Slotted Prosthesis Stem With Deformation-Limiting Projections
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Solution Overview
Problem
Existing prostheses experience stem pain due to elastic recoil forces after implantation, and excessively flexible stem sections may lead to undesirable plastic deformation or failure.
Innovation Solution
The prosthesis features projections on the shaft sections that limit bending deformation, allowing low-force insertion and stable anchorage with minimal restoring forces, preventing plastic deformation and failure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the stem sections are made flexible to reduce elastic recoil forces, then stem pain is reduced, but plastic deformation or stem failure may occur
Solution Approach 1:
The patent changes the geometric parameters of the stem sections by introducing projections that extend into the slot-shaped gap. These projections have specific heights and spacing that control the deformation behavior, allowing the stem to be flexible enough to reduce recoil forces while preventing excessive deformation that would cause failure
Solution Approach 2:
The patent applies different structural characteristics to different parts of the stem. The projections are located at specific positions along the stem length, creating local variations in stiffness. The regions with projections provide structural support and limit deformation, while other regions maintain flexibility for insertion and recoil reduction
2Reliability
If the stem sections are made rigid to prevent plastic deformation, then stem stability is improved, but elastic recoil forces increase causing stem pain
Solution Approach 1:
The patent modifies the structural parameters by adding projections with controlled dimensions. The height and spacing of these projections are optimized to provide just enough structural support to prevent failure while allowing sufficient flexibility to reduce recoil forces and associated pain
Solution Approach 2:
The stem is segmented into multiple shaft sections separated by a slot-shaped gap. Projections on these sections create localized structural reinforcement without making the entire stem rigid. This segmentation allows different regions to have different degrees of flexibility, balancing stability and pain reduction
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The design ensures low restoring forces and high stability by limiting deformation paths with projections, reducing stem pain and preventing failure.
Implementation Method 1
The slot-shaped gap serves the purpose of allowing the stem sections to deform elastically and radially inward as they are inserted into the bone marrow cavity, thereby reducing the size of the slot-shaped gap. After complete insertion into the bone marrow cavity, the stem sections rest against a boundary of the bone marrow cavity under preload.
Data Source
Figure 1~2
Figure 3
AI summary
The invention relates to a prosthesis (10), in particular a knee prosthesis or a hip stem prosthesis, with a stem (12) for arrangement and attachment in a long bone, wherein the stem has stem sections (30, 32) extending parallel to the stem axis (18), which are separated from each other by a slot-shaped gap (28), wherein the stem sections are deformable from an undeformed rest state by bending stress such that the slot-shaped gap decreases, wherein a first stem section has a first projection which is provided on a side of the first stem section facing a second stem section, forms a first narrowing of the gap and has a first boundary surface for abutting the second stem section, wherein the first boundary surface is spaced apart from the second stem section in the undeformed rest state.