Thinning of the Medial Sural Artery Perforator Flap: The Anatomical Examination of the Medial Sural Artery Perforator Branch.

Background: The medial sural artery perforator (MSAP) flap is thin, pliable, and versatile. This study aims to understand the anatomical basis of the MSAP flap and the subcutaneous course of the perforator for safe flap thinning.

Methods: A total of 24 MSAP flaps were dissected under red silicone dye injection guidance. Full-thickness horizontal slides of flaps were performed, and the perforator courses were identified in the subcutaneous plane. Slides were placed on a millimeter board, and the perforator patterns were photographed and observed with loupes.

Results: A total of 68 perforator courses were identified: type 1: 30.9%, type 2: 57.3%, and type 3: 11.8%. They traveled 1-25 mm to the subdermal plexus, with percentile 2.5 at 1 mm, percentile 90 at 18.2 mm, percentile 95 at 21.65 mm, and percentile 100 at 25 mm. The mean flap thickness was 7.75 ± 1.7 mm, with an average of 5.7 ± 1.3 perforators per flap. Perforators clustered between 2 and 18.4 cm from the popliteal crease and 0-8 cm from the posterior midline of the leg. The dominant perforators accounted for 45.2% (62 of 137), averaging 2.58 per flap. The medial sural artery branching pattern types were type 1: 37.5%, type 2: 50%, and type 3: 12.5%. The average pedicle length was 16.2 ± 1.3 cm, and the mean external diameter of the medial sural artery was 1.98 ± 0.13 mm.

Conclusions: MSAPs branch within a maximal radius of 2.5 cm after emerging from the deep fascia. To maintain vascularity, the safe suprafascial dissection should be 2.5 cm apart from the point of emerging.