Dynamic locking plates provide symmetric axial dynamization to stimulate fracture healing

Abstract

Axial dynamization of an osteosynthesis construct can promote fracture healing. This biomechanical study evaluated a novel dynamic locking plate that derives symmetric axial dynamization by elastic suspension of locking holes within the plate. Standard locked and dynamic plating constructs were tested in a diaphyseal bridge-plating model of the femoral diaphysis to determine the amount and symmetry of interfragmentary motion under axial loading, and to assess construct stiffness under axial loading, torsion, and bending. Subsequently, constructs were loaded until failure to determine construct strength and failure modes. Finally, strength tests were repeated in osteoporotic bone surrogates. One body-weight axial loading of standard locked constructs produced asymmetric interfragmentary motion that was over three times smaller at the near cortex (0.1 AE 0.01 mm) than at the far cortex (0.32 AE 0.02 mm). Compared to standard locked constructs, dynamic plating constructs enhanced motion by 0.32 mm at the near cortex and by 0.33 mm at the far cortex and yielded a 77% lower axial stiffness (p < 0.001). Dynamic plating constructs were at least as strong as standard locked constructs under all test conditions. In conclusion, dynamic locking plates symmetrically enhance interfragmentary motion, deliver controlled axial dynamization, and are at least comparable in strength to standard locked constructs. ß

Dynamic Stabilization with Active Locking Plates Delivers Faster, Stronger, and More Symmetric Fracture-Healing

“…Lateral pockets were arranged in an alternating pattern from both plate sides, resulting in a staggered locking hole configuration. The pocket geometry combined with the silicone suspension allowed controlled axial translation, which enabled up to 1.5 mm of axial motion across the fracture gap while providing stable fixation in response to bending and torsional loading 24 .…”

“…Axial compression was applied through a sphere proximally to permit physiological bending under axial loading 17,24,26 . Constructs were stepwise loaded in 50-N increments up to 1000 N. The resulting motion at the medial and lateral aspects of the osteotomy was measured with calipers for calculation of construct stiffness.…”

“…Active plates utilize standard locking screws that lock into the threaded hole of elastically suspended sliding elements embedded inside the plate. A biomechanical study demonstrated that active plates provide axial dynamization without decreasing construct strength 24 . This prospective, controlled animal study evaluated healing of fractures stabilized with active plates in comparison with standard locking plates in an ovine osteotomy model.…”

Biomechanical Concepts for Fracture Fixation

“…Yet with the advent of locked plating came novel strategies for dynamization, 31, 38, 49 since locking plates derive stability from fixed-angle locking screws and thus no longer require plate compression onto the bone surface. The strategy of FCL enables controlled and symmetric interfragmentary motion through elastic flexion of screw shafts within a motion envelope at the near cortex.…”

“…Moreover, “active” locking plates have been developed that provide controlled axial dynamization through elastic suspension of the locking holes within the plate, while using standard locking screws. 49 However, to date, only FCL screws have been fully evaluated by bench-top and cadaveric testing, 32, 57 a prospective randomized animal study, 33 and clinical trials. 50 Alternative strategies for dynamization should therefore be viewed with caution until they have been fully evaluated.…”