Biomechanical analysis of lateral pin placements for pediatric supracondylar humerus fractures

Several clinical studies have shown that lateral pinning alone is of equal stability to crossed pins in the treatment of supracondylar fractures. The aim of this study was to compare the stability of parallel and varied divergent lateral pin configurations to provide an easily reproducible technique for optimal pin placement.

Twelve third-generation synthetic composite humeri were osteotomized at the level of the coronoid and olecranon fossae to simulate a humeral supracondylar fracture. Each fracture was reduced and fixed using two 1.6 mm (0.062 inches) Kirschner wires (1 fixed, 1 varied) in 4 different positions (from parallel to divergent with respect to fixed wire), and sequentially tested in extension, varus, and valgus as well as internal and external rotations using an MTS 858 Minibionix materials testing load frame (MTS Corporation, Eden Prairie, MN). A 2-way analysis of variance was carried out to compare construct stiffness in all 5 modes of testing according to both pin position and testing sequence. A level of P<0.05 was considered statistically significant.

The best torsional, valgus, and extension resistances were found with position 4, which was the most divergent configuration. For both internal and external rotations, position 4 showed statistically higher stiffness as compared with all other configurations (P<0.05). In resistance to extension, both positions 3 and 4 were stiffer than either position 1 or 2 (P<0.05). For resistance in varus testing, position 3 showed statistically greater stiffness than all other pin positions (P<0.05). Although there was no statistical difference between all the 4 positions in valgus testing, position 4 showed greater resistance when compared with other positions.

The lateral pin placed parallel to the metaphyseal flare of the lateral humeral cortex, in combination with a second diverging pin crossing the fracture site at the medial edge of the coronoid fossa (position 4), provided the optimum fixation for supracondylar fractures of the humerus.

Using these readily available landmarks, the treating surgeon can reproducibly provide appropriate pinning treatment for most of these fractures.