Closed-head polyaxial spinal screws for minimally invasive fusion
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Solution Overview
Problem
Existing spinal instrumentation bone screws, particularly polyaxial and monaxial designs with open-heads, face challenges such as increased size requirements for larger screws, which necessitate larger incisions, and smaller screws may lack strength or have limited angle adjustability, leading to cumbersome and costly inventory management and potential surgical errors.
Innovation Solution
The development of closed-head bone screws with a set screw, bone screw, and clamp configuration that allows for adjustable angle placement of rods without compromising strength, featuring a compact design that integrates the closed head with the bone screw and includes dual bone threads for enhanced stability and compatibility with minimally invasive surgery techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If open-head screw design is used, then the head can accommodate larger sizes for stronger screws, but the overall size increases requiring larger incisions
Solution Approach 1:
The bone screw is nested within the closed head structure, with the head encompassing the screw shaft and threads. This nesting arrangement allows the head to provide structural strength while containing the screw components, achieving both strength and compact size requirements for minimally invasive surgery
Solution Approach 2:
Instead of the traditional open-head design where the screw protrudes from an open head structure, this invention inverts the approach by using a closed head that fully encloses the screw, with the head serving as the primary structural element rather than a simple mounting platform
2Volume of moving object
If smaller screws are used to fit smaller incisions, then the incision size is reduced, but the screw strength and angle adjustability are compromised
Solution Approach 1:
The closed head structure serves multiple functions: it provides the primary structural strength, accommodates screws of various sizes through standardized interfaces, enables polyaxial angle adjustment, and facilitates minimally invasive insertion. This multi-functionality allows a single head design to replace multiple screw size variants
3Adaptability or versatility
If multiple screw sizes are stocked for different applications, then various strength requirements are met, but inventory management becomes cumbersome and costly
Solution Approach 1:
A universal closed head design with standardized dimensions and interfaces can accommodate bone screws of various diameters and lengths. The head incorporates features such as a polyaxial connection mechanism and rod receiving structure that remain consistent across different screw sizes, allowing hospitals to stock fewer head variants while maintaining ability to address diverse clinical requirements
4Reliability
If open-head design with locking clamp is used, then the rod can be locked in place, but the overall device complexity and profile increase
Solution Approach 1:
The rod fixation mechanism is merged into the closed head structure itself. The head incorporates an integrated locking mechanism where the rod is received within the head cavity and secured through internal features such as set screws or friction-fit interfaces, eliminating the need for separate external locking clamps and reducing overall device complexity
Data Source
AI summary
A closed-head polyaxial screw for use in spinal instrumentation for spinal fusion, treatment of deformity, or the like. Polyaxial screws may have a two-part design, with the screw fitting into an aperture in the closed head. One or more clamps may secure the bone screw in the aperture. A closed-head polyaxial screw having a one part design is also disclosed. In addition, a one-part monaxial screw is described.