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400 Anne Miu Han CHAN
Bisphosphonates
Bisphosphonates have inhibitory activity on bone
resorption and on inflammatory processes. ey
have proved useful in a series of clinical conditions
such as tumour-induced hypercalcaemia, Paget’s
disease, osteoporosis and metastatic bone disease.
Pharmacology
Mechanisms of action
Since accelerated osteolysis and inflammatory
response are critical in the development of bone
pain, bisphosphonates may have an effect on
bone pain by inhibiting the osteoclast process and
exerting a possible anti-inflammatory effect [27].
Pharmaceutical preparations
e bisphosphonates differ from one and other
by the substitution of active side chains on the
carbon atom of the base central nucleus of the
phosphorous-carbon-phosphorous atoms (P-C-P)
[23]. Some examples of bisphosphonates are:
1. First generation: clodronate, etidronate
2. Second generation: pamidronate, tiludronate
3. ird generation: ibandronate, zoledronate.
Side eects
Toxicity with long-term administration is
uncommon. Particular attention must be taken
in patients with widespread bone metastases
where there is rapid initial osteoblastic response;
bisphosphonates may cause symptomatic
hypocalcaemia.
Indications
Pamidronate and clodronate are used in the treatment
of hypercalcaemia of malignancy; treatment of
osteolytic bone metastasis of breast cancer and
osteolytic bone lesions of multiple myeloma;
slowing of bone disease progression; and reduction
of tumour-associated metastatic bone pain.
Topical Capsaicin
Pharmacology
Mechanisms of action
Capsaicin, the compound in chili peppers that
makes them taste “hot”, binds to nociceptors
in the skin, causing an initial excitation of the
neurons and a period of enhanced sensitivity. ese
changes include itching, pricking, or burning
with cutaneous vasodilation, and are thought to
be due to selective stimulation of afferent C fibres
and release of substance P. is is followed by a
refractory period with reduced sensitivity and after
repeated applications, persistent desensitisation,
possibly due to depletion of substance P [52].
Pharmaceutical preparations
Topical capsaicin is available as a 0.025% cream
(Zostrix) in tubes of 0.7 oz, 1.5 oz and 3 oz; and
as a 0.075% cream (Zostrix HP) in tubes of 1 oz
and 2 oz.
Side eects
e adverse effects are mainly at the application
site (burning, stinging, erythema) and systemic
events are rare [60]. Respiratory irritation has been
reported from inhalation of dried cream [58].
Indications
Topical creams with capsaicin are used to treat
pain from postherpetic neuralgia and diabetic
neuropathy, osteoarthritis and rheumatoid arthritis
[6, 60]. Capsaicin has also been used to treat pain
due to pruritis, psoriasis, mastectomy, bladder
disorders and cluster headaches [60].
Evidence-based material
Topical capsaicin is better than placebo for the
treatment of chronic pain in neuropathic and
musculoskeletal disorders [50, 79]. Mason et
al. in their systematic review calculated the
number needed to treat (NNT) for the studied
conditions [50]. e NNT using topical capsaicin
0.075% was 5.7 for neuropathic conditions and
6.4musculoskeletal conditions. ese NNT results
were lower compared with those calculated from
the Zhang 1994 meta-analysis [79].
Other Drugs —
Antihistamines
e current literature supports the direct analgesic
effects of various antihistaminic agents. e
specific antihistamines identified are hydroxyzine,
orphenadrine and diphenhydramine [62, 68].
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401
Other Medications and Adjuvants in Pain Management
Indications
Despite evidence of analgesic effects in single-dose
studies of various antihistamines, clinical experience
has failed to confirm significant analgesic utility
from this class of drugs [31]. e use of these agents
is associated with potential side effects, including
sedation and dry mouth. ese drugs should only
be considered in patients who have a primary
indication other than pain.
A trial of hydroxyzine, for example, is sometimes
used in cancer patients where pain is complicated
by anxiety, nausea or itching [12].
