Twenty-three adults with acute traumatic distal radioulnar joint (DRUJ) instability undergoing arthroscopic triangular fibrocartilage complex (TFCC) repair were randomized to receive postoperative immobilization using either a modified ulnar gutter slab or a sugar tong slab. One participant was lost to follow-up, leaving 22 for analysis. Outcomes included disabilities of arm, shoulder, and hand (DASH) score, elbow/forearm/wrist range of motion (ROM), DRUJ stability (piano key test and radiographic displacement), and complications. Assessments were conducted at 2, 4, and 6 weeks postoperatively. Overall, the results revealed no between-group differences in DASH scores or forearm/wrist ROM at 4 or 6 weeks. However, the modified ulnar gutter slab produced significantly less elbow extension lag and slightly less elbow flexion loss at 4 weeks. DRUJ healing was comparable, and only the sugar tong group experienced a complication such as complex regional pain syndrome (CRPS). These findings suggest that the modified ulnar gutter slab supports safe TFCC healing while reducing early postoperative elbow stiffness.