Fig. 4.

a Forest plot and pooled relative risk of SSI development in patients undergoing non-instrumented spinal surgery who received both preoperative and extended postoperative AMP compared to patients who only received preoperative AMP. b Funnel plot of all studies with non-zero rates of SSI demonstrating a symmetric distribution of study estimates around the estimated true effect size. The small sample size limits the interpretation of this plot. RR relative risk, CI confidence interval, SSI surgical site infection, AMP antimicrobial prophylaxis