Abstract
Objectives The aim of this study was to compare the compressive effect between preloaded position
screws and lag screws in fracture fixation.
Methods Pairs of semi-cylindrical bone fragments were created on a porcine rib model to simulate
fractured bones. The compressive forces of fracture fixation generated by preloaded
position screws (P group) and conventional lag screws (L group) were recorded by a
film stress sensor. In the P group, a pair of Angus bone holding forceps was used
to compress the interfragmentary interface until reaching the preloading force of
1.3 MPa. Similar preloading procedure was applied on lag screw fixations to explore
its potential of additional compressive force.
Results With 1.3 MPa preloading force and 0.2 Nm screw insertion torque force, the interfragmentary
compressive force of P group was similar to that of L group. When the insertion torque
force was increased to 0.4 Nm, all screws in the L group failed due to thread stripping.
When screws in the P group were installed under 0.4 Nm torque and in the L group under
0.2 Nm torque, the P group generated significantly greater compressive force. With
preloading device applied on lag screw installation, it did not further increase the
interfragmentary compressive force.
Clinical Significance Compared with lag screws, preloaded position screws tolerated greater torque in screw
installation and provided greater interfragmentary compressive force. The study suggests
the applicability of preloaded position screws in fracture fixation requiring interfragmentary
compression.
Keywords
preloaded stress - interfragmentary compression - position screw - lag screw - biomechanical