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Introduction
Interventional procedures for pain management range from
local injections to specific neural blockade of the sensory
supply to specific body structures. ese procedures have
been performed by different medical specialists including the
orthopaedic surgeons, neurosurgeons and anaesthetists. While
they are usually effective in the short term, the efficacies of
these interventional procedures in the treatment of chronic
pain syndromes have been questioned by a number of recent
evidence-based systematic reviews.
In recent decades, with the introduction and acceptance of
the bio-psycho-social model of chronic pain, multidisciplinary
pain management clinics have become very popular. ese
clinics have input from practitioners from multiple medical
specialties including anaesthetists, orthopaedic surgeons,
neurologists, neurosurgeons, psychiatrists, clinical oncologists
and rehabilitative physicians, as well as different allied health
discipline personnel such as physiotherapists, occupational
therapists and clinical psychologists. A number of evidence-
based practice guidelines have been developed to enhance
the efficacy of interventional procedures. It is recommended
that interventional procedures should be performed
with an algorithmic approach and in accordance with a
multidisciplinary treatment plan.
is chapter presents a general overview of interventional
procedures in the management of pain. An account of various
means to aid accurate placement of needles or devices will be
given and some selected common interventional procedures
will be briefly described. e efficacy, limitations and risks of
interventional procedures will be discussed with reference to
recent evidence. Lastly, an algorithmic approach in the clinical
practice of interventional procedures will be described. For
more detailed discussion on some important interventional
Interventional Procedures in Pain
Management: An Overview
25
Steven H. S. WONG
INTRODUCTION
AIDS TO ENHANCE PRECISION OF
INTERVENTIONAL PROCEDURES
MEANS OF NEURAL BLOCKADE IN
INTERVENTIONAL PROCEDURES
Chemical agents
Physical means
COMMON INTERVENTIONAL
PROCEDURES IN PAIN
MANAGEMENT AND THEIR
EFFECTIVENESS
Injection at peripheral sources of
pain
Nerve block
Sympathetic block
Injections for chronic back pain
Implantable devices
AN ALGORITHMIC APPROACH
CONCLUSION
REFERENCES
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406 Steven H. S. WONG
procedures, please refer to Chapters 11 and 26 to
31 of this textbook.
Aids to Enhance Precision of
Interventional Procedures
Fluoroscopy
e use of portable X-ray machines with fluoroscopy
has revolutionised the practice of interventional
procedures. It allows instantaneous production of
the radiological image by the image intensifier and
viewing on the monitoring screen. Fluoroscopy is
most useful in procedures around the spine where
great precision is required to avoid injury to the
spinal cord. e use of radiographic contrast agents
allows direct visualisation and estimation of the
spread of therapeutic agents, which is especially
important in neurolytic blockade.
Special precautions should be undertaken in
performing interventional procedures under
fluoroscopic guidance. It is important to comply
with the radiation safety ordinance to prevent
inadvertent radiation exposure to the patient
as well as the staff [11]. e use of radiographic
contrast media also requires caution because of
their adverse effects; specific enquiry into patients’
allergic history is advised and steroid cover may be
required [49].
Computerised tomography
Computerised tomography produces cross-
sectional views of the body. It has been employed
in interventional procedures involving deeply
seated structures such as the coeliac plexus in the
management of pain in carcinoma of the pancreas.
Despite its higher precision, the technique has not
gained much popularity because it is very tedious,
requiring movement of the operator between the
examination room and the control room for every
radiological exposure after adjustment of the
needle.
Ultrasound
e availability of compact portable ultrasound
equipment has recently made the ultrasound
machine a very popular device among anaesthetists
in the performance of regional blockade [27].
Ultrasound also has the advantage of being free
from radiation hazard. It is especially useful for
locating nerves among other soft tissues, such
as the brachial plexus and peripheral nerves of
the limbs. However, it is not as useful in nerve
blockade around bony structures such as the
spine. e efficacy of ultrasound-guided nerve
blockade is also highly dependent on the skills of
the operator.
