Accuracy and agreement between optical navigation (NDI Polaris) and postoperative CT for glenoid pin placement: a...

Optimizing glenoid component positioning is a key determinant of stability, function and implant survival in total shoulder arthroplasty. Postoperative computed tomography (CT) is considered the reference method for assessing guide-pin or implant alignment, but it remains a retrospective evaluation and is often difficult to obtain in cadaveric research settings. Optical navigation systems such as the NDI Polaris provide immediate intraoperative geometric measurements and may represent a pragmatic alternative. This cadaveric validation study aimed to evaluate the agreement between NDI Polaris optical-navigation measurements and postoperative CT analysis for glenoid guide-pin positioning. Eight cadaveric shoulders underwent augmented-reality-guided placement of a glenoid guide-pin, followed by postoperative CT acquisition. Intraoperative optical-navigation measurements were recorded using an NDI Polaris tracking station. Two accuracy domains were analyzed relative to CT: (1) linear entry-point deviation (mm) and (2) angular deviation in version and inclination (degrees). Agreement between both measurement modalities was assessed using Bland-Altman analysis, complemented by descriptive accuracy statistics. Sixteen paired measurements were available for comparison. The mean absolute NDI-CT difference was 0.98 mm (SD 0.55; range 0.15-2.17 mm) for entry-point localization and 1.58° (SD 0.97; range 0.03-3.28°) for trajectory orientation. Bland-Altman analysis demonstrated a small systematic bias for both linear (-0.15 mm) and angular (-0.75°) parameters, with most discrepancies contained within approximately ±2 mm and ±4°, respectively. These results suggest that, under standardized acquisition conditions, optical navigation provides geometric measurements that closely approximate CT-based reference values and may serve as a practical surrogate in cadaveric research when CT access is limited. NDI Polaris optical tracking demonstrated good agreement with postoperative CT for evaluating glenoid pin positioning and may represent a practical alternative for accuracy assessment in cadaveric studies. These preliminary findings require confirmation in larger validation studies.