Dynamic Interbody Cage Anchor System for Spinal Fusion
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Solution Overview
Problem
Current interbody fusion systems face challenges such as cage/graft retropulsion, lateral migration, and stress shielding due to inadequate load sharing between the vertebral column and posterior musculature, which hinder effective bone fusion and lead to recurrent pain and further degenerative changes.
Innovation Solution
A dynamic interbody cage anchoring system with slots on the anterior surface and a retention plate with a post and locking clip, allowing for axial loading while preventing withdrawal of the bone screw, thereby reducing intervertebral space and promoting bone growth without carrying vertebral loads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional rigid fixation systems are used to secure the interbody cage, then the cage is firmly held in place, but stress shielding occurs and bone fusion is hindered
Solution Approach 1:
The system transitions from rigid fixed anchoring to dynamic adjustable anchoring. The bone screw can be positioned at different locations along the retention plate through the slot, allowing the system to adapt to varying load conditions and promote bone fusion while maintaining cage stability.
Solution Approach 2:
The anchoring system is divided into separate functional components: the interbody cage, retention plate, bone screw, and locking clip. This segmentation allows each component to perform its specific function independently, with the retention plate acting as a load-transfer interface that reduces stress shielding.
2Reliability
If the interbody cage is secured with fixed anchoring, then the cage position is maintained, but cage retropulsion and lateral migration occur due to inadequate load sharing
Solution Approach 1:
The dynamic anchoring system allows the bone screw to be repositioned along the retention plate slot in response to load conditions. This dynamic adjustment capability enables the system to maintain cage position while accommodating physiological movements and promoting proper load distribution to prevent retropulsion and lateral migration.
3Strength
If rigid fixation is applied to prevent cage movement, then initial stability is achieved, but subsidence is prevented which hinders bone growth and fusion
Solution Approach 1:
The system provides initial stability through the bone screw-retention plate-cage assembly, then allows controlled subsidence as the bone screw can move along the slot. This dynamic response enables the cage to settle appropriately to promote bone growth and fusion while maintaining sufficient initial stability to prevent harmful movements.
Data Source
AI summary
A system and method of securing an intervertebral fusion cage within the intervertebral space between adjacent vertebra in which one or more slots are provided in an anterior surface of the cage each extending from an oversized aperture. A retention plate having a post and enlarged head is advanced into each slot via the oversized aperture and captured therein. The post is advanced to the terminal end of the plate and secured to vertebral body at its distal end by a bone screw. A locking clip is slideably positioned on the retention plate to prevent withdrawal of the bone screw. The slots preferably extend to margins of the anterior surface of the cage in, for example, the pattern of an “X” or an “H”. Sliding of the posts in the slots prevents the system from carrying the vertebral load (load shielding) and permits reduction in the intervertebral space to promote bone growth and fusion by graft material retained in the spacer.