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CHAPTER 30/INTRADISCAL ELECTROTHERMAL THERAPY / 313
fissures less than 50% of the time and asymptomatic
patients may have an HIZ (19–22). Therefore, a patient
may have a painful annular tear without concomitant
MRI findings. Disc bulging is due to, and directly associated with, annular degeneration and fissures; however,
this phenomenon does not always create clinically significant low back pain (21).
Certainly not all chronic lumbar pain is discogenic. It
is estimated that more than 50% of patients with chronic
low back pain may have the disc as the primary source of
pain (6), however, an accurate diagnosis can be elusive.
Screening for patients with facet problems, sacroiliac
joint dysfunction, psychosocial problems, systemic disease, neoplasm, and infection should be undertaken when
appropriate. A chronic pain syndrome with primarily soft
tissue pain and somatization often occurs in the low back
pain population. Practitioners must be aw are of the potential existence of these phenomena.
THERMAL IMPACT ON TISSUE
Innervation of the intervertebral disc has been well
documented by researchers since the 1930s. More
recently, Bogduk’s work illustrated the sources of lumbar
disc innervation (23). Coppes et al. found nociceptive
properties in nerves of the outer annular wall. In fact,
they observed nerve fibers “deeper than the outer third of
the annulus fibrosus” (24). Freemont et al. also discovered significant neovascularization with neural expression of substance P, and linked that growth to disc degeneration and back pain. They identified nerve fibers as
deep as the inner third of the annulus fibrosus and into
the nucleus pulposus in several disc samples (25).
Letcher et al. established that irreversible nerve blocks
due to neural thermocoagulation occur at 45°C in the
brain (26), and Cosman et al. (27) used radiofrequency
lesioning to produce 45°C isotherms for neural tissue
lesioning. The intradiscal temperatures generated by the
SpineCATH (48° to 75°C) are in the range necessary to
create thermocoagulation of neural tissue in the target
zone accessed (28, 29).
Collagen contraction, or shrinkage, has been well documented in the use of nonablative laser energy on joint capsular tissue and more recently in radiofrequency application in the glenohumeral joint capsule (30,31). Research
has shown that there is a direct correlation between the
amount of heat and duration of the heating applied to tissue and the resulting collagen contraction (32–36).
The breaking apart of the heat-sensitive bonds of the
collagen fibrils causes tissue shrinkage. The framework
of the intervertebral disc is composed primarily of types
I and II collagen, which have a similar molecular structure. The tensile strength of these collagen fibers is
derived from the extended conformation of the triple
helix molecule, which is cross-linked with hydrogen
bonds. A portion of these bonds is heat sensitive, breaking apart when exposed to a range of temperatures over
time. The disruption of these stabilizing hydrogen bonds
releases the molecular strands, which collapse. This collapse, like the release of a spring-held taut, results in a
new contracted state called the denatured or random coil
conformation of the collagen f iber.
The optimal temperature for collagen contraction is
reported to be 65°C. The lowest practical temperature at
which heat-sensitive hydrogen bonds will start to break is
60° C. As the temperature increases, more bonds break. It
is unclear whether there is an additional shrinkage effect
over 75°C.
Kleinstueck et al. attempted to study intradiscal temperature dispersion from the SpineCATH (37). They
placed the device in the nucleus rather than in the annulus and were able to measure temperatures of great than
42°C (temperature sufficient to thermocoagulate unmyelinated nerve f ibers) at distances g reater than 10 mm from
the probe. However, their use of previously frozen cadaveric discs, and the placement of the heating element in the
nuclear cavity rather than in the annulus as is done in
clinical practice may have limited the peak temperatures.
Freeman et al. presented temperature maps in vivo on
sheep demonstrating higher peak temperatures (38). The y
found temperatures of greater than 65°C adjacent to the
catheter. In a recent report Shah et al. found microscopic
evidence of acute collagen modulation in cadaveric discs
heated with a SpineCATH (29).
Recently Barensde et al. reported on a randomized
controlled trial evaluating the efficacy of a radiofrequency probe placed into the center of the nucleus and
then heated (39). The treated group fared no better than
placebo. Houpt et al. (40) has previously demonstrated
the inability of temperature dispersion for a radiofrequency device to raise intradiscal and annular temperatures. For these reasons the IDET technology (i.e.,
SpineCATH) does not use radiofrequency as a heating
element but rather uses a thermal resistive coil, which
produces conductive heat. Additionally, contrary to the
radiofreqency device studied b y Barendse (39), the IDET
device is deplo y ed into the annulus and is not deployed in
the center of the nucleus (28,41).
