Hip Prosthesis Shock Absorber Mechanism
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Solution Overview
Problem
Current hip prosthesis devices are prone to loosening due to large impact forces during load-bearing activities, leading to micromotion and osteolysis, with existing shock absorption mechanisms being ineffective in addressing motion along the femoral axial direction and lacking longevity.
Innovation Solution
A hip prosthesis device featuring a femoral stem with a shock absorber mechanism between the stem shaft and sleeve, capable of resisting both downward and upward longitudinal sliding motions, incorporating a spring or damping system to absorb impact forces and maintain the prosthesis in its original position.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a shock absorber mechanism is added to reduce impact forces, then the reliability of the prosthesis is improved, but the device complexity increases
Solution Approach 1:
The shock absorber mechanism is nested within the hollow interior cavity of the femoral stem, with the piston rod moving inside the stem's internal space. This allows the shock absorption functionality to be integrated into the existing stem structure without adding external components, thereby improving reliability while minimizing increased device complexity.
Solution Approach 2:
The femoral stem is divided into functional segments: a fixed outer stem structure and a movable internal piston rod assembly. This segmentation allows the shock absorber mechanism to operate independently within the stem, providing impact force reduction while maintaining the structural integrity of the overall prosthesis.
2Force
If the stem shaft is allowed to move longitudinally to absorb impact, then the shock absorption ability is improved, but the risk of micromotion and loosening increases
Solution Approach 1:
The spring element is pre-installed within the shock absorber mechanism between the piston rod and the bottom of the hollow interior cavity. This beforehand cushioning allows the spring to immediately absorb impact forces when they occur, reducing the transmission of shock to the bone-implant interface while controlling the longitudinal movement of the piston rod.
Solution Approach 2:
The piston rod acts as an intermediary element between the external impact forces and the fixed stem structure. It transmits and dampens these forces through its controlled longitudinal movement and the spring mechanism, protecting the bone-implant interface from direct impact while allowing necessary motion absorption.
3Force
If a spring mechanism is used for shock absorption, then the ability to reduce impact force is improved, but the device complexity and space requirement increase
Solution Approach 1:
The spring mechanism is nested within the hollow interior cavity of the femoral stem, utilizing the existing internal space efficiently. The spring is positioned between the piston rod and the bottom of the cavity, maximizing the use of available volume without requiring additional external space or significantly increasing the stem's overall dimensions.
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 shock absorber mechanism effectively reduces loosening and wear by dissipating kinetic energy, allowing controlled telescoping motion and maintaining the prosthesis's orientation, thereby reducing the risk of dislocation and extending the device's lifespan.
Implementation Method 1
a first spring device arranged between a lower end of the stem shaft and a bottom of the blind hole, and a second optional spring device arranged between an upper end of the stem shaft and the closure cap
Implementation Method 2
The shock absorber mechanism may be provided as a spring mechanism, or as a damping mechanism, or as a spring and damping mechanism
Data Source
Figure 1
Figure 2A
Figure 2B
AI summary
A hip prosthesis device including a femoral stem, the femoral stem including an elongate stem sleeve having a blind hole extending in a longitudinal direction and a hole opening at an upper frontal end of the stem sleeve; a stem core having an elongate stem shaft inserted in the blind hole and slidable in the longitudinal direction, a neck having a lower neck portion and an upper neck portion, a lower end of a lower neck portion attached to an upper end of the stem shaft, the upper neck portion attachable to a femoral head; a shock absorber mechanism operatively provided between the stem shaft and the stem sleeve to act against a downwardly directed longitudinal sliding motion of the stem shaft relative to the stem sleeve; and a closure cap positioned to close the hole opening with a through hole which the neck extends with its lower neck portion.