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Mechanical Evaluation of Locking, Nonlocking, and Hybrid Plating Constructs Using a Locking Compression Plate in a
Kathleen M Rowe-Guthrie1, Mark D Markel1, Jason A Bleedorn1
1Department of Surgical Sciences, University of Wisconsin, School of Veterinary Medicine, Madison, Wisconsin.
Objective:
To evaluate the mechanical properties of locking screw placement in hybrid plating in comparison to all-locked and all nonlocked constructs.
Study Design:
Completely randomized design. Forty-eight synthetic bone cylinders (4th generation composite Sawbones(®)) across 6 construct types (n = 8 each).
Methods:
An 8-hole 3.5 mm LCP was placed across a 2 mm cylinder gap to mimic an unstable fracture model. The plates were secured with all locking screws, all nonlocking screws, or a combination of locking screws and nonlocking screws in the hybrid constructs. Constructs were cyclically tested nondestructively in 4-point bending, axial compression, and torsion, and then tested to failure in torsion. The stiffness and strength of each construct were calculated and compared across construct types.
Results:
Constructs with a locking screw located adjacent to the fracture gap were stiffer in bending and stronger in torsion to failure than constructs without an adjacent locking screw. Hybrid and nonlocking screw constructs more frequently failed by catastrophic breakage of the bone cylinder, compared to all locking screw constructs that failed by plastic deformation of the plate.
Conclusions:
Mechanical testing of synthetic bone model constructs shows that hybrid constructs are at least as stiff and strong as entirely nonlocked constructs, and with some screw configurations, are not statistically different from entirely locked constructs.