CLINICAL RESEARCH REVIEW
The first published series of patients treated with IDET
reported the 6-month (range 6 to 9 months, mean 7
months) outcome results for 25 patients with chronic low
back pain of documented discogenic origin with mean
duration of preoperative symptoms of 58.5 months. These
were patients who failed to adequately improve with a
comprehensively applied nonoperative care program and
who elected IDET instead of chronic pain management or
spinal fusion (41). The results demonstrated a statistically
314 /SECTION V/SPECIFIC CLINICAL ENTITIES
significant improvement in functional outcome as measured by Visual Analogue Scale (VAS) scores, Social
Functioning (SF)-36 scores, sitting tolerance times, and
narcotic analgesic medication. Sixty-two patients treated
with IDET and followed for a minimum of 1-year (mean
16 months, range 12 to 23 months) postprocedure
demonstrated outcome evaluation scores that did not statistically vary from the 6-month group. The mean group
change for the SF-36 bodily pain was 17 and physical
function was 20. These scores are consistent with significant clinical improvement (42).
A 2-year follow-up study noted continued improve-
ment of SF-36 scores and sitting tolerance times (43).
Karasek and Bogduk (44) reported on the 1-year outcome of patients treated with IDET (35) and compared
them to a control group of patients (17) similarly diagnosed but denied insurance authorization for IDET. The
researchers used a 50% reduction of VAS scores as an
indicator of success. On this basis, 60% were considered
successes. Additionally, they noted that 23% of the
patients had total relief of symptoms. They reported that
only one patient in the control group improved and the
remainder continued to have similar pain intensity.
Derby et al. (45) reported that 62.5% of patients treated
with IDET had a favorable outcome based upon the
Roland Morris Scale, VAS, North American
Spine Society (NASS) outcome instrument, and a general activity scale. If patients had preserved disc height
and had not undergone previous surgery at the index
level, the success rate was 76%.
Wetzel et al. presented the 2-year results of a multicenter prospective cohort study and found statistically
significant improvement in pain reduction and physical
function in their study group (46). To date, there are no
published randomized controlled trials of IDET. Cleary,
such trials will be extremely valuable in determining the
validated efficacy of IDET and other spine therapies.
Until those data are available, physicians and surgeons
should proceed with caution prior to determining the path
of care for their patients with chronic discogenic pain.
action of IDET. Clearly, further work on the mechanism
of action is required.
DIAGNOSTIC W ORKUP AND P A TIENT
SELECTION FOR IDET
The following 12 criteria represent our present criteria
for IDET candidacy. To date, these criteria have not been
validated by controlled studies. They represent our experience, and are a work in progress.
1. Severe, function-limiting, chronic low back pain for
more than 3 months.
2. Failure to adequately improve with a comprehensively applied aggressive nonoperative treatment
program consisting of stabilization exercise training,
back education, activity modification, and when
appropriate, fluoroscopically guided selectiv e epidural
cortisone injections and, in some circumstances, facet
injections.
3. A duration of 3 months for the nonoperative care program is recommended (this would bring the total
duration of symptoms to an approximate minimum
of 6 months prior to IDET).
4. Normal neurologic examination.
5. Negative straight leg raise (SLR)—no reproduction
of “true sciatica”.
6. MRI that does not demonstrate neural compressive
disease.
7. Preservation of disc height at the symptomatic level
(less than 30% disc space collapse).
8. No measurable segmental instability.
9. No lytic or degenerative spondylolisthesis.
10. Discogram that demonstrates an annular f issure and
reproduces concordant pain at one or more levels at
an injection volume of less than 2 cc, with a documented negative control level.
11. No irreversible psychosocial barriers to recovery.
12. Motivation to improve with realistic expectations of
outcome.
MECHANISMS OF ACTION
The precise mechanism of action of the observed
positive clinical effect is currently under investigation.
Moore et al. attempted to create annular in-growth of
nerve fibers after surgically induced injury. They followed this with IDET in an attempt to determine if IDET
reduced the population of nerve f ibers in treated versus
untreated control specimens. Unfortunately, neither the
control nor the treated specimens had enough neural ingrowth to determine a differential effect (47). Pollintine
et al. presented a cadaveric disc study demonstrating an
equalization of stress across the IDET treated disc (48).
