Polyaxial Bone Screw With Segmented Clamp And Cap
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Solution Overview
Problem
Existing spinal fixation systems face challenges such as limited screw positioning, increased stress on the patient due to large component sizes, unpredictable force exertion during screw attachment, difficulty in accommodating varying bone structures, and post-surgery component loosening due to dynamic loading, which complicates spinal curvature correction and increases surgical risk.
Innovation Solution
A polyaxial bone screw system with a spherical head and multi-sided recess for engagement with a driving tool, allowing for adjustable alignment with a common base member, minimizing component size while maintaining structural integrity, and featuring a rod clamping device that accommodates screws of varying diameters, along with a set screw for secure fixation without excessive torque, enabling modular replacement of components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a larger saddle is used for larger screw diameters, then the screw can be securely anchored, but the placement becomes more difficult and impingement to adjacent body structures increases
Solution Approach 1:
The invention divides the traditional single saddle component into two separate components: a clamp that attaches to the rod and a cap that receives the spherical head. This segmentation allows the spherical head to be smaller while maintaining anchoring strength, as the clamp provides the anchoring function and the cap provides the spherical head reception, eliminating the need for a large saddle aperture.
2Ease of manufacture
If pre-assembled screws and clamps are used with respect to size, then inventory management is simplified, but the system cannot accommodate varying bone structures and requires a large inventory of various sized clamps
Solution Approach 1:
The clamp is designed with a universal mechanism that can accommodate multiple screw sizes through adjustable features. The clamp includes a body with a cavity that can receive spherical heads of varying diameters, and the compression mechanism can adjust to different screw configurations, allowing a single clamp design to serve multiple screw sizes rather than requiring size-matched pairs.
3Ease of operation
If angular insertion is performed to accommodate muscle or tender nerve locations, then the screw can be placed in difficult positions, but unpredictable forces are exerted upon attachment to component connectors
Solution Approach 1:
The invention introduces a polyaxial mechanism that allows the screw to dynamically adjust its orientation after insertion. The spherical head within the cap can rotate and adjust to the optimal angle, allowing the screw to be inserted at various angles while maintaining predictable force distribution through the spherical interface, which naturally accommodates angular variations without creating unpredictable stress concentrations.
4Adaptability or versatility
If a spherical head with polyaxial adjustment is implemented, then screw positioning flexibility is improved, but component size and complexity increase
Solution Approach 1:
The invention merges multiple functions into the cap component: it receives the spherical head, provides the polyaxial adjustment mechanism, and interfaces with both the screw and the rod clamp. This consolidation of functions into a single cap component achieves positioning flexibility without proportionally increasing overall system complexity, as the cap serves as the central hub for multiple operational requirements.
Data Source
AI summary
A fastening system for bone screws used in spinal fixation systems for reshaping the spine of a patient. The bone screw has threads on one end for anchoring in the spine. The other end has a spherical head with a multi sided recess formed therein for engagement with an appropriate driving tool. The system includes a stabilizing rod, a saddle member, a cap member and a set screw with at least one bone screw having a outer diameter that exceeds the diameter of a cavity formed in the saddle, wherein placement of the bone screw is made possible by matching the threads of the set screw to the threads of the bone screw. The head of the bone screw providing proper positioning of the stabilization rod within the patient.