Assessment of Accuracy of Acetabular Cup Orientation in CT-Free Navigated Total Hip Arthroplasty

Abstract

We have used the Orthopilot (Aesculap AG, Tuttlingen, Germany) computed tomography (CT)-free navigation system to ensure accurate and reproducible acetabular cup orientation. In this system, cup orientation is assessed with respect to bony configuration as determined by palpation of the anatomical landmarks (the bilateral anterosuperior iliac spines and the upper margin of the pubic symphysis). In this study, intraoperative cup orientation as presented by the OrthoPilot navigation system was compared with the value obtained through postoperative radiological assessment using CT Digital Imaging and Communications in Medicine (DICOM) data and Medical Image Processing, Analysis, and Visualization (MIPAV; National Institutes of Health, US Department of Health and Human Services, Bethesda, Maryland). Intra- and postoperative results obtained from 27 consecutive navigated total hip arthroplasties (THAs) were analyzed. For cup positioning, the desired inclination and anteversion angles were set within the “safe zone” proposed by Lewinnek. In the intraoperative evaluation, the mean inclination angle as determined by the navigation system was 43.5° ± 2.17° (range, 39.9° to 46.6°) after the final implantation. In contrast, the mean inclination angle determined by postoperative calculation using MIPAV was 44.9 ± 3.3° (range, 38.1° to 55.0°). A discrepancy of >5° was observed in only 1 hip. For the anteversion, the mean intra- and postoperative values were 11.1° ± 5.6° (range, 0° to 17.8°) and 13.5° ± 5.9° (range, 5.1° to 21.6°), respectively. Again, a discrepancy of >5° was observed in 1 case. Mean differences between the intra- and postoperative values were 1.9° ± 1.9° and 2.6° ± 1.6° for inclination and anteversion, respectively. A good agreement between the intraoperative values presented by the navigation system and those in the postoperative CT evaluation was observed, and the validity of this navigation system was confirmed.

Accuracy of acetabular cup positioning using imageless navigation

“…Our results compare favorably with these previous studies, although only Fununkashi et al [19] (one patient with a discrepancy of > 5 0 degrees) and Dorr et al [12] (no outliers) reported outliers. In contrast to the previous authors [12,17-19], we documented similar differences but we have observed more frequent cup placements with a discrepancy of > 5 0 degrees.…”

“…In contrast to the previous authors [12,17-19], we documented similar differences but we have observed more frequent cup placements with a discrepancy of > 5 0 degrees. It may therefore be more important to report on the numbers of outliers rather than documenting mean differences, ranges and standard deviations.…”

Combined anteversion of the total hip arthroplasty implanted with image-free cup navigation and without stem navigation

“…The accuracy of the image-free THA cup navigation system has been assessed and reported in several clinical studies and satisfactory agreement between the intra-operative navigation results and the post-operative values obtained from X-rays have been reported. 11–15 In our previous studies, 7,8 we also reported satisfactory results with cup setting angle with the use of the image-free navigated THA. However, we did not look into stem AT and CA in our initial reports.…”

“…The effectiveness of this system in our clinical experience has been confirmed and reported in previous clinical studies. 7–9 However, this system is not equipped with a tool to evaluate and control torsion of the stem. Consequently, the stem AT was determined arbitrarily by the surgeon and, therefore, the resultant CA value in our navigated THA can vary.…”

Effects of coordinate-system construction methods on postoperative computed tomography evaluation of implant orientation after total hip arthroplasty

“…Many investigators have evaluated the clinical accuracy (deviation of implant orientation from preoperative planning to postoperative measurement) and measurement error (deviation of orientation from intraoperative final measurement by navigation system to postoperative measurement) of navigation systems [18,21,[24][25][26][27][28]. Although a CT-based 3D templating technique is generally used for postoperative implant measurement, those results included errors in the evaluation methods, of course.…”