A revision for an infected arthroplasty (PJI) is a big deal for the patient as described in Periprosthetic infection: what does my patient care about? The mental and physical toll is even greater when a two-stage revision is performed: two big procedures with an interposed period of living with a polymethylmethacrylate spacer between the two sides of the joint. The patient can be expected to ask how likely the two-stage procedure is to be successful if they go through all of that. We are not very good at making such predictions as I pointed out in Objective ignorance - a problem in predicting outcomes in climbing and in orthopaedic surgery
The authors of Isolation of Multiple Positive Cultures at Resection Arthroplasty is a Predictor of Failure Following Reimplantation studied 437 patients with chronic knee PJI of which almost one third had "culture negative infections," according to the 2013 Musculoskeletal Infection Society (MSIS) criteria. The minimum number of cultures obtained for all patients was 3 the average number of positive cultures was 2.9. The most commonly isolated organism at resection arthroplasty was coagulase-negative staphylococci, followed by coagulase-positive staphylococci, gram-negative organisms, and Streptococcus species. Of the positive cultures over 90% were soft issue samples (far outstripping the percent of positive cultures from cultures of synovial fluid and implant sonication).
Among those with postive cultures, more than one of six patients experienced treatment failure defined as either any reoperation for infection or PJI-related mortality.
Almost 96% of the patients who experienced failure following reimplantation had ≥2 positive cultures isolated at the time of resection arthroplasty in comparison to those who had successful treatment (75%) Furthermore, the presence of ≥2 positive cultures at resection was associated with an 8-fold increase in the odds of failure following the completion of a 2-stage protocol when compared with the presence of a single positive intraoperative culture (20% versus 3%).
Interestingly, of the patients with positive cultures at the time of failure over half had discordant culture results, meaning that the cultures from the second revision grew different organisms than those from the first revision. In these cases perhaps the first treatment got rid of the initially infecting bugs only to leave the door open for a second species of invader into unhealthy tissue. Thus, it seems important to take multiple intraoperative tissue samples at the second stage.
A few questions arise that I'd love some help answering:
Taken together do these data suggest that treatment failure of a two-stage revision is due to poor host resistance or to inadequate surgical and antibiotic treatment or both?
In that the average number of cultures obtained per patient was a minimum of 3, how senstive is threshold of ≥2 positive cultures to the number of samples taken?
What is the clinical importance of the observation that 75% of the patients with "successful" treatment had ≥2 positive cultures ; i.e. is ≥2 positive cultures at the time of the second procedure a clinically useful predictor of subsequent failure?
What is the best postoperative antibiotic treatment to implement after revision before the results of intraoperative cultures are finalized?
How should "culture negative infections be treated"?
Is the term "unexpectedly positive cultures" helpful, or do we treat all revisions as if they are potentially infected with intraoperative cultures, debridement and postoperative antibiotics?
Infections Are Intimidating
Austin, Texas
April, 2025
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The smooth and move procedure for irreparable rotator cuff tears (see this link)
Shoulder rehabilitation exercises (see this link).
