Flashcards in Chapter 60 Pulsed Radiofrequency, Water-Cooled Radiofrequency, and Cryoneurolysis Deck (43):
The CRF (radiofrequency currents ) lesions for pain control are created by
the passage of RF (radiofrequency) currents through an electrode placed adjacent to a nociceptive pathway to interrupt the pain impulses and thus to provide the necessary pain relief.
of RF currents imparts energy to the
surrounding the active electrode tip and raises the local tissue temperature, whereas the electrode itself is
heated only passively.
During CRF application the RF current is switched off once the
desired electrode temperature is reached and the repetition of the cycle maintains the selected tissue temperature.
Temperature known to be neurodestructive
Temperatures above 45° C have been known to be neurodestructive, and although selective destruction of unmyelinated C- and A-delta fibers has been suggested
during CRF the tissue
temperatures are typically raised well above
levels, but below the point of tissue gas formation (80° C to 90° C).
Complications of CRF
thermal injury to the motor and sensory nerve fibers and the complications of
weakness, neuritis, and deafferentation pain. the use of high-temperature CRF has generally been restricted to facet denervation.
Lower temperature CRF, in
the range of 55° C to 70° C, has been arbitrarily selected for
dorsal root ganglia (DRG) lesioning
pulsed radiofrequency (PRF)
which attempted to maximize the delivery of electrical energy by
using higher voltage RF currents, while concomitantly minimizing the risk of thermal tissue injury by keeping the
tissue temperatures well below the neurodestructive range
(42° C). These conflicting goals were achieved by applying the RF currents in a pulsatile manner to allow time for the heat to dissipate in between the RF pulses.
pulsed radiofrequency vs radiofrequency currency
Similarly to CRF, PRF is applied via an electrode placed in the vicinity of the target nociceptive structure. However,
unlike CRF, juxtapositioning of the electrode parallel to the
target nerve is deemed unnecessary, as the electrical currents,
and not the thermal lesion, are considered the source of neuronal dysfunction
During typical PRF application,
the RF currents are applied for
20 milliseconds, at 2 Hz,
for a total duration of 120 seconds. Therefore, for most of the lesion duration—480–500 milliseconds—no RF
currents are applied. The current voltage is controlled in a manner that the maximum electrode temperature achieved remains below 42° C.
water-cooled radiofrequency (WCRF) ablation
The basic principle of pain relief during WCRF application is similar to the CRF—a thermal lesion is created by the application of RF energy through an electrode
placed in the vicinity of the target neural structure.
WCRF is applied by using
a specialized multichannel
electrode that is actively cooled by the continuous
flow of water at ambient temperature. The active
cooling prevents the electrode from acquiring the high surrounding tissue temperatures and allows the continued flow of the RF current, with the consequent heating of
a larger tissue volume and the creation of a larger thermal lesion.
The resulting WCRF lesion is consequently comprised of a
few millimeters of cooled tissue immediately
surrounding the electrode, which is surrounded by spherical
isotherms of increasing tissue temperature, which in turn are surrounded by lower temperature isotherms at increasing distance from the electrode
Similar to CRF, the size of the WCRF lesion is dependent on
the probe size, the
electrode temperature, and the duration of RF current applied.
The larger area of neural destruction with WCRF application increases
the probability of successful denervation
of a pain generator with numerous and/or variable
afferent nociceptive innervation.
two distinct forms of WCRF techniques
monopolar and bipolar WCRF lesioning
techniques were applied exclusively for the treatment of
sacroiliac joint dysfunction (SJD) and discogenic pain
unipolar WCRF in the treatment of
SJD was applied to S1, S2, and S3 lateral branches
and either two or three monopolar lesions were created lateral to each sacral foramen. These
lesions were created by using a 17-gauge specialized electrode
with a 4-mm active tip. The RF current was applied for 150 seconds, and the electrode temperature was raised to 60° C.
For the treatment
of DP discogenic pain
bipolar WCRF was applied to the posteriorlateral
disc annulus by placing two 17-gauge introducer
needles and specialized RF electrodes. The
electrode temperature was raised to 55° C over 11 minutes, and this temperature was maintained for an additional 4 minutes.
Cryogenic nerve injury is NOT associated with
neuroma formation, hyperalgesia, and deafferentation pain, which are the attributes typical of nerve injury by other physical modalities such as surgical nerve sectioning, thermal
radiofrequency lesioning, or chemical neurolysis
The mechanism of cryogenic nerve injury appears to emanate from
damage to the vasa nervorum, the resulting
endoneural edema and increased endoneural pressure, and
consequent axonal disintegration.
nerve regeneration after cryoablation
The spared connective tissue elements and the
Schwann cell basal lamina provide a ready substrate for nerve regeneration from intact proximal axons. The axonal regeneration typically occurs at a rate of about 1 to 1.5 mm per week, and the duration of analgesia from cryoablation depends on the time taken by the proximal axons to reinnervate the end organs (typically weeks to months)
critical temperature required to cause
such disintegrative nerve changes
–20° C. It is crucial that the tissue temperatures are maintained below the critical levels for adequate
duration during cryolesioning.
in cryoablation, the likelihood of the target nerve injury, depends on the
probe size, the proximity of the probe to the target nerve, the freezing duration, and the number
of freeze cycles applied. Repeat freeze and thaw cycles increase the size of the eventual ice ball formed.
double lumen aluminum tube that connects to a gas source by flexible tubing, and either nitrous oxide or carbon dioxide is delivered at a pressure of approximately 42 kg/
cm2 (6oo lb/in2 [psi]) to the inner cryoprobe lumen. The gas under pressure escapes through a small orifice from the inner lumen near the cryoprobe tip and returns to the console through the outer cryoprobe lumen. The drastic drop in the pressure at the probe tip (from 600–800 psi to 10–15 psi) allows gas expansion and consequent cooling
an ice ball around the probe tip created by
Heat absorbed from the tissues surrounding
the probe tip lowers their temperature
and creates an ice ball around the probe tip.
cryoprobe sizes include a 14-gauge (2-mm) probe that roughly forms a 5.5-mm ice ball, and an 18-gauge (1.4-mm) probe that forms 3.5-mm ice ball.
