External validation of the joint-specific bone involvement, antimicrobial options, coverage of the soft tissues, and host status (JS-BACH) classification for predicting the outcome in periprosthetic joint infections following total hip and knee arthr

<b>Purpose</b>: Periprosthetic joint infection (PJI) represents a major complication of total joint arthroplasty (TJA). The joint-specific bone involvement, antimicrobial options, coverage of the soft tissues, and host status (JS-BACH) classification of 2021 aims to categorize PJI severity and predict PJI recurrence and quality of life following surgical PJI treatment. Until now, only one external validation has confirmed its predictive value for treatment failure. This study aimed to further validate the classification in an external cohort and to compare outcomes between different pathogen groups. <b>Methods</b>: We applied the JS-BACH classification to a cohort of 249 consecutive gram-positive (staphylococci) and gram-negative PJIs in hip and knee joints treated at our institution between 2010 and 2022 (<i>Staphylococcus aureus</i> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>n</mml:mi> <mml:mo>=</mml:mo> <mml:mn>62</mml:mn></mml:mrow> </mml:math> ; coagulase-negative staphylococci <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>n</mml:mi> <mml:mo>=</mml:mo> <mml:mn>115</mml:mn></mml:mrow> </mml:math> ; gram-negative organisms <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>n</mml:mi> <mml:mo>=</mml:mo> <mml:mn>72</mml:mn></mml:mrow> </mml:math> ). According to the JS-BACH classification, we divided cases into uncomplicated ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>n</mml:mi> <mml:mo>=</mml:mo> <mml:mn>35</mml:mn></mml:mrow> </mml:math> ), complex ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>n</mml:mi> <mml:mo>=</mml:mo> <mml:mn>155</mml:mn></mml:mrow> </mml:math> ), and limited options ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>n</mml:mi> <mml:mo>=</mml:mo> <mml:mn>59</mml:mn></mml:mrow> </mml:math> ). The median (interquartile range, IQR) follow-up was 25.0 (3-59) and at least 12 months. Outcomes were assessed based on the 2013 Delphi consensus on PJI outcome. PJI was defined following the EBJIS classification. <b>Results</b>: A higher JS-BACH category correlated significantly with a lower infection-free survival. Using uncomplicated cases as baseline, the hazards ratio (HR) was 3.2 (95 %-CI 1.3-7.9) for complex and 6.6 (95 %-CI 2.6-16.7) for limited options cases. Similarly, higher JS-BACH categories were associated with lower revision-free survival for recurrent PJI, again with uncomplicated cases as baseline: complex HR 2.2 (95 %-CI 0.9-5.5); limited options HR 4.1 (95 %-CI 1.6-10.8). The mean infection-free survival was 85.7 %, 58.7 %, and 33.9 % for uncomplicated, complex, and limited options cases ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>p</mml:mi> <mml:mo><</mml:mo> <mml:mn>0.001</mml:mn></mml:mrow> </mml:math> ). <b>Conclusion</b>: The novel JS-BACH classification provides reliable predictions of treatment outcome for the proposed subgroups. It provides a structured and simple-to-use option for classifying PJI in daily clinical practice and for scientific purposes.