Cutibacterium acnes (C. acnes) is an anaerobic aerotolerant bacteria commonly isolated during revision shoulder surgery. It is increasingly recognized as a pathogen, mainly in implant-related infections. As an anaerobe, it usually needs a prolonged culture incubation time of up to 14 days for growth and the association between implant surgery and C. acnes infection is not always obvious. Unfortunately, prolonged incubation also increases the risk of false positive cultures in isolating organisms that may exist as a result of contamination. Given high rates of positive C. acnes cultures in cases of both primary and revision shoulder surgery, the ramifications of positive C. acnes cultures for clinical decision making remains uncertain.

The purpose of this study is to prospectively study the efficacy and side-effect profile of surgical treatment plus an oral antibiotic regiment for shoulder PJI with indolent organisms (C. acnes and CNS).

Inclusion Criteria:

1. all patients undergoing single-stage revision arthroplasty with all implants exchanged,
2. all patients undergoing single-stage revision arthroplasty with some implants retained,
3. all patients undergoing explantation of a shoulder arthroplasty and placement of an antibiotic spacer

Exclusion Criteria:

1. patients with polymicrobial infection,
2. patients with infection by organisms other than P. acnes or Coagulase Negative Staphylococcus,
3. patients with clinical suspicion of infection but negative cultures,
4. patients with no preoperative or intraoperative signs of infection and only 1 positive culture.