Biomechanical Analysis of Supracondylar Humerus Fracture Pinning for Fractures With Coronal Lateral Obliquity

Abstract

Closed reduction and percutaneous pin fixation is the recommended treatment of displaced supracondylar humerus fractures. The optimal pin configurations in the treatment of supracondylar humerus fractures with coronal lateral obliquity remain controversial. The aim of this study was to compare the stability of various pin configurations in the treatment of lateral oblique supracondylar humerus fractures to provide an acceptable pin placement. Nine third-generation synthetic composite humeri were osteotomized to simulate a humeral supracondylar fracture with coronal lateral obliquity. Each fracture was reduced and fixed using 2 or three 1.6-mm (0.062 in) Kirschner wires (K-wire) in 3 different configurations, and sequentially tested in extension, varus, valgus, and internal and external rotations using an MTS 858 Minibionix materials testing load frame (MTS Corporation, Eden Prairie, MN). Each fracture was fluoroscopically imaged and the distance between the pins at the fracture site was also recorded. Analysis of variance was carried out to compare construct stiffness for different pin configurations. A paired-samples t test was used to evaluate differences in the distance between the pins for 2 different pin configurations. A level of P<0.05 was considered statistically significant. During extension and internal and external rotation loading conditions, the 2 lateral divergent pins had significantly greater stiffness values than 2 crossed pins. During the valgus loading condition, crossed pins were more stable than 2 lateral pins. During varus loading, there was no statistical difference between the 3 pin configurations (P>0.05). During all the 5 loading conditions, there was a trend for 3 lateral pins to have greater stiffness values than the 2 lateral pins, but this was not statistically significant. The distance between the pins at the oblique fracture site for the 2 lateral divergent pins was statistically greater than the 2 crossed pins. Two and 3 lateral pin configurations had comparable construct stiffness and both were greater than crossed pins, except in the valgus, where crossed pins had greater stiffness. Using these readily available landmarks, the treating surgeon can reproducibly provide appropriate pinning treatment for most of these fractures. In addition, this report represents a helpful reminder that the pinning configuration should be effective and if not, the pins are not positioned correctly.