This case report focuses on a 17-year-old polytrauma patient who suffered a septic wound infection after an open reduction and internal fixation (ORIF) and soft tissue reconstruction with a pedicled flap, which led to a substantial bone and soft tissue defect of the lower leg. After thorough antibiotic treatment and after ensuring a non-septic wound, the defect was reconstructed using a contralateral free fibula flap designed as a flow through flap in a double loop manner to accommodate two fibular fragments and an ipsilateral ALT flap. Early weight bearing was initiated 11 days after the free flap transfer under external fixation, with full weight bearing achieved in 36 days with external fixation. After the removal of external fixation, full weight bearing was able to be reinitiated after 13 days, leading to the patient’s return to normal activity 6 months after the bony reconstruction. This case presents an innovative approach to treating a complex defect, with the final decision on using two separate free flaps instead of a single osteofasciocutaneous free flap resulting in a good bony reconstruction and soft tissue coverage, and with the use of external fixation enabling early rehabilitation.