A 7-year-old patient presents with a fracture of her left supracondylar humerus and distal radius as evidenced in Figure A. She is neurovascularly intact and the skin shows no evidence of open wounds. Radiographs of the elbow show a displaced supracondylar fracture. Radiographs of the wrist show an extra-articular distal radius fracture with 25 degrees of dorsal angulation. This injury is most appropriately treated with which of the following?