Should Plate-Bone Gap be Preserved in Far-Cortical Locking Technique? A Biomechanical Study

Purpose The use of a locking plate eliminates excessive pressure on bone for anatomical reduction and thus preserves the periosteal blood supply, which is important for fracture healing. The far-cortical locking technique with a semi-rigid locking screw reduces structural stiffness and parallel motion, allowing uniform callus formation at the fracture site. Although previous studies demonstrated the superior clinical and biomechanical outcomes of semi-rigid locking screws over rigid ones, it is unclear whether a gap between the plate and bone should be preserved in the far-cortical locking technique. Methods The present study conducted finite element analyses with mechanical calibration to clarify the influence of a plate-bone gap on the biomechanical performance of the far-cortical locking technique. A simulated mid-shaft fracture model was fixed using a locking plate and six semi-rigid locking screws. The plate-bone distance was 0 to 2 mm and the axial compressive load was 500 N. Results Gliding guidance at the plate-bone interface enhanced parallel intersegmental motion but reduced intersegmental movement, which is a mechanical stimulant for callus formation, and may increase pressure on the bone. Screw stresses increased with increasing plate-bone gap distance. Conclusion For the far-cortical locking technique, the results suggest a minor plate-bone gap should be preserved. Engagement between the plate and bone should be avoided both before and after the application of mechanical load.