What Is ‘Success’ When Treating Knee PJI?

Is “success” defined according to Delphi Consensus Criteria or Musculoskeletal Infection Society Criteria? A new retrospective review prospectively collected data for 57 knee arthroplasty cases to see if there was, indeed, a difference—and if it was with distinction.

The new work, “Comparison of Delphi Consensus Criteria and Musculoskeletal Infection Society Outcome Reporting Tool (MSIS-ORT) Definitions of Successful Surgical Treatment of Periprosthetic Knee Infection,” appears in the April 9, 2024, edition of the Journal of Arthroplasty.

“Currently the success of treating periprosthetic infections in hip and knee arthroplasty have wide variability in what research reports as ‘success,’” said co-author R. Michael Meneghini, M.D., adjunct clinical professor of orthopaedic surgery at Indiana University School of Medicine, in Indianapolis, to OTW.

“For example, if a patient is on chronic antibiotics to make sure infection does not return, does that constitute a total eradication of infection from the patient? In addition, if a patient suffers a reoperation of any kind after the PJI treatment surgery, some criteria count that as a failure when the reoperation may not have been infection related, such as for instability or aseptic loosening.”

The team used the Delphi Consensus Criteria and the Musculoskeletal Infection Society Outcome Reporting Tool to quantify treatment outcomes. The Musculoskeletal Infection Society tool categorizes patients in one of 10 tiers based on their worst outcome, ranging from infection control with no continued antibiotic therapy beyond the first postoperative year to death ≤1 year from the initiation of treatment. The tiered results are summed to produce three outcomes: success defined as infection control with no reoperations, failure that is directly or indirectly related to a PJI, and failure due to secondary causes.

The researchers say it is important to note the key differences between the Musculoskeletal Infection Society tool and the Delphi Consensus Criteria include changing the starting point for assessment to the initial infection surgery rather than post-reimplantation, including reinfection with a new organism as treatment failure, recognizing the role of retained spacers in treatment outcomes, including aseptic revisions in the tiered outcomes, and counting all-cause mortality occurring >1 year from the initiation of treatment as failure due to secondary causes.

For this study, the researchers found that success rates were 81% using the Delphi Consensus Criteria and 56% using the Musculoskeletal Infection Society tool. The success rates of the Musculoskeletal Infection Society tool increased to 76% when aseptic revisions and deaths unrelated to PJI were not penalized as failures of treatment.

When OTW asked if there were other things than aseptic revisions and deaths unrelated to PJI that might have also not “counted” as treatment failure, Dr. Meneghini said, “In a two-stage approach, where the implants are removed and a spacer placed, to be reimplanted months later after infection had been eradicated, the ‘index’ surgery was the first resection. In addition, if there was a spacer-related complication, this was considered a failure, rather than part of the complex treatment process itself.”

“Research should try and unify the outcome measures so that studies can be compared from one to the next. At a minimum, future research should report both outcomes until a consensus is reached by the orthopaedic research community.”