The management of displaced midshaft clavicle fractures remains challenge. According to the recent meta-analysis study , surgical treatment for displaced clavicle fractures led to a greater possibility of union at 1 year of follow-up. Patients who hesitate to have surgery for acute displaced midshaft clavicle fractures could have the possibility of nonunion more than 10% of patients. Also, these nonunion would be more difficult to treat compared with acute fractures. Therefore, acute displaced clavicle fractures are recommended surgery to reduce risk of nonunion and malunion.
Open reduction and plate fixation are the standard surgery for displaced midshaft clavicle fractures. Plate fixation provides biomechanically stable strength for early mobilization and then are more used rather than intramedullary fixation. The holes above the fracture site are not usually filled with screws to prohibit nonunion, and just remain empty. However, implant failure is one of the complications in plate fixation. Some FEA studies recommend various type of plates such as anterior plate, spiral plate, superior plate without screws holes above fracture zone and so on [14-17].
According to the FEA comparison between superior locking plate with and without screw holes above fracture zone , the biomechanical property of superior clavicle locking plate without screw holes above fracture zone is superior to the standard locking plate with screw holes above fracture zone, with a significantly lower peak stress on the screw holes above fracture zone in all loading conditions. The reason why we pay attention to this study is that locking plates is the same as a manufactured superior locking plate used nowadays, so we don’t need to develop a new design and set equipment for manufacture. However, it is practically impossible to remove holes only in the fracture area in mass production of clavicle superior locking plates. We wondered that if inserting small screws into an empty hole above the fracture site would have the same effect as superior locking plate without screw holes above fracture zone.
We set a comminuted midshaft clavicle fracture model fixed with 7-hole titanium locking compression superior clavicle plate and did FEA comparison between superior clavicle plate with (model B) and without a screw (model A) above the fracture site. According to the result in Table 2, the FS stress of model A from the cantilever bending force (1000.800 MPa) was much greater than the peak stress from the axial compression (279.810 MPa) and axial torsion force (31.100 MPa). This result means that the cantilever loading force is the force that has the greatest impact on implant failure.
The model B reduced the peak stress on the FS point with 56.179% decrease in cantilever bending force and 55.709% decrease in axial compression loading compared to the model A, whereas the model A’s peak stress was higher approximately 1.765 times rather than the model B. Nevertheless, the maximal stress received by the superior plate under all three loading conditions was low overall in model B with screw inserted, and the biggest difference was the cantilever loading condition.
In axial torsion load condition, peak stress position was changed to another point because counterclockwise moment moved force vector to different direction in Figure 6. As shown in Figure 6, the peak stress position moved to L1 point of rear side plate, it shows same result on both models.
The study had several limitations. First, actual clavicle fracture is not as simple as the model constructed in this study and is very complex, and the number of fracture cases varies greatly in practice. Second, there’s are some considerations such as micromotion between bone and plate, variation of clavicle anatomy, bone quality and quantitative and the stress riser effect of the screws. To simplify simulation, the authors excluded these considerations. Third, the magnitude of the applied forces is not reflected in the magnitude of the force actually acting in the body, but rather the relative nature of the force’s direction.
Further studies will require analysis according to various form of bone and fracture. In addition to the shape of plates, studies on the location, number, size and orientation of screws will also have to be conducted simultaneously.