Dynamic interbody implant with slotted fastener translation
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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 bone growth and fusion due to excessive load absorption, which can result in pseudoarthrodesis and non-union of the fusion site.
Innovation Solution
The development of intervertebral implants with dynamic translation and pivoting mechanisms for fixation members, allowing load distribution to bone graft material during subsidence while maintaining anchorage, using slotted openings and elongated cross-sectional fastener holes to accommodate subsidence and settlement.
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 inhibited bone growth
Solution Approach 1:
The patent applies the dynamics principle by transitioning from rigidly constrained fixation members to dynamic fixation members that can translate and pivot within slotted openings and elongated cross-sectional fastener holes. This dynamic capability allows the fixation members to move with the interbody cage during subsidence, maintaining anchorage strength while enabling proper load distribution to the bone graft material, thereby promoting bone growth and fusion.
2Stability of the object's composition
If rigidly constrained fixation members are used, then initial stability is improved, but subsidence accommodation deteriorates leading to excessive load absorption and pseudoarthrodesis
Solution Approach 1:
The fixation members are designed with dynamic capabilities through slotted openings and elongated cross-sectional fastener holes that allow translation and pivoting. This dynamic design provides initial stability through rigid constraint while simultaneously accommodating subsidence by allowing controlled movement, preventing excessive load absorption that leads to pseudoarthrodesis.
Solution Approach 2:
The patent changes the geometric parameters of the fastener holes from circular to elongated cross-sections, and introduces slotted openings with specific dimensional relationships. These parameter changes enable the fixation members to transition from rigid constraint to controlled movement, allowing the system to adapt to subsidence while maintaining stability.
3Reliability
If dynamic translation mechanisms are implemented, then load distribution to bone graft material is improved, but device complexity increases
Solution Approach 1:
The patent segments the fixation member into distinct functional components: the fixation member body, the slotted opening for translation, and the elongated cross-sectional fastener holes for pivoting. This segmentation allows each component to perform its specific function independently, achieving complex load distribution behavior through simple, modular geometric features rather than complex mechanical mechanisms.
Solution Approach 2:
The patent achieves dynamic load distribution by changing the geometric parameters of simple structural features (slotted openings and elongated holes) rather than introducing complex mechanisms. The dimensional relationships and orientations of these features are carefully controlled to provide the desired translation and pivoting capabilities, maintaining simplicity while achieving sophisticated load distribution.
Data Source
AI summary
An intervertebral implant includes a body having an upper surface, a lower surface and a transverse fastener hole. The body includes a dynamic fixation mechanism for seating a fastener in the fastener hole and translating the fastener relative to the implant to accommodate subsidence of the implant. In one embodiment, an implant includes a transverse slot with an elongated seat for translating a seated fastener relative to the implant. In another embodiment, an implant includes a displaceable sliding member for translating a fastener relative to the implant.