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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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