Offset Keel Knee Prosthesis Reduces Bone Resection
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Solution Overview
Problem
Conventional prosthetic devices for knee joints with large central keels face challenges during implantation and revision, including longer bone preparation times, potential bone fractures, and excessive bone removal due to the deep voids required for keel insertion and removal.
Innovation Solution
A prosthetic device with a body portion and offset keels that project outwardly from the implantation surface, allowing for secure attachment to the bone with reduced bone penetration depth, using a single tool for bone void preparation and minimizing stress concentrations, thereby reducing the amount of bone resection needed for implantation and revision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a large central keel is used to provide sufficient strength and stiffness, then the prosthetic device has adequate mechanical strength, but the bone preparation time increases and multiple cutting tools are required
Solution Approach 1:
The single large central keel is segmented into multiple smaller keels (typically three keels arranged in a triangular pattern). This segmentation allows each individual keel to be smaller and require less bone preparation, while the collective arrangement of multiple keels maintains the overall strength and stiffness of the prosthetic device. The segmented approach also enables the use of a single cutting tool to prepare all keel voids, reducing preparation time and simplifying the implantation process.
2Strength
If a large central keel projects significant length from the bone interface surface, then sufficient strength is provided, but the risk of bone fracture during implantation increases
Solution Approach 1:
Dividing the large central keel into multiple smaller keels reduces the length each individual keel must project from the bone interface surface. This segmentation distributes the mechanical load across multiple smaller structures, reducing the stress concentration on any single keel-bone interface and thereby lowering the risk of bone fracture during implantation while maintaining overall structural strength.
Solution Approach 2:
The multiple smaller keels are strategically positioned to optimize local bone engagement and stress distribution. Each keel is sized and positioned to engage with local bone structures in a manner that minimizes fracture risk, while the collective arrangement ensures adequate overall strength. This local optimization of keel geometry and positioning reduces harmful stress concentrations.
3Reliability
If a large central keel is inserted into a deep void in the bone, then secure attachment is achieved, but a relatively large amount of bone must be resected during revision
Solution Approach 1:
The deep single void required for a large central keel is replaced by multiple shallower voids for smaller individual keels. This segmentation allows the prosthetic device to achieve secure attachment through multiple distributed interfaces rather than one deep interface. During revision, removing multiple smaller keels requires less bone resection than removing a single large keel that extends deeply into the bone, thereby preserving more bone stock for future procedures.
4Manufacturing precision
If multiple planar cuts are made to create the bone interface surface, then proper fit is achieved, but thin material cross-sections result in increased stress concentrations
Solution Approach 1:
The bone interface surface transitions from multiple intersecting planar surfaces to a curved, dome-shaped surface. This curvature eliminates the sharp intersections and thin material cross-sections that create stress concentrations. The curved surface maintains proper fit to the bone while distributing stresses more evenly across the prosthetic device structure, reducing the likelihood of failure.
Data Source
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AI summary
A prosthetic device (50, 60) for a knee joint includes a body portion (56) and a first keel (52, 62). The body portion attaches to a bone of a knee joint. The body portion can have a bearing surface (58) configured to replace at least a portion of the bone and an implantation surface configured to face the bone upon implantation. The first keel (52, 62) can be configured to be inserted into a corresponding first keel void formed in the bone. The first feel can be configured to project outwardly from the implantation surface by an amount sufficient to inhibit movement of the body portion relative to the bone in both medial and lateral directions (M-L) upon insertion into the first keel void. The first keel can extend along a longitudinal direction (L) of the body portion and is offset from a longitudinal centerline (C) of the body portion. Methods of implanting and removing the prosthetic device are also provided.