This study evaluates the biomechanical strength of a modified dorsal double-plating (MDDP) internal fixation on artificial radius bones using the dynamic fatigue test. The plates are 1.6 mm thick and the upper L plate has an adjustable joint to allow the angular disposition of the bone plate to be changed to secure various bone fracture types. A dual-thread locking screw is used to enhance mechanical retention at the screw/bone interface. A finite element analysis is performed to examine the mechanical bone and fixation system response using a dual-microthread locking screw. An MDDP fixation is made with stainless steel by a manufacturer with ISO13485 quality management systems. Eighteen radius Sawbones were randomly placed into three groups and cut to a standard length of 2.5 cm from the articular surface to form 0 °, 30°, and 60° fracture configurations according to the A2 classification in the AO surgery reference. The adjustable joint in the L plates is adjusted and fixed using a fastener connection to have a 0°, 30°, or 60° configuration. Plates and screws are then positioned on the dorso-ulnar side for L plates and the dorso-radial side for I plates to create an angle of 90°. The specimens were subjected to oscillating loads of 10 to 150 N at 5 Hz for 20000 cycles. The average stiffness values after 20000 cycles were 425.7, 461.1, and 532.1 N/mm for the 0 °, 30°, and 60° constructs, respectively. No difference in stiffness was found for constructs with a given angle throughout the 20000 cycles of testing (p > 0.05). However, significant differences (p < 0.05) in stiffness were found between constructs with different angles at each 500-cycle interval. The lack of gross construct failure during cyclic testing and the reasonable stiffness prove that MDDP internal fixation is sufficiently stable to support restricted postoperative loads.