MSIS Criteria for PJI
The 2018 Definition of Periprosthetic Hip and Knee Infection
Parvizi J · J Arthroplasty · 2018
Parvizi and colleagues developed and validated an updated, evidence-based weighted scoring definition for periprosthetic joint infection (PJI) following hip and knee arthroplasty. By incorporating modern biomarkers such as alpha-defensin and D-dimer alongside traditional criteria, this scoring system achieved 97.7% sensitivity and 99.5% specificity, outperforming earlier consensus definitions.
Citation & links
Parvizi J, Tan TL, Goswami K, Higuera C, Della Valle C, Chen AF, Shohat N. The 2018 Definition of Periprosthetic Hip and Knee Infection: An Evidence-Based and Validated Criteria. J Arthroplasty. 2018 May;33(5):1309-1314.e2.
Key findings
- 1.Major criteria remain definitive: presence of a sinus tract communicating with the joint/prosthesis or two positive periprosthetic cultures yielding identical microorganisms independently confirms PJI without needing additional scoring.
- 2.A cumulative point threshold was established for minor criteria: a score of 6 or more confirms infection, a score of 2 to 5 represents an indeterminate/inconclusive presentation requiring further intraoperative assessment, and a score under 2 rules out infection.
- 3.Preoperative minor criteria were assigned weighted points: elevated serum CRP (>10 mg/L) or serum D-dimer (>850 ng/mL) contributes 2 points, elevated ESR (>30 mm/h) contributes 1 point, elevated synovial WBC count (>3000 cells/μL) contributes 3 points, elevated synovial PMN percentage (>70%) contributes 2 points, positive synovial alpha-defensin (signal/cutoff ≥1.0) contributes 3 points, and a positive synovial leukocyte esterase (++) contributes 3 points.
- 4.Intraoperative minor criteria can elevate an indeterminate score: positive intraoperative frozen section histology (>5 PMNs per high-power field in 5 HPFs) contributes 3 points, positive intraoperative purulence contributes 3 points, and a single positive intraoperative tissue culture contributes 2 points.
- 5.The 2018 definition achieved an overall sensitivity of 97.7% and specificity of 99.5%, significantly exceeding the sensitivity of the 2011 MSIS criteria (79.3%) and the 2013 ICM criteria (86.9%).
Background
The diagnostic criteria established by the Musculoskeletal Infection Society (MSIS) in 2011 and refined at the 2013 International Consensus Meeting (ICM) standardized the approach to periprosthetic joint infection (PJI), but both frameworks relied heavily on expert consensus rather than rigorous statistical weighting. Moreover, emerging synovial biomarkers (such as alpha-defensin and leukocyte esterase) and serum markers (such as D-dimer) lacked formal integration into these legacy definitions. Given that culture-negative infections and low-grade indolent organisms regularly posed diagnostic dilemmas, the authors sought to formulate an evidence-based, point-weighted, and validated diagnostic algorithm for hip and knee PJI.
Methods
This multi-institutional diagnostic cohort study was conducted across three high-volume academic arthroplasty centers (Rothman Institute, Cleveland Clinic, and Rush University). Strict baseline cohorts were established: confirmed PJI cases were defined exclusively by traditional major criteria (sinus tract or two identical positive cultures; n = 684), whereas aseptic control cases underwent single-stage revision for mechanical failure and had at least two years of uneventful clinical follow-up without subsequent failure (n = 820). Multiple serum and synovial biomarkers—including serum CRP, ESR, D-dimer, synovial leukocyte counts, polymorphonuclear neutrophil percentage (PMN%), leukocyte esterase, alpha-defensin, synovial CRP, intraoperative histological analysis (frozen section), purulence, and tissue cultures—were evaluated using multivariable logistic regression and classification tree models. Diagnostic performance weights were assigned to each parameter, and the scoring system underwent formal internal and external validation.
Clinical implications
This paper modernized the diagnostic workup of the painful or failing total joint replacement, shifting orthopaedic practice from an unweighted count of positive tests to an objective, evidence-based scoring algorithm. It firmly integrated contemporary synovial biomarkers (specifically leukocyte esterase and alpha-defensin) and serum D-dimer into routine clinical pathways, reducing ambiguous classifications. By establishing a distinct category of 'inconclusive' cases (scores 2–5), it emphasizes to arthroplasty surgeons the critical importance of withholding definitive revision decisions until comprehensive intraoperative testing—including tissue cultures and histology—can definitively rule infection in or out.
Critical appraisal
A primary strength is the robust multi-center design, utilizing very stringent gold-standard criteria for cohorts (confirmed major PJI vs long-term validated aseptic failures) and advanced statistical weighting. However, the study has clear limitations. The cohort was derived retrospectively from tertiary referral centers with specialist pathology and laboratory access that may not be ubiquitous worldwide. Furthermore, diagnostic thresholds for acute postoperative infections (under 6 weeks) or periprosthetic infections in patients with underlying systemic inflammatory arthropathies were not fully stratified within this core paper, necessitating clinical nuance when applying these cutoff values.
Teaching note
Examiners expect candidates to state the two absolute major criteria (sinus tract communicating with the joint or two positive cultures with phenotypically identical organisms) and explain the point-based scoring system (≥6 = infected; 2–5 = indeterminate; <2 = not infected). Be prepared to discuss specific synovial cut-offs (>3,000 WBCs/μL, >70% PMN), the inclusion of alpha-defensin and leukocyte esterase, and the distinction between acute postoperative thresholds versus chronic presentation.
Exam-tested points
- ›Major criteria: Either a sinus tract communicating with the prosthesis or ≥2 positive periprosthetic cultures of the same phenotype constitutes a definitive PJI diagnosis.
- ›Minor criteria scoring threshold: Cumulative score ≥6 confirms PJI; 2–5 is indeterminate/inconclusive; <2 is not infected.
- ›Preoperative serum markers: Elevated CRP (>10 mg/L) or elevated D-dimer (>850 ng/mL) scores 2 points; elevated ESR (>30 mm/h) scores 1 point.
- ›Synovial fluid thresholds (chronic): Synovial WBC >3,000 cells/μL (3 points) and synovial PMN >70% (2 points).
- ›Novel synovial markers: Positive alpha-defensin immunoassay yields 3 points; positive leukocyte esterase (++ strip) yields 3 points.
- ›Intraoperative criteria: Positive histological frozen section (>5 neutrophils/HPF in ≥5 HPFs) awards 3 points, frank purulence awards 3 points, and a single positive culture awards 2 points.
- ›Acute vs chronic nuance: For acute postoperative infections (<6–12 weeks), higher thresholds must be applied (e.g., synovial WBC >10,000 cells/μL and PMN >80–90%, CRP >100 mg/L), as baseline inflammatory markers remain elevated after surgical insult.
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