Stemless Shoulder Implant Fixation via Cortical Screws
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Solution Overview
Problem
Conventional humeral components with stems in shoulder joint prostheses often require bone removal for fitting, complicate revision surgeries due to bone ingrowth, and pose risks of dislodgement, especially in the early stages post-surgery or under high load conditions.
Innovation Solution
A stemless humeral anchor assembly with a humeral anchor and screws that are anchored in the proximal region of the humerus, providing enhanced initial pull-out resistance and long-term fixation, and allowing for secure attachment without medullary canal modification, using a distal portion with a tapered profile and proximal apertures for screw placement into cortical bone.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a stem is used in conventional humeral components, then the component can be secured to the humerus, but bone must be removed to fit the stem to the canal and it complicates revision surgery
Solution Approach 1:
The patent removes the stem component entirely from the humeral prosthesis design, extracting only the necessary functional elements (humeral head and fixation components) that can be secured without requiring insertion into the medullary canal. This eliminates the need for bone removal while maintaining fixation security through alternative means such as cortical bone engagement and screw fixation.
Solution Approach 2:
The fixation function is segmented into multiple independent fixation components (screws, cortical engagement features) rather than relying on a single stem structure. This allows the prosthesis to achieve secure fixation through distributed attachment points in the cortical bone without requiring a continuous stem in the medullary canal.
2Reliability
If a stem is used in conventional humeral components, then the component can be secured to the humerus, but integration through bone ingrowth makes removal difficult during revision surgery
Solution Approach 1:
The fixation mechanism transitions from a static, permanent bone-ingrown stem to a dynamic system where fixation security is achieved through reversible mechanical engagement (screws, cortical features) that can be easily undone during revision surgery without requiring removal of ingrown bone.
Solution Approach 2:
The patent extracts the revision difficulty problem by eliminating the stem structure that causes bone ingrowth issues. The alternative fixation methods used do not rely on long-term bone ingrowth, allowing for straightforward removal and revision without the complications associated with stem extraction.
3Loss of substance
If a stemless design is used, then bone loss is decreased and procedure complexity is reduced, but the component is more challenging to secure and at risk of dislodgement
Solution Approach 1:
The patent employs composite fixation strategies combining multiple fixation mechanisms (screw fixation, cortical bone engagement features, surface characteristics) to achieve reliable fixation in a stemless design. This composite approach compensates for the absence of a stem while maintaining fixation security equivalent to or exceeding traditional stem designs.
Solution Approach 2:
The fixation function is divided into multiple segmented fixation components and attachment points distributed across the humeral head and cortical bone, replacing the monolithic stem fixation approach. This segmentation provides cumulative fixation security without requiring a single large stem structure.
4Duration of action of stationary object
If conventional stemless designs relying on bone ingrowth are used, then long term fixation is achieved, but there is a risk of dislodgement in early days and weeks after surgery
Solution Approach 1:
The patent applies preliminary mechanical fixation actions (screw fixation, cortical engagement) that provide immediate retention strength before bone ingrowth occurs. This preliminary fixation mechanism bridges the early postoperative period, preventing dislodgement until biological fixation develops, while still achieving long-term fixation through the combined mechanical-biological approach.
Data Source
AI summary
An implant assembly may include a first component having a proximal plate and a distal portion extending from the proximal plate, a first screw of a first type, and a first screw of a second type. The proximal plate may have a proximal face, a distal face configured to abut bone, and a periphery. The proximal plate may define a plurality of apertures. An opening may be defined by the proximal plate and extend through the distal portion. Each of the plurality of apertures may be disposed between the opening and the periphery. The first screw of the first type may be sized and configured to be received in the opening and engage bone. The first screw of the second type may be sized and configured to be received in at least one of the plurality of apertures.