Review Question - QID 211372

The patient is presenting with a chronic prosthetic joint infection (PJI) with a calculated score of 11 (≥ 6 is considered positive for an infection) according to the 2018 definition for PJI.

PJIs are devastating complications that are associated with tremendous morbidity and increased treatment costs. Total knee arthroplasty and revision arthroplasty have a higher rate of infection compared to primary procedures and total hip arthroplasty. The Musculoskeletal Infection Society (MSIS) has proposed a formal definition for a PJI to provide uniformity in the reporting and to guide treatment. Acute infections can be treated with I&D with polyethylene exchange, whereas chronic infections (generally more than 4-6 weeks of symptoms) are best treated with two-stage revision arthroplasty.

Diaz-Ledezma et al. performed a questionnaire study of 159 international experts to determine the definition of success in the treatment of PJIs. They reported the definition to include a healed wound without evidence of fistula, drainage, pain, or infection recurrence by the same organism; no subsequent surgical intervention after reimplantation surgery; and no occurrence of mortality related to PJI. The authors concluded that this new definition of success can be used to report and compare the results of treating PJIs.

Parvizi et al. updated the definition of PJI from the original MSIS criteria. The authors removed gross purulence from the minor criteria definition, as this can be found with metallosis, and provided specific laboratory values used for acute and chronic infections. The authors concluded that the proposed definition would aid in the diagnosis and treatment of PJIs.

Parvizi et al. performed a multi-institutional validation study of an updated definition for prosthetic knee and hip infections. Their new definition consisted of a step-wise diagnostic approach and included D-dimer levels, synovial CRP, and alpha-defensin in addition to the criteria set forth in the 2014 definition, which demonstrated higher sensitivity and similar specificity to previous definitions. The authors concluded the new evidence-based definition of a PJI has excellent external validity and should guide accurate diagnosis.

Figures A and B are the AP and frog-leg lateral of the right hip with a right total hip arthroplasty and potential loosening of the femoral stem. Illustration A is the 2018 definition of PJI. Illustration B is the cut-off values for lab results in the 2018 definition of PJI.

Incorrect Answers:
Answer 1: According to the 2018 definition of a PJI, molecular diagnostics (polymerase chain reaction and next-generation sequencing) is considered when there is an inconclusive diagnosis after appropriate serum, synovial, and intraoperative testing.
Answer 2: The patient has already met the criteria for a PJI. A repeat aspiration would not provide any further diagnostic information.
Answer 3: Intraoperative histology (>5 neutrophils per high powered field in at least 5 fields at 400x magnification) is an option if serum and synovial work-up are inconclusive. In this case, the patient has a sufficient diagnosis of a PJI and should proceed with a two-stage revision arthroplasty.
Answer 5: Acute PJI (<6 weeks of symptoms) can be treated with irrigation & debridement and polyethylene exchange. Since the patient has been symptomatic over a 6 month period, she likely has a chronic PJI which is best treated with a two-stage revision.