Prosthetic Shell Ribs for Bone Anchoring Stability
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Solution Overview
Problem
Existing drive-in socket prosthetics for bone joints lack optimal primary stability and often result in bone material damage during insertion, leading to incomplete anchoring and potential loosening over time.
Innovation Solution
A shell design with a convex outer or concave inner surface featuring multiple ribs that increase in pitch angle from 45° to 85°, allowing for a constant advance during rotation, which provides optimal form fit and primary anchoring, preventing bone material damage and ensuring secure integration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If drive-in webs are used as locking elements with increasing pitch, then the socket is locked in the hip bone preventing screw-out, but bone material is plowed away creating grooves that weaken anchoring
Solution Approach 1:
The patent inverts the traditional locking mechanism by using ribs with increasing pitch angles that guide bone material into the socket during insertion, rather than plowing it away. The ribs create compression forces that push bone into the socket interior, transforming the harmful plowing effect into a beneficial anchoring effect through inverse action.
Solution Approach 2:
The patent converts the harmful effect of bone material displacement during insertion into a beneficial anchoring mechanism. The ribs are designed to compress and guide bone material into the socket, transforming the potential damage into a strengthening effect that enhances primary stability and long-term fixation.
2Device complexity
If few and large drive-in webs are used, then the socket structure is simpler, but primary stability is not optimal
Solution Approach 1:
The patent applies segmentation by dividing the socket surface into multiple ribs instead of using few large drive-in webs. This segmentation increases the surface area contact with bone material, improving primary stability while maintaining structural simplicity through the repetitive rib pattern.
Solution Approach 2:
The patent adds the dimension of pitch angle variation to the rib design, creating a three-dimensional effect where ribs with increasing pitch angles provide both structural support and active bone engagement, enhancing stability without significantly increasing complexity.
3Reliability
If the socket is driven in forcefully to achieve stability, then primary stability is improved, but cavities and shears occur in the bone material
Solution Approach 1:
The patent employs preliminary action by pre-shaping the ribs with specific pitch angles that guide bone material compression and distribution before final insertion. This preliminary design of the rib geometry ensures that bone material is progressively compressed and guided into position, preventing cavities and shears during the insertion process.
Solution Approach 2:
The patent provides beforehand cushioning by designing ribs that progressively compress bone material during insertion, cushioning the impact and distributing forces evenly. This prevents sudden impacts that would create cavities and shears, ensuring smooth insertion while achieving stability.
Data Source
AI summary
A shell (1) for a prosthetic joint to be driven into a bone substance. The shell having an outer lateral surface (4) which is convexly curved in cross section and on which a plurality of ribs (5) is arranged. All ribs extend in the same direction at a preferably increasing gradient angle of 45° to 85° at the equatorial end (6) to a pole-side end (7). The cumulative flank projection area of all ribs (5) corresponds to at least a fifth of the entire outer lateral surface. As a result of this measure, a very high primary stability is achieved once the shell has been driven in, the shell being screwed into the bone substance very precisely and without bone material being sheared off. This arrangement can also be applied, similarly, to a concavely curved inner lateral surface.