Purpose: Glenoid replacement remains challenging due to the difficult visualization of anatomical reference landmarks and highly variable version angles. Improper positioning of the glenoid component leads to loosening, early wear, and instability. The objective of this study was to develop and evaluate a tracking system for glenoid implantation. We hypothesized that Computer Assisted Glenoid Implantation (CAGI) would achieve a more accurate and reliable placement of the glenoid component compared to traditional methods.

Methods: 3D CT models of sixteen paired cadaveric shoulder specimens were reconstructed and angles were measured using 3D modeling softwares. Jigs were developed to track instruments and to correct for scapular motion. A standardized protocol for determining in real-time via electromagnetic tracking the glenoid centre, version, inclination and ultimate component placement was previously developed and validated in our laboratory. Specimens were randomized to either traditional or CAGI performed by one of two blinded fellowship trained shoulder surgeons. The mean age was 67 years (range 61–88). Native version and inclination were similar in both groups. All phases of glenoid implantation were navigated.

Results: CAGI was more accurate in achieving the correct version during all phases of glenoid implantation (p < 0.05; paired t-test). CAGI CONTROL Initial pin * 6.3 ± 2.9° Reaming *7.0 ± 3.9° Post drilling * 0.6 ± 0.4° 8.3 ± 4.6°|Post cement * 2.3 ± 2.0° 7.9 ± 3.6°|Post implant CT * 1.8 ± 0.9° 7.7 ± 4.0°. Table 1. Absolute values of the mean error ± SD of version angles obtained with either CAGI or the traditional method (goal = 0° version; * p < 0.05). The largest errors with traditional were observed during drilling and reaming where visualization was especially obscured by the reamer heads. The trend was to retrovert the glenoid. There was no difference with respect to inclination angles (p > 0.05).

Conclusions: Preoperative planning using CT imaging with 3D modeling and intra-operative tracking were combined to produce improved accuracy and reliability of glenoid implantation.

Funding : Other Education Grant

Funding Parties : National Sciences & Engineering Research Council research grant