Dual-Mobility Reverse Shoulder Arthroplasty for Recurrent Dislocation

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Solution Overview

Problem

Existing shoulder prostheses, both anatomical and reverse shoulder arthroplasty, face instability issues leading to recurrent or chronic dislocations, especially in cases of extensive soft tissue and/or bone deficiency, where revision surgeries fail to stabilize the shoulder joint.

Innovation Solution

A dual mobility reverse shoulder arthroplasty device featuring a scapular implant with a fixed small spherical head and a mobile larger head, forming a double ball joint configuration, which allows for increased mobility and stability by preventing mechanical impingement and dislocation through a snap fit assembly.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional reverse shoulder arthroplasty is used, then the shoulder joint can be stabilized in many cases, but it fails to provide sufficient stability in cases of extensive soft tissue and bone deficiency leading to recurrent dislocation

Engineering Contradiction:

Improveshoulder joint stabilityVSAvoidadaptability to extensive soft tissue and bone deficiency

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The mobile head is divided into two functional parts: an inner spherical head that articulates with the scapular implant and an outer spherical head that articulates with the humeral implant. This segmentation allows each head to provide independent stability mechanisms, enabling the prosthesis to maintain stability even when soft tissue or bone support is compromised in one area.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The mobile head is designed to be movable relative to the scapular implant while simultaneously being constrained by the humeral implant. This dynamic configuration allows the prosthesis to adapt to varying degrees of soft tissue and bone deficiency, providing stability through geometric constraint rather than relying solely on soft tissue integrity.

Inventive Principle:

Principle #15Dynamics

2Ease of operation

If conventional shoulder prosthesis design is used, then the basic articulation function is provided, but large mobility angles cannot be achieved leading to mechanical impingement at extremal positions

Engineering Contradiction:

Improvemobility rangeVSAvoidmechanical impingement

Core Design Contradiction:

Ease of operationVSObject-affected harmful factors

Solution Approach 1:

The dual mobility design adds a second degree of freedom by allowing the mobile head to articulate with both the scapular implant (inner articulation) and the humeral implant (outer articulation). This dimensional change enables the prosthesis to achieve large mobility angles through combined rotations, preventing mechanical impingement that would occur in conventional single-articulation designs at extremal positions.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

3Ease of operation

If a mobile head design is implemented to increase mobility, then larger abduction and rotation angles are achieved, but the risk of head dislocation from the scapular implant increases

Engineering Contradiction:

Improveabduction and rotation anglesVSAvoidrisk of head dislocation

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

The humeral implant with its outer cup provides a pre-established constraint that prevents the mobile head from dislocating from the scapular implant. This beforehand cushioning mechanism ensures that even though the mobile head has increased mobility, it remains securely retained through the dual articulation system, eliminating the dislocation risk associated with mobile head designs.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

4Ease of operation

If a dual mobility design with concentric ball joints is used, then large mobility angles are achieved avoiding mechanical impingement, but the device complexity increases

Engineering Contradiction:

Improvemobility angles without impingementVSAvoiddouble ball joint configuration

Core Design Contradiction:

Ease of operationVSDevice complexity

Solution Approach 1:

The mobile head combines two spherical head functions into a single component that articulates with both the scapular implant and the humeral implant. This merging eliminates the need for separate inner and outer head components, reducing the overall device complexity while maintaining the dual mobility configuration and large mobility angles without mechanical impingement.

Inventive Principle:

Principle #5Merging (Combining)

Data Source

PatentUS20250325376A1Reverse shoulder arthroplasty with dual mobility

Publication Date: 2025.10.23 MEDICALEX

AI summary

A dual mobility reverse shoulder arthroplasty device for repairing a shoulder articulation, the device comprising: a scapular implant (1), configured to be attached to a scapula of a patient, a humeral implant (2), configured to be attached to the humerus of the patient, a spherical head (3), rigidly mounted on the scapular implant, a mobile head (4), formed as an intermediate cup, mounted on the spherical head with a snap fit assembly manner, the mobile head can rotate with regard to the spherical head about an articulation axis, thereby forming a first inner ball joint assembly, the humeral implant comprising an outer cup (21) configured to bear on the mobile head, forming a second outer ball joint assembly, concentric with the first ball joint, thereby achieving large mobility angles of the humeral implant with respect to the scapular implant, and thereby avoiding mechanical impingement at extremal positions.