Dynamic Bone Fastener with Preset Range of Motion

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Solution Overview

Problem

Conventional rigid bone fasteners introduce high stresses and strains during cyclic loading, which can lead to loosening and instability in spinal stabilization systems, failing to accommodate normal activities effectively.

Innovation Solution

Dynamic bone fasteners with a flexible portion between the fixation and connection portions, featuring a motion limiter that restricts flexure within a preset range, reducing stress on spinal elements and allowing controlled articulation, and optionally incorporating dampening materials to modulate resistance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Stability of the object's composition

If rigid bone fasteners are used, then structural stability is provided, but high stresses and strains are introduced during cyclic loading

Engineering Contradiction:

Improvestructural stabilityVSAvoidstress on bone structure

Core Design Contradiction:

Stability of the object's compositionVSStress or pressure

Solution Approach 1:

The bone fastener incorporates a flexible portion that allows dynamic motion between the fixation portion and connection portion, enabling the device to adapt to cyclic loading during normal activities while maintaining structural stability. The flexible portion permits controlled flexure within a preset range of motion, reducing stress on the bone structure compared to completely rigid fasteners.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent changes the rigidity parameter of the bone fastener by introducing a flexible portion with specific mechanical properties. The flexible portion has a modulus of elasticity and geometry designed to permit flexure within a preset range, transforming the fastener from a completely rigid structure to a semi-rigid dynamic structure that can accommodate physiological movements.

Inventive Principle:

Principle #35Parameter changes

2Stress or pressure

If flexible bone fasteners are used, then stress on bone structure is reduced, but range of motion is uncontrolled

Engineering Contradiction:

Improvestress on bone structureVSAvoidrange of motion control

Core Design Contradiction:

Stress or pressureVSAdaptability or versatility

Solution Approach 1:

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The flexible portion is pre-configured with a preset range of motion through its geometric design and material properties. This preliminary design constraint ensures that the fastener allows only therapeutic ranges of motion before mechanical limiting surfaces prevent further flexure, thereby controlling the range of motion a priori without requiring additional active control mechanisms.

Inventive Principle:

Principle #10Preliminary action

3Adaptability or versatility

If motion limiting surfaces are added, then range of motion is controlled, but device complexity increases

Engineering Contradiction:

Improverange of motion controlVSAvoidfastener structure

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The motion limiting surfaces are merged into the flexible portion itself, integrating the motion control function directly into the flexible component rather than requiring separate limiting mechanisms. The first and second sets of opposed facing surfaces are formed as part of the flexible portion's geometry, combining the flexible element and motion limiter into a single integrated structure.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The flexible portion acts as a flexible element that inherently provides motion control through its geometric configuration. The flexible portion's shape and the arrangement of opposed facing surfaces create mechanical limits to flexure without requiring rigid constraints, utilizing the flexible element's own structure to control its range of motion.

Inventive Principle:

Principle #30Flexible shells and thin films

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 dynamic bone fasteners provide stability and structural integrity while reducing stress on spinal elements, maintaining therapeutic motion ranges and improving the durability of spinal stabilization systems.

Implementation Method 1

The flexible portion is configured to permit flexure of the connection portion relative to the fixation portion

Methodology Applied

Scientific EffectElasticity: Elasticity

Implementation Method 2

a dampening material is disposed between the first set of opposed facing surfaces and disposed between the second set of opposed facing surfaces

Methodology Applied

Scientific EffectViscous damping: Viscous Damping

Data Source

PatentUS8979901B2Dynamic bone fastener with a preset range of motion

Publication Date: 2015.03.17 WARSAW ORTHOPEDIC INC

AI summary

A bone fastener includes a fixation portion configured to interface with boney tissue, a connection portion having a longitudinal axis and being configured to interface with an elongated support structure, and a flexible portion disposed between the fixation portion and the connection portion. The flexible portion is configured to permit flexure of the connection portion relative to the fixation portion. The flexible portion has a first set of opposed facing surfaces that mechanically limit the range of flexure in a first direction. It has a second set of opposed facing surfaces that mechanically limit the range of flexure in a second direction. The opposed facing surfaces are substantially transverse to the longitudinal axis.