Spinal Rod Anchorage via Plane-Parallel Clamping Surfaces
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Solution Overview
Problem
Existing anchorage methods for plastic connecting rods in spinal stabilization, such as grooved and frictional interfaces, lead to stress peaks and material deformation, failing to provide reliable long-term clamping and uniform force transmission.
Innovation Solution
A clamping arrangement with plane-parallel surfaces and a clamping device comprising a spacer and nut, ensuring congruent contours for uniform peripheral clamping, reducing stress and allowing for the transmission of tensile, compressive, shear, and torsional forces, while maintaining rod integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a frictional anchorage with indirect form-fit is used (clamping rod between screw head and spacer with nominal contour deviation), then the rod can be clamped, but high stress intensities result in the clamped areas and relative movements due to shear deformation occur
Solution Approach 1:
The invention applies local quality by creating a form-fit interface only in the clamping areas through circumferential clamping ridges on the rod and corresponding ridges on the spacer, while maintaining a smooth rod surface elsewhere. This localized geometric fitting concentrates the stabilizing effect exactly where needed (at the clamping interfaces) without requiring nominal contour deviation along the entire rod, thereby avoiding stress intensities in non-clamped areas while maintaining reliable clamping.
2Reliability
If the spacer contour nominally deviates from the rod contour in the area of contact, then clamping action is achieved, but rod material may flow off between the clamping areas if they do not form a closed cage
Solution Approach 1:
The invention localizes the form-fit interaction to specific circumferential clamping ridges rather than requiring a continuously deviating spacer contour. The spacer has a smooth contour that matches the rod except at discrete clamping locations where ridges create localized form-fit anchorage. This prevents material flow off between clamping areas while maintaining effective clamping action through the ridged interfaces.
3Reliability
If grooved surfaces are used for anchorage, then form-fit anchorage is achieved, but positioning the grooved surfaces requires precise introduction to avoid canting and continuous positioning is not allowed
Solution Approach 1:
The invention uses partial form-fit action through circumferential clamping ridges that engage with corresponding ridges on the spacer, rather than requiring complete grooved surface engagement. This partial engagement allows the rod to be inserted more easily without demanding precise positioning of complex grooved surfaces, while still providing reliable form-fit anchorage at the critical clamping interfaces. The smooth portions between ridges tolerate minor positioning variations.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution provides a stress-reduced, durable anchorage that ensures continuous positioning and force transmission, preventing material deformation and allowing for adjustable stiffness, enhancing stability in spinal stabilization.
Implementation Method 1
a frictional anchorage with an indirect form-fit. The connecting rod is smooth and is clamped between two members
Data Source
AI summary
Plastic rod anchorage for the surgical treatment of the spine where the plastic rod (1) has at least two plane-parallel surfaces (1a) in order to uniformly clamp the rod (1) on its entire circumference.