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in the midauxiliary line proceeding medially and curving
inferiorly to the midline anteriorly. The surface and radiologic anatomy must be checked to be sure that the intercristal line passes through the L4-5 disc and appropriate
adjustments in the incision should be made if necessary.
For exposure of the L3-4 level the medial aspect of the
incision should be in the midline at or below the umbilicus. For access to the L4-5 disc, the medial aspects of the
incision should be in the mid- to upper third of the way
between the umbilicus and pubic symphysis. Access to
the L5-S1 disc should be midway between the umbilicus
and pubic symphysis.
Surgical Anatomy
Knowledge of the muscles of the lateral abdominal
wall is the key to this approach. The fascia and f ibers of
the external oblique usually run along the line of the incision, and the fibers of the inter nal oblique run at nearly
90 degrees to the external oblique fibers. The transversus
abdominus muscle runs nearly horizontally above the
transversalis fascia. After blunt dissection between the
fibers of the exter nal and internal obliques, the transversalis fascia is defined and reflected laterally to gain
access to the retroperitoneal space. The peritoneum is
carefully swept off the transversalis fascia and the
retroperitoneal fat is encountered in the retroperitoneal
space. The dissection is bluntly carried down to the psoas
muscle. The mobilization, dissection, and manipulation
of the psoas laterally are important to obtain access to the
lateral aspect of the lower lumbar spine. Care must be
taken to av oid injury to the sympathetic trunk lying along
its medial aspect, the nerves of the lumbar plexus in its
substance, and the genitofemoral nerve along the surface
of the psoas. The ureter is identified by its peristaltic
movement and usually moves with the posterior peritoneum as the peritoneum and its contents are reflected
anteriorly.
The relationship of the major blood vessels, iliolumbar
vein, and hypogastric plexus are the same as with the
direct anterior approach.
POSTERIOR APPRO A CH
This discussion covers the posterior approach to the
lumbar spine through the following incisions and dissections: direct midline, paramedian muscle splitting, and
far lateral or oblique.
The posterior approach provides access to the posterior
column, including the pedicle, transverse process, facet
joint lamina, and spinous process; the vertebral canal; the
middle column, including the disc, posterior longitudinal
ligament, and posterior vertebral body; and limited
access to the anterior column.
The posterior approach is commonly used for the following surgical procedures: decompression of the verte-
bral canal, nerve root canal and foramen; posterior fusion
and instrumentation for management of deformity and
instability; excision of primary and secondary spinal
tumors; and débridement of spinal infections.
Surgical and Radiologic Anatomy
The surface anatomic landmarks include the midline
lumbar spinous processes, intercristal line, and posterior
superior and inferior iliac spines. Usually the sacral dimple area is at the level of the lumbosacral disc.
The radiologic anatomy must be checked on the AP
and lateral X-rays, taking care to ensure that there are no
lumbosacral anomalies such as lumbarization of the
sacrum, or sacralization of L5, spina bifida occult, or
prior laminectomy defect. The intercristal line must be
checked on both the AP and lateral views to see its exact
location with respect to the 4-5 intervertebral disc. Care
must be taken to assure the appropriate level and confirm
this with cross-table lateral X-rays if necessary. The key
to orientation within the spinal canal is the pedicle:
medial to the pedicle is the nerve root and superior to it
is the intervertebral disc.
Patient Position
The patient is placed prone on a suitably padded spinal
frame that provides the required position and posture of
the lumbar spine. This may be in lumbar flexion for a
simple laminotomy and disc prolapse or in extension and
lordosis for decompression of spinal stenosis. The lordotic position is mandatory if instrumentation and fusion
is required to assure that lumbar lordosis is achieved. This
minimizes the risk of developing a “flat back” position.
The spinal frame must allow the abdomen to hang free
to avoid compression of the abdominal contents, which
can cause excessive epidural bleeding by shunting of
blood from the vena ca va through Batson’s plexus into the
epidural veins. Epidural bleeding also can be minimized
by having the anesthesiologists avoid overinflation of the
lungs and overdistention of the diaphragm, which can
increase abdominal pressure and shunt blood from the
vena cava into the epidural veins.
The patient also can be placed in the kneeling position,
which also avoids abdominal compression. Care must be
taken to avoid pressure on the knees and other bony
prominences.
