Abstract: Objective　To explore the clinical application and effect of keystone perforator flap in repairing the donor site defect of anterolateral thigh free flap. Methods　From February 2018 to December 2020, a total of 12 patients were treated with the keystone flap to repair soft tissue defects in the donor site of the anterolateral thigh free flap. The average defect in the flap donor site was 8.1 cm×14.4 cm (8.0 cm×11.0 cm to 9.0 cm×21.0 cm), and the average area of the designed keystone flap was 9.1 cm×16.4 cm (8.0 cm×13.0 cm to 12.0 cm×19.0 cm). The flap characteristics and postoperative complications were followed up. The flap appearance was analyzed by Vancouver Scar Scale (VSS) score and Scar Cosmesis Assessment and Rating (SCAR) score. Results　After an average follow-up of 8.3 months (6-12 months), 2 cases of skin infection around the flap were observed, the infection was controlled by wound dressing change and oral antibiotic treatment. None had osteofascial compartment syndrome (OCS), wound dehiscence, venous return disorder, or skin necrosis. The final follow-up ASS score was 6.8±0.9 and the SCAR score was 7.3±1.0, with satisfactory repair results. Conclusion　The keystone perforator flap is an effective repair method for donor site defect of anterolateral thigh free flap, which not only avoids various complications caused by tension suture but also brings good aesthetics.

Key words: Keystone flap, 　Free flap, 　Soft tissue defect, 　Donor site repair, 　Medical aesthetics