Longitudinally-Adjustable Bone Anchors for Spinal Fixation
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Solution Overview
Problem
Current spinal fixation systems require precise contouring of rods to fit with bone anchors, which is time-consuming and can lead to mal-alignment, instrument failure, and patient discomfort due to excessive reduction forces.
Innovation Solution
Longitudinally-adjustable bone anchors that allow for adjustment of the anchor length independently of the rod, eliminating the need for precise rod contouring and reducing reduction forces by enabling the anchor to be brought up to the rod instead of the rod being bent to fit the anchor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If precise rod contouring is performed to fit bone anchors, then alignment accuracy is improved, but surgical time and complexity increase
Solution Approach 1:
Instead of bending the rod to fit the fixed bone anchors, the invention allows the bone anchor position to be adjusted to match the rod. This reverses the traditional approach where the rod is contoured to accommodate the anchors, and instead the anchors are repositioned longitudinally along the rod to achieve proper alignment, thereby eliminating time-consuming rod bending procedures
Solution Approach 2:
The bone anchor is designed with longitudinal adjustability, transforming from a static fixed-position anchor to a dynamic adjustable anchor. The adjustment mechanism allows the anchor to move along the rod longitudinally, enabling the surgeon to optimize the fit between the rod and multiple anchors without precise pre-contouring, thus reducing surgical complexity and time
2Manufacturing precision
If significant reduction forces are applied to align rod with bone anchors, then alignment is achieved, but bone anchor loosening and construct failure occur
Solution Approach 1:
Rather than applying reduction forces to the rod to make it fit the anchors, the invention applies adjustment forces to the bone anchor itself, moving the anchor along the rod to achieve alignment. This inversion of the force application approach eliminates the need for significant reduction forces that could compromise the anchor-bone interface
Solution Approach 2:
The bone anchor is designed with preliminary longitudinal adjustability built into its structure, allowing it to be positioned optimally before final tightening. This preliminary adjustment capability enables alignment to be achieved through controlled anchor movement rather than through forceful reduction maneuvers that could cause loosening or failure
3Shape
If rod is bent multiple times to accommodate deformities and gravity forces, then spatial relationship between vertebrae is improved, but rod fatigue life is reduced
Solution Approach 1:
The system transitions from a static rod with fixed contours to a dynamic system where the bone anchor position can be adjusted along the rod. This allows the rod to maintain simpler, less contorted shapes while still accommodating spinal deformities and gravity forces through anchor repositioning, thereby reducing cyclic stress and extending rod fatigue life
Data Source
AI summary
Longitudinally-adjustable bone anchors and related methods are disclosed herein. The ability to adjust a bone anchor longitudinally can allow the surgeon to bring an implanted bone anchor up to the rod instead of or in addition to bringing the rod down to the bone anchor, which can simplify or eliminate the rod contouring step and reduce or eliminate reduction forces. For example, the surgeon can use a pre-bent rod or put “ideal contours” into a rod, lay the rod across a series of bone anchors, and adjust each bone anchor longitudinally to meet the rod. As another example, coarse adjustment of the fixation system can be achieved by contouring the rod and then fine adjustments can be made by bringing each bone anchor up or down to the rod. Various adjustment mechanisms are disclosed, including bone anchors with telescoping portions and bone anchors with risers or spacers.