Incisions
Midline
The midline incision is centered over the appropriate
level and is the most commonly used incision in gaining
access to the posterior lumbar spine. It provides ready
access to unilateral or bilateral pathologies. The length of
CHAPTER 20/SURGICAL APPROACHES TO THE LUMBAR SPINE / 223
224 /SECTION IV/SURGERY
the incision can be minimized by taking a cross-table Xray beforehand to accurately identify the level or levels in
question.
The incision is taken directly down through the superficial and deep subcutaneous f ascia to the middle of the
posterior tip of the spinous process and the lumbo dorsal
fascia. Stripping and dissection of the subcutaneous tissue from the lumbar dorsal fascia avoids producing a
dead space that can fill with serous fluid and blood.
Paramedian Incision
The paramedian incision is used for the paraspinal
approach popularized by Wiltse that involves splitting of
the sacrospinous muscle in the sagittal plane, two or three
fingerbreadths from the midline (15,16). Wiltse recommended bilateral skin incisions, whereas others have
advocated a midline skin incision with bilateral incision
of the thoracolumbar fascia and splitting of the
sacrospinalis muscle (Fig. 20-7). This provides access to
the facet joint and transverse processes, and for lateral
pathology such as a far lateral disc prolapse.
A midline incision for the bilateral paramedian
approach has the advantage of a single skin incision but
requires a longer cut than a bilateral skin incision. A
bilateral incision also provides adequate access for pedicle screw and instrumentation insertion.
Far Lateral Incision
This incision is placed over the lateral edge of the erector spinae muscle, usually between the junction of the
medial spinalis muscle and the intermediate longissimus
muscle portion of the erector spinae muscle. This
approach provides access to the transverse process and is
the least used incision or approach to the posterior lumbar spine.
Surgical Anatomy
The lumbar dorsal fascia is detached from the tips of the
spinous process and is follow ed by subperiosteal dissection
of the paraspinal muscles from the spinous process, lamina, and posterior facet joint. If necessary, this can be carried out all the way to the transverse processes.
Posterior Lumbar Muscles
The lumbar musculature can be grouped into the following types:
• short intersegmental muscles, which include inter-
spinales and intertransversarii mediales;
• short polysegmental muscles, which include multifidus
and the lumbar portions of longissimus and iliocostalis
(the lumbar erector spinae ); and
A
B
FIG. 20-7. Midline incision for paraspinal approach.
(Modified from Wiltse LL, Bateman GI, Hutchinson RH,
et al. The paraspinal sacra spinalis splitting approach to
the lumbar spine. J Bone Joint Surg 1968;50A:919;
Wiltse LL. The paraspinal sacra spinalis splitting
C
approach to the lumbar spine. Clin Orthop 1973;91:48,
with permission.)
CHAPTER 20/SURGICAL APPROACHES TO THE LUMBAR SPINE / 225
•long polysegmental muscles, which include thoracic
portions of longissimus and iliocostalis(1).
Short Intersegmental
Interspinalis. There are four pairs of lumbar inter-
spinalis, each pair lying lateral to the interspinous ligament and connecting the adjacent spinous processes.
Intertransversarii Medialis. These arise from the
accessory and mamillary processes and from the
mamillo-acessory ligament between the processes, and
are innervated at each level by the lumbar dorsal rami.
Short Polysegmental
Multifidus. Multifidus is invariably encountered in
posterior midline approaches to the lumbar spine, as it is
the most medial and the largest of the posterior lumbar
musculature.
There is a constant pattern of fascicles, either short
thin fascicles arising from the caudal portion of the dorsal aspect of each lumbar and inserted into the mamillary
process of the vertebra two levels caudal, or larger longer
fascicles arising from the spinous process radiating out in
five overlapping groups that for m the bulk of the multifidus. The fascicles arise either from the base of the spinous process or from the common tendon at the caudal tip
of the spinous process and are inserted three levels caudal into the mamillary process—the posterior superior
iliac spine, the posterior iliac crest, or the sacrum.
Lumbar Erector Spinae. The lumbar erector spinae is
made up of two named muscles—the longissimus thoracis and iliocostalis lumborum—that are separated by
the lumbar intermuscular aponeurosis. Each has two
named portions: lumbar fascicles arising from the lumbar
vertebrae and thoracic fascicles arising from the thoracic
vertebrae.
