Botulinum Toxin Type A for Postoperative Scar Prevention: A Systematic Review and Meta-analysis.

Postoperative scars may impair quality of life. Prophylactic botulinum toxin type A (BoNT-A) may reduce scarring, but optimal timing, dose density, injection plane, and anatomic indications remain uncertain. This systematic review and meta-analysis evaluated prophylactic BoNT-A for postoperative scar prevention and examined effect modification by timing, dose density, and anatomic site; injection-plane practices were summarized descriptively. Four databases were searched through January 2026 for comparative trials of perioperative or postoperative BoNT-A administration. Random-effects meta-analysis used standardized mean differences (SMDs); subgroup analyses and meta-regression examined timing, dose density, and anatomic site. Seventeen studies (656 treatment sites; 456 participants) were included. BoNT-A improved clinician composite scores (SMD, -0.864; 95% CI, -1.137 to -0.591; low certainty), clinician VAS (SMD, -0.951; 95% CI, -1.468 to -0.434; very low certainty), and objective scar width (SMD, -0.924; 95% CI, -1.119 to -0.728; moderate certainty). Exploratory pooled analyses using the original study-level timing assignments suggested a larger effect with delayed injection (SMD, -1.240; moderate certainty) than with immediate injection (SMD, -0.559; low certainty). Timing and anatomic site jointly accounted for 81% of heterogeneity (P = .0008), with effects largest in chest and smallest in fine facial sites. Moderate-certainty evidence supports reduced objective scar width; clinician composite scales improved with low certainty. Pooled clinician-composite analyses suggested larger effects with delayed injection, although direct within-site timing studies have reported conflicting findings. Immediate-injection evidence and patient-reported outcomes remain uncertain, and cross-study dose escalation within 4-10 U/cm was not associated with additional benefit.