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Measurement of acetabular cup orientation in total hip arthroplasty using a volume registration technique
International Congress Series 1268 (2004) 1298
Measurement of acetabular cup orientation in total hip arthroplasty using a volume registration technique W. Yamanashi *, N. Sugano, Y. Watanabe, Y. Sato, T. Nishii, H. Miki, H. Yoshikawa Department of Orthopaedic Surgery, Osaka University Graduate School of Medicine, 2-2 Yamadaoka, Osaka 565-0871, Japan
1. Introduction The purpose of this study is to measure the postoperative acetabular cup orientation in THA based on the reference of the preoperative pelvic coordinate system using a volume registration technique combined with preoperative and postoperative CT images. 2. Methods Postoperative CT images of 18 patients who underwent THA using our CT-based navigation system were obtained. CAD models of the acetabular cup (AnCAFit; Cremascoli-Wright, Italy) were converted to voxel data sets with 0.82 0.82 0.82-mm voxels. The voxel data sets of the acetabular cup that had been implanted in each patient were registered to postoperative CT images using a volume registration technique. Postoperative CT images without scatters from the metal cup were registered to preoperative CT images using the volume registration technique. The two resultant matrixes of the registrations were calculated to measure the postoperative acetabular cup orientation based on the reference coordinate system of the preoperative CT images. Measurements of the postoperative acetabular cup orientation using this method were compared with the corresponding acetabular cup orientation measured intraoperatively using the CT-based navigation system. 3. Results and conclusion The average abduction angle of the acetabular cup measured on the postoperative CT images according to the pelvic coordinates in the preoperative CT images was 41.5j with standard deviation of 2.3j. The average anteversion angle of the acetabular cup was 22.9j with standard deviation of 5.3j. The difference between intraoperatively measured acetabular cup orientation using the navigation system and postoperatively measured acetabular cup orientation was mean 1.5j with standard deviation of 0.9j for abduction, and was mean 3.3j with standard deviation of 2.1j for anteversion. This measurement method using the volume registration technique enabled us to evaluate the clinical accuracy of the cup navigation in theoretically most accurate way.
* Corresponding author. Tel.: +81-6-6879-3552; fax: +81-6-6879-3559. E-mail address: [email protected] (W. Yamanashi). 0531-5131/ D 2004 Published by Elsevier B.V. doi:10.1016/j.ics.2004.03.082
Measurement of acetabular cup orientation in total hip arthroplasty using a volume registration technique W. Yamanashi *, N. Sugano, Y. Watanabe, Y. Sato, T. Nishii, H. Miki, H. Yoshikawa Department of Orthopaedic Surgery, Osaka University Graduate School of Medicine, 2-2 Yamadaoka, Osaka 565-0871, Japan
1. Introduction The purpose of this study is to measure the postoperative acetabular cup orientation in THA based on the reference of the preoperative pelvic coordinate system using a volume registration technique combined with preoperative and postoperative CT images. 2. Methods Postoperative CT images of 18 patients who underwent THA using our CT-based navigation system were obtained. CAD models of the acetabular cup (AnCAFit; Cremascoli-Wright, Italy) were converted to voxel data sets with 0.82 0.82 0.82-mm voxels. The voxel data sets of the acetabular cup that had been implanted in each patient were registered to postoperative CT images using a volume registration technique. Postoperative CT images without scatters from the metal cup were registered to preoperative CT images using the volume registration technique. The two resultant matrixes of the registrations were calculated to measure the postoperative acetabular cup orientation based on the reference coordinate system of the preoperative CT images. Measurements of the postoperative acetabular cup orientation using this method were compared with the corresponding acetabular cup orientation measured intraoperatively using the CT-based navigation system. 3. Results and conclusion The average abduction angle of the acetabular cup measured on the postoperative CT images according to the pelvic coordinates in the preoperative CT images was 41.5j with standard deviation of 2.3j. The average anteversion angle of the acetabular cup was 22.9j with standard deviation of 5.3j. The difference between intraoperatively measured acetabular cup orientation using the navigation system and postoperatively measured acetabular cup orientation was mean 1.5j with standard deviation of 0.9j for abduction, and was mean 3.3j with standard deviation of 2.1j for anteversion. This measurement method using the volume registration technique enabled us to evaluate the clinical accuracy of the cup navigation in theoretically most accurate way.
* Corresponding author. Tel.: +81-6-6879-3552; fax: +81-6-6879-3559. E-mail address: [email protected] (W. Yamanashi). 0531-5131/ D 2004 Published by Elsevier B.V. doi:10.1016/j.ics.2004.03.082