Tibial Prosthesis Stud Offset for Anchoring Stability
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Solution Overview
Problem
Current unicompartmental knee prostheses experience mediocre anchoring resistance, particularly to micro-movements, leading to tibial plateau fractures or loosening, especially in smaller knees and women, due to inadequate bone anchorage.
Innovation Solution
The tibial plateau design features anchor studs positioned near the lateral edge of the tibial plateau, anatomically close to the bone cut, with two or three distributed anchor points, including a fin, to enhance leveraged anchoring stability without bone fracture, using frustoconical or 'diabolo' shaped studs with truncated sections to shift the anchoring center and increase the lever arm.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If anchor studs are positioned near the lateral edge of the tibial plateau to increase lever arm and anchoring stability, then anchoring resistance to micro-movements is improved, but the risk of bone fracture increases due to reduced bone material availability
Solution Approach 1:
The stud geometry is modified by truncating the lateral portion, shifting the anchoring center laterally relative to the stem center. This dimensional change in the stud cross-section allows the anchoring function to be decoupled from the stem positioning, enabling edge placement without proportional increase in bending moment on the stem.
Solution Approach 2:
The stud is designed with non-uniform cross-section along its length, with the anchoring portion having different geometric properties than the stem portion. This local quality differentiation allows the anchoring function to be optimized independently, concentrating stress in the bone at the optimal location while the stem maintains its structural integrity.
2Object-affected harmful factors
If anchor studs are positioned远离from the edge to avoid bone fracture, then bone safety is improved, but anchoring stability and resistance to micro-movements deteriorates
Solution Approach 1:
The lateral truncation of the stud creates an asymmetric cross-section where the anchoring center is displaced laterally relative to the stem center. This dimensional offset allows the stud to be positioned at the optimal anchoring location near the edge while the stem remains properly positioned, achieving both bone safety and anchoring stability.
3Ease of manufacture
If conventional diabolo-shaped studs are used, then manufacturing is simplified, but anchoring resistance to micro-movements is insufficient
Solution Approach 1:
The stud is designed with a truncated lateral portion creating an asymmetric cross-section, differentiating the anchoring region from the stem region. This local geometric modification enhances the anchoring function by shifting the stress distribution while maintaining manufacturability through standard machining operations.
Solution Approach 2:
The stud cross-section is made asymmetric by truncating the lateral side, creating different geometric properties on opposite sides. This asymmetry allows the anchoring center to be positioned optimally relative to the stem center, improving the mechanical advantage for anchoring while maintaining structural integrity.
Data Source
Figure 1~2
Figure 3A~4
AI summary
Tibial part of a knee prosthesis, in particular a unicompartmental prosthesis, comprising a tibial plateau having an inferior, or distal, face (3), delimited by a peripheral edge (6) having at least one lateral segment (9), and from which protrudes at least one anchoring pad (4; 5) intended to be anchored in the tibia, the at least one pad (4; 5) comprising at least one stem portion (14) having a longitudinal axis (30) and a head portion (15), the stem portion and the head portion defining between them an interface (25) which corresponds to the transverse section of the pad, perpendicular to the longitudinal axis, called the anchoring section, which is located at the point(s) (22) of the lateral surface of the pad that is/are furthest from the axis (30), the distance being measured perpendicular to the axis (30), characterized in that the transverse section (dl) at the base of the stem and the anchoring section (25) are mutually offset.