Biomechanical effects of medial comminution and K-wire configurations in pediatric supracondylar humerus fractures

Supracondylar humerus fractures are common pediatric injuries requiring surgical fixation. Beyond technical factors, medial column comminution may substantially influence construct stability, yet its biomechanical impact across different three-pin configurations remains unclear. One hundred twenty synthetic humeri were assigned to six groups (n = 20). Medial comminution was simulated by 25% (small) or 50% (large) wedge removal. Three lateral divergent pinning (3LDP) and two lateral one medial crossed pinning (3XP) configurations were tested under varus bending, torsion, and photographic displacement analysis. In torsional testing, the 3XP configuration showed significantly greater stiffness and maximum torque than 3LDP across all wedge sizes (P < 0.005), including the intact condition (stiffness: 1.19 ± 0.29 vs. 0.51 ± 0.16 Nm/°; maximum torque: 10.70 ± 2.22 vs. 5.37 ± 1.59 Nm). In varus bending, large wedge removal significantly reduced maximum load in the 3LDP group (256.58 ± 50.26 vs. 214.03 ± 37.22 N; P = 0.045), while no wedge-related differences were observed in the 3XP configuration. Fracture-line displacement increased with wedge removal in both constructs (e.g. 0.88 ± 0.41 to 2.23 ± 0.40 mm in 3LDP; P < 0.001); wedge size significantly affected displacement in 3LDP, whereas in the 3XP configuration, displacement increased with wedge removal but did not differ significantly between small and large wedge sizes. Increasing medial comminution negatively affected stability, particularly in lateral-only three-pin fixation. 3XP constructs showed greater torsional resistance and preserved varus stability in this synthetic model. These findings provide biomechanical insight into fixation behavior in unstable supracondylar fractures.