2.4. Postoperative Evaluation

All patients received a CT scan prior to discharge using the same technique as the preoperative scans. Evaluation of the final anteversion was determined by superimposing the previous planned stem position to the actual stem position and compared using Tsai's definitions (Figure 6) [3]. From the top view, the planned and postoperative anteversion was measured. The angle difference between the postoperative femoral prosthesis neck axis and the preoperatively planned center was calculated as accuracy value (Figure 6(c)). Cases with the angle change more than 5° were counted as abnormal case.

Postoperative modeling and registration (a). Fit the postoperative rotation center (b). Calculate the preoperative planning, the actual postoperative anteversion angle, and the difference (c). Red sphere indicates the planned center; blue sphere indicates the actual center.