The Glenoid Vault Outer Cortex a new more accurate radiological reference for shoulder arthroplasty.

Introduction: Correct positioning of the glenoid component is an important determinant of outcome in shoulder arthroplasty. We describe and assess a new radiological plane of reference for improving the accuracy of glenoid preparation prior to component implantation - the Glenoid Vault Outer Cortex (GvOC) plane.

Methods: One hundred and five CT scans of normal scapulae were obtained. Forty six females and 59 males aged between 22 and 30 years. The accuracy of the GvOC plane was then compared against the current "gold standard" - the scapular border (SB). Measurements of glenoid inclination, version, rotation, and offset were obtained using both the GvOC and SB planes. These were then compared to actual values.

Results: The mean difference between version obtained using the GvOC plane and the actual value was 1.8° (-2 to 5, SD 1.6) as compared to 6.7° (-2 to 17, SD 4.3) when the SB plane was used, (p < 0.001). The mean difference between estimates of inclination obtained using the GvOC plane and the actual were 1.9° (-4 to 6, SD 1.6) as compared to 11.2° (-4 to 25, SD 6.1) when the SB plane was used, (p < 0.001).

Conclusions: The GvOC plane produced estimates of glenoid version and inclination closer to actual values with lower variance than when the SB plane was used. The GvOC may be a more accurate and reproducible radiological method for surgeons to use when defining glenoid anatomy prior to arthroplasty surgery.