Spinal fixation constructs with flexible transition segments
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Solution Overview
Problem
Current spinal fixation systems often lead to adjacent segment pathology and failures, particularly proximal junctional kyphosis (PJK), due to excessive strain and stress on the proximal instrumented spinal segment, which can result from suboptimal alignment and rigidity of the screw and rod construct.
Innovation Solution
The development of vertebral fixation systems incorporating flexible transition segments and adjustable bone anchors with semi-rigid elastomeric components that allow for movement and frictional locking of spinal rods, reducing stress and facilitating natural alignment adjustments, thereby alleviating conditions like PJK.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a rigid screw and rod construct is used to stabilize the spine, then immobilization and alignment are improved, but excessive strain and stress on the proximal instrumented spinal segment increases, leading to adjacent segment pathology
Solution Approach 1:
The fixation system is divided into multiple segments with different rigidity characteristics. The distal portion uses rigid fixation for stable immobilization, while the proximal portion incorporates more flexible components that allow controlled motion. This segmentation allows the system to provide necessary stabilization while distributing stresses more evenly and reducing concentration at the proximal junction.
Solution Approach 2:
The system transitions from a static rigid construct to a dynamic system that accommodates physiological motion. The proximal components are designed to allow controlled movement and adaptation, enabling the fixation system to respond to changing mechanical demands while reducing stress concentration on adjacent segments.
2Shape
If a rigid screw and rod construct is used to correct vertebral alignment, then alignment correction is improved, but the transition from motion-restrained to motion-unrestrained segment creates abrupt mechanical discontinuity, causing proximal junctional kyphosis
Solution Approach 1:
Different portions of the fixation system have different mechanical properties tailored to their specific functional requirements. The distal portion employs rigid components for stable alignment maintenance, while the proximal portion uses more compliant components that allow controlled motion. This local differentiation creates a gradual transition zone that reduces mechanical discontinuity and prevents stress concentration.
Solution Approach 2:
The system incorporates dynamic elements that allow controlled motion at the proximal junction, creating a gradual transition from the rigid fixed segment to the mobile non-instrumented segment. This dynamic design eliminates abrupt mechanical discontinuities and distributes stresses more evenly across the junction zone.
3Strength
If traditional fixed-angle bone anchors are used, then rigid fixation is achieved, but the system lacks adaptability for alignment adjustments and stress distribution
Solution Approach 1:
The bone anchors incorporate polyaxial capabilities that allow adjustment of the rod engagement angle after implantation. This dynamic feature enables surgeons to optimize alignment and load distribution based on patient-specific anatomy and pathology, while maintaining strong fixation. The adjustable geometry allows the system to adapt to varying mechanical demands.
Solution Approach 2:
The system allows modification of key geometric parameters such as rod engagement angle and position after implantation. These parameter changes enable optimization of mechanical properties including stress distribution, alignment, and fixation strength, providing adaptability without compromising the fundamental strength of the construct.
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
These systems effectively reduce the occurrence and severity of adjacent segment pathology and failures by absorbing force and allowing for potential alignment corrections, improving patient outcomes and reducing surgical footprint.
Implementation Method 1
maintaining a frictional association with the spinal rod
Implementation Method 2
semi-rigid elastomeric rod engagement insert
Implementation Method 3
absorbing force and allowing for potential alignment corrections
Data Source
AI summary
This disclosure describes a variety of transitional or terminal components that may be implanted as part of a spinal fixation construct to decrease the potential for subsequent development of junctional disease. The fixation construct may extend any number of levels from a single level construct to a long construct spanning multiple spinal levels and multiple spinal regions from the lumbosacral to cervical regions, and with any variety of combination of anchors, rods, and connectors. Terminal and/or transitional components maybe utilized at the caudal and or cephalad ends of the fixation construct to reduce stresses endured by the construct adjacent pathology and prevent or reduce incidence and degree of junctional disease.