Surg Radiol Anat (2007) 29:29–35 DOI 10.1007/s00276-006-0167-z 13 ORIGINAL ARTICLE Assessment of cup position from plain radiographs: impact of pelvic tilting M. Haenle · A. Heitner · W. Mittelmeier · R. Barbano · R. Scholz · E. Steinhauser · R. Bader Received: 5 February 2006 / Accepted: 30 October 2006 / Published online: 10 January 2007 © Springer-Verlag 2006 Abstract The acetabular cup position after total hip arthroplasty (THA) regarding its inclination and ver- sion angles are inXuential parameters concerning the postoperative range of motion and dislocation stabil- ity. Standard anterior-posterior X-rays remain an important diagnostic instrument to observe the post- operative outcome and to secure quality control after THA, where an optimal positioning of the patient is recommended when taking these X-rays. The purpose of this preliminary study was to determine the eVect of pelvic tilting regarding the positioning calculation of the acetabular cup from standard radiographs using a modiWed method according to Pettersson et al. (Acta Radiol Diagn, 23:259–263, 1982). In our model experiment, we were able to show that pelvic tilting to either side causes a considerable diVerence between the radiographic and calculated version angles following approximately linear functions. However, pelvic tilting to either side, leads, regarding the calculation of the inclination, to an average devia- tion between radiographic and calculated inclination angles less than 2°. Keywords Total hip arthroplasty · Dislocation · Acetabular cup position · Experimental model · Anteversion Introduction The position of the acetabular cup is a crucial parame- ter for the range of motion and stability against dislo- cation after total hip arthroplasty (THA) [3, 4, 8, 9, 11]. In order to be able to determine the postoperative position of the implanted cup, either a computer- tomography analysis can be carried out or the position of the acetabular cup (inclination and anteversion) can be calculated by using easier accessible plain stan- dard radiographs. Standard radiographs remain to be widely accepted as a postoperative control after total hip arthroplasty. Various methods have been put for- ward in order to evaluate the inclination and version angles of acetabular cups on standard radiographs [1, 7, 20, 21, 23]. It has already been mentioned that the tilting of the pelvis inXuences the evaluation of the position of the acetabular cup [12, 15]. A change of the acetabular anteversion of healthy persons when tilting the pelvis has also been described [25]. Thereby, an increased ventral tilting of the pelvis has been reported when changing from the sitting to the stand- ing position [12], and from standing to the lying posi- tion [5]. Lazennec et al. [13] have developed a method to determine the acetabular cup position in both the transverse and sagittal planes during standing and sit- ting positions. The impact of the tilting of the pelvis upon the evaluation of the inclination, and version angles has already been described by Pettersson et al. [20], however, it has not been quantiWed. The impact M. Haenle (&) · A. Heitner · W. Mittelmeier · R. Barbano · R. Bader Orthopädische Klinik und Poliklinik, Universität Rostock, Doberaner Straße 142, 18057 Rostock, Germany e-mail: maximilian.haenle@med.uni-rostock.de R. Scholz Klinik und Poliklinik für Orthopädie, Universität Leipzig, Leipzig, Germany E. Steinhauser Klinik für Orthopädie und Unfallchirurgie, Technische Universität München, München, Germany