## 4 Discussion  
The purpose of this cadaveric study was to biomechanically compare fixation strength between central and eccentric screw placements for the volar fixation of horizontal oblique scaphoid fractures. Our hypothesis was that central screw placement would achieve superior fixation strength for this issue. The results showed that central screw placement for volar fixation of horizontal oblique scaphoid fractures provided relatively better strength than eccentric placement in terms of biomechanical stability. The complexity of the scaphoid structure results in different fracture patterns, making comparison of clinical outcomes difficult. Hence, we adopted a cadaveric study to evaluate the biomechanical stability of different screw placement techniques in the same fracture pattern. However, several limitations restrict the scope of this biomechanical comparison investigation. First is its post-mortem nature. Other factors such as postoperative rehabilitation and bone healing could not be taken into consideration in this cadaveric study. Such factors may underlie differences in the clinical results reported by other surgeons. Furthermore, the average specimen age was 57.5 years, whereas patients with scaphoid fractures are younger in our daily practice. Second, we focused our attention on the biomechanical stability of different screw placements, which is only one factor in choosing a fixation of scaphoid fractures. Additional research is needed to address other issues such as different screw designs, dorsal vs. volar approaches to the scaphoid, and proximal vs. waist fractures of the scaphoid. Since most orthopedic devices were made by metallic alloy, the mechanical performance of the orthopedic devices could be similar when the devices were applied under room temperature and body temperature. Therefore, the experiment did not include a normal saline bath under controlled temperature. Here, we only evaluated different screw placements for volar fixation of horizontal oblique scaphoid fractures because we wanted to simplify the conditions of the experiment. Another limitation of this study was that the strength of the scaphoid fixation in both central and eccentric placement groups seemed to be lower than that observed in previous studies [10; 15; 16]. These biomechanical cadaveric studies reported that load to failure (2 mm displacement) ranged from 59.1 to 324.4 N. The cadaveric scaphoids in this study were harvested from an older population (range: 42-71 years), and therefore the bone quality would be weaker than that of younger populations. This is a common shortcoming of all cadaveric studies. We attempted to determine the possible reasons to explain this result. First, other studies chose the longest possible screw because screw protrusion could be visually checked [10; 15; 16]. In contrast, our screw length was computed by subtracting 4 mm from the length of the guidewire. This method is frequently used in our clinical practice [14]. Using this technique, we could ensure a buried depth of 2 mm below the articular cartilage and avoid screw prominence at the articular surface. This resulted in a shorter screw in this study that could affect the fixation strength. However, [PERSON] et al. demonstrated maximizing screw length may not provide superior fixation for proximal scaphoid fractures [20]. Therefore, a 2 mm gap at the fracture site that simulated a scaphoid waist fracture may have been the reason for inferior fixation strength. This setup did not represent the clinical practice that the fracture gap should be closed in order to achieve proper reduction. Nevertheless, this gap ensured that the applied force was carried solely by the implanted screw. Since the objective of this study was to evaluate the stability of the scaphoid fixation, the mechanical effect of bone contact should be eliminated like the test models of scaphoid (3 mm gap) and long bone fracture (10 mm gap) [21; 22].