Constrained Prosthetic Knee Shackle and Bump Stop Design
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Solution Overview
Problem
Constrained knee prostheses with hinge posts often face issues of insufficient soft tissue support, leading to distraction and luxation of the femoral component from the tibial baseplate, resulting in pain and complications for patients, and current designs have limited adjustment options for femoral component rotation relative to the tibial baseplate.
Innovation Solution
The design includes a shackle with increased width and frustoconical profiles to enhance strength and stability, along with a removably attached bump stop that can be adjusted or replaced without removing the prosthesis, allowing for customizable rotation limits between the femoral and tibial components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the hinge post and femoral component are free to move proximal/distal relative to the tibial baseplate, then distraction of the knee joint is allowed, but insufficient soft tissue support leads to luxation of the femoral component from the tibial baseplate
Solution Approach 1:
The patent introduces a distraction stop that changes the positional parameter of the femoral component relative to the tibial baseplate. The distraction stop engages with the hinge post to limit proximal movement, thereby preventing luxation while preserving controlled distraction capability within safe limits.
Solution Approach 2:
The distraction stop provides preliminary counter-action against excessive proximal movement of the femoral component. By being pre-positioned to engage the hinge post at a predetermined limit, it prevents luxation before it can occur, addressing the reliability issue while maintaining adaptability.
2Strength
If component widths are increased to improve strength, then the strength of prosthesis components is improved, but the overall prosthesis envelope increases
Solution Approach 1:
The patent applies frustoconical profiles to the shackle and complementary conical profiles to the walls, transitioning from simple cylindrical geometry to three-dimensional conical surfaces. This dimensional change allows the components to maintain increased width for strength while fitting within the same overall prosthesis envelope through tapered geometry.
Solution Approach 2:
The patent employs frustoconical and conical geometric compositions in the shackle and wall structures, creating composite geometric forms that optimize both strength and space utilization. The tapered profiles distribute structural requirements across varying cross-sections, achieving high strength without uniform increase in overall dimensions.
3Device complexity
If minimal adjustments are made to femoral component rotation, then the existing design simplicity is maintained, but the ability to match individual patient needs is limited
Solution Approach 1:
The patent introduces a dynamic adjustment mechanism through the bump stop that can be repositioned along the femoral component. This allows the rotation limit to be dynamically adjusted to match individual patient needs while maintaining a relatively simple overall design. The bump stop can be positioned at different locations to create customized rotation constraints.
Solution Approach 2:
The patent segments the rotation control function into a separate, adjustable bump stop component rather than fixing it into the main structure. This segmentation allows independent adjustment of the rotation limit without affecting other parts of the prosthesis, enhancing adaptability while keeping the base design simple.
Data Source
AI summary
A prosthesis assembly can include a tibial tray, a tibial bearing component, a hinge post, a femoral component, a shackle, walls, a hinge axle, and a bump stop. The hinge post can extend through the tibial bearing component and be at least partially received in a recess of the tibial tray. The femoral component can contact an articular surface of the tibial bearing component. The shackle can be coupled to the hinge post and configured to be inserted between a medial and a lateral condyle of the femoral component. The walls can be positioned between the femoral component and the shackle. The hinge axle can be configured to secure the femoral component to the shackle. The bump stop can be removably attached to the femoral component and configured to contact the shackle at a set limit of rotation of the femoral component relative to the tibial bearing component.