Load-displacement behavior in a distal radial fracture model - The effect of simulated healing on motion

External fixation of fractures of the distal end of the radius neutralizes external forces and maintains axial alignment during healing. As far res we know, there have been no biomechanical studies of the effects of early rem oval of the fixator in a partially healed fracture model, The purpose of th e present study was to observe the load-displacement behavior of a distal r adial fracture model in which we had simulated partial healing by injection of butyl-rubber caulk and augmented this simulated healing with Kirschner- wire fixation. Sixteen fresh-frozen hand-wrist-forearm specimens from cadav era were mounted in mid-rotation in resin pots, and a load was applied, An osteotomy was used to simulate the fracture, Relative motion at the site of the osteotomy was compared,,vith use of a three-dimensional Optotrak kinem atic device, during physiological loading of six constructs with Kirschner- wire transfixion or outrigger fixation. Zn the experimental group, partial healing,vas simulated by injection of butyl-rubber caulk into the site of t he osteotomy and testing nifh simulated muscle-loading was performed throug h a full range of motion of the wrist. No difference could be detected betw een the relative motion at the osteotomy sites that had been treated,vith s tandard fully augmented external fixation and that in the experimental grou p (p > 0.05). T test analysis revealed that motion was equivalent regardles s of whether Kirschner-wire transfixion or outrigger fixation had been used (p = 0.62) and that all of the augmented constructs had significantly less relative motion than all of the nonaugmented constructs (p < 0.001). CLINICAL RELEVANCE: In clinical practice, early removal of a standard exter nal fixator is desirable to prevent stiffness, provided that the removal do es not decrease the stability of the fracture. We found that the combinatio n of partial simulated healing and augmentation with Kirschner wires in vit ro provided stability that was comparable with that provided by full fixati on without simulated healing in an acute-fracture model. These findings sup port the concept of modular disassembly of the external fixator to allow an early range of motion of the wrist.