17. Development of a
Multifunctional 22-Channel
Functional Electrical Stimulator
for Paraplegia
2011.05.03.LHJ
contents
17.1 introduction
17. Development of a
Multifunctional
22-Channel Functional
Electrical Stimulator
for Paraplegia
17.2 historical aspect
17.3 neural engineering clinic
17.4 Praxis FES-24A system
17.5 conclusion
17.1 introduction
 the authors’ aim
 to develop a generic FES implant for the restoration of
functions in spinal cord injured (SCI) paraplegic individuals
• 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 specific
functions
-> “multifunctional”
17.1 introduction
 the idea (during 1983, Davis)
 the possibilities of modifying and using the 22-channel
cochlear implant technology as the basis for an implantable
FES system for the restoration of multiple functions in SCI
paraplegics
 history
 since 1984,
• 3 FES implant models have evolved from Cochlear’s technology
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
17.2 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
undergoing lower extremity amputation
 stimulation studies
• 0.2 ms pulse duration with 20 pps frequency, with a portable,
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 sciatic)
• 0.6 to 2.5 mA: within the range of the Cochlear receiverstimulating 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 functions
 Roger Avery (Custom Med Laboratories, Durham, New Hampshire) (during 1985)
• design and manufacture for the implantable leads and
electrodes
 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(경골의),
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 resulting
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 phases
1) open-loop sit-to-stand
2) closed-loop stand
3) 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
4.1. bladder control
4.2. Praxis system clinical results
-4.2.1. bladder results
4.3. Praxis FES-24-B
system
17.4
4.4. experience at Shriners
hospital for children
4.5. complications on follow-up
of the first two implanted
at the NEC site, subject(A&B)
-4.4.1.
-4.4.2.
-4.4.3.
-4.4.4.
upright mobility
bladder and bowel
electrode stability
sensors
17.4 Praxis FES-24A system
17.4.1 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(척추후
궁절제술)
 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 system
17.4.1 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 system
17.4.2 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 system
17.4.2 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 system
17.4.2.1 bladder results
 urodynamic testing
 in the Urodynamic Testing Laboratory, subject 2
 sacral roots (S3 and 4) bilaterally stimulated intermittently
 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 system
17.4.3 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 gyroscope
a new implant receiver/stimulator
to be capable of executing a
to provide feedback
information to control
strategies
to mimic an implant and to
provide simple exercise
functions prior to
implantation
wide variety of software
control strategies
to be based on the latest
cochlear implant control
integrated circuit (IC), the
“CIC3”
a range of implantable
electrode leads suitable
for the system’s multiple
functions
17.4 Praxis FES-24A system
17.4.3 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 system
17.4.4 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 subjects
17.4 Praxis FES-24A system
17.4.4.1 upright mobility
 goals
 transitions between sitting and standing, swing-through
and/or reciprocal gait with a walker or crutches, and
prolonged standing
 advanced activities
• ascending and descending stairs and the achievement of
subject-specific goals
17.4 Praxis FES-24A system
17.4.4.1 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 system
17.4.4.2 bladder and bowel
 to improve bowel evacuation
 using two different stimulation paradigms
1)
2)
low frequency electrical stimulation (20 Hz, 350 μs, 8 mA)
a combination of low-frequency and high-frequency stimulation
(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 provide
voiding with stimulation
 both subjects continued to catheterize for bladder emptying
17.4 Praxis FES-24A system
17.4.4.3 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 problems
 2 electrodes (biceps femoris and tibial nerve)
• not replaced, as they did not impact function for the subjects
involved
17.4 Praxis FES-24A system
17.4.4.4 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 prevent a
knee buckle
17.4 Praxis FES-24A system
17.4.4.4 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 fatigued
 the algorithm for increasing and decreasing stimulation did
not create any balance disturbances
17.4 Praxis FES-24A system
17.4.5 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 system
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 system
17.4.5 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 incisions
• 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