Orthopedic Bone Screw Assembly with Rotational Locking Clamp
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Solution Overview
Problem
Existing polyaxial screw assemblies in orthopedic surgery require complex assembly procedures, often necessitating axial forces for insertion and removal, and are limited in flexibility for revision surgeries, as they typically need to be assembled before screwing into the bone and are difficult to adapt for different degrees of movement relative to the clamp.
Innovation Solution
A bone screw with a head featuring two parallel planar sides joined by a curved surface, allowing for controlled movement relative to a clamp, enabling easy insertion after the screw is in place and secure locking through relative rotation, along with interchangeable insert members to adjust the degree of freedom, facilitating easier revision and reducing inventory needs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a polyaxial screw assembly is designed to allow relative movement between the screw and clamp, then the adaptability for different surgical situations is improved, but the device complexity increases due to the need for multiple components and assembly mechanisms
Solution Approach 1:
The screw head is segmented into distinct functional surfaces: a curved surface for engaging the clamp and allowing polyaxial movement, and two opposite substantially planar sides for engaging the insert member. This segmentation enables independent control of different movement degrees by different components.
Solution Approach 2:
The screw head design provides multiple engagement surfaces that can work with different insert members to achieve various degrees of freedom (polyaxial, uniplanar, or fixed). A single screw design can serve multiple functions depending on which insert member is used, reducing the need for multiple screw types.
2Reliability
If the screw and clamp are assembled before screwing into the bone, then the screw can be properly positioned relative to the clamp, but the ease of operation is reduced due to the need for pre-assembly and the clamp sweeping out a cone during insertion
Solution Approach 1:
The clamp is designed with a receiving space and opening that can accommodate the screw head in a preliminary unsecured position. The opening is configured to receive the screw head before final engagement, allowing the screw to be inserted into the bone first, then engaged with the clamp afterward.
Solution Approach 2:
The conventional sequence is inverted: instead of assembling the screw into the clamp before insertion, the clamp is designed to receive and secure the screw head after the screw has been inserted into the bone. This reversal simplifies the insertion procedure by eliminating the need for pre-assembly.
3Reliability
If axial force is applied to insert and remove the screw from the clamp, then the spherical head can be securely located, but the ease of operation is reduced due to the considerable force required
Solution Approach 1:
The screw head incorporates a curved surface that engages with a corresponding surface in the clamp to provide secure retention through geometric interlocking rather than axial force. The curved geometry naturally guides and secures the screw head in position.
Solution Approach 2:
The axial force mechanism is replaced with a geometric locking mechanism. The opening is configured to receive the screw head at a first orientation and retain it at a second orientation through rotational engagement of the curved surfaces, eliminating the need for axial compression forces.
4Adaptability or versatility
If a large inventory of suitable assemblies is maintained to cover all surgical situations, then the adaptability is improved, but the loss of substance increases due to the need to stock multiple screw types
Solution Approach 1:
A single screw design with a multi-functional head can replace multiple specialized screw types. By changing the insert member, the same screw can provide polyaxial movement, uniplanar movement, or fixed positioning, eliminating the need to stock multiple screw variants.
Solution Approach 2:
The system allows dynamic adjustment of the degree of freedom by changing the insert member. The screw head is designed to accommodate different insert members that can be interchangeably installed, allowing the surgical team to adjust the movement characteristics based on the specific surgical situation without replacing the entire screw assembly.
Data Source
AI summary
An assembly for connecting a support element to a bone. The assembly comprises: a bone screw having a head at one end of a threaded shaft; and a clamp comprising: a base at a first end of the clamp delimiting an opening for receiving the head of the bone screw; and at least two side members extending from the base towards a second end of the clamp. The head of the bone screw and the clamp are configured to allow the head of the bone screw to be inserted into the base from the direction of the first end at a first orientation of the base to the bone screw, and to retain an inserted bone screw within the base at a second orientation of the base relative to the bone screw.This allows the screw to be inserted into the bone without requiring prior assembly of the screw and clamp. It also allows later revision whereby the clamp can be removed from the screw without requiring an implanted screw to be removed from the bone.