The influence of screw torque in the application of bone plates

The applied level of screw torque has a significant impact on both the mech anical and vascular environment in bone following the application of a bone plate. The amount of torque applied dictates the resultant level of axial tension generated in the screw and the compressive forces between the plate and underlying bone. The interface contact area between the plate and unde rlying bone is also affected. As a consequence, screw torque can be implica ted in the pathogenesis of implant induced osteopenia and other pathologica l occurrences that follow bone plate fixation. The work performed was designed to evaluate the effect of the applied level of screw torque. The construction stiffness (rigidity) and bone surface st rain was quantitated in response to variable levels of screw torque. This w as performed utilizing intact and osteotomized cadaveric bone. The current level of screw torque applied in the clinical situation, for 4. 5 mm cortical screws, is approximately 5 Newton metres (Nm). It appears fro m the work presented herein, that lowering the level of applied screw torqu e does not adversely affect the rigidity of the final construction. This fa ct may serve to ameliorate the pathological consequences of applying screws and plates using current clinical criteria.