Modular Pedicle Screw Head Bottom-Loaded Design
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Solution Overview
Problem
Conventional pedicle screw assemblies in spinal fixation devices are top-loaded, obstructing surgeons' vision and access during operative tasks, and require removal of previously implanted screws to switch between polyaxial and uniplanar configurations, which can weaken the bone.
Innovation Solution
A modular pedicle screw assembly with a 'bottom-loaded' design, where the bone screw head is inserted through a distal end of the modular head assembly after being secured to the bone, allowing for selection between polyaxial and uniplanar configurations without removing the screw, using a kit of differently configured modular head assemblies with biasing members to prevent 'flopping' and improve handling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a conventional top-loaded pedicle screw assembly is used, then the screw can be assembled with the head positioned within the housing, but the housing obstructs the surgeon's vision and access during operative tasks
Solution Approach 1:
The patent inverts the conventional top-loaded design by implementing a bottom-loaded configuration where the bone screw is inserted from the distal end through the housing. This allows the head of the bone screw to be positioned at the proximal end, clear of the housing, thereby eliminating the obstruction to the surgeon's vision and access during operative tasks while maintaining structural integrity
2Adaptability or versatility
If a conventional top-loaded polyaxial pedicle screw is implanted, then the screw can be secured to bone with the head positioned within the housing, but switching to a uniplanar configuration requires removal of the previously implanted screw which can weaken the bone
Solution Approach 1:
The patent divides the pedicle screw assembly into separable modular components: a bone screw and a replaceable head assembly. The head assembly can be detached and replaced with different configurations (polyaxial or uniplanar) after the bone screw is implanted, allowing surgical flexibility without requiring removal of the bone screw itself, thereby preserving bone integrity while enabling adaptability
Solution Approach 2:
The patent creates a dynamic system where the head assembly can be changed from a fixed polyaxial configuration to a uniplanar configuration (or vice versa) after implantation. The uniplanar head assembly includes features that restrict movement to a single plane when engaged with the bone screw, while the polyaxial version allows multi-axis movement, enabling intraoperative adaptation based on surgical needs
3Adaptability or versatility
If the housing is allowed to freely rotate relative to the screw head in a polyaxial design, then alignment flexibility is improved, but the housing is subject to unwanted movement or 'flop' around the screw head which complicates handling and alignment
Solution Approach 1:
The patent applies different degrees of freedom to different regions of the head assembly. The polyaxial head assembly allows free rotation and movement in multiple axes relative to the screw head, providing alignment flexibility. The uniplanar head assembly restricts movement to a single plane, providing stability during handling. This local differentiation of movement constraints allows optimization for specific surgical needs
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
Enhances surgical access and flexibility by allowing surgeons to choose between polyaxial and uniplanar configurations without compromising bone integrity, improving handling and alignment of the pedicle screw assembly.
Implementation Method 1
a first biasing member arranged to bias the anvil toward the proximal surface of the washer
Implementation Method 2
a second biasing member arranged to bias the retaining ring toward the second portion of the assembly cap
Implementation Method 3
the retaining ring transitionable between a first configuration in which the retaining ring is sized to receive the head of the bone screw and a second configuration in which the retaining ring is compressed about the bone screw
Data Source
AI summary
A spinal fixation device includes a modular head assembly and a bone screw having a head and a shank. The modular head assembly includes: a housing defining a throughhole from a proximal surface to a distal surface of the housing; an anvil slidable within the throughhole; a washer; an assembly cap secured to the housing; a first biasing member arranged to bias the anvil toward the proximal surface of the washer; a retaining ring positioned at least partially within the cavity of the assembly cap; and a second biasing member arranged to bias the retaining ring toward the second portion of the assembly cap. Movement of the retaining ring from a first portion of the assembly cap to a second portion of the assembly cap compresses the retaining ring from a neutral configuration to a compressed configuration thereby securing the bone screw relative to the housing.