## 4 Discussion
Other studies designed a simple osteotomy to simulate non-displaced or minimally displaced scaphoid waist fractures [10; 15; 16]. Therefore, the value for load to failure evaluated from the experiment could be lower than that of other studies. A 3D analysis of scaphoid waist fracture revealed that comminution and displacement rates were 11% and 28%, respectively [13]. This meant the fracture surface apposition may not be as good as we previously perceived. Further studies are warranted to analyze the effect of osteotomy gap and to prove which osteotomy is close to the reality. Not surprisingly, the screw placement for volar fixation of scaphoid fractures may play an important role and affect clinical outcomes. Over the past few decades, several biomechanical studies have demonstrated that central screw placement in the proximal fragment, perpendicular screwtrajectory, and longer screw length could provide better biomechanical and clinical results [15; 22; 23; 24]. The common assumption that screw fixation of scaphoid fractures should be undergone in a uniform procedure and that a single screw direction would give optimal fracture fixation may simplify operations; however, this is usually not true for other fractures and should not be true for scaphoid ones [25]. Clearly, a large number of variables must be taken into account when assessing the healing potential of a scaphoid by screw fixation. The relationship between the fracture plane and scaphoid long axis may influence the healing potential. Scaphoid fractures are generally divided into three types: horizontal oblique, transverse, and vertical oblique, on the basis of the fracture plane [26]. With regards to vertical oblique fractures, [PERSON] et al. conducted several studies and concluded that eccentric screw placement achieved perpendicular screw trajectory and resulted in a similar stability of fixation as central screw placement [16; 25]. Next, the transverse waist fracture, which was considered the most common, accounted for 60% of scaphoid fractures [26]. [PERSON] et al. [10] designed a cadaveric osteotomy-simulated transverse fracture model to analyze the influence of different approaches and showed that the transtrapezial approach achieved central screw placement and perpendicular screw trajectory, and these offered a biomechanical advantage. The current study emphasized the horizontal oblique fracture, which accounted for 35% of all scaphoid fractures [26]. In the past, it was considered the second most common. Recently, some surgeons have reported that most waist fractures were horizontal oblique and not transverse in orientation [13]. Therefore, it is necessary to discern the screw placement that would provide a biomechanical advantage for the most common scaphoid waist fractures. This study showed that central screw placement provided better strength than eccentric placement in terms of biomechanical stability. In contrast, several biomechanical studies demonstrated that more stable fixation of horizontal oblique fractures may be achieved by a screw placed perpendicular to the fracture plane in comparison with that along the long axis of the scaphoid [25; 27], with perpendicular screw placement potentially maximizing the surface area available for healing [28]. Perpendicular screw fixation provides a biomechanical advantage in any fracture, not only in scaphoid fractures [24; 25]. However, the entry point of perpendicular screw for horizontal oblique fractures is different from the current approaches, either central or eccentric. [PERSON] et al. proposed directing a perpendicular screw using a volar and proximal approach in a fully extended wrist and reported that the load to failure averaged 258 N for the perpendicular screw group and 294 N for the central screw group [24]. Due to the proximity of the major neurovascular structures and flexor tendons around the volar wrist, care must be taken during this approach, and further investigation is needed to evaluate the feasibility of this technique. Regarding the fracture angle, [PERSON] et al.