 |
| | Key Paper Summaries Neurostimulation
Technology of Neurostimulation
| Krames ES |
| Overview of spinal cord stimulation:
with special emphasis on a role for dual spinal cord stimulators. Pain Digest
2000; 10: 6-12 |
| Summary of key points
|
- This paper reviews spinal cord stimulation
with particular emphasis on the concept of dual stimulation.
- The early use of SCS involved unipolar
electrodes implanted directly onto dorsal columns. Subsequent technological
advances led to the introduction of multichannel quadripolar and octapolar
leads with bipolar stimulation, which were found to be superior to single-channel
devices.
- Single-electrode arrays have been used
successfully to produce pain relief in both unilateral and bilateral
pain of the lower or upper extremities. However, dual-electrode arrays,
either dual quadripolar percutaneously implanted arrays or surgically
implanted arrays placed parallel to each other on either side of the
midline of the spinal cord, are used more often in this role and are
more effective.
- Recent computer modeling evidence and
clinical reports have revealed that FBSS patients with low back pain
and bilateral leg pain gain effective relief from both their lower extremity
pain and back pain with dual quadripolar or octapolar lead arrays. The
choice of lead depends on surgeon preference, but a case could be made
for improved stability of dual octapolar lead systems over dual quadripolar
systems.
- Another indication for dual, triple or
even quad electrode system placement is for patients with multiple sites
of non-malignant pain (for example, patients with both lumbar and cervical
radiculitis with both upper and lower extremity pain). Because concordant
paresthesia (tingling phenomenon) is necessary for pain relief, it would
be necessary in such patients to place single quad or octapolar leads
in the neck and back, or even dual lead systems to achieve pain control.
|
| Discussion/conclusion |
- The author concludes that based on the added
movement stability, the advent of narrower intralead distances and the
ability to program multiple programs, dual spinal cord stimulation systems
are adding significantly to the management of pain of neuropathic origin.
- Note: The devices mentioned in this study
include Itrel 3, Synergy, Extrel and Matrix (from Medtronic) and Renew
(from Advanced Neuromodulation Systems).
|
| Wesselink
WA, Holsheimer J, King GW, Torgerson NA, Boom HBK |
| Quantitative Aspects of the Clinical
Performance of Transverse Tripolar Spinal Cord Stimulation. Neuromodulation
1999; 2: 5-14 |
| Methods |
- The paper describes the performance of
a transverse tripolar stimulation (TTS) system in a multicentre study.
The main goal was to assess the ability of the TTS system to steer the
electric field in patients, allowing optimal control of the topography
of paraesthesia.
- The electrode has four contacts: two central
contacts separated by 3 mm and two lateral ones, separated by 2.8 mm
from the central contact.
- A total of 31 patients with chronic intractable
pain in the lower limbs and/or trunk were enrolled. The electrodes were
placed through a flavectomy or partial laminectomy at levels from T6
to T12 and after initial tests were internalised and connected to either
a Medtronic X-trel or Itrel conventional pulse generator or Medtronic
Matrix modified dual channel receiver. Tests were performed 4, 12 and
26 weeks after implantation of the electrode.
- Stimulation tests were conducted using
both a dual-channel pulse generator with the lateral contacts, and a
single-channel generator with the central contacts. The voltages for
the thresholds for onset of paraesthesia and for pain or motor responses
were recorded, as were the areas of paraesthesia produced.
|
| Results |
- The results of 484 electrode tests were reported
- 121 single-channel contact combinations
and 363 dual-channel settings, tested in 30 patients.
- The average perception threshold was 2.6 V and
the mean motor/discomfort threshold was 4.4V, therefore the mean usage
range was 1.7 V (range 1.1-10.9 V).
- In 67% of patients, the largest paraesthesia
coverage was obtained with dual channel stimulation. The mean normalised
paraesthesia coverage was 57.6% (range 23.6-100%). A normalised coverage
of 60% or more could be obtained for 37% of patients.
- The ability to steer paraesthesia was quantified
by the normalised steering score. The mean value was 0.63 (0 = no steering,
1 = perfect steering). Worst steering was found for electrodes placed
less than 1.5 mm from the spinal cord.
