Single Versus Double Drainage After Modified Radical Mastectomy: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

Background: Modified radical mastectomy (MRM) with axillary lymph-node dissection frequently leads to postoperative seroma formation, prompting the routine use of closed-suction drainage. While standard practice traditionally involves placing two drains, one axillary and one pectoral/sub-flap, this approach increases patient discomfort and limits mobility. A single-drain strategy may alleviate this burden, but concerns persist that inadequate drainage could increase the risk of seroma. Methods: A comprehensive search across five databases was conducted up to 10 August 2026 for randomized controlled trials (RCTs) comparing single axillary drainage with double (axillary plus pectoral/sub-flap) drainage after MRM. The primary outcome was postoperative seroma formation. Risk ratios (RR) and mean differences (MD) with 95% confidence intervals (CI) were pooled using a random-effects model, and the certainty of evidence was rated using the GRADE approach. Results: Nine RCTs involving 856 patients were included. There was no statistically significant difference between single and double drainage regarding the incidence of postoperative seroma (RR: 1.13, 95% CI [0.86, 1.47]; p = 0.37; low certainty), corresponding to 30 more seromas per 1000 patients (95% CI: 33 fewer to 110 more). Also, the strategies yielded comparable outcomes for the volume of aspirated seroma (MD: 0.19 mL; p = 0.97) and the number of post-removal aspirations (MD: 0.13; p = 0.32). Total drain output, drain duration, and the risk of complications, including hematoma (RR: 2.01; p = 0.27), flap necrosis (RR: 0.72; p = 0.36), and surgical site infection (RR: 0.75; p = 0.60), did not differ significantly between the two groups. Conclusions: Single axillary drainage after MRM was not associated with significant differences in postoperative seroma formation, aspirated seroma volume, number of seroma aspirations, total drain output, drain duration, hematoma, flap necrosis, or surgical-site infection compared with double axillary plus pectoral/sub-flap drainage. However, the certainty of evidence was low for most outcomes and the confidence intervals were compatible with clinically relevant differences, so equivalence cannot be concluded; adequately powered trials with standardized seroma definitions and patient-centered outcomes are needed.