Keyed Crown Orientation for Multi-Axial Spinal Screws

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Solution Overview

Problem

In orthopedic surgery, aligning and securing screw components within the confines of a surgical opening for spinal implant systems can be difficult and tedious, particularly with multi-axial bone screws that require precise alignment of multiple pieces.

Innovation Solution

A coupling assembly comprising an anchor member, a receiver member with a shaped inner surface forming a rotation-limiting feature, and a seat member with a circular and non-circular surface portion that limits rotation, allowing for secure alignment and fixation of implants relative to the spinal column.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If multi-axial bone screws with multiple pieces are used to allow flexible implant configuration, then adaptability is improved, but alignment and securing of components becomes difficult and tedious

Engineering Contradiction:

Improveimplant configuration flexibilityVSAvoidcomponent alignment and securing

Core Design Contradiction:

Adaptability or versatilityVSEase of operation

Solution Approach 1:

The crown feature on the seat member and the corresponding recess feature on the receiver member use non-circular, asymmetric geometries (such as oval, rectangular, or custom shapes) that mate together to prevent rotation. This asymmetric design ensures that the seat member can only be installed in the correct orientation, automatically achieving proper alignment without requiring manual adjustment or complex alignment procedures by the surgeon.

Inventive Principle:

Principle #4Asymmetry

Solution Approach 2:

The rotation-limiting features are designed to self-align and self-lock upon insertion. The asymmetric crown and recess geometries automatically orient the seat member correctly as it is inserted into the receiver member, eliminating the need for separate alignment steps or tools. The features work together to self-correct any misalignment attempts, making the assembly process simpler and more reliable.

Inventive Principle:

Principle #25Self-service

2Manufacturing precision

If rotation-limiting features with non-circular perimeters are used to ensure proper orientation, then manufacturing precision is improved, but device complexity increases

Engineering Contradiction:

Improvecomponent orientation controlVSAvoidseat member geometry

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The non-circular perimeter features (crown and recess) use simple asymmetric geometries such as oval shapes, rectangular outlines, or basic polyhedral forms. These geometries provide sufficient orientation control without requiring complex three-dimensional contours or multiple features. The asymmetric shape alone is enough to prevent rotation and ensure correct alignment, maintaining manufacturing simplicity while achieving the desired precision.

Inventive Principle:

Principle #4Asymmetry

Data Source

PatentEP2088948B1Keyed crown orientation for multi-axial screws

Publication Date: 2017.03.01 WARSAW ORTHOPEDIC INC

AI summary

A coupling assembly (100) may include an anchor member (120), a receiver member (104), and a seat member (106). The receiver member may have an anchor member end (120) that cooperates with the anchor member and may have an implant-receiving aperture (124) for receiving an implant (110). The seat member may be disposable within the receiver member between the anchor member and the implant receiving aperture. First (128) and second (140) rotation-limiting features may be engageable to limit rotation of the seat member relative to the receiver member.