Surface to Perforator Index: Assessing the Importance of the Number of Perforators in Successful Harvesting of the Anterolateral Thigh Flap.

Background:  The use of perforator flaps has become more popular with improvement of surgical technique, technology, as well as understanding of microvascular anatomy. The selection of well-perfused angiosomes is critical to the successful outcome of patients undergoing free tissue transfer. The number of perforators that are needed is dependent upon the surface area of the flap being harvested; however, there have been no studies to assess the optimal surface area supplied by each perforator. We hypothesized that the smaller the surface area supplied by each perforator correlated with fewer flap-related complications in the harvesting of the anterolateral thigh (ALT) flap.

Methods:  All ALT flaps harvested from 2015 to 2021 at our institution were retrospectively reviewed. The surface area of the flap harvested was calculated as  = π, where is the long radius and is the short radius of the ellipse. The surface-perforator index (SPI) was calculated for each flap by dividing the surface area of the ALT flap by the number of perforators supplying the flap. Our primary outcomes were flap-related complications that included: partial flap loss, dehiscence, and venous congestion.

Results:  A total of 106 patients were identified. Twenty-four patients (22.6%) developed perforator-related complications. An increasing SPI and SPI to body surface area were strongly associated with development of complications (adjusted odds ratio [95% confidence interval], adjusted : 1.02 [1.01, 1.03], < 0.001and 1.23 [1.12, 1.42],  < 0.001). An SPI of greater than 150 cm/perforator was associated with a higher probability of complications ( < 0.001).

Conclusion:  Flap-related complications are significantly related to the number of perforators supplying the flap. The smaller the surface area supplied by a single perforator correlates with significantly fewer flap-related complications. SPI is a new index that may be used as a predictive tool to aid in identifying flaps that may be more prone to complications in free tissue transfer.