The longissimus thoracis pars lumborum has f ive fascicles, each arising from the mamillary process and the
adjacent transverse process of each vertebra and inserted
into the medial aspect of the posterior superior iliac
spine.
The iliocostalis lumborum pars lumborum has four
overlapping fascicles arising from the tip of the transverse process of L1, L2, L3, and L4 vertebrae as well as
the adjacent middle layer of the thoracolumbar fascia,
and insert into the iliac crest lateral to the posterior superior iliac crest.
The thoracic portions of these muscles make up the
long polysegmental muscles, arising from the ribs and
transverse processes, and attach to the sacrum and iliac
crest, as well as the tendinous portions forming the erector spinae aponeurosis that are attached to the ilium, the
sacrum, and the sacral and lumbar spinous processes.
The thoracolumbar fascia is made up of three layers—
anterior, middle, and posterior—that separate the poste-
rior lumbar and trunk muscles into separate compartments and has significant biomechanical functions.
The posterior layer is the most significant surgically
and consists of superficial and deep laminae for ming a
retinaculum over the lumbar muscles. The posterior layer
is attached medially to the midline and laterally to the lateral raphe, arising vertically from the iliac crest.
Other anatomical works list these lumbar muscles into
layers:
Superficial: the thoracic por tions of longissimus thoracis
and iliocostalis lumborum.
Intermediate: the multif idus and the lumbar portions of
longissimus thoracis and iliocostalis lumborum.
Deep: the interspinales and intertransversarii.
Ligamentum Flavum
Knowledge of the ligamentum flavum, and understanding its attachment at each level, aids in its safe dissection and removal. The ligamentum flavum runs in a
vertical direction attaching to the cephalic tip of the distal lamina and halfway up the ventral surface of the proximal lamina (Fig. 20-8) (18). The ligamentum flavum
also attaches laterally to the undersurface of the facet
joint, and its fibers blend with those of the anterior capsule of the facet joint.
The facet joints are innervated by the posterior rami of
the spinal nerves, which gain access to the posterior compartment at the lateral edge of the pars interarticularis and
are accompanied by the intertransverse artery , which supplies the muscles of the deep layer. These vessels frequently are breached during posterior exposures and
bleed during routine dissection of the pars, particularly
during dissection out to the lateral tip of the transverse
process at each level.
Lamina
Pedicle
Nerve root
Ligamentum
flavum
FIG. 20-8. Ligamentum flavum, nerve root, and pedicle.
(Modified from Watkins RG. Surgical approaches to the
spine. In: The lumbar spine. Philadelphia: WB Saunders,
1996:1263–1271, with permission.)
226 /SECTION IV/SURGERY
The Pedicle
The superficial landmarks, entry point, length,
breadth, and direction of each lumbar pedicle are important. The pedicle is the key landmark to safely f ind the
lateral edge of the nerve root and the intervertebral disc
immediately above it. Pedicle fixation requires thorough
knowledge of the pedicle entry point, which usually is
located at the junction of the lateral edge of the facet and
the midpoint of the transverse process.
Usually the pars of L5 is in line with the lateral portion
of the L5 pedicle. Proceeding proximally, the lateral portion of the pars moves medially, so in the upper lumbar
spine the medial edge of the pars is in line with the
medial border of the pedicle.
Erector Spinae Muscle
The paravertebral approach of Wiltse exposes the spine
in the interval between the multifidus and lateral muscles
(longissimus and iliocostalis) (Fig. 20-9). The posterior
and lateral aspect of the facet joint is palpated and the lateral muscles are retracted and dissected off the transverse
process. The transv erse process is identified and followed
medially to pedicle, which can be palpated and used to
identify the exiting nerve root. This approach provides
access to a far lateral disc.
Indications and Advantages
The direct posterior approach to the lumbar spine provides safe access to posterior pathology and limited
access to anterior column pathology through the pedicle
or by gentle cauda equina retraction.
Contraindications
Potential contraindications to the posterior approach
include anterior column pathology and significant skin or
post-subcutaneous scarring and f ibrosis related to previous radiation therapy or significant burns.
