Enhanced biomechanical stiffness with large pins in the operative treatment of pediatric supracondylar humerus fractures

BACKGROUND: Various pin configurations have been recommended for the treatment of supracondylar humerus fractures on the basis of the choice between stability versus the risk of iatrogenic nerve injury. However, little attention has been paid to pin size. The purpose of this study was to evaluate the stability of large (2.8 mm or 0.110 inch) and small (1.6 mm or 0.062 inch) pin constructs in 6 configurations. METHODS: A transverse fracture pattern was created by sectioning synthetic humeri in the midolecranon fossa. The specimens were then reduced and pinned in one of 6 configurations: 2 small pins (Kirschner wires) placed crossed or lateral divergent, 2 large pins (Steinmann pins) placed crossed or lateral divergent, or 3 small pins placed crossed or lateral divergent. All specimens were then tested in sagittal extension bending. We investigated the effect of pin configuration and cycle on the sagittal stiffness using multiple linear regression. RESULTS: The 2 small lateral divergent pin configuration was significantly less stable than small crossed pins and large pins in a crossed or a lateral configuration. The addition of a third (lateral) pin to the small crossed pin construct made it significantly less stable than 2 large crossed pins. Although the stability between the remaining configurations was not significantly different, the 2 large crossed pins required the greatest torque to rotate the fragment 20 degrees. There was a significant reduction in torque as a function of cycle, suggesting a loss of fixation during cycling (P<0.05). CONCLUSIONS: Large pins (2.8 mm) in any configuration and the placement of small pins (1.6 mm) in a crossed configuration provided more stable reduction in sagittal extension bending than did the conventional 2 small pins in a lateral divergent pin configuration. The most stable configurations involve crossing the medial and lateral pins. CLINICAL RELEVANCE: There are more stable options than the traditional 2 small lateral pin configuration for fixation of unstable supracondylar fractures. The addition of a third pin is not always advantageous.