Polyaxial Locking Assembly with Cam Profile Bushing
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Solution Overview
Problem
Current locking mechanisms for polyaxial applications, such as in pelvic reconstruction, lack advanced features for secure fixation and stability, particularly in complex anatomical environments like the pelvis, where internal organs and blood flow complicate surgery and require more robust and versatile attachment methods.
Innovation Solution
A polyaxial locking assembly comprising a bushing with a cam profile and an anti-rotation member, along with a split grommet and locking screw, allows for polyaxial motion and secure engagement with a substrate, providing a three-dimensional fixation system that resists pull-out and offers additional stability through a unique interface design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a conventional locking mechanism is used, then the structure is simple, but the fixation strength and stability are insufficient for complex anatomical environments
Solution Approach 1:
The locking mechanism is divided into multiple functional components: a receiving member with cavity, a bushing with cam profile, an anti-rotation member with varying radial thickness, and a locking screw. Each component performs a specific function, allowing the system to achieve high fixation strength through coordinated action rather than a single complex element.
Solution Approach 2:
The invention transitions from conventional single-axis locking to polyaxial locking by introducing angular freedom. The bushing's cam profile and anti-rotation member enable the locking screw to be inserted at multiple angles (polyaxial) while still achieving secure fixation, adding a dimensional aspect of angular variability to the locking mechanism.
2Adaptability or versatility
If a polyaxial locking system is used, then the adaptability to different orientations is improved, but the mechanism complexity increases
Solution Approach 1:
The bushing is given a partially spherical outer surface that closely conforms with the cavity in the receiving member. This spherical geometry naturally accommodates multi-axis rotation and angular adjustment, enabling polyaxial adaptability through geometric form rather than complex mechanical joints or multiple articulation points.
Solution Approach 2:
The anti-rotation member is designed with asymmetric radial thickness, having at least one portion with effective radial thickness R2 greater than at least one other portion R1. This asymmetry creates a cam profile that engages selectively at specific orientations, providing controlled anti-rotation functionality while maintaining overall polyaxial capability.
3Reliability
If the anti-rotation member has uniform radial thickness, then the manufacturing is simpler, but the locking reliability is reduced
Solution Approach 1:
The anti-rotation member features non-uniform radial thickness with specific portions having greater thickness (R2) than others (R1). This local variation in geometry creates targeted engagement points with the cam profile that enhance locking reliability at critical orientations, while the rest of the structure remains simpler. The varying thickness is applied locally where needed rather than throughout the entire component.
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 solution provides a robust and stable polyaxial fixation system that can be oriented in various angles, enhancing the security of attachment in complex anatomical environments like the pelvis, improving surgical outcomes by minimizing complications associated with internal fixation.
Implementation Method 1
the bushing, at that circumference, provides a cam having at least one lobe; there is further provided an anti-rotation member having a substantially annular geometry and a radial thickness R and being contoured such that at least one portion (R2/511) of the anti-rotation member has an effective radial thickness R2 greater than that of at least one other portion R1 such that in use, rotation of the bushing around an axis (521) perpendicular to the plane of the groove (522) causes the at least one lobe of the cam to engage with the at least one effectively radially thicker portion of the anti-rotation member
Implementation Method 2
A bushing with a partially spherical outer surface sized and shaped to closely conform with a cavity in a receiving member
Data Source
AI summary
A locking mechanism for a polyaxial locking screw is provided, together with a polyaxial locking assembly for locking a receiving member to a substrate. Also provided is a plating system for pelvic reconstruction.