Dynamic Interverbral Implant Fixation for Bone Graft Subsidence
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Solution Overview
Problem
Rigidly constrained fixation members in interbody cages lead to subsidence and stress shielding of bone graft material, inhibiting proper fusion and increasing the risk of pseudoarthrodesis and non-union due to inadequate load distribution during settlement.
Innovation Solution
The development of intervertebral implants with dynamic fixation mechanisms, such as ratchet mechanisms and slotted fastener holes, allowing screws to translate and pivot with subsidence, ensuring proper load distribution to the bone graft material while maintaining anchorage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If rigidly constrained fixation members are used in interbody cages, then anchorage strength is improved, but load distribution to bone graft material deteriorates causing stress shielding and inhibition of fusion
Solution Approach 1:
The fixation members are designed with dynamic capabilities including translation along the longitudinal axis of the interbody cage, rotation about this axis, and telescoping motion. This allows the fixation members to adapt to subsidence and maintain optimal load distribution to the bone graft material while preserving anchorage strength, thereby resolving the contradiction between strong fixation and reliable fusion.
2Stability of the object's composition
If rigidly constrained fixation members are used, then initial stability is improved, but adaptability to subsidence deteriorates leading to pseudoarthrodesis risk
Solution Approach 1:
The fixation members incorporate dynamic mechanisms that enable them to translate, rotate, and telescope in response to subsidence. This dynamic design maintains initial stability through secure anchorage while simultaneously adapting to changes in the interbody space, preventing pseudoarthrodesis by ensuring continuous load distribution to the bone graft.
Solution Approach 2:
The fixation members can change their geometric parameters including position along the longitudinal axis, rotational angle, and telescoping length. These parameter changes allow the system to adapt to subsidence while maintaining stability, resolving the contradiction between initial stability and adaptability.
3Reliability
If dynamic fixation mechanisms are implemented, then load distribution to bone graft is improved, but device complexity increases
Solution Approach 1:
The dynamic fixation mechanisms are integrated into the fixation members themselves through translation channels, rotation joints, and telescoping structures. While these add complexity to individual components, they enable effective load distribution to the bone graft by allowing the fixation members to adapt to subsidence, thereby resolving the contradiction between reliability and complexity.
Data Source
AI summary
An intervertebral implant includes a first plate and a second plate that is configured to be moveably engaged with the first plate along an axis of translation. Each plate defines at least one hole or recess for receiving a fastener that is configured to be fastened to a respective vertebrae. In one embodiment, a toothed surface is defined on both the first plate and the second plate. The toothed surface of the first plate is configured for engaging the toothed surface of the second plate such that translation of the second plate with respect to the first plate is limited in a single direction along the axis of translation.