Summary

A reusable patient specific 5D calibrator improves accuracy of glenoid component placement in RSA, potentially leading to better postoperative outcomes.

Abstract

Rationale: Reverse total shoulder arthroplasty (RTSA) is an effective treatment for rotator cuff arthropathy. Nevertheless, the correct positioning and fixation of the glenoid component is challenging and has a significant impact on the postoperative clinical outcomes. Multiple navigation techniques have been developed to guide intra-operative implant positioning. This study presents the first results on the use of a reusable five-dimensional (5D) calibrator which likely improves the accuracy and precision of the glenoid component position. Additionally, no previous studies are conducted comparing navigation based implant positioning with the conventional method.

Objective

The primary objective is to compare the accuracy of glenoid implant positioning using the 5D calibrator with the conventional (freehand) method. It is hypothesized that the accuracy and the amount of correction of version and inclination will increase by using the 5D calibrator compared with the conventional freehand method.

Methods

This case-control study (METC20-093) investigates the accuracy of implants positioning amongst patients undergoing RTSA performed by two fellowship trained shoulder subspecialists. All patient who underwent RTSA are eligible for inclusion. Exclusion criteria are: proximal humerus fracture; loosening of the glenoid component; or inability to understand the Dutch language. The primary outcome measurement is the accuracy of the positioning of the glenoid component. Glenoid positioning was assessed using pre- and postoperative CT scans. The glenoid component positioning accuracy, defined by version and inclination were measured. Glenoid component version were measured according to Friedman’s line. Glenoid component tilt were measured on the oblique cut relative to frontal axis of the scapula (RSA angle). Preliminary results are presented.

Results

Between 2021 and 2024 46 CT-scans of RTSA placed using the freehand method (group 1) and 42 CT-scan using the 5D calibrator (group 2) were compared on glenoid positioning accuracy.
The use of the 5D calibrator showed a significant improvement in retroversion accuracy in the 5D group (median deviation of 2.3°) compared to freehand group (median deviation of 7.8°), with a p-value of 0.000. The inclination accuracy did not significantly differ between the 5D and freehand group (p-value of 0.225), although the median deviation was lower in the 5D group compared to the freehand group (respectively 2.7° and 3.8°). The use of the 5D calibrator also appeared to have less variability in both retroversion and inclination accuracy, compared to the conventional method.

Conclusion

The 5D calibrator significantly improves the retroversion accuracy in RSA compared to the freehand method. Although inclination accuracy did not differ significantly, the 5D group showed less variability in both metrics. This suggests that the 5D calibrator may enhance the accuracy of glenoid component placement in RSA, potentially leading to better postoperative outcomes. Future results from this study might show the importance of accurate implant positioning for optimizing functional outcome and implant survival.