Spinal Anchor Device with Wave Spring Yoke
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Solution Overview
Problem
Existing spinal fixation systems face challenges in providing sufficient multi-axial fixation while maintaining a low profile and ease of construction, as well as ensuring the system can withstand harsh spinal loads and allow for manipulative movement during surgery.
Innovation Solution
A spinal fixation system featuring a multi-axial anchor device with a bone engaging fastener, a yoke that swivels relative to the fastener, and a spring element providing static friction to securely hold the yoke in position, allowing for variable spherical angles and temporary retention during implantation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a multi-axial screw design with spherical projection and internally threaded receiver member is used to achieve various three-dimensional orientations, then adaptability is improved, but device complexity increases
Solution Approach 1:
The anchor device is divided into separate functional components: a bone screw for vertebral engagement, a yoke with channel for rod reception, and a compression member for securing. This segmentation allows each component to be optimized independently while providing multi-axial capability through their assembly.
Solution Approach 2:
The yoke is designed to be movable relative to the bone screw before final tightening, allowing dynamic adjustment of angular orientation. The compression member secures the rod and yoke in the desired position, transitioning from a dynamic adjustable state to a fixed stable state.
2Adaptability or versatility
If compression members are threaded onto a threaded spinal rod to compress and lock the screw, then adaptability is improved, but the rod strength deteriorates due to weakening from threading
Solution Approach 1:
Instead of threading the compression member onto the rod (which weakens the rod), the design inverts the approach by having the compression member press against the rod through friction and geometric locking within the yoke channel, eliminating the need for rod threading.
3Ease of operation
If an open back fixation element with slot and threaded plug is used to position the rod directly beneath, then ease of operation is improved, but adaptability is worsened due to limited pivoting capability
Solution Approach 1:
The yoke is designed to be movable relative to the bone screw before final tightening, allowing dynamic adjustment of angular orientation. The compression member secures the rod and yoke in the desired position, transitioning from a dynamic adjustable state to a fixed stable state.
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 system provides solid anchoring with variable angular positioning, reduces the overall prominence of components, and allows for easy manipulation during surgery, ensuring stability and ease of use while withstanding spinal loads.
Implementation Method 1
a friction member in the form of a spring element disposed between the yoke and the outer sleeve disposed over the head of the fastener, the spring element configured to provide a static friction force that holds the yoke in a predetermined position relative to the fastener
Data Source
AI summary
A spinal fixation system includes a rod and anchor devices that include a bone engaging fastener having a head defining a spherical socket. A ball insert is placed within the socket and rotated so that the ball insert is juxtaposed with the socket. The anchor device further includes a yoke defining a yoke channel for receiving the rod and a stem engaged to the ball insert captured within the socket. A sleeve disposed between the yoke channel and the fastener head supports the rod. A set screw is operable to clamp the rod against the sleeve and draw the insert into engagement within the socket. A friction element in the form of a wave spring is disposed between the yoke and the fastener head is configured to releasably retain the yoke in at least one discrete position relative to the fastener.