This may lend useful insight into the mechanism of
In summary, IDET is intended for psychologically stable and motivated patients with chronic function limiting
low back pain with a documented discogenic source of
pain who have failed to improve with an aggressive exercise-based rehabilitation program. Discography criteria
for low-volume concordant pain provocation attempts to
separate appropriate patients with focal annular lesions
who will experience pain reproduction at low volumes
from patients who are questionable candidates with
global annular degeneration who will often experience
pain reproduction only at larger volumes of injectate (i.e.,
greater than or equal to 2 cc volumes). We have noted that
patients with severe disc space collapse (greater than
50%) may have a lower likelihood of success than
CHAPTER 30/INTRADISCAL ELECTROTHERMAL THERAPY / 315
patients with preserved disc height. This theorem however has not been vigorously tested. In addition, the effectiveness of IDET on the previously operated segment
remains an open question.
PROCEDURAL TECHNIQUE
Overview
Local anesthesia and conscious, monitored sedation is
applied to the patient in an outpatient surgical or radiologic setting. A 17-gauge procedure needle is introduced
into the symptomatic disc under multiplane fluoroscopic
guidance. The SpineCATH is introduced through the procedure needle and navigated to the offending portion of
the annulus. The SpineCATH position is documented in
at least the anteroposterior and lateral radiologic view.
Care must be undertaken to avoid catheter kinking, w hich
may lead to catheter breakage. Treatment may be
achieved with unilateral catheter deplo yment, but roughl y
40% of the time, due to multiple annular fissures, bilateral deployment is necessary to cover the entire posterior
annular wall. The ORA-50 (Smith & Nephew, Andover,
MA) autotemperature heat generator controls the catheter
heat delivery system. Typically a maximum catheter temperature of 90°C is attained (corresponding to tissue temperature adjacent to the catheter of approximately 72°C).
There are occasions when the temperature profile must
be modified to a maximum catheter temperature of 85° to
89°C to achieve patient comfort. The patient must be alert
enough to be observed for the development of radicular
pain during the procedure. If this occurs, the catheter is
repositioned or removed. Most patients will experience
their typical back pain and referral leg pain during the
procedure. However, this must be differentiated from
radicular pain, especially if the patient experiences it
early in the heating cycle (i.e., catheter temperature 65° to
90°C). If this occurs, it is usually indicative of an
extremely attenuated posterolateral annulus or a catheter
that is extradiscal. It is our preference to inject 2 to 5 mg
of cefazolin into the disc after treatment and removal of
the SpineCATH.
A survey of complications was presented noting a 6 per
1,750 incidence of reversible nerve injury due to needle
puncture and a 1 per 1,750 incidence of discitis. There is
one published report of cauda equina injury due to IDET
(49). IDET when performed by a skilled practitioner is relatively safe, but certainly not entirely without risk.
Course of Recovery and Postoperative Rehabilitation
Most patients will experience an increase in their typical pain (back, back and leg) in the early postoperative
period. The postoperative pain gradually subsides over
the first 1 to 7 days. Typically most patients will return to
at least their preprocedure pain level between the 7th and
14th postoperative day. We have noted that patients often
have resolution of their preoperative leg pain symptoms
in the first 4 weeks, whereas the improvement in back
pain requires 6 to 12 weeks to occur. Initial study patients
have been noted to progressively improve between 2 and
9 months. The 2-year data documented that the patient
group demonstrated substantial improvement between 1and 2-year follow-up points (43). The clinical course in
the first 4 to 6 months is often variable. However, many
of these patients will stabilize, and at 1-year follow-up
demonstrate significant improvement. Patients who have
not improved above their preoperative baseline by 6
months should be considered unsuccessful.
The most important postoperative principle appears
to be allowing time for a healing reaction. This requires
delaying aggressive exercise training for at least 3
months postprocedure. It is our practice to place
patients in a semirigid lumbar corset for 8 weeks postprocedure. During this period, patients are encouraged
to walk. At 8 weeks a progressive stabilization exercise
program is begun and the corset is discontinued.
Patients should be able to return to office work or light
duty assignment by 2 weeks and light lifting duties at 6
weeks postprocedure, although return to heavy work
may require 4 to 6 months. Optimization of return to
work timing and postoperative management deserves
further study.
CONCLUSION
IDET may offer a group of carefully selected patients
with chronic discogenic low back pain an option other
than chronic pain management or spinal fusion. Randomized control trials are necessary to validate the efficacy of
IDET as well as spinal fusion for the treatment of patients
with chronic discogenic low back pain.
ACKNOWLEDGMENTS
No funds were received in support of this chapter, and
no benefits in any form have been received from a commercial party related directly or indirectly to the subject
of this manuscript.
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CHAPTER 31
Operative Management of the Degenerative Disc: Posterior and Posterolateral Procedures
Gunnar B.J. Andersson and Francis H. Shen
In medicine, a successful outcome from a specific intervention is intimately associated with making an accurate
diagnosis. In the case of degenerative disc disease making an accurate diagnosis can be challenging (1–3).
