Hybrid Compress Bone Fixator Stem Design
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Solution Overview
Problem
Conventional compress implants for bone-implant interfaces face issues such as poor resistance to bending loads, reliance on precise placement, and failure in patients with poor bone quality, leading to early postoperative fractures and mechanical instability.
Innovation Solution
A hybrid compress stem design combining a press-fit or cemented stem with a compress mechanism, providing immediate mechanical stability and long-term osseous integration, featuring a distal stem section with a smooth surface to reduce bone growth and stress risers, and a proximal stem section with flutes for rotational stability and cement fixation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional compress implant is used to create compression at the bone-to-implant interface, then osseous integration is stimulated, but the implant does not resist bending loads well and is prone to early postoperative fractures
Solution Approach 1:
The stem is divided into two distinct sections: a proximal stem section with flutes for rotational stability and cement fixation, and a distal stem section with a smooth surface to reduce bone growth and stress risers. This segmentation allows each section to optimize its specific function while working together to provide both osseous integration and resistance to bending loads.
Solution Approach 2:
Different portions of the stem are given different surface characteristics: the proximal section has flutes for mechanical interlocking and cement retention, while the distal section has a smooth surface to minimize stress concentration and prevent bone overgrowth. This local differentiation resolves the contradiction by providing appropriate surface properties at different locations to simultaneously achieve strength and osseous integration.
2Reliability
If a compress implant relies on biologic fixation over the long term, then osseous integration occurs, but the implant lacks sufficient early mechanical integrity and is vulnerable to fracture
Solution Approach 1:
The proximal stem section is designed with flutes and cement retention features that provide immediate mechanical interlocking and cement fixation upon insertion. This preliminary mechanical stabilization is established before osseous integration occurs, providing early strength while the biologic fixation process begins in the distal section.
Solution Approach 2:
The stem combines different surface treatments and structural features in a single component: fluted proximal section for mechanical fixation and smooth distal section for stress reduction. This composite design integrates both immediate mechanical strength and long-term biologic fixation capabilities within one implant.
3Force
If the stem outer diameter is made small to withstand anticipated tension, then the compressive force can be applied, but the recipient is at risk of fracture during the first several weeks postoperatively
Solution Approach 1:
The stem is segmented into proximal and distal sections with different diameter characteristics. The proximal section can have a larger diameter for strength while the distal section maintains the necessary compression interface. This segmentation allows optimization of both compressive force application and fracture resistance.
Solution Approach 2:
Different sections of the stem have different diameter and surface properties: the proximal section has larger diameter and flutes for strength, while the distal section has smooth surface for compression. This local quality differentiation resolves the contradiction by providing appropriate mechanical properties at each location.
4Reliability
If precise placement is required for compress implant success, then osseous integration is achieved, but the device is sensitive to eccentricity and placement errors
Solution Approach 1:
The proximal stem section includes flutes and cement retention features that provide immediate mechanical stabilization upon insertion, compensating for minor placement eccentricities. This preliminary mechanical locking reduces sensitivity to placement errors while maintaining the path for successful osseous integration.
Solution Approach 2:
The design incorporates stress-rising features and smooth surfaces that compensate for placement variations by distributing stresses more evenly, cushioning against the harmful effects of minor eccentricity and placement errors while maintaining integration success.
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 hybrid design enhances early fixation and stability, reduces the risk of fractures, and promotes successful osseous integration in challenging clinical scenarios, including those with poor bone quality, by balancing immediate mechanical strength with long-term biologic integration.
Implementation Method 1
a first stem portion extending substantially along a longitudinal axis, the first stem portion including a first diameter larger than a diameter of an intramedullary canal of a bone such that the first stem portion is configured to engage the bone
Implementation Method 2
A compress assembly configured to apply a compressive force to a bone-to-implant interface
Implementation Method 3
a biasing element configured to generate a compressive force within the compress assembly
Data Source
AI summary
A stem for fixating a prosthesis to a bone can include a first stem portion and a second stem portion. The first stern portion can extend substantially along a longitudinal axis. The first stem portion can include a distal portion. The second stem portion can extend substantially distally from the distal portion of the first stem portion along the longitudinal axis. The second stem portion can be securable to the bone, and the second stem portion can include a distal portion couplable to a compress assembly.