Description and reproducibility assessment of a new computerised tomography scan index to measure the glenoid orientation in relation to the anterior glenoid surface.

PURPOSE: To propose and to assess the reproducibility of a new method (GO [glenoid orientation] index) for the estimation of the glenoid orientation in relation to the anterior surface of the glenoid.
METHODS: This is a retrospective study on computed tomography (CT) scan. The GO index was defined as the angle formed by a line perpendicular to the tangent to the anterior surface of the scapula and the glenoid line (which is defined as the line connecting the anterior and the posterior rim of the glenoid). The measurements were performed at the level of the glenoid where its diameter is the greatest. Two independent observers performed each measurement twice. The intra- and inter-observer reproducibility was evaluated by the Pearson coefficient (r) and the intra-class correlation coefficient (ρ, ICC). The correlation between GO index and glenoid version as described by Friedman was also studied.
RESULTS: Seventy-eight CT scans were analysed, 38 shoulders with glenohumeral arthritis and 40 healthy shoulders, 32 females/46 males, mean age 53.9 ± 22.7 years. The measures were all highly correlated (r > 0.50, p = 0.00001). The intra- and inter-observer reproducibility was good to excellent (0.71 < ρ < 0.84, p = 0.00001). GO index was 26.9 ± 6.3°, 28.4 ± 6° in the group with glenohumeral osteoarthritis and 25.5 ± 6.4° in the healthy group, p = 0.04. The glenoid version was -0.8 ± 7.9° in the group with glenohumeral osteoarthritis and -3.9 ± 6° in the healthy group, p = 0.05. No agreement was found between the glenoid version and GO index.
CONCLUSIONS: GO index is simple and reproducible. It could be very useful for the pre-operative planning and intra-operative positioning of the implants in total shoulder arthroplasty.