A 26-year-old male sustained a left wrist injury after an occupational fall from height that was diagnosed as wrist sprain and treated conservatively by a plaster splint in another institution. Eight weeks after injury, the patient could be re-employed in his original occupation as a truck driver. Six years after injury, the patient came in our institution for the first time, and reported increasing pain in his left wrist accompanied with marked restriction of his left forearm's supination and pronation leading to the non-ability to carry out his occupational job 8 weeks previously. On clinical examination, there was pronounced dorsal subluxation of the ulnar head without any given possibilities for it manual closed reduction (i.e. static instability in transverse plane) ( Figure 1A). Posterior-anterior (PA) radiographs of both wrists showed no concomitant ulnar positiv variance (UPV) (i.e. no longitudinal instability) and no posttraumatic arthritic changes in the distal radioulnar joint (DRUJ), but the configuration of the ulnar styloid at the formerly injured left wrist could not be well assessed that suggested an additional rotation deformity of the ulnar head ( Figure 1B). Lateral radiographs of both wrist showed marked fixed subluxation of the ulnar head in dorsal direction (i.e. static instability in transverse plane) ( Figure 1C). Due to these findings, the Sauvé-Kapandji procedure, modified by creating a "quadrangularconstruct", was detected by us. At the preoperative radiographs of the left elbow in both planes there were no signs of any pre-existing degenerative changes with specific regard to the radiocapitellar joint.Intraoperatively, first, the 2 cm long ulna segment was excised typically proximal to the DRUJ, then a Kirschner-wire was drilled into the ulnar head parallel to the plane of the operation table on which the left forearm was positioned at terminal range of pronation (i.e. 90°) ( Figure 2A). After that, the ulnar head was rotated 90° perpendicular to the operation table's plane in dorsal direction using the formerly drilled Kirschner-wire, and so the neutral position of DRUJ could be achieved in which the arthrodesis had to be performed ( Figure 2B). Then, the cartilage of both corresponding surfaces in DRUJ was excised, and the DRUJ arthrodesis in neutral position was carried out using a 3.5 mm titanium malleolar screw, and the Kirschner-wire was removed. The next step included the several years later introduced "quadrangularconstruct" modification of the original Sauvé-Kapandji procedure: After decorticalization of the corresponding radius and ulna shafts proximal to the DRUJ arthrodesis and distal to resection plane of the ulna segment, the formerly excised ulna segment has been inserted transversely between both forearm bones and fixated with a second 3.5 mm titanium cortical screw through the ulna segment graft, and finally, complete restoration of rotation motion arc could be achieved ( Figures 2C-D). The correctly performed surgical procedure was confirmed intraoperatively by flu...