## 4 Discussion
[PERSON] showed that the two coronal lateral entry pinning, which crosses at the fracture site, has very low construct stiffness [18]. [PERSON] et al. suggested that loss of reduction occurs when the pins are too close to each other at the fracture site level [20]. We assumed that the construct weakness in the coronal plane is the result of two pins starting from the same side and crossing near the fracture site level. We applied this assumption to the AP sagittal pin configuration, where two pins also start from the same anterior side and cross near the fracture site, which might explain why the AP sagittal pin configuration has lower construct stiffness than the other sagittal pin configurations. The second area is the divergent sagittal pin had the maximum pin spread at the fracture site, which the highest construct stiffness in extension, valgus, and external rotation loads. [PERSON] recommended that both divergent and parallel coronal pins should be maximally separated at the fracture site for maximal stability [26]. [PERSON] suggested that loss of reduction occurs when the pin spread is less than 2 mm at the fracture site level [20]. [PERSON] divided the distal humerus into medial, central, and lateral columns. Then, it suggested that the divergent configuration should provide adequate spread between pins and engage both the lateral and central columns of the distal humerus [21]. [PERSON] conducted a retrospective review and suggested the pins should be spread at least 13 mm or more than one-third of humeral width at the fracture site to minimize the loss of reduction [32]. The third area is the weakness of the parallel sagittal pin configuration under extension loads despite the fact that it carried significantly high construct stiffness in external rotation loading as divergent sagittal pin configuration. [PERSON] studied the biomechanics of construct stiffness between divergent and parallel pin configurations in the coronal plane [17]. His results showed significantly lower construct stiffness with the parallel compared to divergent pinning. That explains the \"lock\" and \"unlock\" effect of the angle between the two pins, which concurs with our finding that with the divergent sagittal pin configuration, the two pins act together to create a \"lock\" effect, while parallel pins create an \"unlock\" effect under extension load. There were some limitations to our study. The first and most important limitation was the limited number of specimens (\(n=3\)) used for each loading test. According to the power analysis, our study would require at least eight specimens in each loading test to achieve 80% power to detect a significantly large effect size ([PERSON]'s 4.0) accounting for multiplicity. Thus, our results might be considered only for hypothesis-generating. Further research with an adequate study size is still needed to confirm our findings. Second, the material used was not an authentic human bone. Thus, it lacks natural pediatric bone properties such as soft tissue tensioning, periosteal effect, and cartilaginous physics. Pediatric cadavers are very rare and are more expensive than artificial bone. However, a synthetic model does have advantages, e.g., the realistic anatomy truly represents the limitations of pin placement in pediatric bone, the specimens are homogeneous, and the results are reproducible. Real pediatric human bone varies in bone quality, bone density, and periosteal thickening, confounding factors avoided by using the pediatric synthetic bone.