Expandable Corpectomy Spacer with Automatic Locking Mechanism
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Solution Overview
Problem
Conventional vertebral body replacement implants face challenges such as proximity to the dura and spinal cord due to natural lordosis/kyphosis, cumbersome screw installation, and limited space for bone graft material delivery, especially in expandable cages with limited expansion ranges.
Innovation Solution
A curved cage with press-fit endplates that can be actuated to expand or collapse, allowing for greater expansion and facilitating bone graft delivery, while using a locking mechanism for secure attachment without screws and an automatic locking system to prevent implant movement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional corpectomy cages are used with natural lordosis/kyphosis, then the implant can be inserted to replace the vertebral body, but the center segment of the cage settles into a position very close to the patient's dura and spinal cord causing pain, discomfort or further damage
Solution Approach 1:
The cage is designed to be expandable from a compressed delivery configuration to an expanded deployed configuration. This dynamic transformation allows the cage to be inserted in a compact form and then expanded to the correct height, positioning it away from the dura and spinal cord to eliminate the harmful proximity effect.
Solution Approach 2:
The cage height parameter is changed from a fixed dimension in conventional cages to a variable dimension that can be adjusted after insertion. By expanding the cage from its compressed state, the height parameter increases, moving the cage away from sensitive neural structures and eliminating the harmful proximity.
2Adaptability or versatility
If expandable VBR cages are used with limited expansion range (e.g., 3-4 mm for 15 mm cage), then the implant can be expanded to some degree, but there is limited space for packing bone graft materials and limited ability to deliver bone graft material into the implant after expansion
Solution Approach 1:
The cage allows dynamic adjustment of its volume through expansion. The expandable structure provides a mechanism to increase the internal volume of the cage after insertion, creating adequate space for bone graft material packing and delivery while maintaining adaptability to patient-specific requirements.
3Strength
If endplates are secured to the cage with screws, then the implant can be firmly attached to the vertebrae, but the screws are cumbersome to install and make it more difficult to safely remove and replace any component of the construct
Solution Approach 1:
The screw fastening system is extracted and replaced with a snap-fit engagement system. The endplates feature complementary geometric features that engage through a snapping motion, eliminating the need for screws. This provides firm attachment while dramatically simplifying both installation and potential removal or replacement of components.
Solution Approach 2:
The snap-fit system is designed to be self-aligning and self-securing. The geometric features on the endplates and cage automatically guide the engagement process, eliminating the need for precise screw alignment and manual fastening operations. The system serves itself through its inherent geometric design.
4Strength
If screws are used to secure endplates, then firm attachment is achieved, but there is an inherent risk that the screws may be dropped during a procedure
Solution Approach 1:
The screw components are completely extracted from the system and replaced with an integrated snap-fit mechanism. This eliminates the independent screw elements that could be dropped, while maintaining secure attachment through the geometric engagement features built into the endplate-cage interface.
Data Source
AI summary
An implant assembly including an expandable vertebral body replacement implant. Two outer cores disposed on opposing ends of an inner are configured to move away from each other when the inner core is actuated. The implant assembly may include removable endplate configured to engage vertebral bodies as interbody spacer or through a corpectomy. The implant may include a locking mechanism to prevent collapse or movement the implant assembly after implantation. The locking mechanism may be automatically engage after removal of an inserter instrument from the implant assembly.