Effect of Plate Screw Configuration on Construct Stiffness and Plate Strain in a Synthetic Short Fragment Small Gap Fracture Model Stabilized with a 12-Hole 3.5-mm Locking Compression Plate.

Objective:  The aim of the study was to determine the effect of a short and long working length screw configuration on construct stiffness and plate strain in a synthetic, short fragment, small gap fracture model stabilized with a 12-hole 3.5-mm locking compression plate (LCP).

Study design:  Six replicates of short and long working length constructs on a short fragment, small gap fracture model underwent four-point bending. Construct stiffness and plate strain were compared across working length and along the plate.

Results:  With the LCP on the compression surface (compression bending), the short working length had a significantly higher construct stiffness and lower plate strain than the long working length. Conversely, with the LCP on the tension surface (tension bending), transcortical contact between 150 and 155 N induced load sharing at the fracture gap, which significantly increased construct stiffness and decreased plate strain in the long working length. At 100 N (precontact), the short working length had a significantly higher construct stiffness and lower plate strain than the long working length, comparable with our compressing bending results.

Conclusion:  In compression bending, and before transcortical contact occurred in tension bending, the short working length had a significantly higher construct stiffness and lower plate strain than the long working length. Load sharing due to transcortical contact observed in our model in tension bending will vary with fracture gap, working length, and loading condition. These results must be interpreted with caution when considering clinical relevance or potential in vivo biomechanical advantages.