Fig. 3

Measurements of glenoid angles using bones (a, c) and 3D-CT-reconstructions (b, d). a For determination of the inclination angle α, a geometrical triangle was adjusted on the dorsal side below the spine running from root of the spine (J) to the most posterior point at the glenoid rim (C). Another geometrical triangle was placed running from the supraglenoid (A) to the infraglenoid (B) tubercle. The angle γ (green) between these 2 axes was measured and from this, the inclination angle α (red) calculated by the formula: α = γ - 90°. b On the CT scan, the inclination angle α was determined in the coronal plane. A line was drawn from the root of the spine (J) to the midpoint of the glenoid cavity (F). A second line was drawn through the most cranial (A) and caudal (B) points of the glenoid rim. Angle γ (green) was measured between the axes of these two lines in the caudal direction. From this, the glenoid angle α (red) was calculated by the formula α = γ - 90°. c A geometrical triangle was used to designate the intersecting point between the perpendicular starting at A (extrapolation of the dotted line) to the middle of the line between C to D. From this, the angle μ (green) was measured between the axes of these two lines. In a next step, the angle δ was calculated by the formula: δ = 180°- μ and then the ante-/retroversion angle β (red) was converted by the formula: β = δ - 90°. d On the CT scan, the ante-/retroversion angle β was determined in the transversal plane according to Friedman [45]. A line was drawn through the root of the spine (J) to the midpoint of the glenoid cavity (F). A second line was drawn through the most posterior (C) and anterior (D) points of the glenoid rim. Angle δ (green) was measured between the axes of these two lines in the sagittal direction and from this, angle β (red) was calculated by the formula: β = δ - 90°. Ac Acromion, CP coracoid process