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The stem-first technique with image-free navigated THA could effectively achieve accurate and consistent control of the CA value and thus is expected to improve the surgical outcome.

Purpose:The purpose of this study was to examine the accuracy of implant orientation and leg length in total hip arthroplasty (THA) with an image-free navigation system based on a comparison of the intraoperative navigation and postoperative CT evaluations.Material and Methods:A consecutive series of 111 patients (118 hips) who underwent THA using the current version of the image-free navigation system constituted the basic study population. Subsequently, a total of 101 patients (108 hips) meeting the inclusion and exclusion criteria were selected as study subjects for the analysis. THA was performed using an image-free navigation system that was capable of adjusting both the prosthetic position and leg length. Postoperative CT examination was performed for all study subjects, and the prosthetic position and leg length were measured on CT images using the image analysis software. Subsequently, the intraoperative navigation results and the corresponding values obtained from the postoperative CT measurements were compared to test the accuracy of the navigation system.Results:The average discrepancies between the intra- and postoperative assessments were 6.8°, 3.7°, and 5.7° for cup anteversion, cup inclination, and stem anteversion, respectively. The corresponding value in leg length averaged 4.1 mm.Conclusion:Average discrepancies between the intra- and postoperative measurements were less than 10° in all prosthetic alignment parameters and less than 5 mm in leg length. Intraoperative assessments with the use of the image-free navigation in THA could afford satisfactory result.

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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.