Benzoyl Peroxide and Electrocautery Skin Incision to Eradicate Cutibacterium Acnes

Periprosthetic joint infection (PJI) following shoulder arthroplasty is not only detrimental to patients but also immensely burdensome on our healthcare system. The rate of PJI following shoulder arthroplasty is estimated between 0.80 and 1.46%, with the incidence expected to increase as shoulder arthroplasty continues to become more common. Cutibacterium acnes (C. acnes), a gram-positive anaerobe commonly found in sebaceous glands, is the most common causative organism behind PJI of shoulder arthroplasty. The human shoulder skin is heavily colonized with C. acnes, and studies showed that the current standard sterilization practices are not able to completely remove C. acnes from the surgical field. It is theorized that when skin incisions are made, the sebaceous glands in the skin are also cut open, releasing C. acnes and contaminating gloves, instruments, and eventually the surgical field during subsequent part of the procedure. Preventing C. acnes contamination could potentially decrease PJI significantly after shoulder arthroplasty.

Electrocautery has been routinely used for tissue dissection and hemostasis. Studies have demonstrated the safety and efficacy of electrocautery for making skin incisions as an alternative to a scalpel blade. It is hypothesized that the high temperatures generated at the tip of an electrocautery electrode might potentially heat up and destroy the exposed C. acnes at the incised dermal edge. This hypothesis has been recently proven in a randomized clinical trial conducted at the investigators' institution. Cultures taken from the incised dermal edge immediately after making skin incision with electrocautery resulted in zero positive C. acnes culture compared to a 31% positive culture rate observed with incisions made with scalpel blades. Although it appeared that electrocautery initially eliminated C. acnes from the incision sites, cultures taken from surgeon's gloves and instruments towards the end of the case were found to be positive for C. acnes. All positive cultures were exclusively from male patients. It remains to be answered whether the benefits of electrocautery are only temporary or if the skin surrounding the incision site remains a source for potential contaminant bacteria that current skin prep methods are unable to address.

Topical benzoyl peroxide (BPO) has been widely used as an agent for acne vulgaris, also caused by the same C. acnes bacterium. Studies have investigated the benefits of topical BPO application before open shoulder procedures in reducing C. acnes colonization at the surgical site skin. Compared to conventional skin prep methods, the addition of BPO was found to be significantly more effective in reducing C. acnes from the skin. Based on this finding, it seems to be an interesting yet logical hypothesis that combining topical BPO with electrocautery skin incision might have a synergistic effect against C. acnes. However, no studies to date have sought to examine this hypothesis. To this end, the investigators propose a prospective randomized clinical trial to test this hypothesis through the following specific aim.

Specific Aim: To investigate whether a topical BPO skin prep combined with electrocautery skin incision will lead to a critical reduction of positive C. acnes culture rates in the surgical field compared to electrocautery skin incision alone in shoulder arthroplasty patients.

Methods: Sixty-four male patients (based on a priori sample size calculation) undergoing primary shoulder arthroplasty will be randomized into 2 groups - electrocautery incision alone vs. electrocautery incision combined with BPO skin prep. The investigators will obtain a swab culture for C. acnes from the incised dermal edge immediately after skin incision, and then toward the end of procedure (immediately before humeral component insertion), the investigators will obtain another set of cultures from the incised dermal edge, surgeon's gloves, and joint synovium. The primary outcome measure will be the positive culture rates for C. acnes compared between the 2 groups.

Hypothesis: Compared to the electrocautery incision alone group, the group that receives electrocautery incision combined with BPO skin prep will yield significantly lower positive culture rates for C. acnes in the samples taken later during the procedure, but not in the samples taken from the dermal edge immediately after skin incision.

Expected outcomes and impact: It is expected that the combination of electrocautery skin incision and BPO will lead to a significant reduction of C. acnes positive culture rates in the surgical field. This study, if supported by the study finding, could potentially help understand the underlying mechanism of unexpected positive C. acnes cultures in shoulder arthroplasty and may provide a cost-effective solution for this common clinical problem.