Measurement of rotational alignment. a. RFC angle is defined as the angle between A and B. A: Line through the center of both fixation pegs. B: Surgical epicondylar line. b. White line: along the posterior edge of the tibial tray. Black dot: center of the posterior concavity of the tibial tray. c. RTC angle is defined as the angle between C and D. C: Line connecting the medial border of the tibial tuberosity with the black dot. D: Line perpendicular to the white line.