Mechanical comparison of 3.5 mm broad dynamic compression plate, broad limited-contact dynamic compression plate, and narrow locking compression plate systems using interfragmentary gap models.

Objectives: To compare (1) pullout properties between 3.5 mm cortical and locking screws, and (2) mechanical properties and gap displacements between the 3.5 mm broad limited-contact dynamic compression plate (LC-DCP), broad dynamic compression plate (DCP), and narrow locking compression plate (LCP), during axial loading of plate-stabilized diaphyseal fragments with an interfragmentary gap.

Study Design: In vitro mechanical testing of implanted polyurethane foam (PUF) hollow cylinders that simulated compact or osteopenic diaphyseal bone.

Sample Population: (1) Five cortical and locking screws and (2) 4 PUF-plate constructs for each plate type; using high- and low-density (0.8 and 0.32 g/cm(3)) cylinders.

Methods: (1) Screws were completely extracted at 5 mm/min. (2) Plated constructs were axially compressed at 300 N/s for 10 cycles from 5 to 355 N to determine gap displacement during physiologic loading, followed by single cycle increasing load to failure.

Results: Pullout properties were not different between screw types. All plate constructs had yield loads over 3 times trotting loads. Gap closure occurred with LC-DCP and DCP constructs, but not LCP constructs. LCP construct properties were most similar to LC-DCP and DCP construct properties in the low-density model.

Conclusion: All plate systems sustained physiologic limb loads. Only LCP constructs maintained some gap integrity, although LC-DCP and DCP screws were placed in neutral position.

Clinical Relevance: The LCP system is more likely than LC-DCP and DCP systems, with neutrally positioned screws, to maintain a planned interfragmentary gap, although gap strains range from 0% to 15% across the 2 mm gap during a trot load.