These authors defined a culture-negative periperosthetic infection " as one for which cultures of joint aspirate and/or intraoperative tissue samples did not isolate an organism."
Patients were excluded from their study if the results of culture of material from the site of the PJI were unavailable; if they had 1 positive culture, a megaprosthesis, or a subsequent PJI in the same joint; or if they had been followed for <1 year.
Comment: Perhaps the most useful definition of an "infection" is "bacteria doing harm". In the absence of evidence of living bacteria (i.e. positive cultures) it is difficult to be confident that observed harm is due to bacteria. Thus in reviewing the criteria above, only #2 provides convincing evidence that live bacteria are present. The rest of the criteria can lead to the impression of a "suspected PJI".
We are inclined to do a single or two stage exchange followed by the red protocol if our preoperative suspicion of infection is greater that 25%.
They conducted a retrospective review of 219 patients (138 hips and 81 knees) who had undergone surgery for the treatment of culture-negative PJI. The prevalence of suspected culture-negative PJI was 22.0% (219 of 996), and the prevalence of culture negative PJI was 6.4% (44 of 688) as defined by the Musculoskeletal Infection Society (MSIS) (see this link):
Overall, the rate of treatment success was 69.2% (110 of 159) in patients with >1 year of follow-up. Of the 49 culture-negative PJIs for which treatment failed, 26 (53.1%) subsequently had positive cultures; of those 26, 10 (38.5%) were positive for methicillin sensitive Staphylococcus aureus. The rate of treatment success was greater (p = 0.019) for patients who had 2-stage exchange than for those who underwent irrigation and debridement.
Comment: Perhaps the most useful definition of an "infection" is "bacteria doing harm". In the absence of evidence of living bacteria (i.e. positive cultures) it is difficult to be confident that observed harm is due to bacteria. Thus in reviewing the criteria above, only #2 provides convincing evidence that live bacteria are present. The rest of the criteria can lead to the impression of a "suspected PJI".
Cultures may be negative because
(a) no bacteria were present,
(b) while there were bacteria present in the joint, the sample(s) taken did not contain bacteria (for example, culturing of a joint fluid aspirate has a low sensitivity for detecting bacteria in a periprosthetic biofilm),
(c) the culturing protocol (media and time of observation) was not appropriate, and
(d) the growth of bacteria in the sample was prevented or suppressed (for example by antibiotics).
The data from this paper suggest that in the 26 cases with positive cultures at a second surgery, the presence of bacteria at the initial revision may have been missed for reasons b, c, or d.
The data from this paper suggest that in the 26 cases with positive cultures at a second surgery, the presence of bacteria at the initial revision may have been missed for reasons b, c, or d.
For us the bottom line is that patients who are suspected of having a PJI may need to be treated as if they were infected (i.e. single stage or two stage prosthetic exchange with post op vigorous antibiotic treatment) in that the definitive evidence of infection will not be available until days or weeks after the patient leaves the OR. The presence of any of the factors in the chart above (except #2) and other factors (such as painful swelling of the joint, joint tenderness, fevers, chills etc) increases the suspicion of infection but does not prove it.
We are inclined to do a single or two stage exchange followed by the red protocol if our preoperative suspicion of infection is greater that 25%.
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