Misinterpretation of cup anteversion in total hip arthroplasty using planar radiography.
BACKGROUND
Anteroposterior pelvic radiographs are routinely used to monitor cup orientation in total hip arthroplasty (THA). Analysis of planar radiographs leads to a certain degree of measurement error for the cup anteversion (AV). With the current study, we wanted to clarify whether planar radiography can be used for accurate evaluation of the THA position.


METHODS
The postoperative orientation of pelvic implants in 42 patients was analyzed according to five documented mathematical algorithms using planar radiographs. Postoperative computed tomography (CT) pelvis scans were available for all patients. A CT-based navigation system was used to determine AV.


RESULTS
The comparison showed that all five formulas presented substantial variations for the AV angle. Of these, Widmer's algorithm presented the smallest difference compared to the CT. Misinterpretation of postoperative planar radiographs is a common problem in THA.


CONCLUSIONS
Planar radiographs are too imprecise for exact evaluation of the correct cup AV after THA. CT-based analysis may be necessary if exact values are required.
Marx
Axel
A
Department of Orthopaedic Surgery, University of Duisburg-Essen, Hufelandstr. 55, 45122 Essen, Germany. axel@marx.ac
von Knoch
Marius
M
Pförtner
Jörg
J
Wiese
Matthias
M
Saxler
Guido
G
D019644:Arthroplasty, Replacement, Hip; D003951:Diagnostic Errors; D005260:Female; D006622:Hip Prosthesis; D006801:Humans; D007719:Knee Joint / Q000000981:diagnostic imaging* / Q000601:surgery*; D008297:Male; D008433:Mathematics; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed