Volume 5 • Number 3 • 2004
The Surgical Anatomy of Lumbar Medial Branch Neurotomy
Peter Lau, FRACR,* Susan Mercer, PhD,†Jayantilal Govind, FAFOM,* and Nikolai Bogduk, DSc*
*Department of Clinical Research, University of Newcastle, Royal Newcastle Hospital, Newcastle, Australia;
†Department of Anatomy, University of Otago, Dunedin, New Zealand
A B S T R A C T
Objective. To demonstrate the validity of placing electrodes parallel to the target nerve in lumbar
Design. Previous data on the anatomy of the lumbar dorsal rami were reviewed and a demonstra-
tion cadaver was prepared. Under direct vision, electrodes were placed on, and parallel to, the
L4 medial branch and the L5 dorsal ramus. Photographs were taken to record the placement, and
radiographs were taken to illustrate the orientation and location of the electrode in relation to
Results. In order to lie in contact with, and parallel to, the target nerve, electrodes need to be
inserted obliquely from below, so that their active tip crosses the neck of the superior articular
process. At typical lumbar levels, the tip should lie opposite the middle two quarters of the supe-
rior articular process. At the L5 level, it should lie opposite the middle and posterior thirds of the
S1 superior articular process.
Conclusion. If electrodes are placed parallel to the target nerve, the lesions made can be expected
to encompass the target nerves. If electrodes are placed perpendicular to the nerve, the nerve may
escape coagulation, or be only partially coagulated. Placing the electrode parallel to the nerve has
a demonstrated anatomical basis, and has been vindicated clinically. Other techniques lack such a
basis, and have not been vindicated clinically. Suboptimal techniques may underlie suboptimal out-
comes from lumbar medial branch neurotomy.
Key Words. Back Pain; Neurotomy; Denervation; Zygapophysial Joint; Medial Branch; Nerves
© American Academy of Pain Medicine 1526-2375/04/$15.00/289 289–298
Reprint requests to: Nikolai Bogduk, D.Sc., Department
of Clinical Research, Royal Newcastle Hospital,
Newcastle, New South Wales 2300, Australia. Tel:
of anatomy. Shealy  described the articular
branches to the lumbar zygapophysial joints as
rising dorsally across the lateral aspect of the supe-
rior articular processes. Accordingly, he recom-
mended placing electrodes lateral to the articular
process, perpendicular to the coronal plane [2–5].
hen first described, lumbar facet denerva-
tion was based on an incorrect description
It was subsequently shown that the medial branch
of each lumbar dorsal ramus runs caudally across
the neck of the superior articular process and that
articular branches approach each joint from below
and from above [6–9]. No nerve rises dorsally
through the region where Shealy recommended
placing electrodes .
For the purposes
zygapophysial joint, the articular branches are too
small to be accurately targeted, but their parent
medial branch can be targeted. An electrode
placed at the junction of the superior articular
process with the root of the transverse process
would rest on the medial branch. On this basis,
lumbar facet denervation was modified to become
lumbar medial branch neurotomy [6,7]. Not all
of denervating a
operators, however, heeded this explanation of the
correct anatomy. They continued to use the dis-
credited Shealy approach [10,11], even in con-
trolled trials .
Another modification followed when it was
demonstrated that radiofrequency electrodes do
not effectively coagulate tissues distal to their tip;
they coagulate in a radial direction around the
exposed tip, perpendicular to the long axis of the
electrode . Consequently, an electrode whose
tip is placed perpendicular to the target nerve may
fail to coagulate the nerve adequately. Depending
on how far the electrode coagulates distal to its tip,
it may coagulate the nerve only partially or it may
fail to coagulate the nerve at all. From a partial
coagulation, the nerve may rapidly recover, result-
ing in relief from pain of only a limited duration.
For the target nerve to be coagulated reliably and
thoroughly, the electrode must be placed parallel
to the nerve .
This technical warning has not been heeded.
Only one study has described the outcomes of
lumbar medial branch neurotomy in which the
electrode was properly placed parallel to the target
nerve . With this technique, good results can
be obtained. Some 60% of patients maintain at
least 80% relief of their pain at 12 months, and
some 80% of patients maintain at least 60% relief.
That study, however, was based on a small sample
of highly selected patients. Its outcomes have still
to be corroborated in a larger sample. Neverthe-
less, it remains the only published study of paral-
lel placement of electrodes.
Others have persisted in using techniques that
have not been validated anatomically. Most still
advocate placing the tip of the electrode onto the
base of the transverse process in order to reach the
medial branch. However, all variants still have the
electrode essentially perpendicular to the course of
the nerve and rely on lesions being made distal to
the tip. Of those techniques that have been tested
clinically, one has been found to be totally inef-
fective ; others have been partially effective at
6-week  and 8-week  follow-ups. Other
variants have been described but not tested clini-
Ironically, the literature actually lacks any
description that validates what should be the
correct placement of electrodes for lumbar medial
branch neurotomy. Authorities writing on this
topic rely only on verbal descriptions of anatomy
to justify their technique. Citing articles that state
that the medial branch crosses the root of the
transverse process, they advocate placing elec-
trodes onto this bony landmark. No study has
shown how electrodes placed in various positions
actually relate to the target nerve. The present
study was, therefore, undertaken to anatomically
validate why electrodes should be placed parallel
to the target nerve.
The records of data previously reported in
anatomical studies  were reviewed to establish
the course of the medial branches of the lumbar
dorsal rami. These data covered 30 nerves in six
cadavers. For purposes of illustration, another
cadaver was freshly dissected on one side, under a
dissecting microscope, to provide a specimen with
the medial branches in situ, but the surrounding
Under direct vision, an electrode was placed
both parallel to and in contact with the target
nerve at the L4 and at the L5 level. Photographs
were taken to illustrate both the nerve alone and
the electrode in contact with the nerve. With the
electrode held in place, anteroposterior (AP),
lateral, and declined radiographs were taken of the
electrode position using a C-arm fluoroscope.
For the declined views, the X-ray beam was
tilted laterally by 20° from an AP view and then
declined steeply along the length of the body until
a view was obtained along the course of the elec-
trode, that is, end-on, from below.
In order to demonstrate the sizes of lesions
made by radiofrequency electrodes in relation to
the target nerves, ellipses representing the outer
boundaries of lesions were drawn to scale on pho-
tographs and radiographs of electrodes placed
against the nerve. Such ellipses have a longitudi-
nal and a transverse axis, the lengths of which
differ for different electrodes. Laboratory studies
have measured the mean sizes of the lesions made
by SMK and RRE electrodes (Radionics; Burling-
ton, MA) with 5-mm active tips . Respectively,
the active tips of these electrodes are 0.7mm and
1.6mm wide. In order to circumvent errors caused
by magnification and projection, the sizes of
lesions made by these electrodes can be expressed
in terms of electrode-widths. The lesions made by
an SMK electrode have a mean transverse diame-
ter of 5.6 (±0.8 SD) electrode-widths and a mean
longitudinal diameter of 8.5 (±0.4 SD) electrode-
widths. Those made by an RRE electrode have a
mean transverse diameter of 4.2 (±0.6 SD) elec-
trode-widths and a mean longitudinal diameter of
3.5 (±0.2 SD) electrode-widths. In the present
Lau et al.
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