<p class="abstract"><span lang="EN-CA">We report a case of postoperative osteoarthritis infection caused by <em>P. acnes</em> after shoulder arthroscopy<em>, and review possible preventive action. </em>A right-handed 24-year-old man presented an anterior instability of the left shoulder. The patient underwent an anterior stabilization by the latarjet procedure. Stabilization failed, requiring a second and third surgery. The patient returned 10 months later for suspected septic arthritis of his left shoulder. An arthroscopy lavage with bacteriological and anatomo-pathological sampling was carried out. The bacteriological results revealed a positive <em>P. acnes</em> culture. The patient was treated using antibiotherapy for 12 weeks with a combination of clindamicin and moxifloxacin. C-reactive protein (CRP) was negative two months after the onset of antibiotherapy. <em>P. acnes</em> is a anaerobic, non-sporulated, gram-positive bacillus. This commensal germ is part of the normal cutaneous flora and causes acne, but has also been recognized as a causative pathogen in osteoarticular infections since the 1990s, as described by Coden<strong>.</strong> Treatment is achieved via surgical debridement and intravenous antibiotics. We insist on preventive action in the form of a preoperative patient preparation protocol. Previous literature has underlined the important role of chlorhexidine or alcoholic iodinated polyvidone in the prevention of these infections. As <em>P. acnes</em> is a commensal germ of the patient's skin, prophylaxis should be reinforced by the thorough preparation of the surgery and surgical site. Clindamycin antibioprophylaxy specific to this germ should be administered for this surgery. To my knowledge, there is no specific antibioprophylaxy for shoulder surgery to date</span><span lang="EN-IN">.</span></p>