Open Helical Interference Screw for Bone Tunnel Integration
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Solution Overview
Problem
Existing interference screws used in ligament reconstruction surgeries occupy significant space within bone tunnels, limiting bone-to-ligament integration and causing incomplete absorption, leading to suboptimal graft fixation and potential foreign material retention.
Innovation Solution
A delivery device and screw combination featuring a handle assembly with a shaft and an open helical interference screw, where the screw includes a depth stop and longitudinally extending runners, allowing for precise placement and engagement within bone tunnels to enhance bone-to-ligament integration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a traditional interference screw is used to secure the graft ligament in the bone tunnel, then the graft ligament is firmly fixed in place, but the screw occupies substantial space within the bone tunnel, limiting the bone-to-ligament integration region
Solution Approach 1:
The interference screw is segmented into multiple components: a helical body with spaced turns, internal struts providing structural support, and longitudinal runners. This segmentation allows the screw to maintain fixation strength while reducing overall volume and improving bone-to-ligament contact area by creating integration regions between the spaced helical turns
Solution Approach 2:
The helical body is designed with spaced turns creating an open, porous structure that allows bone and ligament tissue to grow through and around the screw components. This porous configuration maximizes the bone-to-ligament integration region while maintaining the mechanical strength needed for graft fixation
2Duration of action of stationary object
If an absorbable interference screw is used to allow bone-to-ligament in-growth, then the screw can eventually disappear over time, but absorption takes a substantial period (e.g., three years) and may never be complete, leaving foreign material retention
Solution Approach 1:
The interference screw is designed as a temporary fixation device that is deliberately discarded (absorbed) after serving its purpose. The biocompatible, bioabsorbable polymer material allows the screw to be gradually broken down and absorbed by the body over time, with the aspiration that complete absorption will occur, eliminating foreign material retention
Solution Approach 2:
The screw is made from biocompatible, bioabsorbable polymers (PLA, PGA, etc.) that change their physical and chemical properties over time through hydrolysis and enzymatic degradation. These parameter changes enable the screw to maintain mechanical strength initially, then gradually soften and break down into absorbable byproducts that the body can process
3Duration of action of stationary object
If an absorbable interference screw is used to promote bone-to-ligament in-growth, then the screw can be replaced by tissue over time, but the quality of in-growth is suboptimal as fibrous mass replaces the polymer rather than well-ordered tissue matrix
Solution Approach 1:
The helical body with spaced turns creates a porous structure that facilitates tissue ingrowth. The open configuration allows bone and ligament tissue to penetrate through the screw structure, potentially improving the quality of integration by enabling direct tissue-to-bone contact rather than tissue-to-polymer contact
Solution Approach 2:
The segmented design with internal struts and longitudinal runners creates multiple surfaces and pathways for tissue attachment and growth. This segmentation may promote more organized tissue formation by providing structured frameworks for cell migration and matrix deposition
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 solution promotes superior bone-to-ligament integration by minimizing the screw's footprint within the bone tunnel, facilitating complete absorption and enhancing the strength of the graft fixation while reducing foreign material retention.
Implementation Method 1
the interference screw essentially drives the graft ligament laterally, into engagement with the opposing side wall of the bone tunnel, whereby to secure the graft ligament to the host bone with a so-called 'interference fit'
Implementation Method 2
These polymers generally provide the substantial mechanical strength needed to advance the interference screw into position, and to thereafter hold the graft ligament in position while bone-to-ligament in-growth occurs, without remaining in position on a permanent basis
Implementation Method 3
various absorbable interference screws have been developed which are made from biocompatible, bioabsorbable polymers, e.g., polylactic acid (PLA), polyglycolic acid (PGA), etc
Implementation Method 4
over time (e.g., several months), the graft ligament and the host bone grow together at their points of contact so as to provide a strong, natural joinder between the ligament and the bone
Data Source
Figure 1
Figure 2~3
Figure 2A~4
AI summary
The present disclosure relates to a delivery device. The delivery device including a handle assembly (11), the assembly including a handle (11a) and a connector (lib) coupled to the handle, the connector including a channel (11b') and an opening to the channel; and a shaft (12) coupled to the handle, the shaft including a proximal end and a distal end, the distal end including threads (12c), grooves (12d) intersecting the threads, and a depth stop (12e). Other delivery devices, screws, and delivery device/screw combinations are also disclosed.