In vitro comparison of stiffness of plate fixation of radii from large- and small-breed dogs

Abstract

To compare in vitro axial compression, abaxial compression, and torsional stiffnesses of intact and plated radii from small- and large-breed dogs. Radii from 18 small-breed and 9 large-breed skeletally mature dogs. 3 groups were tested: large-breed dog radii plated with 3.5-mm limited-contact dynamic compression plates (LCDCPs), small-breed dog radii plated with 2.0-mm dynamic compression plates (DCPs), and small-breed dog radii plated with 2.0/2.7-mm cut-to-length plates (CTLPs). The axial compression, abaxial compression, and torsional stiffnesses of each intact radius were determined under loading with a material testing machine. An osteotomy was performed, radii were plated, and testing was repeated. The stiffness values of the plated radii were expressed as absolute and normalized values; the latter was calculated as a percentage of the stiffness of the intact bone. Absolute and normalized stiffness values were compared among groups. The absolute stiffnesses of plated radii in axial and abaxial compression were 52% to 83% of the intact stiffnesses in all fixation groups. No difference was found in torsion. There was no difference in normalized stiffnesses between small-breed radii stabilized with CTLPs and large-breed radii stabilized with LCDCPs; however, small-breed radii stabilized with DCPs were less stiff than were any other group. Plated radii of small-breed dogs had normalized stiffnesses equal to or less than plated radii of large-breed dogs. The complications typically associated with plating of radial fractures in small-breed dogs cannot be ascribed to an overly stiff bone-plate construct.