Optimization of a Novel Thread Geometry for Various Orthopedic Surgery Applications

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PROJECT SUMMARY/ABSTRACT The majority of threaded interfaces (screws) used in orthopaedics utilize a buttress thread design which has limitations in clinical application. Clinically, orthopaedic screws must resist the dynamic forces generated during common activities of daily living, yet buttress screws are not designed to resist multidirectional force, leading to increased risk of postoperative complications including screw loosening and failure of fixation. Since the modifiable variables of buttress screw designs—including thread pitch, depth, width and face angle—are interrelated, attempts to improve screw functionality by altering these variables is limited. The challenge in bone threaded surface interface is in the optimization of threaded surfaces that meet the loading scenarios at different anatomic sites with varying bone stock, more often than not, one of poor bone quality. The development of innovative bone-screw-fastener technologies for the field of orthopaedic surgery is the underlying focus of OsteoCentric, Inc., a small business based in Austin, TX. The company has designed, manufactured and implemented a new bone-screw-fastener design, the Bone Interlocking Thread Geometry (BITG), based on a technology that creates a circumferential interlocking interface that maximizes bone volume and preserves bone architecture. The BITG overcomes many of the limitations of buttress screws by resisting multidirectional forces and bending moments, minimizing radial forces, and allowing for higher finishing torques. These enhancements can prevent fixation construct failure especially with cases with inadequate bone quality. We have successfully developed and validated bone-thread-interface Finite Element (FE) models for three loading conditions and have conducted a parametric FE analysis to optimize the BITG thread pitch geometry. The SBIR Phase II proposal seeks to build on our early success by optimizing the thread geometry; testing it in a large animal model; and optimizing the BITG thread manufacturing methodology. This will enable OsteoCentric to market a clinically superior product that reduces the overall cost of implants to the healthcare system by utilizing more cost-effective non-locking screws and plates. The specific aims of the Phase II are: Specific Aim 1: Conduct a comprehensive parametric analysis of the BITG using validated FE analysis to optimize cortical and cancellous thread geometry for normal and osteoporotic bones. Specific Aim 2: Optimize methods of BITG manufacturing to enhance cost-effectiveness and efficiency; build internal prototyping and manufacturing expertise; and build an education package for outsource production manufacturers to streamline BITG technology production. Specific Aim 3: Test the optimized BITG thread design against traditional buttress screw using an ovine fracture model in both normal and osteoporotic conditions.