Pedicle Screw Fixation With Radial Expansion Locking

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Solution Overview

Problem

Current screw fixation methods for orthopedic devices in the vertebral column are prone to loosening and pull-out due to repeated loading and unloading, especially in motion preservation procedures, which compromises the integrity of the bone/device interface and the durability of the fixation sites.

Innovation Solution

The development of a pedicle locking technique using a multi-piece shank system with a deformable outer shank member that expands radially to create a locking engagement between the screw and the pedicle, combined with a screw head and receiver system that allows for dynamic adjustment and immobilization, enhancing anchor fixation and resistance to pull-out.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If traditional screw fixation is used in the pedicle portion of the vertebral body, then the device can be anchored to the bone, but repeated loading and unloading will lead to screw loosening and pull-out

Engineering Contradiction:

Improvefixation stabilityVSAvoiddevice fixation durability

Core Design Contradiction:

ReliabilityVSDuration of action of stationary object

Solution Approach 1:

The screw system transitions from a static fixed structure to a dynamic adjustable structure. The inner shank member can slide within the outer shank member, allowing the shoulder to move distally and the locking member to engage with the bone surface, creating a dynamic locking mechanism that adapts to loading conditions

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The screw is divided into multiple independent components: an inner shank member with threads for bone engagement, an outer shank member that expands radially, a locking member that engages the bone surface, and a head member. This segmentation allows each component to perform its specific function independently, improving overall fixation reliability

Inventive Principle:

Principle #1Segmentation

2Strength

If the anchor is driven deeply into the pedicle to improve fixation, then anchor capture increases, but the risk of bone fracture and avulsion at the attachment sites increases

Engineering Contradiction:

Improveanchor fixation powerVSAvoidbone damage

Core Design Contradiction:

StrengthVSObject-affected harmful factors

Solution Approach 1:

The locking member is designed to engage with the bone surface at the pedicle/vertebral body interface before full insertion is complete. This preliminary engagement creates a stopping point that prevents over-insertion and distributes loads to prevent bone fracture and avulsion

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system changes the mechanical parameters of fixation by transitioning from simple threaded engagement to a multi-point locking mechanism involving radial expansion of the outer shank member and engagement of the locking member with the bone surface, increasing fixation strength without requiring deeper insertion

Inventive Principle:

Principle #35Parameter changes

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

This solution significantly increases the resistance to anchor pull-out and improves the fixation power, ensuring stable anchoring of orthopedic implants on the vertebral column, thereby extending the functional lifespan of the implants and maintaining spinal motion preservation.

Implementation Method 1

a deformable outer shank member that expands radially to create a locking engagement between the screw and the pedicle

Methodology Applied

Scientific EffectRadial expansion:

Implementation Method 2

a shoulder protrusion within the proximal aspect of the anchor abuts the bone surface and prevents further anchor travel into the bone

Methodology Applied

Scientific EffectMechanical abutment: Mechanical Force

Implementation Method 3

The latter directly abuts the distal aspect of the pedicle at the pedicle/vertebral body interface. Using this method, the anchor captures the pedicle portion of bone and contains it between the proximal and distal shoulder abutments

Methodology Applied

Scientific EffectMechanical constraint: Mechanical Force

Data Source

PatentUS8388660B1Devices and methods for superior fixation of orthopedic devices onto the vertebral column

Publication Date: 2013.03.05 ABDOU SAMY

AI summary

A bone anchor is driven into the pedicle portion of the vertebral body until a shoulder protrusion within the proximal aspect of the anchor abuts the bone surface and prevents further anchor travel into the bone. A feature within the distal aspect of the anchor is actuated producing the emergence of a distal shoulder protrusion. The latter directly abuts the distal aspect of the pedicle at the pedicle/vertebral body interface. Using this method, the anchor captures the pedicle portion of bone and contains it between the proximal and distal shoulder abutments.