Introduction: Maintaining accuracy of component placement is an important step in ensuring the long-term stability of components during total hip arthroplasty (THA). Computer-assisted navigation has improved accuracy but errors associated with the registration process are known to impact the accuracy of final measurements. The purpose of this cadaver study was to determine the registration error associated with a novel mini-navigation system. Methods: 3 board-certified orthopaedic surgeons performed 4 THA procedures each via the posterolateral approach on 6 cadavers (12 hips) using the mini-navigation tool. Pre- and post-operative radiographs and post-operative computed tomography (CT) images were obtained. Image analysis was performed by 2 radiologists not involved in the surgical procedures. During registration, surgeons aligned the alignment rod with the anterior pelvic plane (APP) to provide a reference plane for comparison with traditional navigation. Cup position from the device was compared with measurements gathered from post-op imaging. Results: The mean difference between CT and device measurements for inclination was -1.7° (standard deviation [SD] 4.9°), while the mean absolute difference was 4.2° (SD 3.2°). The mean difference between anteversion angles calculated from CT scans and from the device was -3.5° (SD 4.5°), with an absolute difference of 4.0° (SD 4.0°). 100% (12/12) of inclination measurements and 92% (11/12) of anteversion measurements fell within both the clinical and statistical limits of agreement when analyzed via the Bland-Altman technique. Conclusions: This study demonstrates that the registration error associated with this new mini-navigation system compares favourably with the known registration error associated with traditional navigation systems.
The figure-of-four axis as a reference to determine stem rotation in hip arthroplasty. What does it really measure? A cadaver study
