Bone Anchoring Device with Independent Head and Rod Locking
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Solution Overview
Problem
Existing polyaxial bone screws lack independent locking mechanisms for the rod and bone anchoring element, limiting their adjustability and applicability in specific spinal stabilization applications, particularly in the cervical and sacro-iliac regions where lateral offset and precise alignment are required.
Innovation Solution
A bone anchoring device with independent locking elements for the head and rod, utilizing a one-part set screw for head locking and a fully threaded receiver member to prevent flank spreading, allowing for easy and precise adjustment and assembly, and accommodating various receiver orientations for optimal screw placement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a dual part locking element is used to lock both the head and rod, then both components can be locked simultaneously, but the locking mechanisms are not independent and adjustment precision is limited
Solution Approach 1:
The locking mechanism is divided into two independent parts: a first locking element for the head and a second locking element for the rod. This segmentation allows each component to be locked and adjusted independently, eliminating the interference present in dual-part locking systems while maintaining simultaneous locking capability.
Solution Approach 2:
A spherical seat acts as an intermediary between the head and the locking mechanism, enabling precise angular adjustment of the head before final locking. The spherical geometry allows for fine-tuned positioning in multiple directions, achieving high adjustment precision that was not possible with direct dual-part locking.
2Volume of moving object
If the rod is arranged above the head with a pressure element, then the structure is compact, but the head and rod cannot be locked independently
Solution Approach 1:
The receiver member is segmented into distinct functional zones: a head receiving chamber with internal threading for the first locking element, and a rod receiving chamber for the second locking element. This spatial segmentation enables independent locking of both components while maintaining a compact overall structure.
Solution Approach 2:
The locking elements operate in different dimensional spaces: the first locking element engages with internal threads in the head receiving chamber, while the second locking element secures the rod in a separate chamber. This dimensional separation allows independent locking without requiring a larger profile.
3Adaptability or versatility
If a conical head section with spherical clamping component is used, then polyaxial adjustment is achieved, but sufficient space is required for tension elements above the head
Solution Approach 1:
Instead of placing the polyaxial adjustment mechanism above the head as in conventional designs, the spherical seat and first locking element are integrated into the head receiving chamber of the receiver member. This inverted arrangement eliminates the need for additional space above the head while maintaining full polyaxial adjustment capability.
Solution Approach 2:
The spherical seat is nested within the head receiving chamber, and the first locking element is nested within the spherical seat structure. This nested arrangement consolidates the polyaxial adjustment mechanism within the existing device footprint, eliminating the need for external tension elements and additional space above the head.
4Reliability
If the receiver member is fully threaded, then flank spreading is prevented and locking reliability is improved, but the structure becomes more complex
Solution Approach 1:
The internal threading is integrated directly into the receiver member body, combining the functions of the receiver and the locking mechanism housing. This merging eliminates the need for separate threaded inserts or additional structural components, achieving high locking reliability through flank engagement without increasing overall device complexity.
Data Source
AI summary
A bone anchoring device includes a bone anchoring element having a shank and a head, a continuous one-piece receiver member, a continuous one-piece first locking element and a second locking element. The receiver member has a first chamber for receiving the head, the head being pivotable in the first chamber, and a second chamber with a channel for receiving the rod. A first locking element fixes the head in the first chamber at an angle, and a second locking element fixes the rod in the second chamber. The receiver member includes a body including both the first chamber and the second chamber. The head and the rod can be inserted and locked independently from each other. The head is fixed by exerting pressure onto it. The bone anchoring device is particularly applicable to the stabilization of the spine in the sacro-iliac and the cervical region.