EFFECT OF DYNAMIZATION ON GAP HEALING OF DIAPHYSEAL FRACTURES UNDER EXTERNAL FIXATION

We asked whether dynamization of externally fixed diaphyseal fractures could improve bone healing in co parison to rigid fixation of fractur es having similar remaining gap sizes. To answer this question we eval uated metatarsal osteotomies in 12 sheep. The osteotomy with a 0.6-mm gap was stabilized with a specially designed high bending and torsiona l stiffness external ring fixator. Osteotomies in six sheep were stabi lized rigidly (axial movement < 0.06 mm) or dynamically (axial movemen t 0.15-0.34 mm). The cyclical axial interfragmentary movement was caus ed by the load-bearing of the operated limb. With increasing healing t ime, the initially allowed movement was decreased by callus formation around the osteotomy. The reduction in interfragmentary movement was m easured and monitored by a linear variable displacement transducer at the external fixator and a telemetry system. After 9 weeks the sheep w ere sacrificed and the healed bones were investigated biomechanically and histomorphologically. Compared to the rigidly fixed osteotomies, t he dynamized osteotomies showed significantly (P < 0.05) greater (+ 41 %) callus formation and 45% greater tensile strength of the newly for med bone in the cortical osteotomy gap. Histological analysis indicate d that the effect of dynamization occurred mainly after the 5th week. Relevance From these results we conclude that dynamic fixation of diap hyseal gaps is advantageous in comparison to stable external fixation.