McNally (2021) — The EBJIS definition of periprosthetic joint infection.

The Ebjis Definition of Periprosthetic Joint Infection.

·Bone Joint J·2021·739 citations·Hip & Knee

PJI diagnosis has long lacked a universally accepted reference standard. This paper presents the EBJIS definition: a three-level framework (infection unlikely, likely, confirmed) built from a review of over 250 studies across 27 diagnostic topics. It was developed with EBJIS, MSIS, and ESGIAI endorsement to address the sensitivity failures of prior binary definitions.

Study Snapshot

Key Findings

The EBJIS framework replaces binary (infected/not infected) classification with three levels, because no test can absolutely confirm or exclude PJI. The levels are:
–Infection Unlikely: all findings negative
–Infection Likely: raised CRP or a clinical sign, plus at least one other positive test
–Infection Confirmed: any single confirmatory test is positive
Synovial WBC and PMN thresholds are tiered across the three levels for hip and knee PJI:
–Unlikely: WBC ≤1,500 cells/µL and PMN ≤65%
–Likely: WBC >1,500 cells/µL or PMN >65%
–Confirmed: WBC >3,000 cells/µL and PMN >80%
Histologic confirmation requires ≥5 neutrophils in ≥5 high-power fields at ×400 magnification. Finding ≥5 neutrophils in even a single HPF is enough to classify the case as 'infection likely' — capturing low-grade infections that a strict confirmatory threshold would miss.
Sonication fluid culture thresholds differ by technique:
–Non-concentrated: >1 CFU/ml (likely), >50 CFU/ml (confirmed)
–Concentrated (centrifugation): >200 CFU/ml (confirmed)
–Any growth from sonication fluid is a potential infection; the cut-off for confirmation depends on the specific protocol used.
A sinus tract communicating with the joint or exposing the prosthesis is the only fully specific clinical finding and alone confirms PJI. Intraoperative purulence is subjective and cannot distinguish PJI from adverse local tissue reaction or crystal arthropathy — it supports 'infection likely' but not confirmed.
Alpha-defensin ELISA has high specificity and sits in the confirmatory category. The lateral-flow (point-of-care) version has significantly lower sensitivity and is not an equivalent substitute. Both are invalidated by metallosis, gout, or acute inflammatory arthritis.
Serum CRP above 10 mg/L (in the absence of another cause) is associated with PJI and contributes to the 'infection likely' threshold, but cannot confirm or exclude infection alone. ESR and D-dimer were excluded from the definition because they add no diagnostic value over CRP.
At revision surgery, a minimum of five tissue samples using separate instruments must be submitted for culture, incubated for at least 14 days. The patient should be off antibiotics for at least two weeks. At least two samples growing phenotypically identical organisms with matching susceptibility confirm infection.

Board PearlThe EBJIS PJI definition uses three levels — unlikely, likely, confirmed — because no single test can definitively confirm or exclude infection alone.

Clinical Relevance

The clinical problem this definition addresses is real: prior binary frameworks (infected vs. not infected) missed low-grade infections and led to aseptic revision surgery on patients who actually had PJI.

The 'infection likely' category is the most operationally important tier. It tells you to keep looking rather than stop. A patient with a raised CRP and synovial WBC of 2,000 cells/µL does not have confirmed PJI by this framework, but they should not be taken to aseptic revision without further workup.

Know the confirmatory thresholds cold, because they determine surgical decision-making: Synovial WBC >3,000 cells/µL and PMN >80% Histology: ≥5 neutrophils in ≥5 HPF Sonication: >50 CFU/ml (non-concentrated) Alpha-defensin ELISA: positive Sinus tract to joint: present

The definition also carries a practical caveat for immunocompromised patients: inflammatory biomarkers may be falsely low despite active infection, so the clinical and microbiologic findings carry more weight than the numbers alone in that population.

Core

The Ebjis Definition of Periprosthetic Joint Infection.

McNally, Trebše, et al.·Bone Joint J·2021·739 citations·Hip & Knee

The Ebjis Definition of Periprosthetic Joint Infection.

Study Snapshot

Key Findings

Clinical Relevance

Related Articles

The Ebjis Definition of Periprosthetic Joint Infection.

Study Snapshot

Key Findings

Clinical Relevance

Related Articles

The Ebjis Definition of Periprosthetic Joint Infection.

Study Snapshot

Key Findings

Clinical Relevance

Related Articles

The Ebjis Definition of Periprosthetic Joint Infection.

Study Snapshot

Key Findings

Clinical Relevance

Related Articles