Spinal Constraint Device for Shear Loading and Flexion Control
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Solution Overview
Problem
Current treatments for degenerative spondylolisthesis, such as fusion and decompression with instrumentation, are invasive, costly, and associated with high morbidity and instability issues, as they fail to effectively address shear loading and anterior translation of spinal segments.
Innovation Solution
A constraint device with an upper and lower tether structure and a compliance member, such as a coil spring, is coupled with the spinal segment to resist flexion and increase engagement between facet joints, thereby enhancing the spinal segment's shear loading capacity and stability, while allowing for extension, lateral bending, and axial rotation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If decompression is performed to relieve pressure on nerve roots, then neurological symptoms are relieved, but flexion instability increases and listhesis can progress
Solution Approach 1:
A compliance member acts as an intermediary element between the upper and lower tethers, providing controlled resistance to flexion while allowing physiological motion. This mediator maintains facet joint engagement during decompression without requiring rigid fusion, thus relieving neurological symptoms while preventing instability progression
Solution Approach 2:
The device changes the mechanical parameters of the spinal segment by providing dynamic resistance to flexion through the compliance member. This allows the system to adapt to different spinal positions and loads, maintaining stability while permitting the decompression necessary to relieve neurological symptoms
2Stability of the object's composition
If fusion with instrumentation is performed to prevent instability, then spinal stability is improved, but morbidity and complication rates increase
Solution Approach 1:
The device applies localized stabilization only where needed - at the specific spinal segment with degenerative spondylolisthesis - rather than requiring extensive fusion instrumentation. The upper and lower tethers with compliance member provide targeted resistance to flexion at the affected level, improving stability while avoiding the widespread tissue disruption and complications associated with traditional fusion instrumentation
Solution Approach 2:
The compliance member provides dynamic resistance to flexion, allowing the device to adapt to physiological motion and loading conditions. This dynamic response maintains spinal stability while avoiding the rigidity of traditional fusion instrumentation, thereby reducing morbidity and complication rates associated with rigid constructs
3Stability of the object's composition
If non-instrumented fusion is performed to treat instability, then fusion healing is attempted, but non-union rates are high and post-operative bracing is required
Solution Approach 1:
The device performs preliminary stabilization by maintaining facet joint engagement and providing resistance to flexion before fusion healing can occur. This preliminary mechanical support prevents instability progression during the healing period, reducing the risk of non-union and eliminating or reducing the need for post-operative bracing
4Stability of the object's composition
If pedicle screws and stabilization rods are used to resist shear loading, then spinal stability is improved, but fatigue and instrumentation failure occur at the screw-rod interface
Solution Approach 1:
The device replaces the rigid mechanical system of pedicle screws and stabilization rods with a compliant tether-compliance member system. This substitution maintains spinal stability through controlled resistance to flexion while avoiding the stress concentration and fatigue failure that occur at rigid screw-rod interfaces
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 constraint device reduces anterior translation, stabilizes the spinal segment, and decreases the risk of instrumentation failure, offering a less invasive, cost-effective solution with lower morbidity and the ability to maintain sagittal alignment, reducing the need for post-operative bracing and fusion.
Implementation Method 1
a compliance member (e.g., a spring) that resists flexion of the spinal segment
Implementation Method 2
increasing the engagement between the facet joints... which increases the capacity of the spinal segment to resist segmental shear loading
Data Source
AI summary
A method for improving shear loading capacity of a spinal segment having a superior vertebra, an inferior vertebra or sacrum, and a facet joint, includes providing a constraint device having an upper portion, a lower portion and a compliance member coupled therebetween. The constraint device is coupled with the spinal segment such that the upper portion of the constraint device is coupled with the superior vertebra and the lower portion of the constraint device is coupled with the inferior vertebra or a sacrum. The constraint device provides a force resistant to flexion of the spinal segment. Also, length or tension in the constraint device is adjusted so as to increase engagement between an upper portion of the facet joint and a lower portion of the facet joint, thereby increasing capacity of the spinal segment to resist shear loading.