Modular Head Assembly Linear Locking for Spinal Stabilization
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Solution Overview
Problem
Existing spinal stabilization systems require additional torque to secure rods to bone screws, which can lead to thread stripping and require complex coordination with anti-torque tools, making the process difficult and dependent on surgeon strength and experience.
Innovation Solution
A linear locking set screw system with a spherical head on bone screws and a clamp body with a compression ring allows for rapid, torque-free engagement of rods to anchored bone screws, eliminating the need for rotational torque and providing a low-profile, reproducible stabilization system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If threaded nuts are used to secure rods to connectors with torque, then the connector/rod construct is firmly secured, but additional torque may strip the purchase between the bone and the threads of the bone screw
Solution Approach 1:
The invention separates the securing function into two independent components: the bone screw provides anchorage to the bone, while the collet provides independent locking of the rod to the connector. This segmentation eliminates the need to apply torque to the bone screw threads during rod securing, preventing thread stripping while maintaining strong connections.
Solution Approach 2:
The collet acts as an intermediary locking mechanism between the rod and the connector. Instead of directly tightening the rod against the bone screw threads, the collet engages with grooves on both the rod and connector, providing a mediated locking action that secures the construct without compromising the bone screw thread purchase.
2Manufacturing precision
If a torque wrench and anti-torque device are used to secure the connector/rod construct, then the required torques are achieved, but the effective use is difficult and dependent on the strength and experience of the surgeon
Solution Approach 1:
The collet and compression ring system is designed to be self-locking through linear compression. The surgeon simply applies axial compression force to tighten the collet against the rod, and the geometry of the components automatically provides the locking action. This eliminates the need for precision torque wrenches and anti-torque devices, making the system easy to operate regardless of surgeon experience.
Solution Approach 2:
Instead of using rotational torque to secure the rod (traditional method), the invention inverts the approach by using linear compression to achieve locking. The compression ring moves linearly along the connector to compress the collet, creating a secure lock without any rotational force applied to the bone screw threads.
3Strength
If additional torque is applied to tighten and lock the rod to bone screws, then the connection is strong and immobile, but it requires complex coordination with anti-torque tools
Solution Approach 1:
The connection strength is achieved through segmented functional components: the bone screw provides bone anchorage, the connector provides rod mounting, and the collet provides independent rod locking. This segmentation allows each component to perform its function without interfering with others, eliminating the need for complex anti-torque tool coordination while maintaining strong, immobile connections.
Data Source
AI summary
A low profile orthopedic device is used to fix and stabilize bones to correct anomalies in skeletal structure occurring naturally or by trauma. Bone screws are screwed into bones by application of torque. Connectors are attached to the anchored bone screws. Each connector includes a clamp and a compression ring. A connecting rod connects several connectors together. The clamps are tightened to hold the rod to the bone screws in a pre-selected position by linear movement of the compression ring.