Fig. 4A–B.
(A) When acetabular abduction is α°, the distance between the inferior point of 40° abduction and the TAN (D1) is |2 × π × 52 mm × (α° − 40°) ÷ 360°| = |0.91 × (α − 40)| mm ≒ |α − 40| mm. (B) Likewise, when acetabular anteversion is β°, the distance between the anterior point of 15° anteversion and the AAN (D2) is |β − 15| mm.