## 4 Discussion  
Adequate fixation stability is the key measure of success in the treatment of displaced pediatric supracondyl fractures. Closed reduction and percutaneous pinning is a standard technique for fixation, especially for Gartland type 2 and type 3 fractures [6,30]. Low construct stiffness is an important factor in the loss of fracture reduction. Many previous studies have discussed construct stiffness in the coronal pin configuration. The divergent lateral entry pin technique has been recommended in many institutes because of the lower risk of iatrogenic ulnar nerve injury than the medial-lateral crossed pin technique [7,31]. In contrast, there have been few studies in biomechanical and clinical evidence about the sagittal pin configuration. Our study aimed to biomechanically evaluate which of the sagittal pin configuration has the strongest construct stiffness in two controlled divergence lateral entry coronal pin configurations. The sagittal pin configuration in this study was based on two considerations: first, limitations on the use of K-wire in small pediatric bones, and second, the K-wire must penetrate only the lateral and medial cortex of the bones. K-wire inserted into the medullary canal must travel without cutting through the bone cortex. For each test, a newly synthetic specimen was used instead of reused specimen because the initial procedure could potentially have damaged the outer cortical and inner cancellous structure of the synthetic bone after previous testing and thus destroyed or changed its material construction. This study investigated three interesting areas. The first area is the weakness of the AP sagittal pin configuration. Although AP is the standard recommendation for sagittal pin configuration, there are many alternative pin configurations for fixation, which have not yet been thoroughly evaluated. The present study found that the AP sagittal pin configuration had the lowest construct stiffness under many load types. We used previous studies associated with coronal pin configuration to explain the lack of this construct stiffness. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Leading** & **AP** & **Crossed** & **Divergent** & **Parallel** & \\ \cline{2-5}
**Condition** & **Mean \(\pm\) SD** & **Mean \(\pm\) SD** & **Mean \(\pm\) SD** & **Mean \(\pm\)SD** & **ANOVA \(p\)-Values** \\ \hline Extension (N/mm) & 3.38 \(\pm\) 1.25 & 4.73 \(\pm\) 0.79 & 5.20 \(\pm\) 0.45 & 3.68 \(\pm\) 0.21 & 0.066 \\ Valgus (N/mm) & 5.54 \(\pm\) 0.72 & 5.79 \(\pm\) 0.75 & 6.21 \(\pm\) 0.78 & 5.63 \(\pm\) 0.77 & 0.726 \\ Varus (N/mm) & 6.36 \(\pm\) 1.64 & 7.13 \(\pm\) 0.97 & 8.01 \(\pm\) 0.57 & 8.46 \(\pm\) 0.40 & 0.132 \\ Internal rotation & 0.085 \(\pm\) 0.006 & 0.073 \(\pm\) 0.006 & 0.093 \(\pm\) 0.020 & 0.098 \(\pm\) 0.010 & 0.134 \\ External rotation & & & & & \\ (Nm/deg) & 0.063 \(\pm\) 0.008 & 0.093 \(\pm\) 0.017 & 0.120 \(\pm\) 0.012 & 0.115 \(\pm\) 0.010 & 0.002 \\ \hline \hline \end{tabular} Abbreviations: AP, anterior to posterior pinning; ANOVA, analysis of variance.  
\end{table} 
Table 1: Comparison of construct stiffness of different pin configurations in the sagittal plane. \begin{table}
\begin{tabular}{c c c} \hline \hline
**External Rotation** & **AP** & **Crossed** & **Divergent** \\ \cline{2-3}
**(Nm/deg)** & **AP** & **Crossed** & **Divergent** \\ \hline Crossed & \(p\) = 0.096 & & \\ Divergence & \(p\) = **0.003** & \(p\) = 0.165 & \\ Parallel & \(p\) = **0.005** & \(p\) = 0.359 & \(p\) = 1.000 \\ \hline \hline \end{tabular} Abbreviations: AP, anterior to posterior pinning; ANOVA, analysis of variance. Statistically significant figures are shown in bold figures.  
\end{table} 
Table 2: Post hoc comparison of external rotation loading of different pin configurations. [PERSON] suggested that the pins cross each other in the lateral entry pin configuration at the fracture site level [25], resulting in horizontal malrotation and the development of cubitus varus.