Variable Bone Fixation Device with Degradable Sleeve
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Solution Overview
Problem
Current bone fixation devices either lose locking stability over time or fail to progressively stimulate callus formation and reduce stress shielding, as they either transition from locking to non-locking mechanisms or provide initial flexibility that does not change during treatment.
Innovation Solution
A composite bone fixation device combining biologically degradable and non-degradable materials, where the degradable sleeve gradually decreases its mechanical properties to allow increased interfragmentary motion, maintaining locking stability and stimulating callus formation by reducing stiffness and stress shielding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a locking mechanism is used to provide stable fixation, then stability is improved, but the ability to progressively stimulate callus formation is worsened due to excessive stiffness
Solution Approach 1:
The fixation device transitions from a static locking mechanism to a dynamic system where the sleeve progressively degrades over time. Initially, the sleeve provides stable locking fixation, but as it degrades, it allows increasing interfragmentary motion to stimulate callus formation, thus adapting the stability characteristics to different healing stages
Solution Approach 2:
The mechanical properties of the sleeve change over time through biological degradation. The sleeve's stiffness and strength parameters progressively decrease, allowing the device to transition from providing rigid locking stability to allowing controlled micromotion, thereby resolving the contradiction between initial stability and progressive adaptability
2Reliability
If a non-resorbable material is used to maintain locking stability, then reliability is improved, but stress shielding and inhibition of callus formation worsen
Solution Approach 1:
The biodegradable sleeve is designed to be temporarily discarded after serving its primary function of providing locking stability. As it degrades and is resorbed by the body, it naturally transfers load to the healing bone, eliminating stress shielding and allowing physiological stimulation for callus formation without requiring active removal
Solution Approach 2:
The device combines a permanent locking mechanism (providing reliable initial fixation) with a temporary biodegradable sleeve (providing initial stability then gradually degrading). This composite structure allows the system to provide both reliable locking stability and progressive stress reduction to eliminate stress shielding effects
3Adaptability or versatility
If a dynamic locking mechanism is provided from the beginning, then adaptability is improved, but initial stability and control over fracture fragments worsen
Solution Approach 1:
The sleeve is pre-installed to provide immediate locking stability and secure the fracture fragments in proper alignment. It performs the preliminary function of rigid fixation, after which it gradually degrades to allow the dynamic micromotion needed for callus formation, thus establishing stability before adaptability is needed
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 device promotes fracture healing by gradually increasing interfragmentary displacement, stimulating callus formation at the cortex, and reducing stress shielding without losing locking fixation benefits, enhancing the bone healing process.
Implementation Method 1
a biologically degradable sleeve (9) surrounding said core (2)... the biologically degradable material of the sleeve (9) is engaging the near (cis) cortex... For a given load or moment, the relative displacement of the bone fragments gradually increases with time upon degradation of the sleeve
Data Source
AI summary
Device for bone fixation with a head portion (5), a tapering front portion (8) and a shaft (3) between said head portion (5) and said tapering front portion (8), said shaft (3) having a distal portion (3a) adjacent to said tapering front portion (8) and a proximal portion (3b) adjacent to said head portion (5); whereby said distal portion (3a) being provided with a thread and having a constant outer diameter DA and an inner core diameter DI; at least the proximal portion (3b) of said shaft (3) has a core (2) consisting of a biologically non-degradable material with degradation rate BND and having a diameter d≤DI; a sleeve (9) surrounding said core and consisting of a biologically degradable material with degradation rate BD, whereby BD>BND and said sleeve (9) being fixed to said core in a non-rotatable manner.