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Abstract Background Proximal humeral fractures are common, and more than half occur in patients over 65 years of age. Operative treatment may be recommended for displaced, complicated fractures; however, surgery may lead to displacement of the greater tuberosity or humeral head. Supplemental tension band sutures have been recommended to prevent such a complication. In this study, we investigate the best combination of suture, washer, and threading angle for proximal humeral fractures from a mechanical view. Methods The mechanical durability of 18 combinations of suture materials (Fiberwire, Ethibond, and Surgilon), threading washers (ring washer, disc washer), and threading angles (15 or 45°) were examined via a cyclic loading test. Results The most durable combination in the cyclic loading test consisted of threading the Fiber Wire to the washer ring using only one hole (ring washer-1) at 45°. In contrast, the most vulnerable combination was threading Ethibond to the washer disc at 15°. Breakage of all suture materials occurred at the suture-washer interface, and no failure or loosening of the knots was observed. FiberWire gradually eroded until the loss of equilibrium; whereas the rupture of Ethibond and Surgilon occurred suddenly. Conclusions From a mechanical viewpoint, we demonstrated that applying a supplemental tension band suture using FiberWire with a single-hole ring washer threaded at a wider angle is recommended.