Biomechanical Analysis of Posterior Intrafocal Pin Fixation for the Pediatric Supracondylar Humeral Fracture

Background: Controversy remains regarding the optimal fixation for displaced pediatric supracondylar humeral fractures. The clinical results of a recently described technique using a posterior intrafocal pin have been good to excellent. The aim of our study was to compare, in a cadaveric model, the stiffness provided by posterior intrafocal pin fixation versus crossed medial and lateral pin fixation and divergent lateral entry pin fixation for the treatment of Gartland-Wilkins type 3 supracondylar humeral fractures. Methods: In 15 pairs of nonosteoporotic adult cadaver specimens, simulated Gartland-Wilkins type 3 supracondylar fractures were created and stabilized using: (1) the posterior intrafocal pin method; (2) medial and lateral crossed pins; or (3) 2 divergent lateral entry pins. Specimens were then subjected to internal rotation to measure the fixation stiffness of each construct. The effects of treatment and cycle number on torsional stiffness and peak torque were assessed for significance using a linear regression model with random effects to account for specimen pairing. Significance was set at P < 0.05. Results: The stiffest fixation was provided by crossed pins (2.4 N m/degree), followed by divergent lateral pins (1.9 N m/degree) and the posterior intrafocal pin (1.9 N m/degree), but none of the differences was statistically significant (P > 0.9). Peak torque was not significantly different between fixations, although the trend suggested that crossed pins were strongest (34.6 N m), followed by divergent lateral pins (30.3 N m) and then posterior intrafocal pin fixation (26.1 N m). Conclusions: Our results suggest that posterior intrafocal pin fixation offers resistance to internal rotation equivalent to that of crossed medial and lateral pins and divergent lateral entry pins. Clinical Relevance: The current biomechanical study supports the use of the posterior intrafocal posterior Kirschner pin for rotationally unstable supracondylar fractures because it is not significantly more compliant than standard techniques. Level of Evidence: Level III.