Disadvantages
One disadvantage to the posterior approach is the
stripping of the paraspinal musculature, which can be
associated with impairment of its nerve and blood supply and the formation of thick scar tissue, which can
contribute to development of the postlaminectomy syndrome. Long and wide muscle stripping can be associated with prolonged recovery and postoperative pain
and disability that can persist despite extensive postoperative rehabilitation.
Postlaminectom y scarring can occur as the muscle grows
back into the laminectomy site and into the exposed dura
and nerve roots. This also can produce difficulty in obtaining safe exposure for a redo posterior decompression. The
scarring is often associated with dural tear and nerve root
damage during repeat decompression.
There have been reports of injury to the aorta, vena
cava, and retroperitoneal viscera with inadvertent placement of the instruments through the anterior longitudinal
ligament. Therefore, it is imperati ve to know the length of
the instruments being used and the depth to which it can
be safely inserted into the disc space. It is also recommended that the pituitary rongeur be placed through the
annulotomy with the jaws closed and then opened to
avoid inadvertent grabbing of neural structures.
Intraoperative ophthalmic complications are uncommon but catastrophic. These include postoperative blindness and visual field defects. Contributing etiologies
include an underlying vascular diathesis, diabetes, and
direct pressure to the globe.
Prolonged positioning in the prone position also can
result in cardiopulmonary shunting, which can be problematic in the elderly population undergoing multilevel
decompression and fusion.
Sacrospinalis
muscle
Psoas
major muscle
Body of 5th
lumbar vertebra
FIG. 20-9. Paramedian muscle splitting approach.
(Modified from Wiltse LL, Bateman GI, Hutchinson RH,
et al. The paraspinal sacra spinalis splitting approach to
the lumbar spine. J Bone Joint Surg 1968;50A:919;
Wiltse LL. The paraspinal sacra spinalis splitting
approach to the lumbar spine. Clin Orthop 1973;91:48,
with permission.)
REFERENCES
1. Bogduk NE, Twomey LT. Clinical anatomy of the lumbar spine. Edinburgh: Churchill Livingstone, 1991.
2. Crock HV. A short practice of spinal surgery. New York: Springer-Verlag Wien, 1993.
3. Hodgson AR, Yau ACMC. Anterior approaches to the spinal column.
In: Apley AG, ed. Recent advances in orthopedics. Baltimore: W illiams
& Wilkins, 1964:289–323.
4. Hollingshead WH. Anatomy for surgeons, 3rd ed. Philadelphia: Harper
& Row, 1982.
5. Selby DK, Henderson RJ, et al. Anterior lumbar fusion. In: White AH,
Rothman R, eds. Lumbar spine surgery. St. Louis: CV Mosby, 1987:383.
6. Dwyer AP. Clinically relevant anatomy. In: Wiesel, Weinstein, Herkowitz, et al., eds. The lumbar spine. 2nd ed. Philadelphia: WB Saunders, 1996:57–73.
7. Hoppenfeld S, DeBoer P. Surgical exposure in orthopedics: the
anatomical approach. Philadelphia: JB Lippincott, 1984.
8. Henderson RJ. Anterior approach for lumbar fusions and associated
morbidity. In: Spine care. St. Louis: Mosby, 1995:1112–1134.
9. Fountain SS. A single stage combined surgical approach for vertebral
resection. J Bone Joint Surg 1979;61A:1011.
10. Hanley ED, Delamater RB, McCulloch JA, et al. Surgical indications
and techniques. In: Wiesel, Weinstein, Herkowitz, et al., eds. The lumbar spine. Philadelphia: WB Saunders, 1996:492–524.
11. Hodgson AR, Stock FE. Anterior spine fusion, a preliminary communication on the radical treatment of Pott’s disease and Pott’s paraplegia.
Br J Surg 1956;44–266.
12. Hodgson AR, Stock FE. Anterior spinal fusion for the treatment of
tuberculosis of the spine. J Bone Joint Surg 1960;42A:295.
13. Fraser RD, Gogan NJ. A modif ied muscle splitting approach to the
lumbar sacral spine. Spine 1992;17:943.
14. Fraser RD. A wide muscle splitting approach to the lumbar sacral
spine. J Bone Joint Surg 1982;64B:44–46.
