Orthopaedic Bone Fastener Sliding Rotational Head Mount
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Solution Overview
Problem
Existing orthopaedic bone fastener systems face challenges in accessing the upper end of the screw during installation due to the head obstructing the driving tool, and require high forces to secure the snap-fit connection, which risks damaging fragile bones during spinal surgery.
Innovation Solution
A bone fastener system with a mount that allows the head to be mounted on the screw post in situ, using a sliding and rotational mechanism that provides a secure lock without obstructing access, enabling easy assembly and minimizing force application to prevent bone damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the head is mounted on the pedicle screw before insertion using a snap-fit connection, then the head can be securely attached, but significant force is required to establish the connection which risks damaging fragile bone
Solution Approach 1:
The mounting process is divided into two distinct phases: first, the head is placed onto the screw shaft in a loose fitted state requiring minimal force; second, a locking mechanism is engaged to secure the head firmly. This segmentation allows the initial placement to avoid bone damage while the locking phase ensures connection security.
Solution Approach 2:
The head is preliminarily positioned on the screw shaft in a loose fitted state before the locking mechanism is activated. This preliminary placement requires minimal force and avoids bone damage, while subsequent engagement of the locking mechanism provides the secure connection needed for reliability.
2Reliability
If the head is mounted on the pedicle screw before insertion, then the connection is established, but the head obstructs access to the upper end of the screw for the driving tool
Solution Approach 1:
The procedure is segmented into distinct steps: first, the screw is inserted into the bone using the driving tool with full access to the upper end; second, the head is mounted on the inserted screw. This segmentation eliminates the obstruction problem while maintaining secure connection.
Solution Approach 2:
The screw insertion is performed as a preliminary action before head mounting. This allows the driving tool to access the upper end of the screw without obstruction from the head, and the head is subsequently attached to the already-positioned screw.
3Reliability
If the snap-fit connection is made very strong to prevent head separation, then connection security is improved, but the force required to mount the head increases significantly
Solution Approach 1:
The connection establishment is segmented into a low-force placement phase where the head is positioned on the screw shaft, followed by a locking phase where the securing mechanism is engaged. This allows the final connection to be strong while the initial mounting requires minimal force.
Solution Approach 2:
The head is preliminarily positioned on the screw shaft requiring minimal force, and only after this preliminary placement is the locking mechanism activated to create the strong snap-fit connection. This separates the high-force locking action from the low-force placement action.
Data Source
AI summary
An orthopaedic assembly comprises a bone fastener and a head. The bone fastener comprises a shaft with a proximal end and a distal end. The proximal end forms a tip of the bone fastener. A head post is located at the distal end, for mounting a separate head on the bone fastener. The head and the head post are each provided with a respective part of a mount for mounting the head on the head post. The mount comprises an opening in a first lockable part in which a second lockable part of the mount can be admitted. The head is mountable on the head post by moving the head towards the head post and thereby sliding the first lockable part over the second lockable part in a sliding direction, to admit the second lockable part in the opening. The head is lockable in position on the head once the second lockable part is admitted to a predetermined depth into the opening by turning the first lockable part around an axis extending in the sliding direction.