The influence of screw torque in the application of bone plates

Abstract

SummaryThe applied level of screw torque has a significant impact on both the mechanical 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 underlying bone is also affected. As a consequence, screw torque can be implicated in the pathogenesis of implant induced osteopenia and other pathological 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 strain was quantitated in response to variable levels of screw torque. This was 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 from the work presented herein, that lowering the level of applied screw torque does not adversely affect the rigidity of the final construction. This fact may serve to ameliorate the pathological consequences of applying screws and plates using current clinical criteria.The amount of torque applied to screws in the application of bone plates has a profound effect on a number of elements, namely the interface contact area and force. The work presented examines the effect of screw torque on the rigidity and bone strain distribution of fractured bone following bone plate reconstruction. It appears that the use of lower levels of screw torque, than currently used in clinical practice, does not adversely effect the rigidity of the final construction. These findings support the notion that the level of screw torque applied may have a role in ameliorating the pathogenic response that occur following bone plate application, namely osteopaenia.