Validation of a computer navigation system and a CT method for determination of the orientation of implanted acetabular cup in total hip arthroplasty: A cadaver study

Background. Successful hip reconstruction to restore the normal hip biomechanics requires precise placement of implants. Computer assisted navigation ill total hip arthroplasty has been proposed to have file potential to help achieve it high accuracy ill implant placement. The goal Of file Study was to evaluate file accuracy Of an imageless computer navigation system oil cadavers and to validate it non-invasive computed tomography method for post-operative determination of acetabular cup orientation. Methods. Total hip arthroplasty was performed oil seven cadaver hips with file aid of all imageless computer navigation system. The achieved cup orientation were recorded using three methods. (1) intra-operatively using file imageless computer navigation system, (2) post-operatively with direct bone digitization and (3) with it computed tomography based three dimensional model interpreted by three raters. Measurements from the direct bone digitization was taken as the gold standard to evaluate file other two methods. The intra-rater and inter-rater consistency of file computer tomography-model method were assessed by Cronbach's alpha determination. Findings. Compared with the cup orientation obtained front the direct bone digitization, file average difference for anteversion and abduction were 3.3 (3.5)degrees (P = 0.045) and 0.6 (3.7)degrees, respectively, for navigation reading. The average differences for computer tomography-model for three raters were 0.5 (2.1)degrees, 0.8 (1.5)degrees and 3.2 (3.3)degrees (P = 0.043) for anteversion and 0.4 (1.6)degrees, 0.3 (1.6)degrees and 2.1 (2.7)degrees for abduction. The intra-rater consistency ranged front 0.626 for a novice rater to over 0.97 for experience raters. The inter-rater consistency (including novice and experienced raters) was over 0.90. Interpretation. While file values for cup orientation determined with imageless computer navigation were comparable to those from direct bone and implant digitization, the measurement for anteversion obtained was not as accurate as that for abduction. The proposed computer tomography-model method has an excellent intra-rater consistency for experienced raters, its well as an excellent overall inter-rater consistency. The study confirms that it non-invasive computed tomography based model analysis call be used ill clinical practice as it valid method for post-operatively evaluating the orientation of the acetabular component. (C) 2008 Elsevier Ltd. All rights reserved.