17. Development of a Multifunc-tional 22-Channel Functional Electrical Stimulator for Para-

plegia

2011.05.03.LHJ

contents

17. Development of a Multifunc-

tional 22-Channel Func-

tional Electrical Stimulator

for Paraplegia

17.1 introduction

17.5 conclusion

17.4 Praxis FES-24A sys-tem

17.2 historical aspect

17.3 neural engineering clinic

17.1 introduction

the authors’ aim to develop a generic FES implant for the restoration of

functions in spinal cord injured (SCI) paraplegic individu-als• to match to individual’s requirements

upright functional mobility, pressure relief and lower extremity exercise, bladder and bowel control» bladder control: less invasive surgical procedures

• to offer more functions and less surgery to patients with a cost-benefit ratio

cf) neural implants have been developed to restore only spe-cific functions

-> “multifunctional”

the idea (during 1983, Davis) the possibilities of modifying and using the 22-channel

cochlear implant technology as the basis for an im-plantable FES system for the restoration of multiple functions in SCI paraplegics

history since 1984,

• 3 FES implant models have evolved from Cochlear’s tech-nology and its subsidiary: Neopraxis Pty. Ltd.

in 1991,• the initial Nucleus FES-22 Stimulator was implanted after

animal and human studies with FDA approval (IDE# G87014)

• Institutional Review Board (IRB) approval in a 21-year-old paraplegic subject

17.1 introduction

17.2 historical aspect

in 1984, the initial animal studies at the Togus VA Medical Center

(Augusta, Maine)

a modified cochlear implant • maximum pulse output of 4.3 mA and 0.4-ms pulse width,

to be suitable for FES use in humans. an initial decision

• epineurally placed electrodes (2.5 mm diameter platinum disks)

the lower stimulation currents less movement of the electrodes

17.2 historical aspect

with the approval of IRB and volunteer patients under-going lower extremity amputation stimulation studies

• 0.2 ms pulse duration with 20 pps frequency, with a porta-ble, battery-operated, calibrated constant-current unit (Cordis Corp., Miami, Florida, Model 910 A).

the pulse amplitudes for producing maximal stimulation and contraction in the largest of the nerves (medial sci-atic) • 0.6 to 2.5 mA: within the range of the Cochlear receiver-

stimulating unit

17.3 neural engineering clinic : two male subjects with necleus FES-22 stimulating system

FES-22 stimulator (first device) to only provide its recipient with enhanced mobility func-

tions Roger Avery (Custom Med Laboratories, Durham, New Hampshire) (during 1985)

• design and manufacture for the implantable leads and elec-trodes

for higher output currents» a new transmitter coil capable of delivering the higher power

each of 22 output channels individually available» a circular epoxy housing with 22 sockets around the perimeter

with the diameter of the housing determined by the diameter of the coil

17.3 neural engineering clinic : two male subjects with necleus FES-22 stimulating system

Nucleus FES-22 system implanted in subject A (21-year-old male paraplegic subject) (during Nov., Dec.

1991) 3 separate surgical procedures (each 2 weeks apart)

• first procedure receiver/stimulator was placed subcutaneously( 피하 ) at the lower

right anterior intercostal( 늑간의 ) margin 11 connecting leads subcutaneously tunneled to the right and

11 to the left hip areas 2.5-mm diameter platinum disk electrodes

» epineurally on the individual branches of the right and left femoral nerves

» by suturing the silicone elastomer ring around each electrode to the connective tissues on each side of the nerve branches

17.3 neural engineering clinic : two male subjects with necleus FES-22 stimulating system

Nucleus FES-22 system 3 separate surgical procedures (each 2 weeks apart)

• in the second and third procedures, electrodes were attached over gluteal( 둔근의 ), posterior tibial( 경골