Patients with degenerative disc disease may present with
a variety of symptoms ranging from predominantly low
back pain at one end of the spectrum, to leg pain at the
other end (3–5). As a result, the management of degenerative disc disease has been controversial (4–8).
In patients with predominantly leg pain the source of
the pain may be a degenerative herniated disc or associated lateral recess or foraminal stenosis resulting in lumbar radiculopathy. However, there is a subset of patients
with axial back pain (low back pain without radiculopathy) where the history, physical findings, and conf irmatory tests attempting to identify the source of pain have
not been as clear. Pain generators in these patients may
arise directly from the annulus of the degenerative disc
(9,10), from arthritic facets (11,12), or from pathologic
segmental instability and micromotion (13). It is this subset of patients that may benefit the most from a lumbar
fusion.
In this section we review the operative indications, surgical options, techniques for posterolateral lumbar fusion,
and role of instrumentation for axial back pain from disc
degeneration. Management of the patient with radiculopathy from a herniated disc or stenosis is addressed in
later chapters.
ETIOLOGY
Studies have focused on the annulus as a source of pain
in the degenerative disc (9,10). Innervation of the annulus has been well characterized, with the outer third being
innervated by pain transmitting free nerve endings (Figs.
31-1,31-2) (14). The sinuvertebral nerve, arising from the
ventral root and gray rami communicants, pro vides inner-
vation to structures within the spinal canal, the posterior
longitudinal ligament, ventral dural sac, and posterior
portion of the annulus (15). The ventral primary rami and
the sympathetic nervous system innervate the lateral
and anterior aspects of the annulus fibrosus, whereas
branches of the gray rami communicants or the sympathetic trunk innervate the anterior longitudinal ligament
(Figs. 31-1,31-2) (14,16). Furthermore, in a degenerative
disc, the annulus fibrosus, as well as the cartilage end
plates and underlying cancellous bone of the adjacent
vertebra have been shown to be more extensively innervated than normal healthy discs and vertebra (17). In a
study of 193 patients by Kuslich and colleagues, direct
mechanical stimulation of the central and lateral portions
of the annulus and vertebral end plates produced typical
back pain symptoms in approximately two thirds of the
patients (10).
Many of these same nerve endings are also involved
with the production of pain-related neuropeptides (18).
The number of neuropeptides known to be present in primary afferent neurons has been steadily increasing (19).
These neuropeptides are produced within the dorsal root
ganglion cell body and are delivered by axonal transport
to the central and peripheral processes of the neurons.
Their release has been demonstrated in response to
intense electric stimulation of peripheral nerves; however, their exact role in pain modulation from degenerative disc disease has not yet been fully elucidated.
Because of the three-joint concept of the lumbar spine
(20), axial back pain is likely the result of several factors
(13). It is possible that with increasing ligamentous and
capsular laxity there is progressive mechanical overload
of the degenerative disc and facets resulting in segmental
instability and pathologic motion potentially causing
additional pain (13,21,22). The associated loss of disc
height can increase stress across facet joints resulting in
facet arthrosis. Although contro versial, facet arthrosis has
317
318 /SECTION V/SPECIFIC CLINICAL ENTITIES
FIG. 31-1. The ner ve supply of a lumbar intervertebral disc
is depicted in a transverse view of the lumbar spine.
Branches of the gray rami communicantes and the sinuvertebral nerves (SVN) are shown entering the disc and the
anterior and posterior longitudinal ligaments (ALL and FLU).
Branches from the sinuvertebral nerves also supply the anterior aspect of the dural sac and dural sleeve. (From Bogduk
N, Twomey LT. Clinical anatomy of the lumbar spine, 2nd ed.
Edinburgh: Churchill Livingstone, 1991:117.)
FIG. 31-2. Neuroanatomic definition of the lumbar motion
segment. 1, Ascending branch of sinuvertebral nerve; 2,
ascending facet branch; 3, sinuvertebral to facet; 4, direct
branch to facet;5, branches to multifidus; 6, medial branch of
posterior primary ramus; 7, local facet branch; 8, descending
facet branch; 9, branch to sacroiliac; 10, sympathetic chain;
11, branch under anterior longitudinal ligament; 12, branches
from gray ramus to disc; 13, sinuvertebral to disc; 14, gray
ramus communicans; 15, branches from anterior primary
ramus to disc; 16, lateral branch of posterior primary ramus.
(From Oudenhoven RC. The role of laminectomy, facet rhizotomy and epidural steroids. Spine 1979;4:145–147.)
also been implicated as a possible source of back pain
(11,12,23). However, the clinical picture is variable.
