Background:Open reduction and intal fixation with plate and screws are the gold standard for the surgical treatment of humeral shaft fractures,this study was to compare the mechanical properties of anteromedial,anterolateral,and posterior plating for humeral shaft fractures.Methods:A distal third humeral shaft fracture model was constructed using fourth-generation sawbones (#3404,composite bone).Atotal of 24 sawbones with a distal third humeral shaft fracture was randomly divided into three Groups:A,B,and C (n =8 in each group) for anteromedial,anterolateral,and posterior plating,respectively.All sawbones were subjected to horizontal torsional fatigue tests,horizontal torsional and axial compressive fatigue tests,four-point bending fatigue tests in anteroposterior (AP) and mediolateral (ML) directions and horizontal torsional destructive tests.Results:In the horizontal torsional fatigue tests,the mean torsional angle amplitude in Groups A,B,and C were 6.12°,6.53°,and 6.81°.In horizontal torsional and axial compressive fatigue tests,the mean torsional angle amplitude in Groups A,B,and C were 5.66°,5.67°,and 6.36°.The mean plate displacement amplitude was 0.05 mm,0.08 mm,and 0.10 mm.Group A was smaller than Group C (P ＜ 0.05).In AP four-point bending fatigue tests,the mean plate displacement amplitude was 0.16 mm,0.13 mm,and 0.20 mm.Group B was smaller than Group C (P ＜ 0.05).In ML four-point bending fatigue tests,the mean plate displacement amplitude were 0.16 mm,0.19 mm,and 0.17 mm.In horizontal torsional destructive tests,the mean torsional rigidity in Groups A,B,and C was 0.82,0.75,and 0.76 N.m/deg.The yielding torsional angle was 24.50°,25.70°,and 23.86°.The mean yielding torque was 18.46,18.05,and 16.83 N·m,respectively.Conclusions:Anteromedial plating was superior to anterolateral or posterior plating in all mechanical tests except in AP four-point bending fatigue tests compared to the anterolateral plating group.We can suggest that anteromedial plating is a clinically safe and effective way for humeral shaft fractures.