Optimization of a Novel Thread Geometry for Various Orthopaedic Surgery Applications

PROJECT SUMMARY ABSTRACTAmong the multiplicity of thread shapesthe buttress thread design remains the historic paradigm for the shape of current orthopedic screwsThe popularity of buttress threads in current orthopedic screw designs is reflected by the advantage of handling high axial thrust in one directionwhich leads to increased shear strength and improved unidirectional pullout resistance compared to other conventional thread shapesHoweverorthopedic screws are typically not challenged by axial loading forces from physiological motion invivoThusstandard buttress screws remain at a significant risk of failure when exposed to multidirectional loading forcesTo address the physiological multiaxial loading environmentnewer generation locking plates have been able to reduce the risk of implant failureparticularly in osteoporotic boneLocked plating relies on the benefit of a fixed angle construct that does not rely on friction and compression between implant and boneHoweverlocking head screws have been shown to have their own set of shortcomingsincluding the stiffness of plate screw constructsasymmetric callous formation and increased costhence the need for continued research towards more effective and cost conscientious solutionsSMV Scientific has designed a new bonescrew fastenerentitled SMV Bone Interlocking Thread GeometryBITGthat distributes forces from the implant onto the bone and subsequently resists loads in all directionsThe new fastener consists of afemale threadbone cutting technology designed to maximize bone volumepreserve bone architectureand create a circumferential interlocking interface between the implant and boneBITG resists multidirectional forces and bending moments to limit toggling and minimize radial forcesthereforeimproving resistance to failure and decreasing risk of creating stress risers and iatrogenic fracturesBITG allows for higher finishing torques compared to buttress screws and resists screw strippingand the BITG cutting mechanism curls the bone chips away from the cutting edges to create a debris freesolid bone implant interface in order to present iatrogenic bone destruction during screw insertionHoweverthis novel thread geometry has not been optimized for cortical and trabecular bone orthopaedic applications in normal and osteoporotic bone stockwhile subjected to different loading conditionsWe hypothesize that the optimized BITG screws will provide improved multidirectional load resistancewhen compared to buttress screwsfor cortical and trabecular screws under different loading conditions and bone typesThereforewe propose to conduct a parametric finite elementFEanalysis based study to optimize the BITG screws for orthopaedic useSpecific AimValidate our existing bone thread interface FE model with a cadaveric study using clinically relevant loading conditionsSpecific AimUse the validated FE model to conduct a parametric FE analysis to optimize thread geometry for cortical and trabecular screws PROJECT NARRATIVECurrentlyall commercially available orthopaedic screws use a buttressed thread designwhich applies an outward force on the bone and is designed to resist load in only one directionHoweverthe real life loading on orthopedic implants is multiaxial and canthereforeresult in loosening ortogglingcausing the screw to erode through the bone and enlargement of the hole within which the screw residesthereby leading to failure of fixationThe novel thread design presented in this proposal instead provides a radial inward force from the screw on the boneand subsequently resists loads in all directionsThe innovation presented here consists of a screw with bone cutting technology to increase bone volumepreserve bone architectureand create a uniquely threaded bone interface