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SMART IMPLANTS FOR ORTHOPAEDICSSURGERY (SImOS)
Peter Ryser
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More than 1 Mio / year hip and knee prosthesis are
implanted in EU and US
General objectives
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General objectives To design innovative tools partly implanted partly
external to measurein vivo
biomechanical parametersof knee prosthesis
To record and analyze in clinical environment andduring daily activity pertinent biomechanicalinformation in order to improve medical treatments:
During surgery: to help surgeon with the positioning phase
After surgery: to detect early migration of the prosthesisand to avoid later complications
During rehabilitation: to evaluate in vivo joint function
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Physician / Surgeon
Better control during operation Evaluation of healing process
Rapid reaction in case of problems
Patient Improvement of quality of life
Project
Implanted prosthesis at the end of the project
General objectives
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A multidisciplinary consortium5Principal Investigator
Peter Ryser
Co-Investigators
Kamiar Aminian, Philippe Renaud, Catherine Dehollain, Pierre-AndrFarine
Co-Investigator
Brigitte Jolles
Co-Investigator
Vincent Leclercq
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Challenge6
Force
sensors
Electronics
Sensors interface
Communication Packaging
Biomechanicalmodeling
Surgical
implantation
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Collaborative nature7
EPFL-ESPLAB
EPFL-RFiC EPFL-LPM2
EPFL-LMAM
CHUV-DAL
Symbios
Strain gage array
Micro-fabricated
Process
Biocompatibility
Ultra thin flexible
printed circuit
Flexible thin filmenergy storage
In vivo Sensors
interconnection
Low power/low noise
sensors interface
Accelerometer & ASICA /D & signal conditioning
Wireless comm.
Remote powering
Load modulationMagnetic coupling
3D kinematics vs. 3D kineticsProsthesis loosening
and wear
Soft tissue artifact
Fusion algorithm
Multiparametric evaluation
Prosthesis withSImOS system
Surgery and
SImOS implantation
EPFL-LMIS4
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External kinematics measurement Two 3D inertial sensors (3D accelerometer /3D gyroscope)
3D knee rotation measurement Issue: soft tissue artifact
Optimal Internal/External fusion to remove soft tissue artifact
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Internal Kinematics Measurement Objectives: Rotation
Measurement of Knee Joint Angles
Measurement of Knee Translation
3D knee rotation measurement
Comparison with a reference
Translation
9 Joint Angles
0 100 200 300 400 500 6000
20
40
60
80
Sample
JointAngle(degree)
Evolution of Joint Angle
Reference Joint Angle
Estimated Joint Angle viainternal sensors and ANN
angle rmserror during
Rot. : 0.6 deg
Trans. : 0.8 deg
Artificial
Neural
Networksensors
+ -
Reference sensor
Feature
Extraction
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Mechanical Simulator 1 This is the first prototype of the demonstrator (simulator of the knee movements)
To demonstrate the feasibility of the measurements
To validate the motion and forces, using motion captures (Vicon cameras) and
reference force sensors
Vicon cameras
Vicon cameras
Reference Force sensors
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Squat Movement
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Simulations by Laboratory of Biomechanical Orthopedics (LBO)
Prof. Dr. Alexandre Terrier and Silvio Ramondetti The pictures should not be published
without permission of LBO
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Squat Movement
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Simulations by Laboratory of Biomechanical Orthopedics (LBO)
Prof. Dr. Alexandre Terrier and Silvio Ramondetti The pictures should not be published
without permission of LBO
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EE22 Strain Component13
Simulations by Laboratory of Biomechanical Orthopedics (LBO)
Prof. Dr. Alexandre Terrier and Silvio Ramondetti
Kneeflexion
angleincreasing
Changeinsurfacecongruenc
e
betweenfemoralcomponen
t
andtibialinsert.
The pictures should not be published
without permission of LBO
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EE22 Strain Component14
Simulations by Laboratory of Biomechanical Orthopedics (LBO)
Prof. Dr. Alexandre Terrier and Silvio Ramondetti
The pictures should not be published
without permission of LBO
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Strain Gauge Positioning & Wiring15
ELECTRONICS
ELECTRONICS
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Prototype16
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Sensor Fabrication Stack-up17
Si
TiW
Al
PI
TiPt
Ti
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Remote Powering & Communication
Rectifier Regulator Remote
ElectronicsL1 L2
Internal PartExternal Part
Downlink
&
Power
Uplink
Power
Amplifier
Mod &
Demodulator
Mod &
Demodulator
Reader
Reader
Antenna
ImplantedAntenna
Image source:
http://healthtopics.hcf.com.au/
TotalKneeReplacement.aspx
The remote powering & communication system will
consist of above elements
Design flow started by realizing the inductive link
by generating suitable coils Target frequency is going to be one ISM band
higher than 1 MHz (6.78 MHz, 13.56 MHz or 27
MHz)
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Configuration 119
External coilcircumferences
the knee
Internal
coil inside
the insert
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Configuration 220
PrimaryInductance
(L1 in uH)
SecondaryInductance
(L2 in uH)
Couplingfactor (k) Figure ofmerit
( )
(Higher is
better)
Conf. 1 7.4 0.9 0.02 0.46
Conf. 2 7.42 0.338 0.034 7.4
Internal
coil insidethe insert
External coil infront of the knee
just lower than
the patella bone
QL1 and QL2 is the quality factor of primary and secondary coils
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AFE, Large-scale demonstrator to ASIC21
From large-scale demonstrator
LPF
CAL & CTRL
uP SPIIFADCAMPS
To ASIC
FromS
enso
rs
FromS
enso
rsASIC TBD
FPGA MCURFID
TX
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Analog Front-End Electronics (AFE)
SpecificationsSensor Type Provider Interface
Sample Rate
[Sample /s]
Accuracy
[Bit]
Number of
Sensors
Force(Strain Gauge)
EPFL Analog 2000 12 4
Magnetic
(Mag. resist) Honeywell Analog 200 12 4
Accelerometer
(Proprietary) Bosch Digital 2000 12 1
Temperature
(Proprietary) ADI Digital 100 12 1
Gyroscope
(Proprietary) Honeywell Digital 2000 12 4
Additional Required Functionality For ASIC
Sensor calibration routines
Sensor powering control (duty cycle)
Data processing (event detection, compression)
Data storage and retrieval
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Outlook
First set of specifications established after 6 months
Large scale demonstrator architecture defined New generations of magnetometers and gyroscope
under evaluation
First measurements to be performed with the
mechanical simulator
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Thank you!
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