The morphology of the glenoid cavity is variable. Most of the methods to measure osseous bone defects in glenohumeral instability use the best-fit circle of the inferior glenoid rim. However, no consensus exists regarding the sizing of this circle. Our hypothesis was that there is a relationship between the best-fit inferior circle, defined by Sugaya, and the circle tangent to the supra- and infra-glenoid tubercles, defined by Itoi.
We examined 95 dry scapulae. The specimens were digitally photographed obtaining perpendicular images of the glenoid cavity. Using HOROS® imaging software, a best-fit inferior circle and a second circle fitting the most inferior and superior points of the glenoid were drawn by two investigators. The diameters and areas of the circles were recorded. Two-way random-effects intra-class correlation coefficients (ICC) were used to measure intra- and inter-observer agreement. Linear regression was used to determine the relationship between Itoi and Sugaya measurements.
The mean glenoid length was 35.1 mm and the glenoid width 25.6 mm
The mean diameter of the Itoi circle was 1767±204 pixels and the mean diameter of the Sugaya circle was 1311±157 pixels. ICC showed excellent inter- and intra-observer agreement for both the Itoi circle diameter (ICC=0.95) and Sugaya circle diameter (ICC= 0.93). The linear regression for the two diameters showed excellent model fit R2=0.85. and very strong, significant Pearson correlation of 0.92 (p<0.001). The areas of the two circles was also highly and significantly correlated (r=0.94; p<0.001). The ratio of Sugaya to Itoi diameters was 0.74
There is a strong relationship between the two circles defined by Itoi and Sugaya. This study provides arguments to use the Itoi diameter to predict the Sugaya diameter for a more reproducible bone loss measurement.