A comparative study for tension-reducing effect of Type I and Type II keystone perforator island flap in the human back.

The keystone perforator island flap (KPIF) is popular in reconstructive surgery. However, despite its versatility, its biomechanical effectiveness is unclear. We present our experience of KPIF reconstruction in the human back and evaluate the tension-reducing effect of the KPIF. Between September 2019 and August 2020, 17 patients (51.82 ± 14.72 years) underwent KPIF reconstruction for back defects. In all cases, we measured wound tension at the defect and donor sites before and after KPIF reconstruction using a tensiometer. All defects occurred after complete excision of complicated epidermoid cysts and debridement of surrounding tissues. The defects were successfully covered with Type IIA KPIFs. All flaps survived, and there were no significant postoperative complications. The mean "tension change at the defect after Type I KPIF" and "tension change at the defect after Type II KPIF" were - 2.97 ± 0.22 N and - 5.59 ± 0.41 N, respectively, (P < 0.001). The mean "rate of tension change at the defect after Type I KPIF" and "rate of tension change at the defect after Type II KPIF" were - 36.54 ± 1.89% and - 67.98 ± 1.63%, respectively, (P < 0.001). Our findings confirm the stepwise tension-reducing effect of KPIF and clarify the biomechanics of this flap.