI risk score.

Parvizi et al. most recently presented the 2018 updated MSIS evidence-based criteria for diagnosis of periprosthetic hip and knee infections (Illustration A). The authors updated the original crtieria, expanding and refining the contributions from each of the minor criteria. The authors supported that a score >6 was diagnostic of periprosthetic infection. They concluded that this criteria was 97.7% sensitive and 99.5% specific for diagnosis of prosthetic joint infection.

Figures and Illustrations:
Figure A shows the AP and lateral radiographs of a TKA prosthesis with evidence of osteolysis and marked loosening of the femoral and tibial components.

Illustration A is the updated 2018 MSIS criteria for diagnosis of a PJI.

Incorrect Answers:
Answer 1: A repeat knee arthrocentesis is not indicated given the clinical history and objective laboratory data suggestive of a PJI.
Answer 2: Revision of loosened femoral component without antibiotic therapy would be indicated in TKA with aseptic femoral loosening, not with a PJI.
Answer 3: A one-stage revision is not the accepted standard of treatment and is not as successful in the clearance of pathogens in PJI compared to two-stage revision. While there is increasing support in the literature for one-stage revision, the current gold standard for a chronic PJI remains a two-stage revision.
Answer 5: Revision of loosened tibial component without antibiotic therapy would be indicated in TKA with aseptic tibial loosening, not with a PJI.