Custom Hexapod Struts for Wider Excursion in External Fixators
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Solution Overview
Problem
Existing hexapod external fixators face limitations due to factory-assembled struts with fixed range of excursion, requiring frequent changes and inventory management of various lengths, and instability from universal joints, necessitating multiple hospital visits and increased costs.
Innovation Solution
Custom-assembled struts with a threaded rod portion and hollow cylindrical body, allowing adjustable length and three degrees of rotational freedom, enabling the surgeon to choose optimal length and avoid strut changes during deformity correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If factory-assembled struts with fixed length are used, then manufacturing is simplified, but the range of excursion is limited and frequent strut changes are required during deformity correction
Solution Approach 1:
The strut is divided into two separate components: a cylindrical body and a threaded rod. This segmentation allows the strut length to be adjusted by changing the threaded rod length while keeping the cylindrical body constant, thereby extending the range of excursion without complicating the manufacturing of individual components.
Solution Approach 2:
The strut transitions from a fixed-length design to a dynamic, adjustable-length design. The threaded rod can be changed to different lengths based on the specific deformity correction requirements, allowing the strut to adapt to varying operational needs throughout the treatment course.
2Adaptability or versatility
If multiple strut lengths are kept in inventory, then the range of excursion requirement is met, but inventory management complexity and costs increase
Solution Approach 1:
A single cylindrical body design serves multiple functions by accommodating threaded rods of various lengths. This universal design eliminates the need to maintain separate inventories for different strut lengths, as all variations can be achieved by simply changing the threaded rod component.
3Ease of operation
If universal joints are used to connect struts to rings, then rotational freedom is achieved, but mechanical clearance causes instability
Solution Approach 1:
The patent removes the universal joint from the strut assembly, extracting the source of mechanical clearance and instability. Instead, spherical joints are used at the connection points between struts and rings, which provide the necessary rotational freedom without the clearance issues inherent in universal joints.
4Reliability
If ball and socket joints are used, then mechanical stability is improved, but spatial clearance between rings is insufficient for adequate range of movement
Solution Approach 1:
The patent introduces strut connectors as intermediary components between the rings and struts. These connectors incorporate spherical joints that provide the necessary range of movement while maintaining mechanical stability. The strut connectors act as mediators that resolve the conflict between stability and mobility by providing an intermediate structure with appropriate clearance.
Data Source
AI summary
An external bone fixation system includes a first platform which is a ring around the limb holding a segment of bone, a second platform which is another ring around the limb holding another segment of bone, interconnected with six length-adjustable telescoping custom-assembled struts using connecting elements in the form of strut connectors consisting of pivoting and rotating holders that allow three degrees of rotational freedom for each strut.