Complications of Free Flap Reconstruction in Maxillary and Mandibular Defects: A Systematic Review and Meta-Analysis

<b>Background:</b> Microvascular osseous free flaps play a central role in head and neck reconstruction; surgeons often rely on fragmented and inconsistently reported data when counselling patients and planning reconstructive strategies. This systematic review and meta-analysis aimed to quantify postoperative complication rates and to evaluate complication patterns according to flap type. <b>Methods:</b> The study protocol was registered in PROSPERO (CRD420251237516). Studies published between January 2000 and November 2025 reporting postoperative complications following mandibular or maxillary reconstruction with osseous free flaps were identified. Eligible studies included adult cohorts with a minimum sample size of twenty patients. Random-effects meta-analyses of proportions were conducted. Risk of bias was assessed using the ROBINS-I tool. <b>Results:</b> Fourteen retrospective studies encompassing 1198 flaps were included. The pooled incidence of total flap loss was 6% (95% CI 3-9%), and partial flap loss was 6% (95% CI 3-10%). The pooled rates for postoperative infection, fistula formation, and wound dehiscence were 7% (95% CI 2-22%), 12% (95% CI 7-20%), and 16% (95% CI 8-31%), respectively, with substantial heterogeneity. Fibular free flaps demonstrated pooled rates of 6.1% for total flap loss, 6.6% for partial flap loss, 9.0% for infection, 10.4% for fistula formation, and 17.1% for wound dehiscence. For scapular free flaps, pooled total flap loss was 5% (95% CI 1-29%). DCIA flaps demonstrated hardware-related complications (8.1%), fistulas (16.7%), bone exposure (4.2%), and wound dehiscence (29.7%). Donor site morbidity was inconsistently reported and could not be quantitatively synthesized. <b>Conclusions:</b> Osseous free flap reconstruction shows relevant complication rates, highlighting the need for standardized reporting to support evidence-based decision-making.