Biomechanical evaluation of medial column comminution amount and different K-wire fixation configurations in synthetic bone models of pediatric supracondylar humerus fractures

Supracondylar humerus fractures (SHF) are among the most common fractures in childhood requiring surgery. Loss of reduction can occur at rates of 3-15%. Although the most frequent cause of reduction loss is deficiencies in surgical technique, fracture morphologies such as medial column fragmentation, low fractures, and sagittal oblique fractures also reduce stability and increase the risk of reduction loss. The aim of this study is to biomechanically investigate the effect of the size of medial column fragmentation on stability and the stabilities of three K-wire configurations that can be used in medial column fragmentation. 120 synthetic humerus bones and 700 Kirschner wires were obtained. Six groups of 20 bones each were formed. Groups were created by planning the removal of wedges to account for 25% and 50% of the fracture line on the medial side for the lateral divergent three K-wires (3LDP) and the cross three K-wires (3XP) configurations, which include two lateral and one medial entry. Torsion and varus bending tests were applied. Data on stiffness, maximum torque/load, and photographs of changes at the fracture line were obtained in these tests. ANOVA, Mann Whitney U, and Fischer LSD pairwise comparison tests were used for data evaluation. In the torsion test, the stiffness and maximum torque of the 3XP configuration were found to be higher than those of the 3LDP configuration. The torque values required for 5° and 10° rotations were significantly higher in the 3XP configuration group without wedge removal compared to the groups with wedge removal. There was no significant difference between the configurations in the varus bending test. The size of the removed wedge had no significant effect on stability in the 3XP configuration groups. In the 3LDP configuration groups, the maximum load of the group with large wedge removal was significantly lower than that of the group without wedge removal, while there was no significant difference in stiffness, although it was observed to be less stiff. It was observed that the changes at the fracture line due to the configurations did not result in a significant difference. While there was a significant change at the fracture line in all configurations due to wedge removal, the size of the wedge did not have a significant effect on the change at the fracture line in the 3XP configuration. In the configurations created with three K-wires, it was observed that the size of the wedge and the removal of the wedge had no significant effect on stiffness. In the 3LDP configuration groups, large wedge removal significantly reduced the maximum load in the varus bending test, while there was no such finding in the 3XP groups. While wedge removal caused a significant change at the fracture line in the 3XP configuration, the size of the wedge had no effect on this change. Biomechanically, the 3XP configuration is the most stable and safe configuration in cases of medial column fragmentation according to these findings.