"type A: centred humeral head, concentric wear, no subluxation of the humeral head"
"type B: humeral head subluxated posteriorly, biconcave glenoid with asymmetric wear"
"It was initially measured on 5 mm thick slices on axial CT scans of the shoulder 1, which had mixed results for inter- and intra-observer agreement but this has improved with the modified classification system (which includes B3, C2, and D) using 3D CT reconstructions 2,3."