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

Area of Science:

• Orthopedic Surgery
• Biomedical Engineering
• Spinal Fusion Technology

Background:

• Spinal fusion surgery requires precise metallic rod shaping to match pedicle screw placement.
• Improper rod conformity can lead to screw overload, loosening, or pull-out, compromising surgical success.
• Manual freehand rod bending is inconsistent, time-consuming, and requires significant surgeon expertise.

Purpose of the Study:

• To evaluate a novel computer-supported workflow for shaping spinal fusion rods.
• To compare the mechanical outcomes and efficiency of computer-assisted versus manual freehand rod bending.
• To assess the impact of rod bending technique on screw-bone loading during spinal fusion.

Main Methods:

• A multi-objective optimization algorithm was developed to compute ideal rod shapes, minimizing bends and angles.
• Seven spine surgeons performed rod bending for a 7-level configuration using both freehand and computer-supported methods.
• Screw forces were measured in a test rig, alongside bending time and re-bend frequency.

Main Results:

• Computer-supported bending reduced median peak and residual forces by 41.9% and 28.5% (p<0.05), respectively.
• This method eliminated re-bends, unlike the freehand group which required a median of 2.5 re-bends.
• Bending and fixation time were non-significantly reduced by 27.4% (p=0.077).

Conclusions:

• Computer-supported spinal rod bending yields mechanically superior constructs with reduced screw-bone forces.
• This technique enhances consistency and efficiency in multi-level spinal fusion procedures.
• The workflow offers a balance between automated precision and manual flexibility, potentially improving patient outcomes.