63 y.o. male, 6 m fall from a tree, pelvic fracture 61-C1.2.1c1. a: initial posterior-anterior 2D tomography, b: clinical photography of the operative set up with patient positioning and draping, reduction by traction on the leg and marking the skin incision with the navigated drill guide placed in the axis of the planned screw. c + d: intraoperative fluoroscopic images of the dislocation in posterior-anterior and inlet view, e: provisional fixation of the required height of ilium and sacrum with a k-wire, f: reduction and stabilization with two lag screws in the S1 body. g: postoperative loosening of the screws and re-dislocation of the SI joint h: despite operative revision with open reduction and anterior double plate fixation a new dislocation occurred.