Single-Rod Spinal Derotation to Reduce Pedicle Screw Pullout
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Solution Overview
Problem
Current surgical methods for correcting spinal deformities, such as scoliosis, face challenges including pedicle screw pullout and loosening due to high stress, especially in osteoporotic bones, and limited rotational correction in the axial plane, leading to pseudoarthrosis and inefficiency.
Innovation Solution
A system utilizing a single pivot point with a pivot tool and saddle reducer, allowing for derotation off a single rod, distributing forces evenly across multiple pedicle screw fixation points, and using polyaxial screws to reduce stress shielding and screw loosening.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If multiple shafts with handles and wrenches are used to apply forces for derotation, then rotational correction in the axial plane is achieved, but the pedicle screws may pull out or loosen due to extreme forces applied to individual screws
Solution Approach 1:
The system divides the derotation force application into multiple independent force vectors applied through separate shafts and handles to different groups of pedicle screws. This segmentation distributes the mechanical stress across multiple fixation points rather than concentrating extreme forces on individual screws, reducing the risk of screw pullout or loosening while achieving the required rotational correction in the axial plane.
Solution Approach 2:
The pedicle screws are implanted and rods are attached to the screw heads before the derotation maneuver is performed. This preliminary action establishes a stable fixation framework that distributes subsequent derotation forces across multiple screws and rods, preventing screw pullout or loosening during the actual derotation process when corrective forces are applied.
2Manufacturing precision
If extreme forces are applied to individual pedicle screws during derotation, then vertebral derotation is achieved, but stress shielding occurs that can loosen the bone screw interface and create pseudoarthrosis
Solution Approach 1:
The derotation system segments the force application across multiple pedicle screws and bilateral rods, distributing the mechanical load to prevent stress shielding at any single bone-screw interface. This segmentation maintains adequate stress transmission to promote bone healing while achieving the necessary vertebral derotation correction.
Solution Approach 2:
The system merges multiple force vectors applied through separate shafts and handles into a coordinated derotation maneuver. By combining these forces through the rod-screw construct, the system achieves effective vertebral derotation while distributing stresses to prevent interface loosening and pseudoarthrosis formation.
3Manufacturing precision
If multiple shafts and handles are clustered en bloc using clamps and wrenches, then derotation force is applied to correct the spine in the axial plane, but the procedure becomes complex and time-consuming
Solution Approach 1:
The system employs universal shafts and handles that can be configured and clustered in various arrangements to apply derotation forces. These multi-functional components can be adapted to different spinal deformity patterns and surgical approaches, reducing the need for specialized instruments while achieving effective axial plane correction.
Solution Approach 2:
Rather than requiring a single complex en bloc cluster of all shafts and handles, the system segments the derotation process into manageable groups that can be applied and adjusted independently. This segmentation simplifies the overall procedure by allowing stepwise application of corrective forces rather than requiring simultaneous coordination of all components.
Data Source
AI summary
Methods and systems for axial spinal derotation for ameliorating or correcting aberrant spinal column deviations, such as but not limited to those associated with scoliosis. The systems and methods help facilitate the application of significant derotational forces to individual vertebrae and posterior elements. The present invention describes a two-piece system comprising a pivot tool with a handle and a saddle reducer, e.g., a temporary rod. The systems herein can replace more complex systems for axial spinal derotation. The systems have the advantage of axial rotation off of one rod instead of two.