Cannulated Bone Screw Expansion for Facet Joint Compression
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current facet joint fixation devices fail to effectively create and maintain compression between vertebrae, leading to loosening and potential damage, and often require invasive procedures or are not suitable for small bones due to design limitations.
Innovation Solution
A cannulated and partially threaded bone screw assembly that expands within the bone to increase compression and prevent loosening, featuring an outer shank, inner shank, and tip that deform to secure the device, allowing for efficient insertion through a small incision and use of a guide wire for accurate placement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a standard fully threaded bone screw is used to fasten facet joints, then the device can adjoin two bone surfaces, but it cannot create significant compression between the surfaces and is prone to loosening over time
Solution Approach 1:
The bone screw is divided into two distinct segments: an outer screw that provides structural support and thread engagement with the bone, and an inner screw that can be independently rotated to expand the distal end. This segmentation allows the expansion mechanism to generate compression force while the outer screw maintains positional stability and prevents loosening.
Solution Approach 2:
The distal end of the outer screw is designed to be dynamically expandable through the rotation of the inner screw. This dynamic expansion capability allows the device to transition from a compact insertion state to an expanded compression state, generating significant compressive force between bone surfaces while maintaining secure anchorage.
2Reliability
If an expansion device is used to prevent loosening, then loosening can be prevented, but the hoop stress generated makes it unsuitable for small bones like those in the facet joint
Solution Approach 1:
The expansion mechanism is localized specifically to the distal end of the outer screw, rather than expanding the entire screw body. This localized expansion at the tip generates the necessary compression force between bone surfaces while minimizing hoop stress on the bone, making the device suitable for small bones in the facet joint.
3Productivity
If a minimally invasive approach with small incision is used, then operative time and blood loss are reduced, but accurate placement becomes more difficult
Solution Approach 1:
A guide wire is introduced as an intermediary tool to establish the precise trajectory and placement of the bone screw through the facet joint. The guide wire is inserted first through the small incision, providing a visual and tactile guide for subsequent screw insertion, thereby ensuring accurate placement while maintaining the benefits of minimally invasive surgery.
4Reliability
If traditional immobilization hardware is anchored through pedicles with plates or rods, then vertebral segments can be immobilized, but the procedure is more invasive with greater risk to nearby structures
Solution Approach 1:
The invention extracts and eliminates the need for extensive pedicle anchoring, plates, and rods by using a simplified bone screw that directly fastens the facet joints together. This removal of unnecessary components reduces the invasiveness of the procedure and minimizes risk to spinal nerve roots and the spinal cord while maintaining effective immobilization through direct facet joint compression.
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 device provides stable compression across facet joints, prevents loosening, and facilitates accurate placement, reducing operative time and risk of damage, while being suitable for small bones and minimally invasive procedures.
Implementation Method 1
The external surface of the tip is threaded at the proximal end such that the inner shank can screw into the tip. Once the outer shank is positioned such that it extends through the bones, the outer shank is held stationary and the inner shank is turned. The tip is drawn into the outer shank via the threads on the inner shank which causes the outer shank to deform.
Implementation Method 2
The deformation caused by the tip serves to increase the size of the outer shank such that it becomes larger in diameter than the hole through which it was inserted. The deformation increases the compressive force across the facet joints and also prevents the screw from loosening or backing out of the hole through which it was inserted.
Data Source
AI summary
A placement tool for positioning a multipart cannulated screw assembly to fixate first and second bone elements. The placement tool includes a stem and a head carried on the stem. The head has an outer shank engagement provision that engages the proximal end of an outer shank of a bone screw assembly and permits selective rotation of the outer shank. The head also has an inner shank engagement provision that engages the proximal end of an inner shank of the bone screw assembly and permits selective rotation of the inner shank. The inner shank and outer shank engagement provisions are connectable to one another such that the inner shank and outer shank engagement provisions rotate together.