Biomechanical analysis of pinning techniques for pediatric supracondylar humerus fractures

BACKGROUND: Closed reduction and percutaneous pin fixation is the recommended treatment of displaced (Gartland types 2 and 3) supracondylar humerus fractures. The need for a medial pin for maximal stability remains controversial. The purpose of this study was to develop a model of supracondylar humerus fractures simulating medial column comminution and to evaluate the torsional stability of various pin configurations recommended in the current literature. METHODS: Transverse cuts were made in synthetic humeri with a wedge taken from the medial aspect of the proximal fracture fragment in one half of the specimens to simulate medial column comminution. Each fracture was then reduced and fixed with 1 of 4 pin configurations using 0.062 in K-wires. The fixed specimens were then subjected to a torsional load producing internal rotation of the distal fragment. Rotation in degrees and the corresponding torque was recorded for statistical analysis. RESULTS: Specimens with the medial wedge removed demonstrated less torsional stability than their identically fixed counterparts with the intact medial column. In specimens with the intact medial column, the greatest torsional stability was achieved with the 2 lateral divergent and medial cross pin configuration followed by 3 lateral pins, then standard crossed pins with 2 lateral divergent pins demonstrating the least torsional stability. For the medial comminution group the 2 lateral, 1 medial pin construct again had the greatest torsional stability and 2 lateral pins the least. The standard crossed pin and 3 lateral pin constructs were not significantly different in the presence of medial comminution. CONCLUSIONS: In a synthetic humerus model of supracondylar humerus fractures, medial comminution was shown to reduce torsional stability significantly in all pin configurations. There was no statistical difference in torsional stability between 3 lateral pins and standard crossed pins in specimens with medial comminution.