Posterior Offset Humeral Adapter Tray for Reverse Shoulder
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Solution Overview
Problem
Reverse shoulder patients often experience loss of external rotation and excessive internal rotation, impairing their ability to perform daily activities due to insufficient external rotation capability, even with lateralized reverse shoulder designs, which limits active internal rotation and alters normal muscle function.
Innovation Solution
A posterior offset humeral adapter tray with a boss posteriorly offset by 12mm to 24mm is used in conjunction with a humeral liner, shifting the humeral stem posteriorly to increase external rotation moment arms of the posterior rotator cuff, improving functional capabilities for patients with weak external rotators.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a lateralized reverse shoulder design is used, then the glenoid articulation is improved, but external rotation capability remains insufficient and internal rotation is excessive
Solution Approach 1:
The adapter tray introduces a new dimensional parameter (posterior offset) to the humeral component positioning. By offsetting the boss 12-24mm posteriorly from the central bore, the system achieves external rotation improvement not present in conventional lateralized designs, thereby resolving the contradiction between glenoid articulation and external rotation capability.
Solution Approach 2:
The patent changes the positional parameter of the humeral stem relative to the glenoid by using a posteriorly offset adapter tray. This parameter change (posterior offset of 12-24mm) fundamentally alters the moment arms of the rotator cuff muscles, transforming the rotational dynamics to improve external rotation while maintaining glenoid articulation integrity.
2Force
If the humeral stem is positioned anteriorly, then internal rotation is enhanced, but external rotation moment arms are reduced
Solution Approach 1:
Instead of positioning the humeral stem anteriorly to enhance internal rotation, the patent inverts the approach by using a posteriorly offset adapter tray. This inversion places the humeral stem in a more posterior position, which paradoxically improves external rotation moment arms while reducing excessive internal rotation, directly addressing the force imbalance.
3Device complexity
If conventional reverse shoulder components are used, then the prosthesis structure is simplified, but muscle tension is altered and deltoid over-tensioning occurs
Solution Approach 1:
The adapter tray applies a localized posterior offset (12-24mm) specifically at the boss location on the distal face, while maintaining the overall simplicity of the prosthesis structure. This localized modification restores anatomic muscle tension by precisely adjusting the position of the humeral stem relative to the glenoid, thereby reducing deltoid over-tensioning without complicating the overall device.
Data Source
Figure 1A~1D
Figure 2A~2C
Figure 3
AI summary
A reverse shoulder prosthesis includes a humeral adapter tray (300) configured to sit near a resected surface of a humerus, the humeral adapter tray (300) comprising: a cavity (302); a central bore; and a distal face (304) including a boss (310), the boss (310): (i) configured as an extension of the distal face, (ii) posteriorly offset from the central bore by at least 10 mm, and (iii) configured to engage a humeral stem; and a humeral liner (250) comprising: a distal rim (252) configured to sit within the cavity (302) of the humeral adapter tray (300); and a concave articulating surface configured to mate with a convex articulating surface of a glenosphere. Offsetting the reverse shoulder humeral adapter tray shifts the humerus in the posterior direction so as to result in better deltoid wrapping, more anatomic muscle tensioning, and larger muscle moment arms during both abduction and internal/external rotation.