Although nociceptive nerve fibers have been clearly
identified in f acet joint capsules and pericapsular tissue,
facet joint injections as a diagnostic and therapeutic
modality are not always effective (23). Randomized studies have not demonstrated a difference between the efficacy of placebo and that of steroids and local anesthetics
during facet injections (24,25).
OPERATIVE INDICATIONS
Before the diagnosis of degenerative disc disease can
be made, a careful history, physical examination, and
appropriate confirmatory studies should be performed.
Once the diagnosis has been made, nonsurgical options
should be exhausted before operative treatment is considered. The authors agree and stress that most individuals
with chronic disc degeneration and axial back pain can
be managed effectively with nonoperative treatment (2,4,
8,26). The natural history of axial back pain is continued
improvement with resolution over time. In cases where
pain persists, it often becomes a diffuse process throughout the entire lumbar spine, and it becomes difficult to
determine with certainty which of the several levels are
the source of the pain.
Although the majority of patients improve with nonoperative measures, surgical intervention has a v aluab le role
in selected cases. In a recent multicenter study, the
Swedish Lumbar Spine Study Group randomized 294
patients with severe chronic low back pain into either
surgical or nonsurgical treatment groups. The investigators concluded that in carefully selected patients with
severe chronic low back pain without symptoms of leg
pain or signs of nerve root compression, the improvement
in pain and disability after surgical fusion was significantly superior to that of nonsurgical treatment (7). Current indications for fusion include the patient with (a)
unremitting pain and disability for greater than 1 year; (b)
failure of aggressive physical conditioning and conservative treatment for at least 3 to 4 months; (c) magnetic
resonance imaging consistent with advanced disc degeneration limited to one or two disc levels; and (d) a negative psychiatric evaluation and lack of secondary gain
(27,28).
CHAPTER 31/POSTERIOR AND POSTEROLATERAL PROCEDURES / 319
TABLE 31-1. Fusion techniques for
degenerative disc disease
Lumbar fusion techniques
Posterolateral intertransverse fusion
Posterior lumbar interbody fusion
Transforaminal lumbar interbody fusion
Anterior lumbar interbody fusion
Combined antero-posterior lumbar interbody fusion
Although some agreement has been reached concerning operative indications, the ideal surgical procedure for
the management of the symptomatic degenerative disc
has not yet been answered. Because the pain is believed
to originate from either mechanical degeneration of the
intervertebral disc or pathologic motion between vertebrae segments, the majority of surgical interventions
focus on lumbar arthrodesis (Table 31-1). Fusion of the
pathologic and painful lumbar segments would theoretically stabilize the progression of mechanical disc degeneration and eliminate pathologic motion and pain (2,4).
SURGICAL OPTIONS
Once the decision for operative intervention is decided
on, then the options for arthrodesis include posterior-posterolateral fusions, posterior lumbar interbody fusions,
anterior lumbar interbody fusions, and combined anterior-posterior fusions (4,5,27). There are fe w comparati v e
studies that analyze the various techniques (29); the decision of whether or not to fuse the intervertebral disc is
still under debate.
Some authors believe that a posterolateral fusion alone
may be insufficient to address anterior pathology at the
level of the intervertebral disc (30–32). The y argue that if
the annulus fibrosus has been identif ied as a potential
pain generator, then treatment should address the pathology directly by complete elimination of the disc. Some
studies have demonstrated anterior motion and concordant pain on discography of levels that lie beneath a solid
posterior fusion (33). Proponents of posterolateral fusion
argue that the posterior fusion alone is sufficient to provide relief of axial back pain symptoms in the majority of
patients and that the associated morbidity from an interbody fusion cannot be justified (2,5,34).
Reported fusion rates vary among surgical techniques.
Because of decreased vascularity of the vertebral endplates, pseudoarthrosis rates have been reported to be
higher with interbody techniques (3,29). MacNab and
Dall compared anterior interbody, posterior, and intertransverse fusions and found that the incidence of
pseudoarthrosis after intertransverse fusions was significantly lower than with the other two methods. The investigators felt that the larger bone surface av ailable from the
transverse processes, lateral articular processes, and
intervening isthmic region, combined with local vascu-
larity, enhanced the rate of neovascularization of the bone
graft (29). Furthermore, interbody fusions often par tially
collapse and may potentially extrude during g raft incorporation. Newer instrumentation and surgical techniques
may improve fusion rates and decrease graft settling;
however, long-term follow-up is still unavailable.
Biomechanically, the closer the fusion is to the centrode of the motion segment, the greater the stiffness
achieved (3). Theoretically, interbody fusion techniques
should have the highest rigidity, and the posterior and
posterolateral fusions should have the least. However, the
relatively larger fusion masses created posterolaterally
during intertransverse process arthrodeses increases considerably the area moment of inertia, thus improving stability, particularly in axial rotation and lateral bending.
