## 4 Discussion
Clinically, using a clavicle hook plate with a posterior hook offset is more flexible and tolerant for fixing it at any acromion position during surgery in order to reduce the reaction force on the acromion. If a clavicle hook plate without a posterior hook offset is used, hook fixation at the middle acromion is recommended if space permits it. The greatest stress was located on the bend of the hook plate in contact with the acromion in all groups. In the groups with a posterior hook offset, the stress was also distributed on part of the plate, indicating that the shape of the posterior hook offset may cause a larger deformation in the plate of the clavicle hook plate, leading to greater stress on the plate according to Hooke's law. However, the maximum stress in all models was less than the yield strength of the material of the clavicle hook plate, with the yield strength of stainless steel and titanium being 700 MPa and 490 MPa, respectively [28]. Hence, if a  
Figure 9: The existence of a posterior hook offset increases the lever arm length, resulting in a smaller reaction force on the acromion. higher stress is located on the hook corner and the plate, deformation or fracture of the implants rarely occurs. Regarding the stress on the six screws in the clavicle, the highest stress was located on the innermost screw (S6) in all groups. The groups without a posterior hook offset experienced less stress, whereas the groups with a posterior hook offset had greater stress. Although the stress on the innermost screw was less than the yield strength of the bone, the innermost screw must be placed carefully in order to avoid high stress on the clavicle that may increase the risk of peri-implant fracture, especially for the clavicle hook plate with a posterior hook offset. This study has several limitations. The model simulates an acromioclavicular joint with an implanted clavicle hook plate which assumes that the acromioclavicular ligament and coracoclavicular ligament are total torn, so the external force is only applied to the sternocleidomastoid muscle. Since this study only discusses the biomechanical analysis of the clavicle hook plate, acromioclavicular joint, and clavicle, the scapula model was simplified to the acrom only. Due to the anatomic differences among individuals, verifying the models with the computer research data established in this study and other previous research data was difficult. This study only selected representative bone models for analysis. Therefore, only the computer models established in this study were verified by a mesh convergence test. In addition, the material properties are assumed to be homogeneous, isotropic, and linearly elastic based on the assumptions of previous studies [20; 21; 22]. Although we also wanted to use anisotropic material properties to set the bone tissue, the finite element analysis of nonlinear material properties was challenging to solve. Therefore, it was possible that the nonlinear material setting used in this study could lead to more influencing factors for the topic discussed in this study. Thus, this study simplified the establishment of computer models and material properties, mainly to make biomechanical evaluations for the main issues discussed in this study so as to avoid too many factors that affect the results of computer simulation studies. Given the experimental design of this study, it was indeed unable to prove directly that variations in the posterior hook offset led to peri-implant fracture or subacromial osteolysis; however, this study can still explain that the posterior hook offset made the biomechanical difference in the strain on the clavicle. Although these assumptions are slightly different from the actual situation, this study evaluated the biomechanical trends of the implantation of clavicle hook plates with different posterior hook offsets at various positions in the acrom.