Meticulous localization of the target nerve is necessary to increase the likelihood of the target nerve disruption. Done by
Most currently used cryoprobes are therefore equipped with a built-in nerve stimulator function that allows both motor (2 Hz) and sensory (100 Hz) testing. The probe also
has a thermistor incorporated into the tip to precisely monitor the target tissue temperatures. The console unit is equipped with the nerve stimulator controls, temperature
and gas pressure gauges, and a gas regulator switch
that allows precise control of the gas flows.
To ensure safe and effective cryoablation, the gas flows must be precisely regulated-----inadequate and excessive gas flows causes
inadequate gas flows are ineffective in lowering
tissue temperatures below critical levels, while excessive gas flows may lead to tissue freezing proximally along the probe length and may cause unintended freeze lesions such as skin burns
The cryoprobe should be withdrawn only
after the ice ball has thawed, because withdrawing the probe with the ice ball still present may cause local tissue injury and avulse the nerve segment.
use of an introducer, such as a large-gauge intravenous catheter, is often recommended during cryoprobe placement. why?
sharper introducer tip facilitates the placement
of the less rigid cryoprobe and affords additional skin
protection during cryolesioning of the superficial nerves.
Typically, a 12-gauge intravenous catheter is used for the 2.0-mm probe, and a 14- to 16-gauge catheter is used for the 1.4-mm probe.
PRF has been applied to
the DRG at all spinal levels in the treatment of multiple
pain syndromes, including
radicular pains, post-herpetic neuralgia, herniated intervertebral disc, post-amputation
stump pain, and inguinal herniorrhaphy pain.
PRF has been applied to wide variety of peripheral nerves for the following
it is applied to the medial branch nerve for facet syndrome, the suprascapular nerve for
shoulder pain, the intercostal nerves for postsurgical thoracic
pain, the lateral femoral cutaneous nerve for meralgia paresthetica, the pudendal nerve for pudendal neuralgia,
the dorsal penile nerves for premature ejaculation, the splanchnic nerves for chronic benign pancreatic pain, the sciatic nerve for phantom limb pain, the obturator and femoral nerves for hip pain, the glossopharyngeal nerve for glossopharyngeal neuralgia, the occipital nerve for occipital
neuralgia, and the genitofemoral, ilioinguinal, and iliohypogastric
nerves for groin pain and orchialgia.
PRF has been applied to various central nervous system and autonomic
the gasserian ganglion for trigeminal neuralgia, the sphenopalatine ganglion for head, neck, and facial pain, and to the lumbar sympathetic chain in the treatment of complex regional pain syndrome
the target neural structure for PRF application has been unclear
the sacroiliac joint for sacroiliac joint dysfunction, intradiscally for discogenic pain, myofascial trigger points for myofascial pain, scar neuromas for postsurgical scar pain, the spermatic cord for testicular
pain, and intra-articularly for arthrogenic pain
the use of WCRF is confined to
pain syndromes in which the pain generator is considered to have
numerous and variable sources of innervation. WCRF was used for the treatment of SJD, and
treatment of DP
use of cryoablation in the treatment of
post-thoracotomy pain. chronic pain conditions of the chest wall, including postoperative neuroma, costochondritis, postherpetic neuralgia, and rib fractures
In the head, neck, and facial region, cryolesioning of several
These nerves have included inferior alveolar, mental, lingual, buccal,
inferior dental, auriculotemporal, supraorbital, and infraorbital nerves
painful head, neck, and facial conditions
treated with cryoablation included
post-herpetic neuralgia, atypical facial pain, and various postsurgical neuralgias
Cryoablation used in the treatment of spinal and extremity pains
for the treatment of lumbar facet syndrome, where it was applied to the lumbar medial branches. For extremity
pain, its use is reported for the treatment of intermetatarsal space or Morton’s Neuroma. Cryolesioning of the
ulnar, median, sural, occipital, palmar branch of the median and digital nerves has also been performed for mostly traumatic nerve injuries and for carpal tunnel syndrome.
Cryoablation used for the treatment of several painful conditions of the abdomen, pelvis, and perineum.
the treatment of post-inguinal herniorrhaphy
pain, where it was applied to the iliohypogastric and ilioinguinal nerves. It has been applied to the lower sacral nerve roots for intractable perineal pain to the ilioinguinal and iliohypogastric nerves for corresponding neuralgiform chronic abdominal pain, and to the ganglion impar for intractable rectal pain
Cryoablation used for pregnancy-related and post-partum pain in women
cryolesioning of the ilioinguinal nerve was performed for late-pregnancy abdominal pain, it was applied to the sacral extradural canal for severe post-partum sacrococcygeal pain, and it was applied to the symphysis pubis for pregnancy-associated symphysis pubis diastasis pelvic pain.
PRF has been used most frequently for the treatment of
lumbar or cervical radicular pains. The second most commonly reported PRF application
is in the treatment of facet syndrome (FS).