Low Friction Rod Persuader with Rolling Camming Interface
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Solution Overview
Problem
Existing spinal fixation systems require significant force to correctly align and secure spinal rods, often resulting in bulky and friction-prone instruments that are difficult to clean and may cause binding issues during surgery.
Innovation Solution
A low-friction rod reducing instrument with a threadless drive system using a rolling camming interface and a one-way locking mechanism, such as a ratchet mechanism, to facilitate easy alignment and securement of spinal rods with reduced mechanical advantage and improved cleanability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a threaded locking member is used to secure the spinal rod, then the locking function is achieved, but friction and binding issues occur during insertion and operation
Solution Approach 1:
The patent replaces the traditional threaded locking mechanism with a camming mechanism that uses rotational motion to achieve locking. The camming interface converts rotational movement into linear displacement of the rod, eliminating the high friction associated with threaded systems while maintaining reliable locking through the mechanical advantage of the cam profile.
Solution Approach 2:
The invention changes the fundamental parameter of the locking mechanism from threaded engagement (screw thread geometry) to camming engagement (rotational-to-linear motion conversion). This parameter change transforms the friction-prone threaded interaction into a low-friction camming interface that achieves the same locking function with significantly reduced binding issues.
2Reliability
If conventional top loading pedicle screw systems are used, then spinal fixation is achieved, but significant force is required to align and secure the spinal rod
Solution Approach 1:
The patent substitutes the direct force application method of conventional systems with a camming mechanism that provides mechanical advantage. The camming interface allows the surgeon to apply rotational force to the driver, which is then converted into the linear force needed to secure the rod, reducing the direct force requirement during alignment and securement.
Solution Approach 2:
The invention introduces a dynamic camming mechanism that allows for controlled movement and adjustment during the rod securement process. The camming interface enables the rod to be gradually aligned and secured through rotational motion, making the process more dynamic and less force-intensive compared to static conventional systems.
3Reliability
If traditional instruments with multiple moving parts are used, then the spinal rod can be secured, but the instruments become difficult to clean and maintain
Solution Approach 1:
The patent extracts the locking function from the traditional multi-component threaded system and consolidates it into a simplified camming mechanism. This extraction eliminates unnecessary moving parts such as separate locking nuts and threaded interfaces, resulting in an instrument with fewer components that are easier to clean and maintain while preserving the essential rod securement function.
Solution Approach 2:
The camming mechanism serves multiple functions within a single integrated structure: it provides the locking function, the mechanical advantage for force reduction, and the interface for rod alignment. This multi-functionality reduces the number of separate components needed, thereby improving cleanability and maintenance compared to traditional instruments with multiple specialized parts.
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 instrument provides a mechanical advantage for easier alignment and securement of spinal rods with reduced friction and improved cleanability, minimizing the need for lubrication and reducing the complexity of the surgical procedure.
Implementation Method 1
a rolling camming interface which transfers a rotational movement of a drive actuator into a linear motion of a reducing member
Implementation Method 2
a one-way locking mechanism, such as a ratchet mechanism
Data Source
AI summary
Instruments are provided for shifting elongate members, such as spinal rods, with respect to coupling members of spinal fixation systems. The instruments include a low friction drive mechanism having one or more rolling elements that ride along a helical groove or track in order to transform rotational movement of a drive member into linear shifting of a reducer member that shifts the elongate member. A one-way locking mechanism may be provided to selectively prevent unwanted counter-rotation of the low friction drive mechanism. The one-way locking mechanism may include annular ratchet teeth arranged on the exterior of the drive member and a ratchet pawl located adjacent to the teeth and selectively engageable therewith.