Nerve stimulators
e nerve stimulator is useful in localisation of
nerves in performing neural blockade. Sensory
and motor nerves can be differentiated by varying
the frequency of stimulation, with 50–100 Hz
producing paraesthesia while 1–2 Hz produces
visible muscle twitching. e proximity of
the needle to the nerve can be assessed by the
minimum amplitude of current required for
stimulation, and amplitudes of less than 0.3 mV
usually suggest optimal positioning of the needle.
e nerve stimulator is routinely employed in the
radiofrequency thermocoagulation technique. It
is important that local anaesthetics should not be
given via the needle until accurate positioning of the
needle has been confirmed, as even a tiny volume
of local anaesthetic will completely block off the
stimulation response and obviate subsequent use of
the technique.
Means of Neural Blockade in
Interventional Procedures
Neural blockade can be achieved by using chemical
agents such as local anaesthetics or neurolytic
agents, or the use of physical means such as cold
or heat.
Chemical agents
e choice of chemical agents for neural blockade
depends on whether the procedure is diagnostic or
therapeutic. Local anaesthetics are used for both
diagnostic and therapeutic procedures. Neurolytic
agents may be considered for therapeutic procedures
in selected patients. Novel agents, such as botulinum
toxin and ziconotide, have been employed to block
pain transmission in interventional procedures for
a much longer duration than local anaesthetics
provide.
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407
Interventional Procedures in Pain Management: An Overview
Local anaesthetics
e most commonly used local anaesthetics are
the amide group derivatives. ey differ in their
onset time and duration of action. Lignocaine has
the fastest onset time of about 10 to 20 minutes
and the shortest duration of action of about 1 to
2 hours if given for peripheral nerve blockade.
Bupivacaine has a slower onset time of about
half an hour and a longer duration of action of
about 4 to 5 hours. e most serious risk with
the use of local anaesthetics is systemic toxicity
if injected into the circulation inadvertently and
results in convulsion, arrhythmias and cardiac
arrest. Bupivacaine has the highest cardiotoxicity
and it is often irreversible while ropivacaine has
less cardiotoxicity. Precautions should be taken to
prevent intravascular injection and not to exceed
the recommended dose limit.
In patients with chronic pain, the effect of neural
blockade using local anaesthetics may sometimes
outlast the duration of the local anaesthetic itself.
It is more commonly seen with sympathetic
blockade in complex regional pain syndrome.
erefore, repeated sympathetic blockade with
local anaesthetics is recommended in this group of
patients when appropriate.
Neurolytic agents
Alcohol (ethanol) and phenol are the two most
commonly used neurolytic agents. ey have
similar mechanism of action and cause destruction
to neural tissues resulting in axonal degeneration
and Wallerian degeneration. In addition, phenol
has high affinity for vascular tissues and injection
of a large volume in highly vascular areas such as
the coeliac plexus is not recommended.
e use of neurolytic blockade is reserved for
management of cancer pain patients with limited
life expectancy. is is because the duration of
effect usually lasts 3 to 6 months and pain tends to
recur with regeneration of nerve fibres. Also, there
is a possibility of development of deafferentation
pain after somatic nerve injury. Phenol is available
as a 10% solution in a mixture with X-ray contrast
media, such as iothalamate meglumine (Conray).
Alcohol is available as an absolute 100% solution
and is often diluted to a 50–75% solution with
bupivacaine.
Botulinum toxin
Botulinum toxin is the most potent biological
toxin produced by the bacterium Clostridium
botulinum. It inhibits the release of acetylcholine
at the neuromuscular junction, thereby causing
muscle paralysis. Newer studies show that it may
also have a direct analgesic action. Postulated
mechanisms include inhibition of release of
substance P, glutamate and other peptides and
neurotransmitters from nociceptors, suppression
of neurogenic inflammation and reduction of
sympathetic activity [29].
Ziconotide
Ziconotide is the synthetic equivalent of the basic
peptide present in the venom of a marine snail. It
produces potent antinociceptive effects by selectively
binding to the N-type voltage-sensitive calcium
channels, thereby blocking neurotransmission
from primary nociceptive afferents. Intrathecal
ziconotide has been demonstrated to have a place
in the treatment of patients with severe chronic
pain who are intolerant of or refractory to other
analgesic therapies [37].
Physical means
Various physical means to produce destruction
of neural tissues have been employed in the
management of chronic pain. ese include
cryotherapy and radiofrequency treatment.
