Minimal number of cultures needed to detect Cutibacterium acnes in primary reverse shoulder arthroplasty: a prospective study

Unexpected positive cultures of humeral head detected with dithiothreitol in primary shoulder arthroplasty

BACKGROUND

Unexpected positive cultures (UPCs) are frequently observed in primary shoulder arthroplasty, and its clinical significance has not yet been well defined. This study aimed to evaluate the UPCs in humeral head in primary shoulder replacement and to understand if UPCs increase in patients with risk factors for contamination (previous surgery or infiltrations).

METHODS

Patients undergoing total shoulder replacement were enrolled in this prospective observational study. To reduce the risk of humeral head contamination, all known procedures to reduce Cutibacterium acnes burden of the skin were implemented. Patients were divided into 2 groups, namely, patients who had undergone previous rotator cuff repair or infiltration and patients with no risk factors for contamination. All the humeral heads harvested were treated with dl-dithiothreitol, in a specific device (MicroDTTect), to increase the sensitivity of the cultures for bacterial identification. The cultures were analyzed for aerobic and anaerobic bacteria for up to 14 days.

RESULTS

The UPCs' positivity rate of the 80 patients in the study was 19% (15 patients). The positivity rates for UPCs in the group with and without risk factors were 30% (12 patients) and 7.5% (3 patients), respectively. The rate of positive culture was higher in men (87%) than in women (13%). The observed positivity was due to C acnes and Peptoniphilus asaccharolyticus, both slow-growing anaerobes.

CONCLUSIONS

Patients with previous surgery or infiltrations had a 4-fold higher rate of positivity for UPCs compared with patients without previous risk factors. The higher percentage of positivity in patients with risk factors could be related to changes in the joint microenvironment after shoulder procedures. We do not know whether the presence of UPCs could be associated with the development of periprosthetic infections at longer follow-up.

Vancomycin Soaking to Reduce Intraoperative Contamination by Cutibacterium acnes During the Latarjet Procedure

BACKGROUND

Postoperative infection after the Latarjet procedure, ranging from 1% to 6%, can compromise the functional outcome of young athletes. Cutibacterium acnes is a main pathogen as a consequence of an intraoperative contamination.

PURPOSE

To evaluate intraoperative contamination with C. acnes and the effectiveness of the local application of vancomycin during the Latarjet procedure.

STUDY DESIGN

Cohort study; Level of evidence, 2.

METHODS

This was a single-center study including 75 patients (mean age, 26 years; range, 15-55 years) operated on for anterior shoulder instability with the primary open Latarjet procedure; they underwent the same protocol of skin preparation and preoperative prophylactic antibiotics. Three groups of 25 patients were created and divided sequentially, without the results of each group being known before the end of the study: group A (5 mg/mL of vancomycin), group B (20 mg/mL of vancomycin), and group C (control group with no vancomycin). Swab samples of the coracoid were taken before sectioning the coracoid process (time 1) and after its preparation (time 2). The coracoid was then wrapped in gauze impregnated with different concentrations of vancomycin, except for group C. A final sample (time 3) was taken before screwing the bone block onto the glenoid. All samples were cultured for 21 days, and patients underwent clinical and radiological follow-up for 6 months.

RESULTS

The C. acnes contamination rates at times 1, 2, and 3 were 25%, 44%, and 45%, respectively, without significant difference. There was no significant difference between groups A and B with respect to the number of positive cultures at each time point. Of 9 positive cultures at time 1, all were still positive at time 3 in group A, whereas 3 of 5 were negative in group B (P = .027). The rate of C. acnes at time 3 in the control group was higher than that in the 2 other groups (68% vs 44% for group A and 20% for group B; P = .003). Body mass index was the only prognostic factor for a C. acnes-positive culture (26.05 ± 3.39 vs 23.34 ± 2.33; P = .018). No clinical infection was reported at the 6-month postoperative follow-up.

CONCLUSION

The rate of C. acnes contamination ranged from 25% to 68% during the open Latarjet procedure in young athletes. Vancomycin reduced the bacterial contamination when it was used at high concentrations in a gauze wrap on the coracoid. The type of C. acnes detected and its clinical implications remain to be studied.

[Shoulder periprosthetic infections-what to do? : Diagnosis and treatment]

Treatment of an infected shoulder prosthesis differs significantly from other joint infections because of the unique microbiome, dominated by Cutibacterium acnes. The cause of an infection, its time of onset, the bacterial spectrum and comorbidities have to be considered for evaluation and treatment. The diagnostic workup is sometimes complex, and the recognition of a chronic and low-grade infection is often difficult because typical clinical and laboratory markers may be normal. Treatment is surgical; the therapeutic spectrum ranges from arthroscopic irrigation and open debridement with the exchange of components to one- and two-stage revisions using antibiotic-loaded spacers. Early detection and a targeted, appropriate therapy are crucial to avoid extensive soft tissue and bone damage.