Here are 10 things we think we know about shoulder PJI
1. A pragmatic definition of PJI is "bacteria doing harm", thus the diagnosis depends on identification of a causative organism and the demonstration of harm to the shoulder. A 'culture-negative infection' does not meet this definition. Neither does the isolation of an organism from a normally functioning shoulder.
2. Cutibacterium is the most common organism causing periprosthetic infection of the shoulder.
3. Cultures for Cutibacterium are not finalized until 2-3 weeks after surgery, so the results cannot be used to guide operative or post-operative antibiotic therapy. Cultures from a revised shoulder can be characterized in terms of the Shoulder Cutibacterium Score: the sum of the Cutibacterium values for each specimen from the shoulder ( 0 = no-growth, 0.1 = broth only or one colony only, 1 = 1+ growth, 2 = 2+ growth, 3 = 3+ growth).
4. A substantial presence of Cutibacterium in a revised shoulder is indicated by ≥ 2 positive cultures for Cutibacterium and a Shoulder Cutibacterium Score > 1.
5. Cutibacterium are not evenly distributed throughout the shoulder. Culturing prosthetic explants increases the yield of positive cultures because of the tendency of this bacterium to form biofilms on prosthetic surfaces.
6. No preoperative test of serum (WBC, ESR, C-reactive protein, D-dimer) or joint fluid can rule out the presence of a Cutibacterium PJI.
7. Cultures of preoperative arthroscopic or open biopsies cannot rule out the presence of a Cutibacterium PJI.
8. Intraoperative histology of frozen sections cannot rule out the presence of a Cutibacterium PJI.
9. The suspicion of a Cutibacterium PJI is increased in young, male patients who had initially satisfactory return of comfort and function after their arthroplasty followed by the unexplained onset of pain and stiffness (a "honeymoon preriod), in patients taking supplemental testosterone, and in patients with high levels of Cutibacterium on the unprepared skin of the shoulder.
10. Single stage revision followed by a course of intravenous antibiotics is effective in resolving many cases of Cutibacterium periprosthetic infections, but some cases - especially those with high loads of Cutibacterium on the skin and in the shoulder - can be refractory to this treatment.
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