Does Cutibacterium skin load impact the outcomes of primary shoulder arthroplasty?

Cutibacterium is the most common bacteria recovered from shoulder prosthetic joint infections (PJIs). The correlation between Cutibacterium skin load at the time of primary shoulder arthroplasty and patient-reported outcomes and incidence of PJI has not been investigated. The purpose of this study was to evaluate the correlation of Cutibacterium load in (1) the unprepared skin surface and (2) the freshly incised dermal wound edge during primary shoulder arthroplasty with patient-reported outcomes and reoperation rate.

Cultures were obtained of the unprepared skin overlying the surgical incision and from the freshly incised dermal wound edge in patients undergoing primary shoulder arthroplasty (ream-and-run [RnR], anatomic total shoulder arthroplasty [aTSA], and reverse total shoulder arthroplasty [rTSA]) with a minimum of 2-year follow-up. A semi-quantitative assessment of the load of bacteria in each culture was used, assigning a value based on the report from the microbiology laboratory: 0 for "no growth"; 0.1 for "growth of 1 colony only" or for "growth in broth only"; and 1, 2, 3, and 4 for 1+, 2+, 3+, and 4+ growth, respectively. Univariate and multivariate regression models and Kendall tau rank correlation were used to assess the relationship between Cutibacterium value with patient-reported outcomes and revision surgery. Data were analyzed for all total shoulder arthroplasties (TSAs) (aTSA + rTSA) and RnRs separately.

Two hundred and fifty-six patients were included, consisting of 119 RnRs and 137 TSAs (105 aTSAs and 32 rTSAs). The average follow-up was 3.9 ± 1.3 years. In TSA patients, higher skin surface Cutibacterium loads were weakly associated with higher preoperative simple shoulder test (SST) scores (Tau = 0.196; P = .004) and postoperative SST scores (Tau = 0.140; P = .044). In RnR patients, skin surface Cutibacterium load was weakly associated with higher postoperative SST scores (Tau = 0.155; P = .048) and dermal wound edge load was weakly associated with higher percent of maximal possible improvement (Tau = 175; P = .024) on univariate analysis. There were no other statistically significant associations between Cutibacterium load and patient-reported outcomes. Neither skin surface nor dermal wound edge bacterial load was significantly associated with reoperation rate. Only 1 enrolled patient was diagnosed with PJI.

The clinical significance of Cutibacterium load in the skin remains poorly understood. In this study, Cutibacterium skin load was not strongly associated with clinical outcomes and reoperation rate. Longer-term follow-up is necessary to better understand the clinical significance of Cutibacterium skin load and risk of PJI.