Semi-constrained Spinal Spacer Preventing Screw Backout
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Solution Overview
Problem
Conventional spinal implants face challenges such as dislodgment and screw backout due to normal spinal motions and subsidence, leading to discomfort and potential separation from vertebrae, as they fail to maintain space and allow for bone growth effectively.
Innovation Solution
An intervertebral implant system comprising a spinal spacer with semi-constrained bone screws that include a shank with helical threads and a rod member, allowing axial and radial movement, which secures the screws to the spacer while accommodating spinal flexibility and subsidence, preventing screw backout and dislocation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If conventional bone screws are used to secure the spinal spacer, then the spacer is firmly fixed to the vertebrae, but the screws tend to back out or withdraw from the bone due to normal spinal motions and subsidence
Solution Approach 1:
The bone screw is designed with dynamic components including a expandable cuff that can inflate within the vertebral body to prevent backout, and a rod member that can rotate relative to the shank to accommodate spinal motions. This dynamic design allows the screw to adapt to changing mechanical conditions while maintaining secure fixation.
Solution Approach 2:
The screw includes a pre-configured expandable cuff that can be activated before backout occurs, and a rod member with predetermined rotational capability. These preliminary features are designed into the screw structure to proactively prevent backout and accommodate motion before problems arise.
2Reliability
If the spinal spacer is rigidly fixed to prevent any movement, then screw backout is prevented, but normal spinal torsional and bending motions are restricted
Solution Approach 1:
The bone screw incorporates dynamic elements including a rod member that can rotate relative to the shank and an expandable cuff that can inflate to prevent backout. These dynamic features allow the screw to accommodate normal spinal torsional and bending motions while maintaining reliable fixation, thus resolving the contradiction between rigidity and flexibility.
3Shape
If bone screws are used to maintain space between vertebrae, then lordosis is preserved, but the screws become loose and rise above the plate assembly surface due to subsidence
Solution Approach 1:
The screw design includes a pre-configured expandable cuff that can be activated to prevent backout before subsidence occurs, and a rod member with rotational capability that anticipates motion changes. These preliminary features maintain lordosis while preventing the screws from becoming loose and rising above the plate assembly surface.
Solution Approach 2:
The dynamic expandable cuff and rotational rod member allow the screw to adapt to vertebral subsidence while maintaining its position relative to the plate assembly. This dynamic capability preserves lordosis maintenance function while preventing screw loosening and surface protrusion.
4Shape
If conventional prosthetic implants are used to replace damaged discs, then disc spacing is maintained, but the implants may be dislodged or moved from their desired location before bone growth occurs
Solution Approach 1:
The bone screw with its expandable cuff and rotational rod member provides dynamic stabilization that prevents implant dislodgment. The expandable cuff anchors the screw within the vertebral body while the rotational capability allows accommodation of motion, maintaining implant position stability during the bone growth period.
Solution Approach 2:
The screw's expandable cuff is designed to be activated before dislodgment can occur, providing preliminary stabilization. The rod member's rotational capability is pre-configured to accommodate motion changes, preventing implant movement before bone fusion is complete.
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 system maintains spinal flexibility, provides desired lordosis, and allows bone ingrowth while preventing screw backout, ensuring secure positioning and accommodating natural subsidence and motion, thus reducing patient discomfort and implant failure.
Implementation Method 1
The semi-constrained bone screw includes a shank defining a lumen extending at least partially therethrough from a proximal end thereof, a head defining a lumen therethrough and including a threaded portion configured to engage the lip of the screw opening
Implementation Method 2
The rod member is fixedly engageable with the shank and moveably coupled to the head such that both the rod member and the shank are moveable with respect to the head
Data Source
AI summary
An intervertebral implant system is disclosed which includes a spinal spacer for engagement between vertebrae and at least one semi-constrained bone screw assembly. The spinal spacer includes a body extending between first and second end surfaces to define opposing top and bottom vertebral engaging surfaces. The second end surface of the body includes at least one aperture formed therethrough at an angle relative to the centerline axis and a screw opening defined therethrough. The semi-constrained bone screw assembly is adapted for insertion through the screw opening and includes a shank, a head and a rod member. The rod member is fixedly engageable with the shank and moveably coupled to the head such that both the rod member and the shank are moveable with respect to the head.