Bone Screw Washer Angular Locking Mechanism
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Solution Overview
Problem
Existing bone screw systems for angular stable locking of implants are technically complex and costly, requiring modifications to existing implants and lacking backward compatibility.
Innovation Solution
A bone screw system comprising a standard screw and a washer with a larger washer bore diameter than the screw shaft, allowing sideward displacement and tilt, enabling angular locking without the need for threaded bores, using inclined surfaces for engagement to secure the screw at an angle within the bore.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If standard bone screws and smooth-walled bores are used, then device complexity is reduced and backward compatibility is improved, but angular stability and locking reliability deteriorate
Solution Approach 1:
The washer bore diameter is intentionally made larger than the screw shaft diameter, creating radial clearance that enables the screw shaft to tilt and rotate within the washer bore. This dimensional change from a tight-fit to a clearance-fit configuration allows angular adjustment in a new dimension, achieving angular stability without modifying the bore wall structure or increasing system complexity
Solution Approach 2:
The screw shaft is designed to be dynamically adjustable within the washer bore, transitioning from a fixed positional relationship to a movable one. The engagement portions with inclined surfaces allow the screw to tilt and rotate, creating a dynamic locking mechanism that adapts to angular requirements while maintaining simplicity and reliability
2Reliability
If existing implants are modified with threads or complex structures, then angular stability improves, but manufacturing cost and device complexity increase
Solution Approach 1:
The angular stability function is segmented from the implant bore and transferred to the washer-screw assembly. The washer with its enlarged bore and the screw with tilted engagement portions carry the complexity required for angular locking, while the implant itself remains simple and unmodified. This segmentation allows standard implants to be used without modification while achieving enhanced functionality through the washer component
Solution Approach 2:
The washer acts as an intermediary component between the standard implant bore and the bone screw. It provides the enlarged bore and engagement portions that enable angular stability, mediating between the simple implant structure and the requirement for reliable angular locking without requiring modification of the implant itself
3Adaptability or versatility
If the washer bore diameter is increased to allow sideward displacement, then angular adjustment capability improves, but precision of screw positioning deteriorates
Solution Approach 1:
The engagement portions feature asymmetric inclined surfaces that guide the screw shaft's tilting motion. While the washer bore provides radial clearance for angular adjustment, the asymmetric engagement geometry constrains the screw to tilt along a controlled path, maintaining positioning precision even as angular adjustability increases
Solution Approach 2:
The system allows parameter changes in screw orientation through the tilted engagement portions while maintaining precise control over the degree and direction of tilting. The inclined surfaces transform the screw's linear insertion motion into a controlled angular adjustment, enabling versatile positioning without sacrificing manufacturing precision
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 system provides reduced complexity and cost, increased axial stiffness, and improved angular stability, facilitating effective fracture healing, especially in unstable fracture situations, without modifying existing implants.
Implementation Method 1
At least one of these engagement portions comprises an inclined surface or chamfered geometry. The inclined surface is configured to force the screw shaft sideward upon screwing in of the screw into the washer bore so that a longitudinal axis of the screw is tilted relative to a longitudinal axis of the washer bore.
Data Source
AI summary
The invention relates to a bone screw system, an implant system and a method of locking a bone screw system into a bore. The bone screw system comprises a bone screw and a washer. The screw comprises a screw head and a screw shaft. The washer comprises a washer bore. A diameter of the washer bore is larger than an outer diameter of the screw shaft. This allows a displacement of the screw shaft within the washer bore. The diameter of the washer bore is smaller than an outer diameter of the screw head. This prevents the screw head from moving through the washer bore. The screw and the washer comprise each an engagement portion for an engagement with each other. At least one of these engagement portions comprises an inclined surface. The inclined surface is configured to force the screw shaft sideward upon screwing in of the screw so that a longitudinal axis of the screw is tilted relative to the axis of the washer bore.