Bone Fixation Element with Reduction Tabs for Spinal Rod Alignment
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Solution Overview
Problem
Surgeons face difficulties in aligning longitudinal rods within rod-receiving channels in bone fixation elements due to misalignment caused by spinal curvature and varying vertebrae sizes, which complicates spinal fixation procedures.
Innovation Solution
A bone fixation element with integrally formed reduction tabs that temporarily extend the channel to facilitate rod insertion, featuring break-off points for removal after the rod is seated, and a locking cap system with negative thread profiles to secure the rod and limit splaying.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the bone fixation element is designed with a compact structure to minimize implant profile, then the rod insertion becomes difficult due to limited alignment tolerance, but if the structure is extended to facilitate rod insertion, then the implant profile increases
Solution Approach 1:
The bone fixation element is divided into two functional segments: a permanent body portion that maintains the compact implant profile, and temporary reduction tabs that extend the structure to facilitate rod insertion and alignment. The reduction tabs are designed to be removed after serving their alignment function, leaving only the compact body portion in place.
Solution Approach 2:
The reduction tabs are pre-positioned on the bone fixation element body to temporarily extend the rod-receiving channel, providing preliminary alignment guidance for the rod insertion process. This preliminary structural extension makes rod insertion easier before the tabs are removed.
2Ease of operation
If reduction tabs are used to extend the rod-receiving channel for easier rod insertion, then rod alignment is improved, but sharp edges may be created during tab removal that could cause post-operative complications
Solution Approach 1:
The break-off grooves are strategically positioned at specific locations on the reduction tabs to control the fracture behavior. These grooves create predetermined weak points that guide the breaking process, ensuring that when the tabs are removed, the fracture occurs in a controlled manner that minimizes sharp edge formation.
Solution Approach 2:
Break-off grooves are pre-formed on the reduction tabs during manufacturing, creating predetermined fracture paths before the tabs are used in surgery. This preliminary preparation ensures that when tab removal is necessary, the breaking process will follow a controlled path that reduces harmful sharp edges.
3Strength
If the reduction tabs are made strong to maintain structural integrity during insertion, then they can withstand insertion forces, but they become difficult to remove after rod seating
Solution Approach 1:
The reduction tabs exhibit non-uniform structural properties: the main body of the tabs maintains sufficient strength to withstand rod insertion forces, while the break-off grooves create localized weak points that facilitate easy removal after insertion. This local variation in quality allows the tabs to serve dual functions of strength and ease of removal.
Solution Approach 2:
The reduction tabs are designed as separable components with a clear division between the functional insertion portion and the removable portion. The break-off grooves create a natural segmentation point that allows the tabs to be cleanly separated from the bone fixation element body after serving their alignment purpose.
Data Source
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AI summary
A bone fixation element for use in posterior spinal fixation including a pair of spaced apart arms defining a rod-receiving channel and a pair of reduction tabs integrally formed and extending from the arms to facilitate insertion of a rod into the channel. The reduction tabs also preferably include a break-off region so that after the rod has been inserted in the channel, the reduction tabs can be removed leaving behind the bone fixation element and rod. The reduction tabs may also include a cap for coupling a proximal end of the reduction tabs.