Historically, techniques that extend the fusion mass
posteriorly to include the laminae, facet joints, and spinous processes have increased the rigidity of posterior
fusions proportionally. However, this technique can lead
to iatrogenic spinal and foraminal stenosis from bony
overgrowth (4) and has been associated with a high rate
of pseudarthrosis (35). In McBride’s original description
of the posterior fusion, he stressed the importance of the
facet joint and used a morselized transfacet bone block
for lumbosacral arthrodesis (36). Cadaveric studies performed by Boden et al. analyzed the axial and torsional
stiffness of various techniques and questioned that
method (37). Those authors concluded that disruption of
the facet joint capsule required for placement of the transfacet bone blocks resulted in loss of spinal stability as
compared with posterior intertransverse process arthrodesis alone. One significant advantage of the posterolateral
technique over posterior fusions is that it can be performed
in the absence of posterior elements. Posterior fusions are
rarely performed today, and posterior and posterolateral
techniques most commonly refer to intertransverse process
arthrodeses (38).
POSTEROLATERAL INTERTRANSVERSE
LUMBAR AR THRODESIS
Historical Perspective
Spinal fusions were first reported in 1911 for the treatment of Pott disease by providing mechanical stability to
inhibit progressive deformity and the spread of the tuberculous infections (39). Also in 1911, Hibbs described his
experience with spinal fusion for tuberculosis and suggested that this technique could be used in the treatment
of scoliosis (40). He performed his f irst fusion for scoliosis in 1914, and reported on his f irst 59 cases in 1924
(40). Eventually this led to the use of spinal fusions for
the treatment of a variety of spinal deformities and diseases, including fractures, spondylolisthesis, scoliosis,
kyphosis, and intervertebral disc disease.
Since that time, the techniques and surgical approaches
for posterior-posterolateral lumbar fusions have changed
320 /SECTION V/SPECIFIC CLINICAL ENTITIES
significantly. There has been a signif icant increase in the
basic science behind lumbar fusions and the understanding
of the role of instrumentation. All fusion techniques
involve surgical preparation of the site of intended fusion
and an attempt to stimulate the formation of bone (41).
Traditionally, graft materials were either autologous or
allograft bone. How e ver , an increasing number of synthetic
and bioactive substances are currently in use or under
investigation. Three basic requirements are necessary for a
successful fusion: (a) graft material with adequate osteogenic, osteoinductive, and osteoconductive properties; (b)
adequate local vascularity to produce and support the bone
healing; and (c) an acceptable local environment for bone
formation (41). A fusion is considered fused when the
newly synthesized bone is mechanically contiguous with
the local host bone and can sufficiently bear physiologic
loads without failure of the fusion mass. A pseudarthrosis
is said to take place if this does not occur.
Technique
This operation usually is performed under general
anesthesia with the patient in the prone position. Chest
and iliac crest rolls are placed with the chest and
abdomen hanging free to allow pulmonary excursion,
minimize abdominal compression, and minimize distention of the epidural veins. The use of prophylactic antibiotics is recommended.
A midline incision is centered slightly superior to the
spinous processes of the involved levels, and the incision
is extended proximally and distally to include the levels
above and below to ensure adequate exposure. Electrocautery is used to divide the subcutaneous tissue down to
the fascia in line with the skin incision. The fascia is
incised in the midline and the paraspinous muscles are
stripped subperiosteally from the spine with electrocautery and a Cobb periosteal elevator. Radiographs
should be scrutinized for evidence of previous surgical or
congenital bony defects to minimize inadvertent entry
into the spinal canal. As the dissection progresses,
sponges are packed tightly within the wound to help control bleeding. The facet joints are preserved until the
appropriate levels have been identified. An intraoperative
radiograph should be obtained if any question exists.
Once the level is confirmed, the dissection should
progress laterally out to the transverse processes. This is
performed by incising the fascia directly lateral to the
facet joints and following the superior articular facet of
the inferior vertebra out inferolaterally onto the transverse process. Deep retractors are repositioned as needed
throughout the dissection. The muscle and soft tissue are
carefully cleared off the transverse process, making sure
not to fracture it. The dissection is carried superiorly and
inferiorly as needed to include the appropriate lev els. The
spinous processes at the involved levels are connected by
dissecting the muscle off the intertransverse ligament,
thus creating space for the graft.
If the fusion is to extend to the sacrum, the ala should be
prepared in a similar manner. The ala is exposed by dissecting lateral to the superior articular facet of the sacrum.