- In 83% of patients, best pain coverage
was achieved using dual-channel stimulation. On average, paraesthesia
overlapped 63.2% of the painful areas.
|
| Discussion/conclusion |
- One of the problems in the management
of chronic pain is the change in pain patterns over time, which can
be solved by appropriate steering. Nevertheless, long-term success of
the TTS system still requires accurate placement of the electrode.
- The transverse orientation of the tripole
allowed stimulation of the median parts of the dorsal columns without
discomforting side-effects related to activation of the dorsal root
fibres, which were shielded by the lateral anodes.
- The TTS system may improve the efficacy
of spinal cord stimulation in the management of chronic pain, particularly
when the optimal balance settings are determined for individual patients.
|
| Holsheimer
J, Wesselink WA |
| Effect of Anode-Cathode Configuration
on Paresthesia Coverage in Spinal Cord Stimulation. Neurosurgery 1997; 41:
654-660 |
| Methods |
- The aim of this study was to provide
a theoretical basis for the selection of the anode-cathode configuration
in spinal cord stimulation (SCS) using one percutaneous epidural electrode
or two electrodes in parallel.
- A computer model of SCS, consisting of
a three-dimensional volume conductor model of the spine and models of
myelinated nerve fibres, was used to calculate the dorsal column areas
covered by stimulation with different electrode configurations at T8-T9.
|
| Results |
- The most extensive paraesthesia coverage is
achieved with tripolar or bipolar stimulation with a single electrode
placed over the dorsal columns midline. Similar results may be achieved
with two symmetrically placed electrodes connected in parallel to a
single generator, since the distance from the spinal cord is generally
shorter, but no 'summation effect' (which would result in stronger stimulation
of median regions of the dorsal columns) exists.
- Stimulation with two offset electrodes
results in activation of a smaller dorsal column area, compared with
symmetrically placed electrodes; again, no summation effect is seen
under these conditions. With a laterally placed electrode or transverse
bipolar stimulation, paraesthesia is unilateral, and usually segmentary.
|
| Discussion/conclusion |
- The relative positions of the electrodes
and their distance from the spinal cord are the major determinants of
paraesthesia coverage in SCS. The large variability in the thickness
of the cerebrospinal fluid (CSF) layer between patients will lead to
marked variations in paraesthesia coverage, and hence in the success
of SCS. It is therefore recommended that CSF thickness should be a criterion
for patient selection.
- Changes in paraesthesia coverage over
time (for example, related to scar tissue formation) are more likely
when multiple electrodes are used.
|
| Struijk
JJ, Holsheimer J |
| Transverse Tripolar Spinal Cord Stimulation:
Theoretical Performance of a Dual Channel System. Medical and Biological
Engineering and Computing 1996; 34: 273-279 |
| Methods |
- This paper reports the performance of
a tripolar stimulation method for spinal cord stimulation, measured
using a computer model of the spinal cord and the most relevant neural
elements.
- The lead had three metal contact strips
connected to pulse generators, which were voltage sources. In monopolar
stimulation, only the central contact of the lead was used and the second
contact was the metal can of the implantable pulse generator.
- There were two parts of the model: firstly
a 3-D conductor model of the spinal cord and its surroundings, comprising
the major macro-anatomical structures and stimulating electrodes; secondly
models of large myelinated dorsal root and dorsal column nerve fibres
- the primary targets of the stimulation. The potential field in the
spinal cord was first calculated, then the field applied to the nerve
fibre models.
|
| Results |
- During tripolar stimulation, the potential field
and recruited area were more restricted to the medial part of the dorsal
columns than during monopolar stimulation.
- In tripolar stimulation, the threshold
for stimulation of dorsal root fibres was higher than that for dorsal
column fibres, and than during monopolar stimulation. There was therefore
a preference for stimulation of dorsal column fibres by tripolar stimulation.
This means that motor reflex loops would be less likely to be activated.
- With the tripolar lead, it was possible to change
symmetrical into asymmetrical stimulation without changing the symmetrical
position of the lead. Likewise, non-symmetrical positioning of the lead
could be corrected to produce symmetrical stimulation.
