Fig 1.

Demonstration of preoperative planning and measurement (right shoulder). (A) Preoperative CSA (yellow line, 38°) is measured on the standard anterior view of 3-D shoulder. And the postoperative target CSA is set at 31° (white line). (B) The cutting plane is created and positioned at the measuring line of 31°. (C) The green region outside the cutting plane is the part of the acromion to be resected. (D) The measurement of resected bone borders, including the distance of AB (approximately 13 mm) and BC (approximately 27 mm). “A” denotes anterior acromial edge of acromioclavicular joint, “B” denotes anteromedial resection margin, and “C” denotes posterolateral resection margin; CSA, critical shoulder angle.