Bioabsorbable Humeral Fixation System for Gradual Load Transfer
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Solution Overview
Problem
Existing shoulder fixation devices lack the ability to articulate and reposition the upper and lower portions, which limits their effectiveness in repairing humeral fractures and soft tissue damage, and they do not efficiently transfer load back to the bone during the healing process.
Innovation Solution
An anatomical fixation system with a lower stem and upper plate or leaf that can be angularly displaced and locked using a bioabsorbable locking mechanism, allowing for adjustable positioning and gradual load transfer to the bone and soft tissues, fabricated using 3-D printing for a custom fit, incorporating flexible materials and channels for stress distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a solid one-piece fixation device is used, then the device provides initial stability, but it cannot be repositioned and transfers all load immediately to the bone
Solution Approach 1:
The fixation device is divided into an upper portion and a lower portion that can move relative to each other. The upper portion contains engagement features that interface with the lower portion, allowing independent movement and positioning adjustment before final locking.
2Strength
If a rigid fixation device is used, then strong mechanical support is provided, but stress concentration occurs and prevents natural bone healing
Solution Approach 1:
The device transitions from a rigid static structure to a dynamic system where the upper portion can move relative to the lower portion. This dynamic capability allows controlled stress transfer to the bone, promoting natural healing while maintaining necessary mechanical support.
Solution Approach 2:
The mechanical properties of the device change over time through the controlled degradation of the bioabsorbable lower portion. Initially providing strong rigid support, the device gradually reduces its stiffness and load-bearing capacity as the polymer degrades, allowing progressive stress transfer to the healing bone.
3Reliability
If a permanent locking mechanism is used, then stable fixation is maintained, but it prevents gradual load transfer to bone during healing
Solution Approach 1:
The bioabsorbable lower portion acts as an intermediary element between the permanent upper portion and the bone. It provides initial stable fixation while its controlled degradation enables the timing of load transfer to the bone, serving as a temporary mediator that transitions the load path over time.
Solution Approach 2:
The lower portion of the device is designed to be temporarily discarded through bioabsorption. As the bioabsorbable polymer degrades and is absorbed by the body, it releases its held load to the bone, allowing the upper portion to eventually lock in place while the degraded lower portion is naturally eliminated.
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
Enables effective repositioning and healing of humeral fractures by allowing for the gradual transfer of load from the fixation system to the bone and soft tissues, reducing the risk of stress concentration and promoting natural bone healing.
Implementation Method 1
The locking mechanism may comprise an element that is bioabsorbable, such that the locking mechanism becomes less effective over time, allowing stress to be accommodated by the anatomical fixture system, initially, and by the bone and soft tissues, eventually, when the bioabsorbable element is partially or fully bioabsorbed.
Implementation Method 2
By choosing a bioabsorbable polymer, such as polylactides or other known bioabsorbable polymers
Data Source
AI summary
An anatomical shoulder fixation system having a stem having a plurality of holes configured to receive bone screws. The stem having compressible suture locking members protruding from the flared head portion configured to receive and lock an elongated member. The plurality of holes configured to have locking mechanisms abutting the holes. The locking mechanisms preventing the bone screw from backing out while also providing the screw the freedom necessary to realign itself during the healing process. In one locking mechanism embodiment, a locking member utilizing a frustoconical split ring configured lock within a retention groove of the bone screw. Another embodiment has a rotating member with a protrusion that locks into a retention groove of the bone screw. An alternative embodiment has a rotating member that rotates over the bone screw utilizing a complimentary angle between the screw head and the protrusion.