Stresses in plated long‐bones: The role of screw tightness and interface slipping

Abstract

Using a three-dimensional finite element model of a plated long bone, we studied the influence of screw tightness, sliding frictional interfaces, and loading magnitude on the stresses within the plated bone. The model incorporated frictional interface elements that allowed stress-free separation under tensile loading to occur between the plate and bone and between the screw heads and the plate. The applied loading stimulated both static preloads created by tightening the screws that secure the plate to the bone and physiologic loads created by activity. Initial screw tightening with plate application created regions of bone hydrostatic compressive stress that may be partly responsible for ischemia under the plate. The inclusion of frictional interfaces resulted in a nonlinear relationship between physiologic loan and bone strain that was dependent on screw tightness. This nonlinear response correlated well with the results of previous in vitro studies showing that slippage between the plate and the bone can occur at physiologic load levels. The results showed that the effect of such slippage can be at least as important as plate material, rigidity, and placement in determining the degree of stress shielding. The results also indicated that previous plated bone models that assumed tight interfaces may have overestimated the extent of mechanical stress shielding.

Reasons why dynamic compression plates are inferior to locking plates in osteoporotic bone: a finite element explanation

“…This novel application induces normal stresses in the axial direction of the screw and does not require any artificial constraints or prescribed displacements. Values of preload vary widely in the literature; a value of 500 N was chosen based on an average of some (Rybicki and Simonen 1977;Zand et al 1983;Cheal et al 1985;Beaupre et al 1988;Perren 2002;Kim et al 2010;Ya'ish et al 2011). In the DCP models where the fracture was completely reduced, this approach was also used to simulate a 500 N tensile preload in the plate (Figure 3(b)).…”

“…While compression plate preloads have been included in some previous numerical studies (Rybicki and Simonen 1977;Cheal et al 1985;Beaupre et al 1988;Ferguson et al 1996;Kim et al 2010), their inclusion is via application of concentrated loads or as prescribed displacements. The effect produced by such techniques is not completely realistic; for example, an applied displacement to the bottom of a screw does not induce loads akin to screw fastening as the threads closest to the displacement will carry larger loads.…”

A biomechanical assessment of plate fixation, with insufficient bony support

“…During the later remodeling stages of healing, plating the compression side may not be beneficial. In the remodeling stage, reduced bone stresses when plates are applied to the compression side have been predicted in finite element models of plated bones (2) and from beam theory considerations (J. Cordey, private communication). As a result, the issue of plate-induced osteopenia needs to be considered as well.…”

Rigid versus flexible plate fixation for periprosthetic femoral fracture—Computer modelling of a clinical case

“…Computational models, based on finite element (FE) methods, have the potential to assess the mechanical performance of different fixation techniques [13,19]. These methods allow certain 1350-4533/$ -see front matter © 2011 IPEM.…”