Assessing glenoid orientation on the axillary view: a novel technique using the posterolateral acromion-to-coracoid...

In shoulder arthroplasty, three-dimensional computed tomography (3D CT) has become the gold standard for preoperative version assessment. Meanwhile, postoperative version is usually evaluated using radiographs (XR), in particular an axillary view, in which the view of the scapular body is often truncated, preventing the scapular plane from being used as a reference. This study introduces the posterolateral acromion-to-coracoid (PLAC) line, which can be assessed on a standard truncated axillary radiograph.

Forty-six shoulders were studied. Four angles were measured including 3D CT (CT Version), 3D CT PLAC line to glenoid face angle (CT PLAC-GFA), 2) radiographic PLAC line to glenoid face angle (XR PLAC-GFA), and 3) the radiographic glenoid vault line to glenoid face angle (XR GV-GFA). Variation and linear relationship between these angles were calculated.

The mean difference between CT PLAC-GFA and XR PLAC-GFA was 1.0º (95% CI -0.7 to 2.8)(IQR = 8.5º, -3.0º to 5.4º), with a strong correlation on linear regression (R² = 0.76, p < 0.001). XR PLAC-GFA and XR GV-GFA demonstrated strong correlations with CT measured version (R² = 0.72 and 0.70, respectively; p < 0.001). Inter-rater reliability was excellent for all metrics (ICC ≥ 0.93).

The PLAC and the glenoid vault lines are highly reproducible references on truncated axillary views. These alternative reference lines allow accurate comparison of preoperative and postoperative glenoid orientation using standard axillary radiographs.