Design and Additive Manufacturing of a Rod Holding and Placement Instrument (RHAPI) for Spinal Rehabilitative Surgery

Abstract Conventional spinal instrumentation systems relying on hex wrenches often face challenges in achieving precise, efficient rod placement. These traditional methods typically require multiple manual adjustments, limited adjustability during positioning, and lateral rod movements that risk misalignment, prolonging surgery and complicating optimal rod orientation. To address these limitations, a novel instrument, the Rod Holding and Placement Instrument (RHAPI), has been developed through an additive manufacturing-driven design process. Initial prototypes were fabricated using fused deposition modeling (FDM) to rapidly evaluate ergonomics, knob mechanics, and jaw geometry at low cost. Iterative refinement was then performed using aluminum and titanium versions, balancing mechanical performance, biocompatibility, and durability while validating torque capacity, angular resolution, and rod stability against clinical benchmarks. Additive manufacturing enabled accelerated design iteration, ergonomic testing, and seamless progression from concept to surgical-grade prototypes. Unlike hex-wrench-dependent systems, RHAPI integrates a single-handed rotational control mechanism via an ergonomic top-mounted knob, minimizing lateral displacement and ensuring precise rod orientation. Designed primarily for spinal reconstructive surgeries, including fusion and scoliosis correction, RHAPI also demonstrates how additive manufacturing can bridge conceptual design with functional surgical instrumentation, offering a versatile, scalable, and efficient pathway for medical device innovation.