SImOS

Smart Implants for Orthopedic Surgery

Prof. Dr. Peter Ryser EPFLon behalf of SImOS partners

Outline

General objectives and the concept of the project

Consortium and tasks International state of the art Architecture of the technology demonstrator Remote powering and data transmission Force and motion sensors Sensor electronics interface Knee simulator Next steps

General objectives

More than 1 Mio / year hip and knee prosthesis are implanted in EU and US

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Introduction: on the concept of the

project: Provide in-vivo parameters for the clinicians and prosthesis designers

Estimate contact force Correct unbalanced wearing Provide adequate rehabilitation Model force distribution Design new generation of prosthesis

3D joint angles by fusing with skin mounted sensors Extract kinematics metrics relying on movement

limitation

Provide micro-motion of the prosthesis relative to the bone Estimate loosening using vibrating plate-form

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A multidisciplinary consortium

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one project with several subprojects 19 months

5 EPFL Labs, CHUV, Symbios

Focus to one functional demonstrator

Specifications, modeling, simulation, prototyping

Integration and test Monthly review meetings

with all team members

Introduction: the concept of the project

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Force & motionsensors

ElectronicsSensors interface

Communication Packaging

Biomechanicalmodeling

Surgicalimplantation

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International state-of-the-art

Bergmann group1

Force and moments D ’Lima group2

Force and moments Serpelloni group3

Force and moments

No kinematics studies missing clinics thematic

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1. Biomechanics laboratory of Charité-Universitätsmedizin, Berlin, Germany

2. Orthopaedic Research Laboratories, Scripps Clinic, San Diego, USA

3. Department of Information Engineering, University of Brescia, Brescia, Italy

Large-scale demonstrator architecture

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A smaller version of the demonstrator, acquiring the signals of the force sensors inside the polyethylene part of the prostheses, has been developed.

MagnetometersHMC5843

I2C

Accelerometers

I2C/SPI

Analog sensors

Sensor Interfacevdd2.7vdd1.8

I2C

Vdd1.8

vdd1.8

I2C/SPI

vdd2.7

ip1ip2in1in2DISCRETE

COMPONENTS

CPLD

PMU Power management unitMAX17710vdd2.7

vdd1.8

MCU

I2Cand/orSPI

SPI

JTAG

SPI

MSP430Serial

memory

JTAGBridge

ForISP

CPLD

JTAG

Batteryand/or

supercap

RF transponder

TMS 37157SPI

SensorAnalogfront-end

Microcontroller

Communication

Power management

Remote Powering9

Reader Antenna

Implanted Antenna

Image source: http://healthtopics.hcf.com.au/TotalKneeReplacement.aspx

External coil circumferences the knee

Internal coil inside the insert

Best performance under the influence of the metallic parts.

[Atasoy, Prime2010]

Si

TiWAlPITiPtTi

Strain gauge

Fabrication

Design

Realization

Force sensors

Specifications

Excitation: 1.5VPower: 0.7mWGauge factor: ~2Volume: 0.24mm2

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AMR sensors

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Magnet

AMR sensors

d

+

(L)

Motion sensors

Artificial Neural

Network

Reference sensor

0 100 200 300 400 500 6000

20

40

60

80

Sample

Join

t Ang

le (d

egre

e)

Evolution of Joint Angle

Reference Joint AngleEstimated Joint Angle viainternal sensors and ANN

angle rms error during Rotation : 0.6 degTranslation : 0.8 deg

Sensitive dist. range

L=25mm

L=8mm

L=5mm

d

Sensor electronics design

Discrete components based system 4 analog channels Digital controller (FPGA +

µController) Digital offset calibration Temperature calibration Force Sensor Power

Consumption Power = 2 mW @ Cont.

Operation Power = 20W @ 1% Duty Cycle

Electronics Power Consumption Power = 405W @ Cont.

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Analog front-end

8 Channel Readout Electronic

Remotely powered 1 Channel board

Test boards

Analog Digital Convertor

Low-power Sigma-Delta Modulator ADC conversion. So far, two Implementations were studied: DC Current = 24 µA, Bandwidth = 10 kHz, Sampling clock = 2 MHz,

SNDR > 64 dB, Technology 0.18m CMOS DC Current = 100 µA, Bandwidth = 16 kHz, Sampling Clock = 2 MHz,

SNDR > 80 dB, Vdd = 1.8 Volt, Technology 0.18m CMOS

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[1] S.Ali, S.Tanner, P-A.Farine “A Novel 1V, 24uW, Sigma Delta Modulator using Amplifier and Comparator based technique, with 64.7dB SNDR and 10KHz Bandwidth”, IEEE Int. Conf. on Circuits and Systems, December 2010

1. 3-rd order amplifier and comparator based SC SDM

2. Multi-bit SDM with DAC calibration

First technology demonstratorA first demonstrator has been developed for

validating the system.

Only signals from analog force sensors are acquired

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A microcontroller is programmed for data acquisition and transmission

The signals are transmitted to an external reader by a Passive Low- Frequency RFID Transponder Interface

First technology demonstrator

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From large scale demonstrator…

to knee simulator16

Knee simulator (MTS)

Definition of micro-fabrication process and materials for force sensors array fabrication

Tape-out of final sensor electronics ASIC

Development of the implanted transceiver

Improve large-scale to in vitro demonstrator

Additional founding

Commercial knee simulator Requested amount 212 kCHF Starting date June 2011

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Prospect for the next milestones

Development of an improved large-scale demonstrator

Definition of micro-fabrication process and materials for force sensors array fabrication

Tape-out of final sensor electronics ASIC

Development of the implanted transceiver

Set-up of the commercial knee simulator

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Peter Ryser EPFL/STI/IMT/LPM2 Kamiar Aminian EPFL/STI/IBI/LMAM Catherine Dehollain EPFL/STI/GR-SCI-STI/ Pierre André Farine EPFL/STI/IMT/ESPLAB Philippe Renaud EPFL/STI/IMT/LMIS4 Brigitte Jolles-Haeberli CHUV/DAL Vincent Leclercq Symbios Orthopédie SA Scientists: Arnaud Bertsch, Eric Meurville, Steve Tanner, Hossein

Rouhani PhD students: Arash Arami, Matteo Simoncini, Oguz Atasoy, Willyan

Hasenkamp, Shafqat Ali

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Thanks to all the team members

Thank you for your attention!

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