Comparison of the accuracies of computed tomography-based navigation and image-free navigation for acetabular cup insertion in total hip arthroplasty in the lateral decubitus position

Image-free navigation has been proven as reliable as that using computed tomography (CT) in positioning the acetabular cup in total hip arthroplasty (THA), but previous studies rarely included hip dysplasia cases. The purpose of the present study was to determine the accuracies of CT-based navigation and image-free navigation for acetabular cup insertion, including hip dysplasia cases. Sixty-three hips were studied, including 57 with hip dysplasia. The hips were divided into two groups based on the registration point of image-free navigation. In Group I, the ipsilateral anterior superior iliac spine (ASIS) and the L5 spinous process were registered in 31 hips. In Group II, bilateral ASIS points were registered in 32 hips. Final component orientation was measured from postoperative CT scans. The accuracy of cup orientation was compared between CT-based and image-free navigation. In Group I, the cup inclination was more accurate with CT-based navigation (1.9°) than with image-free navigation (4.4°, p=.009). Cup anteversion was also more accurate with CT-based navigation (2.9°) than with image-free navigation (7.1°, p<.001). In Group II, the accuracies of cup inclination and anteversion showed no differences between CT-based and image-free navigation. The accuracy of cup positioning was better with CT-based navigation than with image-free navigation when the ipsilateral ASIS and L5 spinous process were digitized. However, accuracy was similar when bilateral ASIS points were digitized