Cryotherapy
Cryotherapy produces destruction of neural tissue
by freezing it with the tip of a cryoprobe which is
cooled by rapid expansion of a gas passed inside it.
e tip of the probe can reach as low a temperature
as -60˚C with carbon dioxide, or -70˚C with nitrous
oxide. e cryoprobe is inserted to the target site
under fluoroscopic guidance.
Cryotherapy is gradually losing its position
to radiofrequency treatment as the physical
means of neural destruction. Disadvantages of
cryotherapy include the bulkiness of the cryoprobe
in comparison with the radiofrequency electrode,
and the subsequent need for larger doses of local
anaesthetics during placement, which interferes
with the use of the nerve stimulator.
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408 Steven H. S. WONG
Radiofrequency treatment
Conventional radiofrequency treatment produces
a heating effect on the nerve by passing a
radiofrequency current through a circuit which
consists of an active electrode, a ground electrode
and the radiofrequency generator. e active
electrode has an insulated body and a non-
insulated tip which is available in various lengths.
It is inserted to the target site under fluoroscopic
guidance. e ground electrode is a gel pad which
is applied on the patient’s body. e two electrodes
are connected to a radiofrequency generator which
delivers a radiofrequency current at a frequency of
460 kHz [46, 55].
When the circuit is completed, a high current density
generated at the tip of the active electrode will heat
up the surrounding tissues. e temperature at the
tip of the electrode is constantly measured by a
thermocouple. By selecting the appropriate length
of non-insulated tip and adjusting the amplitude
and the duration of the current, a controlled
thermal lesion can be produced. With conventional
continuous radiofrequency current, the tissue is
heated to a temperature of 60–70˚C for a period
of about 60 seconds. Irreversible nerve damage
due to coagulation of tissue proteins will occur at
temperatures of above 60˚C.
A new technique of radiofrequency treatment has
recently been developed. It delivers pulses of high-
voltage radiofrequency current to the nerve without
heating it to a degree at which tissue coagulates, as
the heat generated is dissipated between pulses. e
apparent lack of nerve damage is advantageous in
the lesioning of somatic nerves, which have a higher
chance of developing deafferentation pain [1]. e
mechanism of action of pulsed radiofrequency is still
not clear. It is postulated that the electric field, rather
than the temperature, induces changes in the neuron
and produces a neuromodulatory effect [14].
Common Interventional
Procedures in Pain
Management and Their
Eectiveness
A wide variety of interventional procedures are
practised in pain management. ey can be
classified according to their sites and mechanisms
of action. Some common interventional procedures
in pain management are outlined below.
Despite the enthusiasm and the wide acceptance
of interventional procedures in the management of
chronic pain, high level research-based evidence is
still lacking in the support of their practice. ere
have been few high quality randomised controlled
studies on the effectiveness of interventional
procedures. Some recent systematic reviews have
examined the effectiveness of various interventional
procedures, but contradictory results were found
regarding their efficacy. Brief discussions on the
efficacy will be given for individual procedures.
Injection at peripheral sources of
pain
ese include simple injection techniques like
trigger point injection and injection over inflamed
tendons or fasciae for treatment of conditions
like tennis elbow or plantar fasciitis. e injectate
used is usually a local anaesthetic and may have
in addition a depot corticosteroid preparation.
Local anaesthetics produce a transient effect
through blocking of neural transmission while
corticosteroids exert a more long-lasting effect
by their anti-inflammatory actions. Recently,
botulinum toxin has been used in the treatment
of various disorders associated with painful muscle
spasms with a much longer duration of action than
local anaesthetics.
Trigger point injection
Trigger points are discrete, focal, hyperirritable
spots located in taut bands of skeletal muscle. ey
are mostly found in muscles that maintain body
posture, such as those in the paraspinal and girdle
regions. e trigger points are tender on palpation
and may cause a specific referred pain pattern. e
cause is unclear but is postulated to be related to
repetitive microtrauma of muscle fibres. It is more
common in middle-aged females and is usually
associated with anxiety states. e diagnosis is often
myofascial pain syndrome or fibromyalgia [2].
