Fig. 5
From: Cup implantation accuracy using the HipCOMPASS mechanical intraoperative support device
a To assess the accuracy of the angle of the indicator in RA, the bed is rotated and aligned so that the device itself is horizontal. At the same time, the inclines from the horizon of the cup holder and the indicator are each measured with a level gauge, and the difference between them is defined as the operator error in RA. b Similarly, to calculate the operator error in RI, two points are established on both the indicator and the bar, which is attached to and in parallel alignment with the cup holder, as shown in the diagram. The sides of the four-sided figure formed by these four points are defined as A, B, C, and D, while one of the diagonals is defined as E. Lines A–E, as projected onto the intraoperative horizontal plane, are defined as lines Aʹ–Eʹ and the lengths of each are calculated. Then, after calculation of the angle formed by Aʹ and Cʹ using the law of cosines, the angle formed by C as Aʹ is projected onto the plane where C lies is calculated, and defined as the operator error in RI