의 ), peroneal( 종아리뼈의 ), and sciatic nerves( 좌골 ( 궁둥 ) 신경 ) bilaterally

• a total of 22 electrodes were implanted epineurally• one electrode placed subcutaneously in a Teflon bag in

each of the femoral triangles, as a spare lead

17.3 neural engineering clinic : two male subjects with necleus FES-22 stimulating system

Nucleus FES-22 system first testing (Jan. 1992)

• threshold and maximal muscle contractions as tested in 22 channels

second testing session (Feb. 1992) • implanted system did not function properly

owing to a suspected electrostatic damage in the implant re-sulting in the loss of 7 channels

• hardware and software changes the remaining 15 channels

third testing (in Dec. 1992)• 15 channels were retested• change of electrode locations

17.3 neural engineering clinic : two male subjects with necleus FES-22 stimulating system

Nucleus FES-22 system subject A exercised his lower extremity muscles at home

• using a PC computer to control the implanted stimulator• a battery-operated external Portable Conditioning System

(19×11×6 cm) (Jan. 1997)

exercise protocols• stimulates the right and left knee extensors( 신근 ) and

ankle plantar( 발바닥 )/dorsi flexors( 굴근 ) alternately (4 s ON/4 s OFF), for a total of 20 min

• bilateral knee extension torque of 45 to 55 Nm at 30° and 65 Nm at 60° of knee flexion

• at least three days a week

17.3 neural engineering clinic : two male subjects with necleus FES-22 stimulating system

laboratory PC-based FES-22 system 10-ms duty-cycle state machine for open- and closed-

loop control for use in prolonged standing mode

controller is divided into three phases1) open-loop sit-to-stand 2) closed-loop stand3) closed-loop stand-to-sit initiation of standing up and sitting down

• use a remote switch on a hand glove sensors used for closed-loop control

• electrogoniometers across both knees• accelerometers attached to the back at T6

17.3 neural engineering clinic : two male subjects with necleus FES-22 stimulating system

controlled Nucleus FES-22 stimulation to the motor nerves uninterrupted standing for over 60 min bilateral knee-angle goniometer sensors with Andrews’

stabilizing Anterior Floor Reaction Orthosis (AFRO)• stimulator “ON” when a 10° buckle

between 3 and 8% of the standing time

• automatic switch “OFF” (on recovery) knee flexion less than 5°.

ankle-foot brace

17.4 Praxis FES-24A system

Neopraxis Pty. Ltd. (in 1998) a subsidiary company of Cochlear Ltd. produce the Praxis FES-22A System

• multiple functions — bladder and bowel control, enhanced mobility and seated pressure relief — in an effort to provide recipients with a cost-effective device

17.4 Praxis FES-24A system

1

17.44.3. Praxis FES-24-B system

4.3. Praxis FES-24-B system

4.1. bladder control4.1. bladder control

4.5. complications on follow-upof the first two implanted

at the NEC site, subject(A&B)

4.5. complications on follow-upof the first two implanted

at the NEC site, subject(A&B)

4.4. experience at Shriners hospital for children

4.4. experience at Shriners hospital for children

4.2. Praxis system clinical results4.2. Praxis system clinical results

-4.2.1. bladder results

-4.4.1. upright mobility-4.4.2. bladder and bowel -4.4.3. electrode stability-4.4.4. sensors

17.4 Praxis FES-24A system17.4.1 bladder control

Finetech–Brindley Stimulator, and now Vocare (NeuroControl Corp., Cleveland, Ohio)

traditional bladder stimulator stimulate the sacral anterior roots two primary drawbacks

1) posterior sacral rhizotomies ( 척추신경근절단수술 ), via a laminectomy( 척추후궁절제술 )

an areflexive bladder( 무반사성 방광 ) with increased capacity

2) a sacral laminectomy is done to access the anterior sacral roots for fitting cuff-type electrodes eliminates reflex erection in male recipients

-> “Praxis system”

17.4 Praxis FES-24A system17.4.1 bladder control

Praxis FES-24A stimulator implanted in subject B (35-year-old male paraplegic subject)

