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Biomechanical analysis of pinning configurations for a supracondylar humerus fracture with coronal medial obliquity

Despite hundreds of studies of pinning configurations for transverse supracondylar humerus fractures, very few studies have investigated the optimal pin configurations in the treatment of supracondylar humerus fractures with coronal medial obliquity. The aim of this study was to develop a model of supracondylar humerus fractures with coronal medial obliquity and compare the stability of three various pin configurations to provide an acceptable pin placement. Oblique cuts were made in synthetic humeri at the level of the coronoid and olecranon fossae to simulate a humeral supracondylar fracture with coronal medial obliquity. Each fracture was reduced and fixed using two 0.062 inch K-wires in three different configurations, and sequentially tested in extension, varus, valgus, and internal and external rotations using an MTS 858 Minibionix materials testing load frame. We performed analysis of variance to compare construction stiffness of different pin configurations and the standard level of significant (P-value⩽0.05) was used indicate statistical significance. In resistance to extension and valgus loading, there was no statistical difference between all the three pin configurations (P=0.22 and 0.130, respectively). During the varus loading condition, the greatest stiffness values were obtained with the two crossed pin configuration, followed by the two medial pins, and the two lateral pin configuration showed the lowest values. For resistance in internal and external rotation testing, although there was no statistical difference between the two medial pins and the two crossed pins configurations (P=0.06 and 0.75, respectively), they were significantly greater than that of the two lateral pin configuration (P=0.003 and 0.004; P=0.001 and 0.02, respectively). In a synthetic humerus model of supracondylar humerus fractures with coronal medial obliquity, the two crossed pin configuration provided statistically greatest or comparable stability in the varus, and internal and external rotation loading conditions.