15. Watkins RG. Surgical approaches to the spine. In: Wiesel, Weinstein,
Herkowitz, et al., eds. The lumbar spine. Philadelphia: WB Saunders,
1996:1263–1271.
16. Wiltse LL, Bateman GI, Hutchinson RH, et al. The paraspinal sacra
spinalis splitting approach to the lumbar spine. J Bone Joint Surg
1968;50A:919.
17. Nakano N, Nakano T. Anterior extraperitoneal lumbar discectomy without
fusion. In: Wiesel, Weinstein, Herkowitz, et al., eds. The lumbar spine.
Philadelphia: WB Saunders, 1990:987–989.
18. Watkins RG. Surgical approaches to the spine. New York: SpringerVerlag, 1983.
19. Nakano N, Nakano T. Anterior extraperitoneal lumbar discectomy
without fusion. In: Wiesel, Weinstein, Herkowitz, et al., eds. The lumbar spine. Philadelphia: WB Saunders, 1990:1273–1274.
20. Wiltse LL. The paraspinal sacra spinalis splitting approach to the lumbar spine. Clin Orthop 1973;91:48.
CHAPTER 20/SURGICAL APPROACHES TO THE LUMBAR SPINE / 227
CHAPTER 21
Posterior and Anterior Surgical Approaches to the Lumbosacral Junction
Peter A. Robertson
SEGMENTATION
Normal segmentation at the lumbosacral junction is
frequently assumed, yet abnormal segmentation has been
described in 33% of a cohort of patients (1). The presence
of a transitional vertebra at the lumbosacral junction confuses nomenclature. Failure to recognize abnormal segmentation may cause incorrect interpretation of pathology, incorrect recognition of anatomic features at surgery ,
and increased risk of operating at an incorrect level.
Segmentation variations include extra or missing vertebrae within the spinal column (2); supernumerary or
absent ribs; transitional lumbosacral segmentation with
L5 transverse process articulation with the sacral ala; and
incomplete coalescence of S1 and S2 with a well-formed
S1-2 intervertebral disc. A wide variety of combinations
may make it difficult to define levels with certainty.
Options include classification of the whole spinal segmentation from proximal to distal, or counting from the
sacrum up, to define levels. The former gives accurate
labeling of the whole spine yet requires cumbersome total
spinal X-rays and unwarranted exposure to radiation. The
latter is more practical when dealing with the lumbosacral spine.
A practical approach to the nomenclature of atypical
lumbosacral segmentation is to identify the transitional
vertebra and describe it based on its most salient characteristics. A transitional vertebra that has all the appearances of an L5 vertebra, apart from a unilateral articulation between a transverse process and the sacral ala, is
described as a sacralized L5. Conversely, if the upper
sacral segment has all the hallmarks of an S1 segment,
yet there is a significant rudimentary disc between S1 and
S2, it is regarded as a lumbarized S1 (Fig. 21-1).Clear
identification of a transitional lumbosacral segment
requires lateral and special antero-posterior (AP) radiographs. The lateral allows definition of the vertebral
body and sacral shape and the degree of formation of the
abnormal disc. The AP views must include a view so that
the X-ray beam is parallel to the lumbosacral disc. The
beam should be centered on the disc. The lordosis thus
requires the beam to be angled cephalad by approximately 20°, although this angulation varies dependent on
the lordosis and should be judged from the lateral view.
This is to accurately define the anatomic relationship
between the transverse processes of L5 and the ala of the
sacrum.
Once the transitional vertebra characteristics are defined and clarif ied, the adjacent segments can be numbered. When the number of lumbar vertebrae differs from
normal (as def ined by the absence of articulating ribs),
some refer to the lumbosacral segment as the L4-S1 level
or the L6-S1 level. Alternatively, the lumbar vertebrae
may be numbered above an L5 segment to maintain
familiarity with traditional segment numbering.
Because of the potential for confusion, it is essential
that the treating doctors recognize any segmentation
abnormalities and label the segments consistently.
Consistent vertebral numbering and close correlation
between preoperative and intraoperative lateral radiographs offer the best chance of avoiding incorrect levels.
POSTERIOR SURGICAL APPRO A CHES T O THE
LUMBOSACRAL JUNCTION
The midline posterior approach to the lumbosacral junction, through a longitudinal incision, is an extensile
approach that allows access to the posterior elements, the
canal and the foramina, the posterolateral gutters, and the
intervertebral disc space. It is the most frequently used
approach and obviously can be extended to link with
proximal dissection.
