Asymmetrical Locking Mechanism for Reverse Shoulder Prostheses
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Solution Overview
Problem
Current Reverse Shoulder Arthroplasty (RSA) techniques often result in undesirable effects such as scapular notching and limited range of motion, which can lead to increased load on the liner locking mechanism, causing liner dissociation.
Innovation Solution
The implementation of an asymmetrical locking mechanism in prosthesis systems, featuring a tray with lateral and medial grooves and a liner with resiliently deformable fingers and a toe, allowing for selective rotational orientation to resist disassociation under physiological loading conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a steeper humeral implant angle and lateralized center of rotation are employed to reduce scapular notching and improve range of motion, then joint mobility is improved, but the load on the liner locking mechanism increases causing liner dissociation
Solution Approach 1:
The locking mechanism transitions from a symmetrical circumferential design to an asymmetrical directional design. The lateral groove and medial groove are positioned at different orientations, with the lateral groove receiving a lateral toe and the medial groove receiving resilient medial fingers. This asymmetrical configuration creates directional locking that specifically resists the physiological loading forces generated by the steeper humeral implant angle and lateralized center of rotation, allowing improved range of motion without compromising locking strength.
Solution Approach 2:
Different portions of the locking mechanism are given different properties to handle different loading directions. The lateral groove is designed to be rigid and receive a fixed lateral toe for resisting primary loading forces, while the medial groove receives resiliently deformable medial fingers that can flex and then lock. This local differentiation of mechanical properties allows the locking mechanism to handle the complex multi-directional forces resulting from the modified implant geometry.
2Ease of manufacture
If conventional symmetrical locking mechanisms are used, then manufacturing is simplified, but the locking strength is insufficient under physiological loading conditions
Solution Approach 1:
The locking mechanism uses an asymmetrical configuration with a lateral groove and medial groove at different orientations and depths. The lateral groove extends deeper and receives a fixed lateral toe, while the medial groove is shallower and receives resilient medial fingers. This asymmetrical design provides directionally optimized locking strength that is specifically tailored to resist physiological loading forces, improving reliability while remaining manufacturable using conventional techniques.
3Strength
If resiliently deformable medial fingers are used instead of rigid tabs, then the locking mechanism can better absorb loading forces, but the complexity of the locking mechanism increases
Solution Approach 1:
The locking mechanism applies local quality by using resiliently deformable medial fingers only in the medial groove, while the lateral groove receives a fixed rigid lateral toe. The resilient fingers are strategically placed to absorb and distribute loading forces in the medial direction, where flexibility is most beneficial. This localized use of resilient elements provides enhanced strength and force absorption while minimizing the overall complexity of the locking mechanism.
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 asymmetrical locking mechanism maintains approximately 60% higher shear loading than conventional circumferential lock mechanisms, reducing the risk of liner dissociation and improving joint stability.
Implementation Method 1
The locking portion can comprise a lateral toe positioned generally diametrically opposite a plurality of resiliently deformable medial fingers defined in the locking portion
Data Source
AI summary
The present disclosure relates to prosthesis systems having trays and liners having an asymmetrical locking mechanism to bias the strength of the liner to resist loading forces and associated methods. The tray has a lateral groove disposed in an inner surface of a lateral circumferential portion of the tray and a medial groove disposed in an inner surface of a medial circumferential portion of the tray. The liner has an upper segment and a lower segment. The liner has a locking portion for lockingly engaging the tray that includes the lower segment. The locking portion has a lateral toe positioned generally diametrically opposite a plurality of resiliently deformable medial fingers defined therein. The liner and the tray are engageable in a lateral-to-medial direction so that the plurality of medial fingers can resiliently deform to engage the medial groove subsequent to engagement of the lateral toe within the lateral groove.