Validation of New Shoulder Periprosthetic Joint Infection Criteria
These authors point out that the 2018 International Consensus Meeting (ICM) on orthopedic infections has provided new criteria for classifying revised shoulders into "definite", "probable", "possible", and "unlikely" periprosthetic infection (PJI) of the shoulder.
They retrospectively reviewed 87 of their patients receiving a spacer made of antibiotic-loaded acrylic cement spacer from 2016 through 2019. In their practice spacers were placed for "suspected infection, mechanical loosening, failed hemi or anatomic total shoulder arthroplasty with massive rotator cuff tear, and failed shoulder arthroplasty with massive bone loss". In other words, many the patients receiving spacers in this series appear to not to have been suspected of having an infection.
Each case was categorized using the 2018 shoulder ICM criteria.
Based on the 2018 ICM criteria, 20 cases were classified as definite (30.0%), 19 as probable (21.8%), 6 as possible (6.9%), and 42 as unlikely (48.3%) infections. So, in effect, about half of the spacers were placed in shoulders not thought to be infected. Half of the cases had positive intraoperative cultures.
Cutibacterium acnes (C. acnes) was the most common infectious organism overall (77.3% of culture positive cases) and was present in 39.1% of cases overall.
Of the 34 patients in which Cutibacterium was thought to be the infectious organism, only 9 were classified in the "definite" category and 15 in the "probable" category with the remaining 10 as "possible" or "unlikely".
A 23 of 31 patients with loose humeral stem were classified as having definite or probable infection and 21 had at least one positive intraoperative culture.
The great majority of patients with elevated sedimentation rate and C-reactive protein were classified definite or probable infection (odds ratio of 11). Similarly, the great majority of patients with elevated synovial WBC count were classified definite or probable infection (odds ratio of 47).
Shoulders with positive frozen sections were usually classified as definite infections.
Preoperative joint aspirates did not appear to be useful in the classification of infections
Comment: For the revision arthroplasty surgeon, the challenge is not "classifying" revised shoulders. Rather the frequently encountered challenge is to estimate the likelihood of a periprosthetic infection before and at the time of surgery so that the surgery and postoperative antibiotics can be directed at managing the possibility of intraoperative cultures becoming positive during the weeks post op.
As this article points out, any evidence of acute inflammation (elevated CRP, ESR, fluids WBC) points to a high probability of infection. We refer to these as "obvious" infections. The problem lies with "stealth" infections.
The key question is "how can infection be anticipated in patients without elevated inflammatory markers?" Shoulder periprosthetic infections from Cutibacterium (Propionibacterium) often present as unexplained delayed onset of pain and stiffness in an otherwise successful shoulder arthroplasty (i.e. a "honeymoon period"). This scenario is addressed a recent article, Prognostic factors for bacterial cultures positive for Propionibacterium acnes and other organisms in a large series of revision shoulder arthroplasties performed for stiffness, pain, or loosening. In this study, 108 of 193 revision arthroplasties were associated with positive cultures; 70% of the positive cultures demonstrated growth of Cutibacterium. Fifty-five percent of the positive cultures required observation for more than one week. Male sex, humeral osteolysis, and cloudy fluid were each associated with significant increases of ≥ 600% in the likelihood of obtaining a positive Cutibacterium culture. Humeral loosening, glenoid wear, and membrane formation were associated with significant increases of >300% in the likelihood of obtaining a positive Cutibacterium culture.
Another recent article Preoperative Skin Cultures Predict Periprosthetic Infections in Revised Shoulder Arthroplasties found that the results of a simple culture of the unprepared skin surface obtained in a clinic prior to revision shoulder arthroplasty is of value in assessing the chances of a Cutibacterium periprosthetic infection. A preoperative clinic skin Cutibacterium value of >1 predicted the presence of a culture-positive Cutibacterium PJI with an accuracy of 89%, and a clinic skin Cutibacterium percentage of ≥75% predicted the presence of a culture-positive Cutibacterium PJI with an accuracy of 94%. For male patients, a preoperative clinic skin Cutibacterium value of >1 predicted the presence of a culture-positive Cutibacterium PJI with an accuracy of 91%, and a clinic skin Cutibacterium percentage of ≥75% predicted the presence of a culture-positive Cutibacterium PJI with an accuracy of 100%.
While there is no perfect set of tests that will predict the presence of multiple positive cultures obtained at the time of surgical revision of a failed arthroplasty, the combination of clinic skin cultures, preoperative x-ray findings and surgical findings provide substantial evidence on which the surgeon can plan intraoperative and postoperative management.
In our practice we consider a complete single stage exchange to a hemiarthroplasty followed by major antibiotic treatment in cases where the suspicion of a stealth infection is high. For obvious infections, failed single stage revisions, shoulders know to be infected with other bacteria, and shoulders with draining sinuses, we consider a spacer. It is worth noting that some of the commercially available spacers contain Gentamicin, which does not have good activity against Cutibacterium.
