Captured Keel Unicompartmental Knee Prosthesis Fixation
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Solution Overview
Problem
Current knee arthroplasty procedures require significant resection of subchondral bone and use of PMMA cement for implant fixation, which can lead to prosthesis subsidence and increased risk of complications, especially in patients with unicompartmental disease or obesity.
Innovation Solution
A prosthesis with a captured keel design that provides positive interlocking without the need for PMMA cement, utilizing a keel shape with a negative draft and a recessed or hooked appearance to secure the implant on the remaining subchondral bone, allowing for minimal bone resection and reduced motion against the tibia.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If PMMA cement is used for implant fixation, then immediate fixation strength is improved, but prosthesis subsidence and long-term reliability deteriorate
Solution Approach 1:
The patent removes the PMMA cement component from the fixation system entirely. Instead of using cement to bond the implant to bone, the design relies solely on the captured keel mechanism that mechanically interlocks with the subchondral bone, eliminating the harmful effects of cement while maintaining fixation strength.
Solution Approach 2:
The keel design performs self-fixation by capturing the subchondral bone through its hooked geometry. The keel's shape allows it to engage and lock into the bone naturally during insertion, providing self-sustaining fixation without requiring external cement or additional fastening components.
2Ease of manufacture
If significant subchondral bone resection is performed, then implant placement and fixation are improved, but structural support and reliability deteriorate
Solution Approach 1:
The patent applies localized bone resection only where the keel needs to engage, rather than removing large amounts of subchondral bone. The captured keel design concentrates the preparation work to specific areas that allow the keel to hook into the bone, preserving the overall structural integrity of the tibial plateau.
Solution Approach 2:
Instead of removing bone to create a flat bearing surface for implant placement, the patent inverts the approach by using the remaining subchondral bone as a positive feature to capture the keel. The hooked keel engages with the bone in an interlocking manner, turning the bone's presence into a fixation advantage rather than requiring its removal.
3Strength
If cement is used to bond implant to bone, then initial fixation is improved, but surgical time and procedure complexity increase
Solution Approach 1:
The patent eliminates the cement application step entirely from the surgical procedure. By removing the need for cement mixing, application, and curing time, the surgery is significantly shortened while the captured keel provides immediate mechanical fixation upon insertion.
Data Source
AI summary
A unicompartmental knee prosthesis for implantation in a knee joint between a femoral condyle and a corresponding tibia plateau is provided including a generally elliptical body having opposed femoral and tibial face, the body having an anterior end and a posterior end. A keel is provided on the tibial face having a generally anterior-posterior orientation, the keel having an anterior end and a posterior end, where the keel posterior end includes a distal posterior portion that extends farther toward the body posterior end compared with a proximal posterior portion of the keel posterior end.