Convertible Humeral Stem for Anatomic-Reverse Conversion
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Solution Overview
Problem
Existing shoulder prostheses face challenges in converting from anatomic to reverse reconstruction, with difficulties in removing integrated parts causing bone loss and altering kinematics, and in reverse to anatomic conversions, leading to modularity issues and potential disassembly or breakage.
Innovation Solution
A convertible prosthesis system with a humeral anchor and modular inserts that can be converted without removing integrated parts, featuring a humeral anchor with a proximal face having distinct engagement features for both anatomic and reverse inserts, allowing direct coupling and interference fits to maintain biomechanics and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If an anatomic prosthesis is converted to reverse reconstruction by removing integrated parts below the resection plane, then the reverse insert can be positioned to reduce distance to lateral contour, but excessive bone loss occurs and removal becomes difficult
Solution Approach 1:
The prosthesis is divided into modular components: a stem component that remains integrated in the bone, and a separate reverse insert that can be independently positioned and coupled to the stem. This segmentation allows the reverse insert to be optimally positioned without removing the integrated stem, thereby avoiding bone loss while achieving the desired positioning.
Solution Approach 2:
The stem component is designed with universal coupling features that can accommodate both anatomic inserts and reverse inserts. This multi-functionality allows the same stem to serve in different reconstruction types without requiring removal or modification of the integrated stem, thus preventing bone loss while enabling proper positioning of the reverse insert.
2Adaptability or versatility
If an adaptor is added above the resection plane for conversion, then reverse reconstruction is achieved, but the cavity position is pushed out further altering kinematics and increasing modularity to 3 components
Solution Approach 1:
The stem component incorporates universal coupling features that directly accept both anatomic and reverse inserts without requiring additional adaptors. This design maintains the system at 2 components while enabling conversion capability, thereby reducing device complexity while preserving adaptability.
Solution Approach 2:
Instead of adding an adaptor above the resection plane to achieve conversion, the design inverts the approach by integrating direct coupling features into the stem that allow the reverse insert to be positioned correctly without additional components. This eliminates the need for adaptors and maintains optimal kinematics.
3Device complexity
If the bearing surface materials are inverted with harder cavity and softer semi-spherical device, then modularity is limited, but this deviates from proven clinical design where cavity is softer
Solution Approach 1:
The stem component is designed with universal coupling features that can accommodate both anatomic inserts and reverse inserts without requiring material inversion or deviation from proven clinical designs. This maintains the established softer cavity material while enabling modularity for different reconstruction types through design flexibility rather than material changes.
4Adaptability or versatility
If modular components are used for conversion, then conversion between anatomic and reverse is possible, but disassembly or breakage of the construct may occur
Solution Approach 1:
The coupling features between the stem and inserts are designed with preliminary engagement mechanisms that ensure secure attachment before use. The interference fit and geometric interlocking are pre-configured to prevent disassembly or breakage during normal operation, while still allowing for controlled conversion between anatomic and reverse configurations when needed.
Solution Approach 2:
The coupling interface employs asymmetric geometric features including non-circular cross-sections and specific locking geometries that prevent accidental disassembly while allowing controlled insertion. This asymmetric design enhances construct stability and reliability by making the connection irreversible under normal physiological loads while maintaining conversion capability through surgical intervention when required.
Data Source
Figure 1A~1B
Figure 2A~2B
Figure 3
AI summary
The stem for a shoulder prosthesis comprises a distal shaft portion adapted to be anchored in a medullary canal of a humerus. The stem further comprises a proximal portion having a stem face, the stem face comprising a first engagement feature configured to couple with a reverse insert and a second engagement feature configured to couple with an anatomic insert. The stem also comprises a metaphyseal portion comprising a medial portion and first and second lateral arms extending between and connecting the shaft portion and the proximal portion.