Modular Bone Fastener With Expandable Rings
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Solution Overview
Problem
Current spinal implant systems for treating disorders such as scoliosis and degenerative disc disease face challenges in providing stable fixation and minimizing preload on vertebrae during assembly, often requiring instrumentation and resulting in potential disengagement of components.
Innovation Solution
A modular bone fastener system with a head assembly and screw shaft assembly, featuring expandable rings and a sleeve mechanism that allows for uni-axial movement and secure engagement of spinal rods, enabling manual assembly without instrumentation and resisting disengagement, using materials like commercially pure titanium and cobalt chromium for enhanced strength and rigidity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional spinal implant systems are used, then stable fixation can be achieved, but instrumentation is required for assembly and components may disengage
Solution Approach 1:
The bone fastener is designed with self-assembling features where the head assembly and screw shaft assembly can be manually connected without external instrumentation. The receiver and engagement surfaces are configured to automatically align and secure components through their own structural features, eliminating the need for specialized assembly tools while ensuring reliable component engagement.
Solution Approach 2:
The bone fastener employs a nested structure where the screw shaft assembly is received within the head assembly's receiver. The crown engages with the spinal rod within the implant cavity, and the overall structure nests components concentrically along the longitudinal axis, creating a compact integrated unit that resists disengagement without requiring external fixation instrumentation.
2Strength
If traditional bone fasteners are used, then spinal rod fixation can be achieved, but preload on vertebrae increases during assembly
Solution Approach 1:
The bone fastener incorporates dynamic adjustment capabilities through the crown and sleeve mechanism that can be adjusted after initial assembly. This allows the fixation strength to be optimized post-assembly without requiring excessive preload during the assembly process itself, reducing stress on the vertebrae while maintaining adequate fixation strength through controlled adjustment.
Solution Approach 2:
The fastener is divided into modular segments (head assembly, screw shaft assembly, crown, sleeve) that can be assembled separately and then connected. This segmentation allows each component to be optimized for its specific function while distributing forces more evenly during assembly, reducing peak preload on the vertebrae compared to monolithic designs.
3Ease of operation
If modular design is used, then manual assembly without instrumentation is enabled, but component engagement stability may be compromised
Solution Approach 1:
The modular components are designed with self-aligning and self-securing features. The receiver in the head assembly has engagement surfaces that automatically mate with corresponding features on the screw shaft assembly when brought together manually. The crown and sleeve have configured surfaces that self-lock into place, providing reliable engagement without requiring instrumentation to secure the modular components.
Solution Approach 2:
The bone fastener utilizes materials with enhanced mechanical properties (such as cobalt chromium and commercially pure titanium) that provide both the flexibility needed for manual assembly and the strength required for stable component engagement. These materials allow the modular components to be easily manipulated during manual assembly while ensuring durable, stable connection once assembled.
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 system provides stable fixation with reduced preload on vertebrae, allows for manual assembly without instruments, and ensures secure engagement of spinal rods, enhancing the treatment of spinal disorders like scoliosis and degenerative disc disease with improved strength and durability.
Implementation Method 1
the first ring is positionable and allowed to expand into the third groove in the expanded orientation; and when the head translates further into the receiver, the first ring passes over the ridge and resiliently contracts about the head within the third groove to provisionally capture the screw shaft assembly
Implementation Method 2
the second ring expandable between a contracted orientation and an expanded interference orientation and configured for disposal within a second groove in the contracted orientation or within the third groove in the expanded interference orientation
Data Source
Figure 1
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AI summary
A bone fastener comprises a first member defining an implant cavity and a plurality of adjacent grooves. A first band is configured for disposal within the grooves. A second band is configured for disposal within the grooves. A second member is configured to penetrate tissue and includes a head engageable with the first band to provisionally connect the members. A first part is engageable with a spinal rod disposed with the implant cavity. A second part is attached with the first part and engageable with the second band to dispose the second band adjacent the first band to fix connection of the members. Implants, systems, instruments and methods are disclosed.