Reverse Shoulder Prosthesis Center-of-Rotation Positioning
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Solution Overview
Problem
Existing reverse total shoulder prostheses suffer from improper center of rotation placement, leading to limited motion, dislocation, excessive stress on bones, bone fractures, and premature wear, among other issues.
Innovation Solution
A novel reverse total shoulder prosthesis with optimally placed prosthetic center of rotation (pCOR) medial and inferior to the natural center of rotation (nCOR), and humeral bone displacement in a specific inferior direction, achieving a 0.6 to 1.2 ratio and 75 to 105 degrees below horizontal, with optimal ratios of 0.85 to 1.15 and 90 degrees, respectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the prosthetic center of rotation is placed at the natural center of rotation, then the joint alignment is simple, but the range of motion is limited and dislocation occurs
Solution Approach 1:
The patent applies parameter changes by systematically varying the position of the prosthetic center of rotation relative to the natural center of rotation. Specifically, the prosthetic center of rotation is positioned inferior and medial to the natural center of rotation, with the inferior displacement ranging from 60-80% and medial displacement from 40-60% of the humeral head radius. This parameter optimization resolves the contradiction by achieving improved range of motion through calculated positional adjustments while maintaining manufacturing precision through defined geometric relationships.
Solution Approach 2:
The patent applies dimensionality change by moving the prosthetic center of rotation from the original natural center of rotation position to a new position in the inferior-medial direction. This spatial repositioning in multiple dimensions (inferior and medial displacements) enables the joint to achieve better range of motion while the specific dimensional ratios (0.6-1.2 ratio of inferior to medial displacement) ensure proper alignment and reduce dislocation risk.
2Ease of operation
If the humeral bone is displaced inferiorly, then the range of motion improves, but the stress on bones increases causing fractures
Solution Approach 1:
The patent applies parameter changes by optimizing the inferior displacement of the humeral bone to a specific range (60-80% of humeral head radius) rather than maximum displacement. This controlled parameter adjustment achieves improved range of motion while preventing excessive stress on the bone that would cause fractures. The medial displacement parameter (40-60% of radius) is also optimized to balance stress distribution.
3Reliability
If the prosthetic components are placed with high precision, then the joint performance improves, but the implantation complexity increases
Solution Approach 1:
The patent applies preliminary action by pre-calculating and pre-defining the optimal positions and dimensional ratios for prosthetic component placement before surgery. The specific geometric relationships (inferior displacement of 60-80%, medial displacement of 40-60%, and the 0.6-1.2 ratio of inferior to medial displacement) are established in advance, allowing surgeons to follow predetermined guidelines during implantation. This reduces intraoperative complexity while maintaining high precision and joint performance.
Data Source
AI summary
Disclosed is a prosthetic joint assembly for joining a humerus bone to a scapula bone, comprising a humeral component adapted for engagement with said humerus bone and a concave dish; a scapular component adapted for engagement with said scapula bone and a convex surface adapted to engage said concave dish; wherein when said components are implanted and engaged in a rest position said prosthetic center of rotation is displaced in a direction that is inferior and medial relative to a natural center of rotation and said humerus bone is displaced in a direction that is inferior relative to said natural center of rotation.