Pivoting Rod Clamp for Spinal Fixation Stability
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Solution Overview
Problem
Existing spinal fixation devices, such as those used for spondylodesis, often cause undesirable stresses due to vertical clamping of rods, which can lead to irregularities and discomfort for patients, especially when dealing with curved spine conditions like kyphosis or lordosis.
Innovation Solution
A device featuring a pivoting rod clamp and clamping screw system with spherical zones and undercuts, allowing for relative pivoting and secure connection, ensuring a reliable and uniform power transmission, and accommodating different rod diameters through a system of radial projections and grooves, enabling angled clamping without punctiform contact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a clamping screw is used to secure the rod to the pedicle screw head, then the rod is firmly clamped, but the vertical clamping force creates undesirable stresses on the rod and surrounding structures
Solution Approach 1:
The invention replaces the traditional vertical clamping screw with a spherical rod clamp that contacts the rod through a spherical surface. This curved contact geometry distributes the clamping force radially rather than concentrating it vertically, reducing undesirable stresses on the rod while maintaining firm clamping. The spherical zones allow for angular adjustment and accommodate spinal curvatures like kyphosis and lordosis.
2Strength
If the rod diameter is increased to improve structural strength, then load-bearing capacity increases, but the contact area with the clamping screw remains limited leading to stress concentration
Solution Approach 1:
The spherical rod clamp with its curved contact surface increases the effective contact area with the rod regardless of rod diameter variations (5-6mm). The spherical geometry naturally distributes forces over a larger area compared to a point-contact screw, reducing stress concentration while accommodating different rod sizes through the same clamping mechanism.
3Ease of manufacture
If fixed angular alignment is used between pedicle screws and connecting rods, then manufacturing and installation are simplified, but the device cannot accommodate spinal curvatures like kyphosis and lordosis
Solution Approach 1:
The invention introduces a dynamic, adjustable angular alignment system through the spherical rod clamp that can pivot relative to the pedicle screw head. This allows the connecting rod to be positioned at various angles to accommodate spinal curvatures (kyphosis, lordosis) while maintaining a simple overall device structure. The spherical zones enable angular adjustment without complex mechanisms.
Solution Approach 2:
The spherical rod clamp allows changing the angular parameter of the connecting rod relative to the pedicle screw head. By adjusting the angle at which the spherical zones contact, the device can adapt to different spinal curvatures and anatomical variations, transforming a fixed-parameter system into a variable-parameter system that maintains simplicity.
4Device complexity
If a punctiform contact between clamping screw and rod is used, then the device structure is simplified, but reliable power transmission and uniform force distribution cannot be achieved
Solution Approach 1:
The spherical rod clamp replaces point-contact clamping with surface-contact clamping. The spherical surface of the rod clamp contacts the rod over an area rather than at a single point, ensuring reliable power transmission and uniform force distribution. This maintains relative structural simplicity while significantly improving contact reliability.
Data Source
Figure 1~2
Figure 2a
Figure 3
AI summary
The invention relates to a device (1) for securing a rod (10) to a bone, comprising a tulip (3), a pedicle screw (2) and a tightening screw (5). A rod clamp (6) can be pivoted relative to the tightening screw and can thus follow the transverse movements of the rod. This increases the stability of the whole structure, especially in its application in spinal surgery.