Trigger point injection should be performed in
conjunction with relaxation and stretch exercises,
as well as psychological therapy if indicated. e
trigger points are injected in a fanwise fashion
using a small gauge hypodermic needle with a
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Interventional Procedures in Pain Management: An Overview
small amount of local anaesthetic. A series of three
to four injections over a period of 1 to 2 months
may be effective in abolishing the trigger points
with marked relief of pain. e operator should
note the total amount of local anaesthetic to be
injected in patients with multiple trigger points, to
avoid overdose toxicity.
A randomised double-blind crossover trial
comparing trigger point injections using local
anaesthetic with normal saline (n = 15) has
shown that both techniques resulted in significant
reduction in pain even up to 7 days after treatment
[13]. In another double-blind study comparing
trigger point injections using local anaesthetic (n =
13) with dry needle (n = 20), it was found that dry
needle was more effective than injection with local
anaesthetic [12]. A systematic review pooling the
results of these and some other studies concluded
that trigger point injection was no more effective
than placebo injection [30].
It is now believed that the mechanism of action of
trigger point injections in the treatment of myofascial
pain syndrome is the release of contraction in the
contractile units of the myofibrils by the insertion
of the needle rather than the local anaesthetic. It
explains why a dry needle works. It would then
become very difficult to compare local anaesthetic
injection with “placebo” injection, which in fact is
an effective treatment.
Injection for tennis elbow
Tennis elbow is caused by overuse of the extensor
tendons of the forearm. e resulting lateral
epicondylitis presents most commonly with
localised pain over the bony origin of the tendons of
the extensor carpi radialis brevis and less commonly
those of the extensor carpi radialis longus. e
pain can be effectively treated by injection over
the inflamed tendons with depot steroid in a small
volume of local anaesthetic. It is important to
employ strict aseptic technique and avoid direct
injection into the tendons [54].
Injection for plantar fasciitis
Plantar fasciitis involves the inflammation of the
plantar fascia and is associated with prolonged
walking or exercise. e pain can be effectively
treated by injecting over the medial aspect of the
calcaneus with depot steroid in a small volume of
local anaesthetic [54].
Injection for painful muscle spasms
Botulinum toxin, originally developed for treatment
of dystonia and movement disorders, has been
found to be effective for the treatment of a number
of chronic pain conditions associated with painful
muscle spasms. ese include myofascial pain
syndrome or fibromyalgia, temporomandibular
joint pain and orofacial pain. Botulinum toxin has
also been used to treat some headaches associated
with muscle contractions such as chronic tension
headache and cervicogenic headache [16].
Nerve block
Nerve block plays a crucial role in the diagnosis and
treatment of pain syndromes. e procedure can
be applied to nearly all body structures that have
got a nerve supply. Commonly practised nerve
blocks include intercostal nerve block for chest wall
pain, and injection of the trigeminal nerve and its
branches in trigeminal neuralgia or other causes of
orofacial pain.
Sometimes, the pain in the body structures is
a referred pain that has occurred as a result of
pathology in the supplying nerve or as a result of
entrapment of the supplying nerve by surrounding
tissues or fibrosis of scarred tissues. Common
examples include intercostal nerve block for
entrapment by thoracotomy scars, occipital nerve
block for cervicogenic headache as a result of
nerve compression or occipital neuralgia, and
suprascapular nerve block for shoulder pain caused
by nerve entrapment.
Accurate placement of needles in somatic nerve
block is facilitated by the use of fluoroscopy, or by
the use of a peripheral nerve stimulator. In recent
years, the availability of ultrasonograpy has allowed
clear visualisation of nerves and has popularised the
practice of nerve blockade.
Intercostal nerve block
Intercostal nerve block is useful in alleviating chest
wall pain caused by fracture of ribs, or cancer
infiltration of the chest wall. It is also useful when the
chest wall pain is a referred pain due to entrapment
of the intercostal nerves by thoracotomy scar tissues
[10].
e most serious risk of intercostal nerve block
is pneumothorax and meticulous care should be
exercised during the procedure. A chest radiograph
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