Mechanical Testing of Sliding on Pivot-Locking Clamp (SOP-LC) Fracture Repair System in Four-Point Bending and Torsion.

Objectives:  The first objective of this study was to compare the mechanical performance of a straight and contoured rod for the sliding on pivot-locking clamp (SOP-LC) system. The second objective was to compare single-cycle bending and torsion of the SOP-LC rod-bone constructs to a bone gap model between two clamp configurations.

Study design:  First experiment, 5 mm diameter rods from the 3.5 mm SOP-LC system, 4 straight and 4 bent rods were mechanically compared in four-point bending. The second experiment, 8 constructs with clamps on a single side of the rod and 8 constructs with clamps on alternating sides were compared in four-point bending and torsion. A torque limiting screwdriver at 2.5N was used for all constructs.

Results:  There were not significant differences between the noncontoured versus contoured rods. Constructs with clamps on a single side had a significantly higher yield load, yield displacement and bending strength, but the constructs with alternating clamps had a significantly higher initial torsional stiffness. There were no other significant differences. Mild clamp slippage and mild screw bending were noted in all the torsion tested constructs graphically with multiple stiffness slopes and visually on the post-tested constructs.

Conclusion:  Torque applied to initial screw placement may play a role in reducing clamp slippage. Although bending yield load, bending yield displacement, bending strength and torsional stiffness were improved by different clamp placement, clinically this will depend on fracture type. Further studies are needed for clinical significance.