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Comparison of 2D and 3D Metacarpal Fracture Plating Constructs Under Cyclic Loading
Eric P. Tannenbaum, MD; Geoffrey Burns, MS; Nikhil Oak, MD; Jeffrey N. Lawton, MD
University of Michigan, Ann Arbor, MI

Purpose: To determine if any differences in fixation construct stability exists under cyclic loading and subsequent load-to-failure between locking double-row (3D) plates and single-row (2D) plates in a metacarpal sawbone fracture gap model simulating mid-diaphyseal comminution.
Hypothesis: 1.5-mm locking 3D plates will demonstrate equal or greater stability under cyclic loading in comparison to 2.0-mm locking 2D plates in a sawbone model simulating an aggressive range of motion post-operative protocol. Furthermore, we predict the 3D plates will demonstrate a higher tensile strength when loaded to failure.
Methods: Thirty metacarpal saw bones were cut with a 1.75mm gap in between the two pieces simulating a comminuted fracture pattern. Half of the bones were plated with 2D plates and half with 3D plates. The plated bones were then mounted into a Materials Testing System (MTS) Mini Bionix testing apparatus where they were cyclically loaded under cantilever bending for 2,000 cycles at 70N, 2,000 cycles at 120N, and then monotonically loaded to failure. Throughout the testing sequence, fracture gap sizes were measured, failure modes were recorded, and construct strengths and stiffnesses were calculated for comparison.
Results: All double-row constructs survived both cyclic loading conditions. Ten of the fifteen (67%) single-row constructs survived both cyclic loading conditions, while five constructs failed during the 120N loading at 1377 +/- 363 cycles. When loaded to failure, the double-row constructs failed at 265 N +/- 21 N, whereas the single-row constructs surviving cyclic loading failed at 190 N +/- 17 N (p < 0.001). The double-row plates exhibited significantly lower stiffness (p<0.001), however, the construct stiffness was not significantly different.
Conclusion: Double-row metacarpal plates offer a lower profile metacarpal fixation option that provides the stability necessary for an early post-operative range of motion protocol. Double-row plates demonstrated increased resistance to failure in a cyclic loading model and increased load to failure compared to higher profile single-row metacarpal plates.

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