Computer-supported spinal fusion rod shaping yields improved conformity compared to freehand bending.

Abstract

During spinal fusion surgery, metallic rods must be shaped to conform to pedicle screw positions. Poor conformity can overload screws, causing pull-out or loosening. Manual freehand rod bending is perception-dependent, time-consuming, cognitively demanding, and variable. We propose and evaluate a workflow in which rod shape is computed virtually via multi-objective optimization and then manually realized with a custom tool. The algorithm minimizes bend number and angle to improve efficiency and preserve rod strength. Seven spine surgeons each bent rods for a 7-level screw configuration using both freehand and computer-supported methods in randomized order. Screw poses were reproduced in a custom test rig with uniaxial load cells to measure anteroposterior forces during seating and after fixation. Bending time, peak and residual forces, and re-bends were recorded. Compared with freehand bending, computer-supported bending reduced median peak and residual forces by 41.9 % (p = 0.043) and 28.5 % (p = 0.027), respectively, and reduced bending and fixation time non-significantly by 27.4 % (p = 0.077). No re-bends or screw pull-outs occurred in the computer-supported group, whereas the freehand group required a median of 2.5 re-bends per trial. Computer-supported rod bending produced mechanically favorable constructs while eliminating re-bending. The observed force reductions align with previous benchtop studies, consistent with improved rod-screw conformity and reduced screw-bone loading. This workflow may offer a practical compromise between the precision of automated shaping systems and the flexibility of manual intraoperative bending, with potential to improve consistency in multi-level spinal fusion procedures. Effects on operative time and clinical outcomes remain to be established.