THE CLIENT’S REQUEST
Historically, bending a metal rod to fit the spine of a particular patient either for preventative or corrective surgery was an inexact science and potentially a long and arduous procedure. Calculating and placing significantly longer percutaneous rods using traditional methods required a high level of skill. New hardware and software solutions were required to add predictability and efficiency.
NOVO was contracted to assist in developing a software application for a spinal rod bending system created by NuVasive, Inc., a medical device company specializing in minimally invasive, procedurally integrated spine solutions. The complete rod-bending system for spinal fusion required an intelligent software application to integrate with NuVasive’s existing Integrated Global Alignment™ (iGA) technology platform.
TECHNICAL CHALLENGES: SPINAL ROD-BENDING AUTOMATION
The process of constructing a custom rod begins with data acquisition, in particular, the location and direction of the tulip-head screws that have already been implanted by the surgeon into a patient’s spine. Geometry data is fed into the software application via a hardware system consisting of an IR vision system together with a stylus manipulated by the surgeon. An array of IR-reflective spheres, temporarily mounted to the tulip-head pedicle screws, captures the precise location of the tulip heads in 3D space and provides full directional information in the form of a quaternion.
The software automatically calculates bend locations and angles between each screw by employing well-known methods from numerical analysis, vector calculus, and machine learning. There are various constraints the bend locations must adhere to that the software uses when generating and validating potential results. Constraints considered by the software include the physical limitations of the hardware that bends the rod, rod material, rod diameter, and the smoothness of the bends along the curvature of the rod. User-specified constraints, such as rod overhang, are also considered.
Once the software has computed a valid set of bend locations that fit the construct within some specified tolerance, it then transforms those bend locations into a set of bend instructions consisting of bend location, rod rotation, and bend angle. The bend instructions are generated and presented in such a way that they are readily used with the rod-bending apparatus that is provided as part of the hardware system.
The rod-bending software is designed to be used interactively in the operating room (OR). As the surgeon acquires data for each tulip in the construct, visual feedback is provided in the form of a virtual screw construct on the screen, showing both the coronal and sagittal views. Once the surgeon has completed data acquisition, a virtual rod is bent using a virtual bender and aligned to the virtual screw construct for yet another form of feedback, representing the expected physically bent rod.
THE ENGINEERING BEHIND GREAT PRODUCTS
The result was the Bendini® spinal rod-bending system, an award-winning innovation in spine that expedites manual rod manipulation via computer-assisted bend instructions. The system is part of the iGA platform from NuVasive, which includes procedurally integrated technologies designed to enhance clinical and economic outcomes by increasing the predictability of achieving global alignment in all spinal procedures.
NOVO’s software engineers developed a C#.NET WPF application and provided NuVasive with a custom user interface, incorporating UI design elements provided by another contractor, and a suite of algorithms designed to solve the problems described above. A combination of NOVO’s expertise in machine learning and computational mathematics, workflow design, and UI design implementation, coupled with their software engineering and experience interfacing with third-party hardware devices, such as the IR optical system, allowed the team to focus on solving the problem and assist NuVasive with the development of the product.