Fig. 2

Illustration of the model of a contracted digit. For simplifying the calculation, make line P'’ = P + H (the combined length of line P and line H; purple line). Triangle CDE is the area of the digital artery-based V–Y advancement flap. The distance from the midpoint of the middle phalanx to its base on the contralateral hand is labelled as L'. The same interval on the affected injured finger is named L (\(\overline{AC }\); orange dashed line). Line P (\(\overline{BC }\); red line), length of proximal phalanx; line M (\(\overline{AB }\); blue line), half of length of middle phalanx; and line W (\(\overline{CD }\); yellow line), width of digital base. When Line H (\(\overline{FE }\); brown line) = 1.5 W, α (angle of flap apex) = ∠CED = 36.9°. Angle θ (angle of limitation of extension in the PIP joint with flexion contracture) = ∠ABC