THE VASCULAR-RESPONSE TO FRACTURE MICROMOVEMENT

Micromovement has been shown to promote the healing of experimental fr actures, but its role in the clinical management of fractures with sof t-tissue injury is less certain. In a 2-mm transverse osteotomy of the ovine tibia held in an instrumented external fixator, axial interfrag mentary displacement was quantified in vivo for six weeks after osteot omy. Group I(n = 11) had an axial fixation stiffness of 460 N/mm and G roup II (n = 12) had a stiffness of 238 N/mm. With a 25% difference in micromovement, a fourfold change in corticomedullary blood flow was o bserved at two weeks after osteotomy (p < 0.01). Although by six weeks mechanical properties in torsion were similar, there were marked diff erences in the periosteal cross-sectional perimeter, area, and intraco rtical porosity that complemented the hemodynamic changes. The early v ascular response is very sensitive to the initial mechanical environme nt, and appears to precede and determine the organization of osteogene sis. Further understanding of this relationship may prove to be of dir ect clinical relevance in the augmentation of healing of devascularize d diaphyseal fractures.