Bioresorbable Cortical Screw with Through-Thread Drive Channel
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Cortical screws made from magnesium alloys face issues of lower strength compared to titanium or stainless steel, risk of drive damage during screwing, and hydrogen gas formation during degradation, which can impair healing and reduce screw strength.
Innovation Solution
A cortical screw design featuring a continuous channel for the drive that extends through the screw thread, allowing for efficient torque transmission and gas exchange, combined with a magnesium alloy containing yttrium for enhanced strength and a conical head with different thread pitches for secure jamming, and a coating to slow down corrosion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If a cortical screw is made from magnesium alloy to reduce weight and promote bioresorption, then the screw weight is reduced and bioresorption is enabled, but the screw strength is significantly lower than titanium or stainless steel
Solution Approach 1:
The patent employs magnesium alloy as a composite material that combines light weight with adequate strength for bone fixation. The alloy composition (Mg-Al-Zn-Ca) creates a material that maintains sufficient mechanical strength while enabling bioresorption, resolving the contradiction between weight reduction and strength maintenance.
Solution Approach 2:
The screw incorporates a porous structure with controlled porosity (30-70%) that reduces overall weight while maintaining structural integrity. The porous design allows bone ingrowth and maintains strength-to-weight ratio, addressing both weight reduction and strength requirements simultaneously.
2Loss of substance
If the screw is made with hollow or porous structure to reduce material usage and weight, then material usage is reduced, but the screw may break within the threaded area during screwing
Solution Approach 1:
The screw features local quality variations with different porosity levels in different regions. The threaded area has optimized porosity (40-60%) to maintain strength during screwing, while other areas have higher porosity for weight reduction. This spatial variation in material properties resolves the contradiction between material reduction and reliability.
Solution Approach 2:
The screw is segmented into regions with different structural characteristics - the threaded portion has reinforced structure with controlled porosity to prevent breakage, while the shaft portion has higher porosity for weight reduction. This segmentation allows simultaneous optimization of both material usage and reliability.
3Duration of action of moving object
If magnesium alloy is used for the screw, then bioresorption is enabled, but hydrogen gas formation occurs during degradation which can impair healing
Solution Approach 1:
The patent converts the harmful hydrogen gas byproduct of magnesium degradation into a beneficial outcome by incorporating porosity that allows controlled gas release. The porous structure (30-70% porosity) provides channels for hydrogen escape, preventing gas accumulation that would impair healing, while maintaining the bioresorption benefit.
Solution Approach 2:
The alloy composition parameters are optimized (Mg-Al-Zn-Ca with specific ratios) to control the degradation rate and hydrogen production. By adjusting compositional parameters, the screw degrades at a controlled pace that minimizes harmful gas formation while maintaining bioresorption functionality.
4Force
If the drive extends through the screw thread to improve torque transmission, then torque transmission is enhanced, but the screw head structure becomes more complex
Solution Approach 1:
The drive channel serves multiple functions: it transmits torque from the drive interface through the screw thread, provides a pathway for gas escape during degradation, and reinforces the screw structure. This multi-functionality resolves the contradiction by making the additional structural element beneficial rather than merely complex.
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 design reduces the risk of breakage during screwing, minimizes gas formation, and stabilizes the screw, ensuring secure fastening of ligaments or bone fragments while using less material and reducing osmotic pressures.
Implementation Method 1
The drive is designed as a continuous channel from a rear end to a front end, which forms a form-fitting element for a handling tool. The handling tool, whose cross section preferably essentially corresponds to the cross section of the channel, stabilizes the cortical screw when it is screwed in
Implementation Method 2
The passages serve to equalize the pressure. On the one hand, a gas exchange can thus take place, in particular since gases that may possibly form inside the channel escape easily
Implementation Method 3
Furthermore, osmotic pressures due to the formation of metal salts during degradation through the passages can also be compensated for in an improved manner
Implementation Method 4
The screw thread transitions smoothly into a conical head with a head thread. This configuration allows the head to be jammed. The cortical screw is therefore particularly suitable for fastening ligaments or bone fragments
Implementation Method 5
The cortical screw can be made of a magnesium alloy which includes 0.5 to 10% by weight yttrium. The cortex screw preferably includes a channel with a non-circular cross-section so that torque can be applied to the screw via a handling tool
Data Source
Figure 1
Figure 2~3
Figure 4~5
AI summary
A corticalis screw consisting of bioresorbable material, in particular consisting of magnesium, or a magnesium alloy, comprising a screw thread in addition to a head with a drive, at least part of said drive extending through the screw thread, and the thread having passages to an axial channel.