Rod Reduction Device Spring Force Distribution
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Solution Overview
Problem
Current rod approximating devices in orthopedic surgery fail to evenly distribute forces across multiple pedicle screws during spinal realignment, leading to potential screw failure and increased surgical complications due to their stiff construction, which tends to overload a few screws, risking pull-out or loss of grip.
Innovation Solution
An orthopedic rod reduction device featuring an actuator with a drive surface and a spring positioned between the drive surface and a rod engagement element, which maintains a controlled force on the rod relative to the actuator, ensuring even load distribution across multiple bone anchors during spinal column stabilization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If current rod approximating devices with stiff construct are used to force rod into screw head, then the rod can be positioned into the screw head, but the force is concentrated on two or at most three screws which risks pulling the screws out of the bone or weakening the screws' grip
Solution Approach 1:
The device segments the force application mechanism by introducing individual springs between the actuator and rod engagement element for each screw. This segmentation allows the force to be distributed across multiple screws independently, preventing force concentration on just two or three screws while maintaining the ability to position the rod into each screw head effectively.
Solution Approach 2:
The device changes the mechanical parameter of force distribution by introducing compliant spring elements. These springs allow controlled force application that can be distributed evenly across multiple screws, transforming the force application from a concentrated stiff construct to a distributed compliant system that maintains screw grip stability.
2Ease of operation
If stiff construct rod approximating devices are used, then the rod can be forced into the screw head, but the uneven force distribution leads to increased surgical complications
Solution Approach 1:
The device applies beforehand cushioning by incorporating spring elements between the actuator and rod engagement element. These springs act as cushioning elements that distribute force evenly across multiple screws during the rod positioning process, preventing the harmful concentration of force that would otherwise lead to surgical complications such as screw pull-out or loss of grip.
Solution Approach 2:
The spring elements serve as intermediary components between the actuator and the rod engagement element. This intermediary mechanism allows the actuator to apply force while the springs distribute this force evenly across multiple screws, mediating the force transmission to eliminate the harmful effects of force concentration and reduce surgical complications.
3Productivity
If multiple rod approximating devices are connected to screws in scoliosis surgery, then the rod can be positioned into multiple screw heads, but the stiff construct fails to spread the force evenly over all the screws
Solution Approach 1:
The device segments the force application to each individual screw-actuator-rod assembly by incorporating separate spring elements in each device. This segmentation enables each device to independently apply and distribute force through its own spring mechanism, allowing multiple devices to work simultaneously while maintaining even force distribution across all screws, thereby improving rod positioning efficiency without compromising force uniformity.
Solution Approach 2:
The device changes the force distribution parameter by introducing compliant spring elements in each actuator-rod-screw assembly. This parameter change transforms the system from a stiff construct that concentrates force to a compliant system that distributes force evenly across multiple screws, enabling efficient rod positioning while maintaining force distribution uniformity.
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 device effectively maintains a consistent force on the rod across a range of translations, reducing the risk of screw failure and improving surgical outcomes by evenly distributing loads across multiple bone anchors, thereby stabilizing the spinal column more effectively.
Implementation Method 1
a spring member positioned between the drive surface of the actuator and the rod engagement element
Implementation Method 2
The spring of the device may impart a force on the rod engagement element to thereby maintain a force on a target portion of an elongate rod even if forces applied to other portions of the rod cause movement of the target portion of the rod relative to the actuator
Data Source
AI summary
An orthopedic bone rod reduction device and method is disclosed. The device includes an actuator having a drive surface and a bone rod engagement element for engaging with a bone rod. The assembly further includes a spring positioned between the drive surface of the actuator and the rod engagement element. The rod reduction assembly controls movement of a bone rod relative to a bone anchor positioned in a bone.