- When the two outer contacts were stimulated
simultaneously, the resulting superposition of two overlapping fields
produced a narrow field and recruited area. On the other hand, when
the contacts were stimulated alternately, the union of the two overlapping
fields produced a much wider recruited area.
|
| Discussion/conclusion |
- According to the model, stimulation with
a transverse tripolar electrode configuration is very flexible and has
some important advantages over the usual monopolar or rostrocaudally
arranged multipolar systems.
- The configuration is able preferentially
to stimulate dorsal column fibres, compared with other electrodes, thereby
increasing the threshold for unwanted motor responses.
- Lead positioning during surgery is less
critical than for monopolar electrodes, as corrections of paraesthesia
coverage can be made after implantation.
- The voltages required to excite fibres
are higher than those for monopolar electrodes, so the current drain
would also be relatively high during tripolar stimulation. Therefore
battery life will be shorter than for conventional leads.
|
| Barolat
G, Massaro F, He J, Zeme S, Ketcik B |
| Mapping of Sensory Responses to Epidural
Stimulation of the Intraspinal Neural Structures in Man. Journal of Neurosurgery
1993; 78: 233-239 |
| Methods |
- This paper presents the sensory responses
to spinal cord stimulation (SCS) at different spinal levels. The aim
of the analysis was to relate patterns of stimulation-induced paraesthesias
to the position of the electrodes in the spine.
- The study population consisted of 106
patients receiving SCS for chronic pain management. All received implants
of Resume electrodes placed in the epidural space on the dorsal surface
of the spinal cord at levels between C-1 and L-1, with Itrel I or II
pulse generators.
- The occurrence of stimulation-induced
paraesthesias was reported by the patients during 3-7 days' testing.
|
| Results |
- It was relatively
easy to obtain stimulation-induced paraesthesias on the median aspect
of the hand, the abdominal wall, the anterior aspect of the thigh, and
the foot. By contrast, it was particularly difficult to obtain stimulation-induced
paraesthesias at sites covered by the C-2 distribution (the ipsilateral
posterior occipital area and the angle of the jaw) and on the neck,
the low back, and the perineum.
|
| Discussion/conclusion |
- The data reflect the sensory equivalents
of electrical activation of the dorsal root or dorsal column at various
spinal levels.
- The most effective stimulation was obtained
with electrodes planted within 3 mm of the midline. However, the C-2
area, the chest and the abdominal wall can be stimulated more easily
with laterally placed electrodes. To obtain bilateral paraesthesias,
the electrodes need to be placed as close as possible to the midline.
- The use of different electrode placements,
intercontact distances and stimulation parameters might allow more precise
mapping of paraesthesias, and hence more accurate direction of current
flow and more consistent stimulation of the desired region of the body.
|
| North
RB, Ewend MG, Lawton MT, Piantadosi S |
| Spinal Cord Stimulation for Chronic,
Intractable Pain: Superiority of "Multi-channel" Devices. Pain
1991; 44: 119-130 |
| Methods |
- This paper reports the outcome in 62 patients
who underwent spinal cord stimulation (SCS) between 1983-1987. Of these,
50 had failed back surgery syndrome (FBSS), five had spinal cord injuries
and seven had peripheral pathology or stump pain.
- Permanently implanted electrodes (Medtronic
Pisces or Pisces Quad or Neuromed 1980JF) were placed percutaneously
in 63% of patients and by laminectomy (Medtronic Myelostat and Resume
electrodes) in 37%.
- Patients were interviewed at an average
time of 2.14 years after implantation.
|
| Results |
- Of the 62 patients, 55% reported at least
50% sustained pain relief and 66% indicated that they would be prepared
to go through the procedure again for the same result; 53% fulfilled
both criteria, and were considered to be treatment 'successes'.
- The best overall pain relief was obtained at
a mean of 15 months postoperatively.
- Among patients with FBSS, most reported an improvement
in their ability to perform everyday activities, and the majority had
either discontinued using analgesics or were using lower doses.
- A majority of patients (55%) required
no adjustment of the implanted hardware during the follow-up period.
|
| Discussion/conclusion |
- Technical developments in SCS, particularly
the development of multi-contact percutaneous electrode arrays and supporting
programmable electronics, have significantly improved clinical outcome.
- In this series of patients, the majority
reported continuing relief of previously intractable pain at an average
of more than 2 years after implantation.
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