It is important to note that in this area there are dense ligaments that must be dissected from the sacrum in order to
obtain a clear exposure of the ala. At the end of the dissection, a continuous trough should exist laterally betw een the
transverse processes and the ala. Bilateral decortication of
the transverse processes, lateral portion of the pedicle, lateral portion of the articular facets, and ala is performed
with a burr or sharp curettes (Fig. 31-3).
A,B
FIG. 31-3. Preparation of the fusion bed. A: Oblique view of meticulous decortication of the outer face
of the facet joint, transverse process, pars, and alar cortical surfaces. B: Posterior view of decorticated
bilateral lateral graft bed. C: Oblique view of fusion bed packed with cancellous and corticocancellous
bone graft. (Zindrick MR, Selby D. Lumbar spine fusion: different types and indications. In: Wiesel SW,
Weinstein JN, Herkowitz H, et al., eds. The lumbar spine, 2nd ed. New York: Lippincott Williams &
Wilkins, 2004:600.)
C
CHAPTER 31/POSTERIOR AND POSTEROLATERAL PROCEDURES / 321
At this point a preliminary sponge count should be performed and the wound checked both visually and with
manual palpation to look for retained sponges. The
wound is then irrigated and the posterolateral trough is
packed ideally with autologous bone graft (see the following). The graft should not be harvested until the transverse processes, ala, and lateral structures have been
exposed and decorticated to minimize the period when
the bone is not in contact with tissue. At the end of the
case hemostasis is obtained, any devitalized tissue is
débrided, and a suction drain inserted into the wound if
necessary. The fascia and subcutaneous tissue are closed
in the standard manner.
Bone Graft Harvesting: Posterior Iliac Crest
Despite rapid advances in bone graft substitutes, the
use of autologous iliac crest bone remains the gold standard at this time. Iliac crest is still the most common
source of autologous bone harvest for posterolateral lumbar fusions because of its superior osteogenic, osteoconductive, and osteoinductive properties combined with
easy accessibility.
If amenable, the same midline incision used during the
exposure of the posterior spinal elements can be used to
obtain access to the posterior ilium. Maintaining a full
thickness flap, dissect just superficial to the fascia out laterally to the posterior superior iliac spine. If using the
same incision results in excessive dissection or inadequate exposure, a second separate incision can be used.
The second incision can be oriented either vertically or
obliquely, with the posterior superior iliac spine at approximately the inferior or medial margin of the incision.
Regardless of the approach, care should be taken, if possible, not to expose beyond 8 cm lateral to the posterior
superior iliac spine, because this may result in injury to
the superior cluneal nerves and cause numbness in the
skin overlying the gluteal region (42).
Dissect down to the posterior superior iliac spine and
expose the iliac crest. Incise the iliac crest periosteum
and subperiosteally dissect the muscle and periosteum off
the outer table of the posterior ilium. This is performed
with a combination of electrocautery and a Cobb elevator. After the muscles and periosteum are stripped, a Taylor or similar retractor is placed deeply into the wound,
taking care not to inadvertently enter into the greater sciatic notch distally.
Once the graft donor site is exposed, begin harvesting
corticocancellous strips using a half-inch osteotome.
Make sure to score the outer table only by creating several vertical strips approximately 7 mm in width. The distal extend of the vertical cuts are then connected horizontally with a curved osteotome to prevent distal
propagation of the strips during harvest. Start at the top
of the iliac crest, and use a curved osteotome wedged
between the inner and outer tables of the ilium to remove
the precut corticocancellous strips. Once they are removed, the intramedullary cavity is available for cancellous bone removal with gouges or curettes. When an
appropriate amount of bone graft has been obtained
hemostasis is achieved, the wound irrigated, and a drain
inserted if necessary. The incision is closed in the standard fashion.
Postoperative Management
Antibiotics are continued until the drains are removed,
usually on the first or second postoperative day. Typically
the diet is advanced as tolerated unless an ileus develops.
The patient is encouraged to be out of bed and is allowed
to ambulate the day of or day after surgery. An external
orthosis or brace is recommended for support and comfort, particularly if multiple level fusions were performed. Early mobilization has not been shown to lower
the rate of successful fusion and may actually improve
muscle tone, decrease edema, promote hematoma resolution, and improve patient function and psychologic outlook.
After discharge from the hospital, the initial visit is
often scheduled at 2 to 3 weeks postoperatively. The
patient is then reevaluated at 6-week intervals for the first
3 months, and then every 3 months for the first year. The
patient can usually return to light duty or part-time work
by 4 to 6 weeks, although heavy lifting and vigorous athletics should be avoided for 6 months. As the patient’s
recovery improves, a more vigorous exercise program is
gradually instituted with focus on proper back care and
mechanics.
