Slit Ring Pressure Element for Bone Anchoring
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Solution Overview
Problem
Existing polyaxial bone anchoring systems require complex handling and multiple parts, making them costly and difficult to assemble and disassemble during surgery, with existing pressure elements requiring significant force and axial movement for head insertion and locking.
Innovation Solution
A receiving part with a monolithic slit ring pressure element that expands radially for easy head insertion, reducing the necessary force and axial movement, allowing for a friction fit for angular adjustment and easy disassembly, and featuring a few parts for reduced manufacturing costs and improved handling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a conventional pressure element with longitudinal or coaxial slits is used, then the structure is simple, but the force required for head insertion is high and axial movement distance is large
Solution Approach 1:
The pressure element is segmented into a rigid body portion and a flexible ring portion with circumferential slits. This segmentation allows the ring portion to expand radially in a controlled manner during head insertion, significantly reducing the axial force required compared to conventional solid pressure elements that require large axial movements to create clearance.
Solution Approach 2:
The invention transitions from conventional one-dimensional axial compression to two-dimensional radial expansion by introducing circumferential slits in the pressure element. This dimensional change enables the pressure element to accommodate the head through radial widening rather than requiring large axial displacement, thereby reducing the force and movement distance needed for insertion.
2Ease of operation
If a complex polyaxial bone anchoring system with multiple parts is used, then functionality is comprehensive, but handling difficulty increases and surgical time increases
Solution Approach 1:
The receiving part integrates multiple functions into a single unified structure combining the receiving cavity, pressure element with circumferential slits, and friction-lock mechanism. This merging eliminates the need for separate components, reducing the number of parts to handle while maintaining comprehensive functionality for head insertion, angular adjustment, and secure locking.
Solution Approach 2:
The receiving part is designed as a universal component that performs multiple operations: receiving the bone anchoring element head, enabling angular adjustment through friction locking, and providing secure retention through the pressure element mechanism. This multi-functionality reduces the need for multiple specialized components, simplifying surgical handling and reducing operative time.
3Productivity
If a pressure element requiring large axial movement is used, then locking is achieved, but in situ mounting becomes difficult and time-consuming
Solution Approach 1:
The pressure element incorporates a dynamic flexible ring portion with circumferential slits that can expand radially during head insertion and then contract to provide friction locking. This dynamic behavior enables the system to achieve both easy in situ mounting through radial expansion and secure locking through subsequent contraction, eliminating the need for large axial movements required by static pressure elements.
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
Facilitates easier in situ mounting and disassembly of the bone anchoring device, reduces the force required for head insertion, and provides a modular system with secure friction locking, enhancing surgical efficiency and cost-effectiveness.
Implementation Method 1
The slit ring can expand in a radial direction to allow for insertion of the head of the bone anchoring element. The force necessary for introducing the head into such a flexible portion of the pressure element is reduced compared to known pressure elements that have only longitudinal or coaxial slits.
Implementation Method 2
By means of the elasticity of the slit ring, the head of the bone anchoring element can be clamped by friction between the head and the slit ring. A friction fit between the head of the bone anchoring element and the pressure element allows for a preliminary holding of the bone anchor relative to the receiving part in a desired angular position of the bone anchoring element.
Data Source
AI summary
A receiving part for coupling a rod to a bone anchoring element includes a receiving part body having a first end, a second end, a channel for receiving a rod, an accommodation space for accommodating a head of a bone anchoring element, and an opening at the second end for inserting the head, and a pressure element configured to be positioned at least partly in the accommodation space, the pressure element having a first end, a second end, a central axis, and a flexible portion to clamp an inserted head. The flexible portion has a first slit spaced apart from the second end of the pressure element that extends at least partially around the central axis, and a second slit that extends from the second end of the pressure element into the first slit. The first slit extends away from the second slit and is longer than the second slit.