Implant Strain Sensor Normalization for Bone Healing Assessment
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Solution Overview
Problem
Current methods for tracking bone healing using strain gauges on orthopedic implants require known loads to assess healing progress, which limits their effectiveness as they are influenced by both bone strength and applied load.
Innovation Solution
A system with a first sensor on a weakened portion of the implant and a second sensor on a non-weakened portion of the bone, measuring strain ratios to isolate the effect of bone healing from load variations, using passively powered MEMS sensors for wireless data transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If strain gauges are placed on orthopedic implants to track bone healing, then bone healing progress can be monitored, but the measurements are influenced by both bone strength and applied load making it difficult to isolate healing effects
Solution Approach 1:
The system segments the measurement function by using multiple strain sensors positioned at different locations on the implant. One sensor measures strain at the fracture site while another measures strain at a reference location, allowing the healing-specific strain component to be isolated from the total strain through differential measurement.
Solution Approach 2:
The reference strain sensor acts as an intermediary that measures the load-related strain component separately. By comparing the fracture site strain with the reference strain, the system can subtract the load influence (mediated through the reference measurement) to isolate the bone healing effect.
2Measurement precision
If known loads are applied to assess bone healing using current strain measurement methods, then healing progress can be evaluated, but the requirement for controlled loading conditions limits the effectiveness and practicality of the assessment
Solution Approach 1:
The system performs self-calibration and self-normalization by using the reference sensor to automatically account for varying load conditions. The strain ratio calculation inherently normalizes the measurements, eliminating the need for external load control or calibration procedures.
Solution Approach 2:
The system changes the measurement parameter from absolute strain values to a strain ratio between two locations. This parameter transformation makes the measurement independent of load magnitude, allowing assessment under natural, uncontrolled loading conditions while maintaining accuracy.
3Measurement precision
If multiple strain sensors are used to normalize load effects, then accurate bone healing tracking is achieved, but the device complexity and cost increase
Solution Approach 1:
Both strain sensors serve multiple functions: they simultaneously measure total strain at their respective locations, provide reference data for normalization, and enable calculation of the strain ratio. This multi-functionality reduces the need for additional specialized components.
Solution Approach 2:
The reference sensor creates a copy of the load-related strain information that can be used to normalize the fracture site measurement. This copying approach simplifies the calculation by using a proportional relationship rather than requiring complex load measurement and correction systems.
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 accurate tracking of bone healing progress by normalizing load effects, providing a decreasing strain ratio trend over time indicative of healing, while maintaining independence from external load variations.
Implementation Method 1
a first sensor measuring a strain on a first portion of the implant, the first portion of the implant being configured to be mechanically coupled to a weakened portion of a bone
Data Source
AI summary
A device for treating bone in a living body includes (a) comprises an implant configured for attachment to a bone; (b) a first sensor measuring a strain on a first portion of the implant, the first portion of the implant being configured to be mechanically coupled to a weakened portion of a bone when the implant is coupled to the bone in a target position in combination; and (c) a second sensor measuring strain in a non-weakened portion of the bone.