Biomechanical Testing of Unstable Humeral Shaft Fracture Plating

This study compared the biomechanical performance of 4.5-mm limited-contact dynamic compression plates (DCPs) and 3.5-mm locking compression plates (LCPs) for the fixation of unstable humeral shaft fractures. Composite humeri were divided into two groups: 3.5-mm LCPs and 4.5-mm DCPs. Osteotomy gaps of 5 mm, simulating diaphyseal comminution, were created. Stiffness tests were performed in anterior–posterior (AP) bending, medial–lateral (ML) bending, torsion, and axial compression. Results showed that while construct stiffnesses in ML bending and torsional loading are significantly higher for the 4.5 DCP group (p < .05), no statistically significant differences were observed in AP bending or axial compression. Fatigue characteristics under cyclic AP bending conditions were also evaluated, although no failures occurred. Data from the literature suggest that stiffness results for the LCP constructs perhaps afford sufficient fixation strength capable of supporting the physiologic loads most commonly applied during postoperative rehabilitation. However, results indicate that the DCP construct is mechanically advantageous for stabilizing diaphyseal comminuted fractures. (Journal of Surgical Orthopaedic Advances 18(4):175–181, 2009)