Objective
Reconstruction of severe lower extremity injuries using free flaps has become a reliable approach. Numerous studies on free tissue transfer in lower extremity reconstruction have been well discussed, including selection of an appropriate donor flap, selection and algorithm of recipient vessels, vascular anastomosis methods, and vein grafting. According to our clinical experience, single free tissue transfer may not be adequate for functional recovery, especially for extensive soft tissue and bone defects in the lower extremity. Simultaneous or sequential double free tissue transfer for functional recovery is still warranted.

Material and Methods
A retrospective study was conducted from 2002 to 2021 at Chang Gung Memorial Hospital, Linkou Branch. Patients who underwent second free tissue transfer in purpose of functional recovery in lower limb reconstruction were included. Patients with lower limb tumor recurrence post wide excision were excluded. Demographics, comorbidities, defect characteristics, details of first and second free tissue transfer, complications, and secondary procedures were documented.

Results
A total of 31 patients with simultaneous or sequential double free tissue transfer in lower extremity reconstruction were included. The most common cause was trauma (95.8%) and the most common type of injury was crush injury (79.1%). The most common flap in the first free tissue reconstruction is anterolateral thigh flap (54.2%), and the most common flap in the second free tissue reconstruction is anterolateral thigh flap (33.3%), followed by fibula flap (20.8%). The most common recipient vessels were posterior tibial artery and vena comitans (33.3%) and anterior tibial artery and vena comitans (29.2%) in the first free tissue reconstruction. The most common recipient vessels were posterior tibial artery and vena comitans (41.7%) and anterior tibial artery and vena comitans (29.2%) in the second free tissue reconstruction. Soft tissue defect reconstruction took precedence over bone defect reconstruction in first free tissue transfer, compared to second free tissue transfer (p< 0.05). No significant difference in flap survival and the incidence of take-back between the first and second flap reconstruction.

Conclusion
The majority of the patients showed acceptable functional recovery after second free tissue transfer in lower extremity reconstruction. The second free tissue transfer optimizes clinical outcomes and particularly improves functional outcome in lower extremity reconstruction. Using the authors’ proposed algorithm for flap selection may help the reconstructive microsurgeons optimize functional recovery in the lower extremity reconstruction.

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