Investigations into the mechanical performance of a locking plate and evaluation of models to examine cortical bone and periosteal vascular perfusion after plate fixation

Abstract

Introduction Studying mechanical changes occurring during fracture repair with locking plates, and associated cortical-periosteal vascular changes, is vital for understanding bone healing. Methods Paired femora (n=6 pair) had conical coupling locking plates applied. One of each pair had a plate-bone distance (PBD): 0 mm and the other: 2 mm. Constructs were cyclically loaded to failure. Testing was repeated with aluminium tubing replacing bone, eliminating screw-bone cutout. All constructs were examined under stereo zoom and scanning electron microscope, at the screw-implant, screw-bone/metal interfaces. Blood flow in sheep cortical bone was assessed using stable isotope microspheres. Vascular mapping of the hind limb via contrast computer tomography (CT) and radiographic imaging was performed. The final in vivo study assessed two models for examining periosteal capillary perfusion beneath locking plates, with and without an ostectomy. CT and histological studies were performed. Results Biomechanical study: mean sustained loads in the 0 mm PBD group (420.8 Newtons, 7612 cycles) were significantly greater than in the 2 PBD mm group (337.5 Newtons, 4252 cycles) p<0.001. The conical coupling component of the locking mechanism did not uncouple. Cortical bone study: injecting stable isotope microspheres systemically and locally yielded inconsistent results. A critical review of procedures is needed. Periosteal study: New blood vessels were detected (not quantified), on histological examination. CT could not assess capillary perfusion. The design of a suitable study for examining periosteal capillary perfusion requires further evaluation. Conclusion Conical coupling locking plates can be elevated 2 mm from bone without uncoupling the locking mechanism. Capillary perfusion of the periosteum was identified qualitatively but not quantitatively. Examining ovine cortical and periosteal vascular perfusion requires further study to investigate the damage from screw placement.