Learning curve associated with CT-based navigation assisted cup orientation for muscle-sparing total hip...

The accurate cup placement is still crucial for total hip arthroplasty (THA). However, achieving adequate registration accuracy is difficult in the initial cases, which leads surgeons to discontinue the use of CT-based navigation. The objective of this study was to evaluate its learning curve using a cumulative summation (CUSUM) analysis of the absolute registration error for cup orientation. A retrospective review was performed on 75 consecutive patients who underwent minimally invasive THA, allowing the calculation of the difference in cup anteversion and inclination between the intraoperative values shown on the navigation system and postoperative values measured by postoperative CT. We reviewed those absolute registration errors and the patient reported outcomes (PROMs) one-year postoperatively. We plotted the CUSUM values of the absolute registration error in chronological order and added subgroup analysis regarding body mass index (BMI). CUSUM analysis revealed that performing THA using CT-based navigation was associated with a learning curve in 7 cases for cup inclination and anteversion. There were no significant differences in the absolute registration error of cup orientation between high and low BMI groups, or in the mean PROMs at one-year postoperatively, regardless of time sequence or BMI. In conclusion, CT-based navigation assisted acetabular cup placement was associated with a learning curve of 7 cases for achieving suitable registration accuracy. These findings are important, as orthopedic surgeons often discontinue CT-based navigation surgery early in the initial cases, despite its benefits in severe cases. Therefore, careful use of CT-based navigation is critical particularly within the first 7 cases.