Validation of the triangular prism method using computed tomography to estimate DIEP flap weight in routine clinical practice - a St Andrew free flap audit registry study.

[INTRODUCTION] An accurate preoperative estimation of deep inferior epigastric perforator (DIEP) flaps in breast reconstruction facilitates planning. Different methods have been proposed, but few methods have been validated for the degree of agreement with harvested volume, and none have been validated in a more significant cohort. This article aimed to validate the triangular prism method using computed tomography (CT) to estimate DIEP weight in routine clinical practice.

[METHODS] The triangular prism method, previously described by Nanidis, Ridha, and Jallali, uses CT to estimate DIEP flap weight, used in clinical practice in the department, was evaluated. The study included 1 year of consecutive patients, and data were extracted from the department's free flap audit registry. Bland Altman plots with mean bias and limits of agreement (LOA) with confidence intervals were drawn to estimate agreement between the estimated and actual flap weight.

[RESULTS AND CONCLUSIONS] A total of 164 DIEPs were recorded, and complete data were available for 119 DIEPs (73%). The mean estimated flap weight was 979 g (range: 251-2,125, SD [standard deviation] 448), and the actual flap weight was 937 g (range: 303-2,792, SD 461). The Bland-Altman plot showed that the estimated weight overestimated the actual weight by an average of 41 grams. However, the LOAs of -530 and 614 grams far exceed the a priori set limits of maximum acceptable difference (100 grams) between the estimated and the actual flap weight. Further studies are needed regarding how the triangular prism method can be combined with clinical measurements to become an easily used and reliable tool.