Accuracy of measuring acetabular cup position after total hip arthroplasty: comparison between a radiographic planning software and three-dimensional computed tomography.
Various methods are available for measuring acetabular cup position after total hip arthroplasty (THA) on standard anterior-posterior (AP) radiographs. We compared the accuracy of a commercial radiographic planning software program with that of three-dimensional computed tomography (3D-CT) scans.



We obtained plain AP radiographs and 3D-CTs from 65 patients after THA. In addition to calculating cup anteversion and inclination with 3D-CT, we determined the cup position using the radiographic planning software program mediCAD® 2.5 (Hectec, Niederviehbach, Germany). Furthermore, we compared the measurements using the inter-teardrop and bi-ischial lines as pelvic landmarks.



The mean difference in anteversion between 3D-CT and mediCAD® software was 0.1° using the inter-teardrop line (standard deviation [SD], 8.8°; range, -21° to 23°; p = 0.97) and 0.4° using the bi-ischial line (SD, 8.8°; range, -23° to 21°; p = 0.72). Inclination showed a mean difference of 0.6° using the inter-teardrop line (SD, 4.4°; range, -9° to 21°; p = 0.24) and 0.5° using bi-ischial line (SD, 4.6°; range, -9° to 22°; p = 0.35). The means for absolute differences were 7.2° for anteversion and 3.1° for inclination. With regard to using the bi-ischial or inter-teardrop line, no significant difference was found between the two pelvic landmarks. The intra-class correlation coefficient (ICC) was analysed for anteversion and inclination using either the inter-teardrop line or the bi-ischial line as radiographic baseline.



A radiographic planning software program (mediCAD®) is a helpful tool for measuring cup inclination on AP radiographs. With respect to anteversion, measurements are rather susceptible to mistakes with mean inaccuracies of over 7°. Thus, 3D-CT remains the "gold standard" if a lower tolerance limit (±3°) is required for more complex biomechanical evaluations. As a pelvic landmark, the interteardrop line is preferential to the bi-ischial line because of its lower impact on the position of the pelvis.
Department of Orthopaedic Surgery, Regensburg University Medical Centre, Asklepios Klinikum Bad Abbach, Kaiser-Karl V.-Allee 3, 93077, Bad Abbach, Germany.
Vahdettin
V
Bayraktar
Department of Orthopaedic Surgery, Regensburg University Medical Centre, Asklepios Klinikum Bad Abbach, Kaiser-Karl V.-Allee 3, 93077, Bad Abbach, Germany.
Markus
M
Weber
Department of Orthopaedic Surgery, Regensburg University Medical Centre, Asklepios Klinikum Bad Abbach, Kaiser-Karl V.-Allee 3, 93077, Bad Abbach, Germany.
Frederik
F
von Kunow
Centre for Clinical Studies, Regensburg University Medical Centre, Franz-Josef-Strauß-Allee 11, 93053, Regensburg, Germany.
Florian
F
Zeman
Department of Orthopaedic Surgery, Regensburg University Medical Centre, Asklepios Klinikum Bad Abbach, Kaiser-Karl V.-Allee 3, 93077, Bad Abbach, Germany.
Benjamin
B
Craiovan
Department of Orthopaedic Surgery, Regensburg University Medical Centre, Asklepios Klinikum Bad Abbach, Kaiser-Karl V.-Allee 3, 93077, Bad Abbach, Germany.
Tobias
T
Renkawitz
Department of Orthopaedic Surgery, Regensburg University Medical Centre, Asklepios Klinikum Bad Abbach, Kaiser-Karl V.-Allee 3, 93077, Bad Abbach, Germany.
Joachim
J
Grifka
Department of Orthopaedic Surgery, Regensburg University Medical Centre, Asklepios Klinikum Bad Abbach, Kaiser-Karl V.-Allee 3, 93077, Bad Abbach, Germany. m.woerner@asklepios.com.
Michael
M
Woerner
D000077:Acetabulum / Q000000981:diagnostic imaging* / Q000601:surgery; D000368:Aged; D019644:Arthroplasty, Replacement, Hip / Q000379:methods*; D005260:Female; D006622:Hip Prosthesis; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008297:Male; D008875:Middle Aged; D010388:Pelvis / Q000000981:diagnostic imaging*; D015203:Reproducibility of Results; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed / Q000379:methods*
3D-CT; Acetabular cup orientation; Anteversion; Inclination; Pelvic landmark; Radiographic software; Total hip arthroplasty