18 channels for stimulating individual nerves or branches for muscle contractions and limb movements• 10 thin flexible platinum cuffs (Flexi-Cuff)

electrodes implanted for epineural stimulation sized, cut, and sutured closed with at least twice the diameter

of encircled nerve

• 8 electrodes 3-mm-diameter platinum buttons on the epineurium( 신경외막 )

sutured to the adjacent connective tissue on each side of the nerve

17.4 Praxis FES-24A system 17.4.1 bladder control

Praxis FES-24A stimulator 3 channels

• for bladder control (bowel control and erection) bilateral sacral root stimulation (S2-4)

• LPR electrodes (10-mm long, solid platinum tubing of 1.0-mm diameter)

inserted in external sacral foramina( 천골공 )

1 channel • an epidural spinal cord stimulating electrode (Pisces Quad: Medtronic

Inc., Minneapolis, Minnesota) • for conus medullaris( 척수원뿔 ) modulation of spastic bladder

and bowel reflexes

17.4 Praxis FES-24A system17.4.2 Praxis system clinical results

prior to implantation, subject B stands without knee bracing with Andrews’ Anterior Floor Reaction Orthosis + closed-

loop skin surface FES applied directly over the femoral nerves

closed-loop control of stimulation • stand uninterrupted for 30 min, and up to 70 min • with training, “C” posture and stood with the stimulation

“OFF” for more than 50% of the standing time

17.4 Praxis FES-24A system17.4.2 Praxis system clinical results

after implantation of Praxis FES 24-A system (in 1998) standing with doing a variety of one-handed tasks while

in the “C” posture with closed-loop activation to the lower extremity muscles

balance maintained by the other upper extremity daily stimulation decreased his muscle spasms

17.4 Praxis FES-24A system17.4.2.1 bladder results

urodynamic testing in the Urodynamic Testing Laboratory, subject 2 sacral roots (S3 and 4) bilaterally stimulated intermit-

tently on Sept. 1998,

• bladder contractions with pressures of between 45 and 50 cm of water

on Dec. 1998, • three sustained bladder contractions

5 s on / 5 s off, 20 Hz, 8 bursts

• pressures of 40 to 55 cm water and urination on April 1999,

• two bladder reflex activations 5 s on / 5 s off, 20 Hz, 8 to 14 bursts

• pressures of 50 to 70 cm of water

17.4 Praxis FES-24A system17.4.3 Praxis FES-24-B system

FES-24B System eliminates internal wire breakage possibility consists of

• body-worn controller “Navigator” • skin surface stimulator “ExoStim” • “sensor packs” incorporating accelerometers and a gyro-

scope • a new implant receiver/stimulator to be capable of executing

a wide variety of software control strategies

to mimic an implant and to provide simple exercise functions prior to implanta-tion

to provide feedback in-formation to control strategies to be based on the latest

cochlear implant control in-tegrated circuit (IC), the “CIC3”

a range of implantable electrode leads suitable for the system’s multi-ple functions

17.4 Praxis FES-24A system17.4.3 Praxis FES-24-B system

Praxis FES-24B system maximum current output of 8 mA in a constant-current

mode stimulation

• biphasic (negative and positive phases) current pulses• pulse widths: from 25 to 500μs• a per-channel pulse frequency of 0 to 400 Hz on each of the

twenty-two channels • stimulator

real-time data telemetry functions» the ability to measure the impedance of the current path through

each electrode» the ability to transmit voltage measurements from each electrode

17.4 Praxis FES-24A system17.4.4 experience at shriners hospital for children

3 males with paraplegia, ages 18, 21, and 21 years Praxis FES-24B System between Jan. 2002 and May 2003 18 epineural electrodes

• implanted for upright mobility in all subjects three pairs of bifurcated linear pararadicular electrodes

• extradurally on the bilateral S2, S3, and S4 mixed nerve roots for bladder and bowel function in the first two sub-jects

