Cam-style locking mechanism for spinal bone screw retention
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Bone screws in spinal fixation plates tend to back out due to bodily movement, posing risks to surgical success and patient safety, despite various designs attempting to address this issue, there is a need for improved locking mechanisms with enhanced functionality and ease of use.
Innovation Solution
A rotational locking mechanism with a cam-style locking feature is integrated into the fixation plate, featuring a base member with an interlock portion that engages the fastener's threads, allowing secure locking by rotating the locking element from an unlocked to a locked position, and is constrained within the plate to prevent axial removal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a bone fixation plate with bone screws is used to secure vertebrae, then spinal fixation is achieved, but the bone screws tend to back out under bodily movement stress
Solution Approach 1:
The locking mechanism is designed to be engaged after screw insertion but before the screw can back out under stress. The cam-style locking feature is pre-configured to engage with the screw shaft, and when activated, it proactively prevents backout rather than reacting to it.
Solution Approach 2:
The locking mechanism transitions from an unlocked state (allowing screw insertion and adjustment) to a locked state (preventing backout). The cam-style feature dynamically changes its engagement with the screw shaft based on the rotational position of the locking mechanism, providing stability only when needed.
2Reliability
If a locking mechanism is added to prevent screw backout, then screw retention is improved, but the device complexity increases
Solution Approach 1:
The locking mechanism is integrated into the bone fixation plate structure itself, with the locking mechanism, cam-style locking feature, and plate body forming a unified assembly. This merging eliminates the need for separate locking components and reduces overall system complexity.
Solution Approach 2:
The locking mechanism serves multiple functions: it prevents screw backout, provides structural support, and maintains the integrity of the bone fixation plate. The cam-style locking feature simultaneously engages the screw shaft and transfers load, combining locking and load-bearing functions in a single element.
3Reliability
If a cam-style locking feature with increasing radius is used, then locking engagement is enhanced, but the manufacturing precision requirements increase
Solution Approach 1:
The cam-style locking feature utilizes a changing radius parameter along its engagement surface. As the locking mechanism rotates into the locked position, the radius of the cam feature increases, providing progressively stronger engagement with the screw shaft. This parameter change enhances locking reliability while the feature can be manufactured using standard machining processes.
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 cam-style locking mechanism effectively secures the fastener to the fixation plate, preventing backout and ensuring stability under stress, thereby enhancing the reliability of spinal fixation and patient safety.
Implementation Method 1
A rotational locking mechanism is provided with a cam-style locking feature to provide secure locking of the fastener into the fixation plate. As the locking mechanism is rotated, engagement of the cam-style locking feature with a portion of the fastener (e.g., a plurality of threads) increases because the radius of the locking feature on the locking mechanism increases.
Data Source
Figure 1
Figure 2
Figure 3
AI summary
Devices and methods for locking one or more bone screws to a fixation plate. A camstyle locking feature may be disposed in the fixation plate such that, when the locking feature is in a first position, the bone screw is able to traverse an opening in the fixation plate and engage adjacent bone; and when the locking feature is rotated into a second position, an interference between the locking feature and bone screw causes the bone screw to be firmly secured to the fixation plate.