E. Mayr, O. Kessler, A. Prassl, F. Rachbauer, M. Krismer, and M. Nogler, “The frontal pelvic plane provides a valid reference system for implantation of the acetabular cup: Spatial orientation of the pelvis in different positions”, ActaO, vol. 76, no. 6, pp. 848–853, Jan. 2005.