The utility of routine autologous bone-flap swab cultures in predicting post-cranioplasty infection.

Objective: To evaluate the utility of autologous bone-flap swab cultures performed at the time of cranioplasty in predicting postcranioplasty surgical site infection (SSI).

Design: Retrospective cohort study.

Participants: Patients undergoing craniectomy (with bone-flap storage in tissue bank), followed by delayed autologous bone-flap replacement cranioplasty between January 1, 2010, and November 30, 2020.

Setting: Tertiary-care academic hospital.

Methods: We framed the bone-flap swab culture taken at the time of cranioplasty as a diagnostic test for predicting postcranioplasty SSI. We calculated, sensitivity, specificity, positive and negative predictive values, and positive and negative likelihood ratios.

Results: Among 282 unique eligible cases, 16 (5.6%) developed SSI after cranioplasty. A high percentage of bone-flap swab cultures were positive at the time of craniectomy (66.7%) and cranioplasty (59.5%). Most organisms from bone-flap swab cultures were or coagulase-negative staphylococci (76%-85%), and most SSI pathogens were methicillin-susceptible (38%). Bone-flap swab culture had poor sensitivity (0.07; 95% CI, 0.01-0.31), specificity (0.4; 95% CI, 0.34-0.45), and positive likelihood ratio (0.12) for predicting postcranioplasty SSI.

Conclusion: Overall, autologous bone-flap swab cultures performed at the time of cranioplasty have poor utility in predicting postcranioplasty SSI. Eliminating this low-value practice would result in significant workload reductions and associated healthcare costs.