17.4 Praxis FES-24A system17.4.4.1 upright mobility

goals transitions between sitting and standing, swing-through

and/or reciprocal gait with a walker or crutches, and pro-longed standing

advanced activities• ascending and descending stairs and the achievement of

subject-specific goals

17.4 Praxis FES-24A system17.4.4.1 upright mobility

tested mobility activities subject 1 & 3

• swing-through gait pattern• a walker with wheels

subject 2 • reciprocal pattern for ascending stairs • forearm crutches

None of the subjects required physical assistance bilateral ankle–foot orthoses were worn for all upright

mobility activities

17.4 Praxis FES-24A system17.4.4.2 bladder and bowel

to improve bowel evacuation using two different stimulation paradigms

1) low frequency electrical stimulation (20 Hz, 350 μs, 8 mA) 2) a combination of low-frequency and high-frequency stimu-

lation (500 Hz, 350 μs, 8 mA). daily use of electrical stimulation

• reduction in the time to complete defecation by 40% with the first stimulation strategy and by 60% with the second strategy

despite numerous attempts with varying stimulation parameters to the sacral nerve roots, neither subject could obtain detrusor( 배뇨근 ) pressures sufficient to pro-vide voiding with stimulation both subjects continued to catheterize for bladder emp-

tying

17.4 Praxis FES-24A system17.4.4.3 electrode stability

3 of 52 electrodes placed for lower extremity stimulation changes in the responses of the muscles one electrode

• due to a disconnection at the connector site between the implant and the electrode lead

• repaired and continued to function without further prob-lems

2 electrodes (biceps femoris and tibial nerve) • not replaced, as they did not impact function for the sub-

jects involved

17.4 Praxis FES-24A system17.4.4.4 sensors

closed-loop standing using sensor packs with subject 1 incorporating accelerometers and a gyroscope attached externally on the thigh and the calf

• to detect the position of the knee while standing stimulation would decrease until a change in the knee

joint angle was detected at which time stimulation would again increase to pre-

vent a knee buckle

17.4 Praxis FES-24A system17.4.4.4 sensors

the use of the sensors for closed-loop feedback to the right quadriceps muscles during standing stand with less stimulation stand for a longer period of time before the muscle fa-

tigued the algorithm for increasing and decreasing stimulation

did not create any balance disturbances

17.4 Praxis FES-24A system17.4.5 complications on follow-up of the first two implanted at the NEC site, subject (A & B)

subject A accidentally cut his left foot (in 2002) left lower extremity was swollen with an infection swelling resolved tissues around the Nucleus FES-22 sys-

tem were swollen and inflamed after treated with intravenous antibiotics, the implanted

system was explanted

subject B intermittent pain in the T7-8 vertebra (in 2001) in 2003, implanting the Praxis FES-24B stimulator Neopraxis Company had been closed

• without further support, leads and electrodes removed

17.4 Praxis FES-24A system17.4.5 complications on follow-up of the first two implanted at the NEC site, subject (A & B)

subject 2 at the SHC site, during the training period sustained a stress fracture( 피로골절 ) of the left proximal first

metatarsal( 중족골 )

immobilized for 6 weeks in a soft boot

subject 1 at the end June of 2002

• sustained an abrasion near his ankle• antibiotics were started

at the beginning of Aug. 2002, • high fevers and inflammation around one of his surgical inci-

sions• antibiotic treatment appeared to temporarily suppress• the majority of the system has been removed

17.5 conclusion

in the developing field of FES and implantable neural prosthetic devices a need for reliable and safe, multichannel implantable

stimulating systems the stimulating systems’ functions

• design for individual’s requirements an energy-efficient mobility aid for prolonged use

two Praxis FES Systems a new rehabilitation aid for restoration of function in

spinal cord injury paraplegia

the more channels available, the more nerves that can be activated and the more modes of functionality that can be restored

Thank you for your attention

2011.05.03.LHJ