## 2 Materials and Methods
### Methods  
We controlled coronal plane pinning with two divergent lateral entry pin configurations following the technique of [PERSON] [29]. Different pin placement configurations in the sagittal plane were evaluated for feasibility, given the limited area/size of pediatric bones. All configurations were bicortical medial and lateral cortex fixation. We established zones of pin entry and exit using the transverse diaphyseal diameter of the humeral shaft in the sagittal plane as reference. We first divided the anterior and posterior with an anatomical axis line, after which we drew a vertical line separating the cortical bone and the intramedullary canal. Then we designated four zones where pins would penetrate the bone cortex: zone 1 = the anterior diaphyseal cortex, zone 2 = the anterior diaphyseal medullary canal, zone 3 = the posterior diaphyseal medullary canal, and zone 4 = the posterior diaphyseal cortex (Figure 1). In each case, both pins were started from the lateral part of the distal fragment to the medial diaphyseal cortex. Pin trajectories were labeled numerically by entry and exit zone, e.g., 2-3 represents pin entry at the lateral part of the distal fragment (zone 2) and exit at the medial diaphyseal cortex (zone 3). In the coronal plane: the first pin was proximal and was parallel to the lateral metaphyseal flare of the humeral cortex; the second pin was distal and crossed the fracture site at the medial edge of the coronoid fossa. In the sagittal plane: the combined pin configuration designation listed the proximal pin trajectory first and distal pin trajectory second. For example, if the first proximal pin trajectory was 2-2 and the second distal pin trajectory was 1-1, the pin configuration was represented as [2-2,1-1]. Finally, four different pin configurations were chosen for study: the AP sagittal pin configuration [2-3,1-3] (currently the standard recommendation), the crossed sagittal pin configuration [2-4,4-2], the divergent sagittal pin configuration [3-3,3-1], and parallel sagittal pin configuration [3-3,2-2]. Four pin targeting guides were created from an epoxy resin casting to provide pin placement consistency and reproducibility. The specimens were securely encased in the epoxy mold and 1.5 mm holes were predrilled using the pin targeting guide. Transverse osteotomies were made at the level of the epicondyle (mid olecranon fossa) perpendicular to the anatomic axis of the humerus (28 mm from the distal end of the trochlea humerus) with a 0.5-mm cutting blade and the custom-built guide cutting. After fracture reduction, two pieces of 1.6 mm diameter Kirchner wire were inserted through the predrilled in the center of each of the four zones. After pinning, a fluoroscopic evaluation was accomplished to confirm the placement of all wires. Bone specimens underwent axial torsion and displacement load tests using an Instron ElectroPuls(tm) E10000 (Instron, Norwood, MA, USA). In external and internal torsion tests, we created an epoxy resin mold jig system consisting of outer and inner parts (Figure 2). The outer mold jig was attached permanently to the testing machine at the center of rotation of the long anatomical axis of the humerus to ensure that the position did not vary between specimens. The inner part could be moved into and out of the outer mold jig. After the bone specimen was inserted into the proximal and distal parts of the inner mold jig, it was mounted vertically on an outer jig and secured tightly with multiple bolts and nuts. Loads were applied to the proximal part of the bone by an actuator. The actuator allowed 0-25\({}^{\circ}\) of internal and external rotation, and samples were tested at a rate of 0.5 degrees/second. Torque (Nm/degrees) and degrees of rotation were recorded. Based on previous studies, rotational testing beyond 25-30\({}^{\circ}\) resulted in a plastic deformation or failure of the construct [16; 18]. Thus, in this study, we limited the degree for rotational testing at 25 degrees.