William O. Witt, M.D.
Anesthesiology and Neurosurgery
Department of Anesthesiology
University of Kentucky
In discussing invasive management, it is imperative to
remember that invasive management is only one modality involved in the
treatment of pain. Similarly, it is important to remember that nociception
is only one component involved in the total experience of pain. Nociception,
pain, suffering, pain behavior, pain impairment, and disability must all be
identified and treated. Accordingly, treatment should also include a
multi-disciplinary approach involving physical, medical, behavioral, and
perhaps surgical interventions as well as invasive pain management.
Finally, it is important to remember that conservative treatment for low
back pain is generally very effective, and the vast majority of patients
improve on their own within four weeks of the onset of pain. Having laid
this background, it is appropriate then to discuss invasive modalities.
Invasive modalities fall into three broad groups,
those that produce partial resolution of the problem, those that are
involved with neuromodulation of the problem, and neurodestructive
techniques. Partial resolution is perhaps best demonstrated by epidural
steroid injection. This may be accompanied by epidural lysis of adhesions,
and may involve different routes of administration into the epidural space,
including single nerve root injection. A new technique of laser
annuloplasty has recently been described as well.
Neuromodulation involves the use of nerve blocks,
intrathecal infusion, spinal cord stimulation, and peripheral nerve
stimulation. Intrathecal infusion and spinal cord stimulation are discussed
in another lecture, and peripheral nerve stimulation is beyond the scope of
this presentation. Nerve blocks are known to have effects at multiple
levels. Clearly they produce direct afferent nerve blockade as well as
efferent blockade. They also exert an influence indirectly by interfering
with “wind-up” of wide-dynamic-range neurons in the dorsal horn.
They also produce decreased receptor sensitivity and buffer hydrogen ions.
There is also a component of dilution of inflammatory mediators, which
explains the observation that even physiologic saline can produce pain
relief when injected into inflamed tissue.
Neuroablation has a limited but important role in the
peripheral nervous system. In addition, neuroablation may be utilized in
the autonomic nervous system, the spinal cord, and the brain. The latter
two are beyond the scope of this lecture. Historically, destruction of the
Gasserian ganglion in 1891 was the first application of neuroablation, and
remains one of the great success stories in modern pain medicine. Prior to
any neurolytic technique it is wise to inject local anesthetic first.
Whereas this will not necessarily predict the effect of neurolysis,
it may well predict the extent of the neurolysis. In performing
neurolytic lesions in the peripheral nervous system it is critical to avoid
techniques that produce destruction of the nerve sheath, unless dealing with
a terminal disease states that is expected to be terminal within a few
months. The importance of this cannot be overstated in that the axon will
always regenerate, and if the nerve sheath is destroyed, neuromas will form
and result in pain that is often worse than the original pain being
treated. It is also more refractory to subsequent treatment. Both
radiofrequency heat lesioning as well as cryotherapy achieve this objective.
The temperature for radiofrequency lesioning should not exceed 80°
Celsius if deafferentation pain is to be avoided. Radiofrequency
destruction of a portion of the dorsal root ganglia is useful in the
treatment of neuralgias in selected conditions. The use in tic douloureux
has already been described and is extraordinarily effective. It may have an
application in any radicular pain syndrome.
One of the more common and well-accepted applications
of radiofrequency lesioning is treatment of “facet syndrome”. This was
first described in 1933 and accounts for 80% of “sciatica”. In dealing with
patients afflicted by this syndrome, it is important to recognize that
radiographic imaging is not useful and that the diagnosis is made by
clinical examination. This clinical examination includes aggravation with
extension, rotation, and side-bending and a typical sclerotomal
pattern of radiation. Prior to radiofrequency lesioning, local anesthetic
should be administered in the form of medial branch blocks, and this should
produce a dramatic reduction of pain with active range of motion. It
is critical to restrict the amount of volume of local anesthetic used for
these blocks to no more than 1 milliliter in the lumbar spine and no more
than ˝ milliliter in the cervical spine, if reasonable specificity is to be
obtained. The success of medial branch lesioning is critically dependent
upon precise needle placement. It is also important to remember that each
zygapophyseal joint has multiple sources on innervation, and that
accordingly, pain relief can be expected only with multiple sites of
lesioning. Medial branch lesioning also plays a role in the management of
thoracic degenerative joint disease, although this is much less common.
Published results of successful
treatment of chronic pain with radiofrequency medial branch lesioning range
from 30% to more than 90%. This extreme variability is probably accounted
for by variability of patient selection and of technique.