Polyaxial Washer Screw Implant for Sacroiliac Backout Prevention
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Solution Overview
Problem
Existing screw implants face challenges with inadvertent backout due to the curved surfaces of the ilia, particularly in the sacroiliac joint, and do not effectively address the varying bone quality between the sacrum and ilium, leading to issues like migration and haloing.
Innovation Solution
The screw implants feature a flexible washer member that can be polyaxially angled to conform to the ilium contour, preventing backout, and a dual inner diameter thread design to accommodate varying bone quality, along with biomaterial windows for enhanced fusion and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a standard screw implant is used in the sacroiliac joint, then the implant can provide initial fixation, but the curved surfaces of the ilia cause inadvertent backout and migration
Solution Approach 1:
The washer member features a non-circular, oval-shaped opening that corresponds to the curved contour of the ilium bone. This curved geometry allows the washer to conform to the iliac surface, preventing the screw from backing out by distributing contact pressure along the curved interface rather than at a single point.
Solution Approach 2:
The washer member is designed with flexible material properties and a thin profile that enables it to adapt to the curved iliac surface. The flexibility allows the washer to maintain intimate contact with the bone contour, ensuring stable positioning and preventing screw migration while accommodating anatomical variations.
2Device complexity
If a single thread design is used, then the implant structure is simple, but it cannot accommodate varying bone quality between the sacrum and ilium
Solution Approach 1:
The screw implant features a dual thread design where the first portion has a first thread pitch optimized for the denser ilium bone, while the second portion has a second thread pitch optimized for the more cancellous sacral bone. This local differentiation of thread characteristics allows each portion to optimally engage the specific bone quality it encounters, enhancing overall fixation reliability.
3Stability of the object's composition
If a rigid washer is used, then the structure is stable, but it cannot conform to the curved ilium contour
Solution Approach 1:
The washer member is constructed from flexible material with a thin profile that enables it to conform to the curved iliac surface while maintaining structural integrity. This flexibility allows the washer to adapt to anatomical variations and curved bone contours, ensuring stable contact and preventing screw backout without requiring complex rigid structures.
Data Source
AI summary
Systems, apparatuses and methods for bone fusion are disclosed. In particular, a fixation screw assembly is provided that comprises a bone engagement portion including a shaft and a head member. The assembly also includes a flexible washer member that can be operably attached and secured around the head member of the bone engagement portion. The washer member is polyaxial relative to the bone engagement portion, such that it can assume a variety of angles. The washer member can help prevent back out of the bone engagement portion when the bone engagement portion is implanted into a bone member. The design of the fixation screw assembly can be used in different fusion procedures, including fusion of the sacroiliac joint.