Spinal Flexion Restriction via Elastic Compliance
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Solution Overview
Problem
Current spinal implants that restrict flexion for discogenic pain often provide excessive stiffness, leading to potential damage and trauma to vertebrae, and are bulky and complex, making them difficult to implant and prone to failure, while also not effectively managing flexion-related pain over long periods.
Innovation Solution
The development of spinal implants that apply a low elastic resistance to flexion, typically below 20 N/mm, using flexible straps and compliance members to limit spinal segment motion without restricting extension or lateral bending, with a focus on minimizing size and complexity to facilitate easier implantation and reduce the risk of failure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high force tension or elongation is applied to bone cerclage devices to fix the segment in one position, then motion restriction is improved, but device complexity and size increase making implantation difficult
Solution Approach 1:
The patent changes the mechanical parameters of the compliance member by using a spring mechanism with controlled stiffness (spring constant) to provide elastic resistance. This allows the device to restrict motion effectively while maintaining a simple structure that is easy to implant, resolving the contradiction between reliability and device complexity.
Solution Approach 2:
The patent introduces dynamic elasticity through the spring compliance member, allowing the device to adapt to physiological motion ranges while restricting excessive flexion. This dynamic behavior provides reliable motion restriction without requiring complex rigid structures, thereby reducing device complexity.
2Reliability
If bone cerclage devices are designed for static applications with no motion allowed, then motion restriction is improved, but adjacent segment morbidity increases due to abnormal loading
Solution Approach 1:
The patent employs a dynamic spring mechanism that allows controlled elastic motion within a physiological range while restricting excessive flexion. This dynamic approach distributes loads more evenly across adjacent segments, preventing the abnormal loading and morbidity associated with completely static devices, while still providing reliable motion restriction.
Solution Approach 2:
The patent optimizes the spring constant and elastic resistance parameters to allow beneficial motion while restricting harmful excessive flexion. This parameter optimization enables the device to protect against adjacent segment morbidity by maintaining physiological motion patterns, while still achieving effective motion restriction for pain relief.
3Ease of operation
If compliant structures with low elastic resistance are used, then ease of implantation and reduced trauma risk are improved, but motion restriction effectiveness decreases
Solution Approach 1:
The patent carefully optimizes the spring constant and elastic resistance parameters to achieve the right balance. The compliance member is designed with specific stiffness values that provide sufficient motion restriction effectiveness while maintaining low enough resistance to facilitate easy implantation and minimize trauma risk, resolving the contradiction between these two requirements.
Solution Approach 2:
The patent uses a dynamic spring mechanism that provides progressive resistance - low initial resistance for easy implantation and motion control, increasing to appropriate levels for effective motion restriction. This dynamic behavior resolves the contradiction by allowing the device to be both easy to implant and effective at restricting motion.
4Reliability
If completely rigid structures are used to restrict flexion, then motion restriction effectiveness is improved, but risk of damage and trauma to vertebrae increases
Solution Approach 1:
The patent optimizes the elastic resistance parameters of the spring compliance member to provide effective motion restriction while maintaining forces below trauma-threshold levels. By carefully selecting spring constants and pre-loads, the device achieves reliable flexion restriction without the excessive forces that cause vertebral damage, resolving this contradiction.
Solution Approach 2:
The patent replaces rigid structures with a dynamic spring mechanism that provides compliant, adaptive resistance to flexion. This dynamic compliance allows the device to restrict motion effectively while absorbing energy and reducing peak forces, thereby preventing vertebral damage and trauma that would occur with completely rigid structures.
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 implants effectively reduce flexion-related pain with minimal risk of damage to spinal structures, allowing controlled degrees of motion and reducing the risk of adjacent segment morbidity, while maintaining stability over millions of cycles with minimal creep and plasticity.
Implementation Method 1
a compliance member (16, 18) providing elastic resistance to the tension members
Data Source
Figure 1
Figure 1A
Figure 2
AI summary
A system for restricting spinal flexion includes superior and inferior tether structures joined by a pair of compliance members. Compliance members comprise tension members which apply a relatively low elastic tension on the tether structures. By placing the tether structures on or over adjacent spinous processes, flexion of a spinal segment can be controlled in order to reduce pain.