Preoperative planning

In both groups, 3D digital preoperative planning and a surgical simulation were performed prior to surgery. Corrections to and the placement of implants were simulated using software developed by one of the authors (Zed-Trauma, LEXI Co., Ltd., Tokyo, Japan). Computed tomography (CT) of the affected and unaffected wrists using contiguous images with a slice thickness of 1–1.5 mm were taken for the simulation. Images were taken approximately 12 cm proximal to the radial joint surface. A total of 80–120 axial CT images were used for the simulation. After importing DICOM images into the software, a 3D image of the distal radius was made for both wrists. In dorsally angulated malunion, the placement of a volar locking plate was initially simulated. Computer-aided design models of different-sized implants are installed in the software; a placement image of the plate was created by calculating the correction angle required to restore volar tilt, radial inclination, and rotational deformation (Fig. 3). Stellar II locking plates (HOYA Technosurgical, Inc., Tokyo, Japan) were used in the present study. This plate system has small, medium, and large widths as well as short and long plate lengths. The plate size was selected to cover the distal radius maximally and not exceed the width of the distal radius. In addition, a sufficient length plate for the insertion of at least three screws into the radius shaft after reduction was chosen. The lengths for the distal screws were selected and a contour extraction image of the initial plate placement was saved for image fusion. The osteotomy line was set at a position that did not interfere with distal screw holes. After the osteotomy simulation, the plate and distal fragment were grouped, and the distal fragment was repositioned by adapting the proximal side of the volar locking plate to the radius shaft (Fig. 4). After repositioning the fragments, the 3D bone shape was compared with a mirror image of the unaffected radius. In the next step, simulations of the screw choices were performed for the proximal screw holes and the screw lengths for each screw hole were selected. This final reduction and implant placement image was also saved for image fusion. To compare planned and postoperative reduction shapes, preoperative plan and postoperative 3D images were created for all patients.

Preoperative image of plate placement. An image of plate placement was created by calculating the correction angle required to restore volar tilt, radial inclination, and rotational deformation. The plate was placed so that the distal margin was parallel to the articular surface. An image of each frame shows the plate fixed to the distal radius. The blue dotted line on the frame (a) shows the correction angles for the coronal view. The blue dotted line on the frame (b) shows the correction angles for the sagittal view. The blue dotted line on the frame (c) shows the correction angles for the axial view

Preoperative image of reduction. After separating the distal part of the radius, reduction was achieved by fixing the proximal side of the plate to the radius shaft. The gap between the distal and proximal parts of the radius indicates the predicted bone defect. a Coronal view, b sagittal view, c axial view