INSTRUMENTED VERSUS
NONINSTRUMENTED POSTEROLATERAL
FUSIONS
Significant interest and debate exists over the use of
instrumentation in posterolateral lumbar fusions. Various
constructs have been investigated and include wires,
hooks, and pedicle-screw based segmental fixation techniques. Currently, segmental instrumentation with pedicle-screw fixation is the construct of choice because of
the ability to control all three columns of the spine from
a posterior approach, the ability to limit the fusion to
involved motion segments, the ability to obtain spinal
fixation in the absence of posterior elements, and the
capability to avoid placement of instrumentation within
the spinal canal (27,43,44).
From a theoretical standpoint, spinal instrumentation
provides immediate stability to the spinal segments being
fused and therefore increases fusion rates. Multiple studies support this hypothesis (4,44–47). For a single level
posterolateral fusion without instrumentation pseudoarthrosis rates are reported to be between 10% and 15%.
The addition of pedicle instrumentation may lower this to
322 /SECTION V/SPECIFIC CLINICAL ENTITIES
5%. In a prospective, randomized trial of 49 patients,
Zdeblick demonstrated a statistically significant difference in fusion rates between instrumented and noninstrumented posterior fusions for degenerative disc disease.
The fusion rate for the group with pedicle instrumentation was 93% compared to 45% without instrumentation
(47).
The use of instrumentation has been shown to reduce
the pseudoarthrosis rate in patients undergoing multiple
level fusions. In a prospective study by Grubb and Lipscomb (45) that looked at one- and two-level fusions, the
authors found higher fusion rates in patients having
instrumentation. Similar results from a prospective, multicenter trial were reported by Wood and colleagues (44),
who examined the use of instrumentation in one- to fourlevel fusions, with the majority of them being two levels
or greater. Compared to historic controls, the authors
found that patients who underwent fusion without instrumentation were over 24 times more likely to develop a
pseudoarthrosis when compared to patients with instrumented fusions.
Other reported advantages of instrumentation include
decreased rehabilitation time, reduced need for postoperative bracing (47), and possible reduced requirement for
postoperative use of pain medication (43,47,48). However, these findings should not mandate the routine use of
instrumentation during lumbar arthrodesis. Compared to
fusion in situ, the use of instrumentation has been associ-
ated with higher morbidity and mortality (Table 31-2). A
cohort study sponsored by the North American Spine
Society for the use of pedicle instrumentation reported an
overall instrument related complication rate of 5% (48).
The risks and benefits of instr umentation should be considered in each individual case, particularly in the elderly
patient, where the advantages must be balanced carefully
with the potential risks associated from the use of instrumentation. Furthermore, the use of instrumentation
should be performed only by experienced surgeons, who
are knowledgeable and comfortable with the specific
techniques. The occasional use of instrumentation by the
inexperienced surgeon is associated with an unacceptably
high complication rate and should be avoided.
We believe that in cases where an increased risk of
pseudoarthrosis is present, the use of adjuvant instrumen-
TABLE 31-2. Complications of spinal instrumentation
Complication Reported rates
Neurologic injury 1%–5%
Infections 3%–6%
Instrumentation failure 6%–10%
Reoperation 20%
Source: Adapted from Yuan H, Garfin S, Dickman C, et al.
A historical cohort study of pedicle screw fixation in thoracic,
lumbar, and sacral spinal fusions. Spine, 1994;19(suppl
20):S2279–S2296, with permission.
tation is beneficial for posterolateral intertransverse lumbar fusions. In particular, this includes patients with risk
factors such as diabetes and smoking, in multilevel
fusions and in revision cases for failed back or surgical
treatment of established pseudoarthrosis.
CONCLUSION
Significant debate exists over the role of surgery in the
management of degenerative disc disease. The lack of
randomized, prospective studies makes the comparison
and evaluation of outcomes difficult to assess. Furthermore, studies on the role of posterolateral arthrodesis for
the treatment of disc degeneration often includes patients
with multiple pathologies, including herniated discs,
spondylolisthesis, and spinal stenosis, some of whom
may have undergone prior decompressive procedures or
arthrodesis. Despite these shortcomings, posterolateral
arthrodesis in properly selected patients is a viable option
for the treatment of axial back pain from degenerative disc
disease. Currently autologous iliac crest remains the gold
standard for bone graft material during posterolateral lumbar fusions. The adjuv ant judicious use of instrumentation
improves fusion rates by providing immediate stability;
however, its routine use should be avoided and decisions
about its use should be made on an individual basis.
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