Identification of the level of incision is by relationship
to the iliac crests (approximately L4 body level), palpa-
228
CHAPTER 21/SURGICAL APPROACHES TO THE LUMBOSACRAL JUNCTION / 229
A B
FIG. 21-1. A: A lateral X-ray of a transitional lumbosacral junction. The rudimentary disc space is
between the upper sacral segment and the remainder of the sacrum. B: The anteroposterior radiograph
angled parallel with the disc demonstrates the transitional vertebra with lateral articulation between the
vertebra transverse processes and the sacral ala.
tion of the lumbosacral spinous process gaps, or use of
skin markers and radiology.
Longitudinal division of the skin and subcutaneous tissue displays the deep fascia. This is a double-layered sheet
that attaches to the spinous processes medially, and encloses the multifidus, the most medial of the paraspinal
muscles. Although subperiosteal dissection is possible in
children and adolescents, adults require division of the
deep fascial attachment to the spinous process. The multifidus muscle attachment to the spinous processes and laminae of L5 and S1 is easily sw ept aside with a Cobb or Harrington periosteal elevator. The tendinous attachment of
the multifidus is to the midline structures at the level of the
supraspinous and interspinous ligaments. This attachment
requires sharp division. Preoperative identification of any
spina bifida is mandator y to allow cautious dissection of
the upper sacrum—preventing inadvertent canal entry.
Self-retaining retractors hold the multifidus muscle laterally and allow midline access to the canal by midline
laminectomy or unilateral laminotomy. The parasagittal
muscles can be swept further laterally, to display the glistening white lumbosacral facet joint capsule. The Taylor
pointed retractor can then be placed lateral to the facet joint
and levered laterall y to retract the paraspinal muscles. This
retraction technique is ideal for unilateral posterior lumbosacral approaches. Dissection proximal to the lumbosacral facet joint displays the pars interarticularis of L5.
Definition of the lateral aspect of the pars is necessar y to
allow sufficient pars preservation when performing L5
laminectomy (Fig. 21-2).
More lateral development of this approach allows
exposure to the posterolateral gutters, where bone grafting is performed in a posterolateral fusion. The multi-
fidus muscle has a fur ther attachment to the posterolateral facet capsule and superior articular facet, which,
when divided in a longitudinal direction, reveals loose
fatty tissue that can be swept laterally to reveal the superior ala of the sacrum. Display of the transverse process
of L5 requires detachment of multifidus from the posterolateral facet capsule of L4-5. Again, loose fatty tissue
covers the transverse process of L5 and is easily swept
laterally.
Troublesome bleeding may occur with exposure of the
posterolateral gutters. The segmental vessels that accompany the nerve roots as they enter the foramen also give
branches that course lateral to the pars interarticularis and
supply the paraspinal muscle complex. These posterior
vessels give off small, but occasionally troublesome, vascular branches that pass distally, lateral to the facet joint
capsule and superior articular facet of the joint below (3).
They frequently bleed as the transverse process or ala of
the sacrum is displayed. Direct visualization can be difficult because of the paraspinal muscle mass that prevents
retraction, so that it is difficult to see lateral to the facet
joint capsule and superior articular facet. Useful tricks to
prevent troublesome bleeding lateral to the facet joints
include preemptive use of bipolar coagulation forceps in
the loose fatty tissue lateral to the facet joint capsule
(before sweeping the fatty tissue aside to display the
transverse process or sacral ala), or bending the tip of the
unipolar diathermy and sweeping that diathermy tip up
the lateral aspect to the superior articular facet superior to
the sacral ala or the lumbar transverse process. Troublesome bleeding is controllable with lateral gutter packing.
More constant vascular ooze from the lateral gutter occurs after the transverse process and the lateral aspect of
230 /SECTION IV/SURGERY
Ligamentum Flavum
Facet Joint Capsule
Lamina
S1 Nerve Root
Retracted Medially
A B
L5 Nerve Root
L5S
1
Disc Space
S1 Nerve Root
C D
Retracted Medially
FIG. 21-2. Diagrammatic representation of the posterior approach to the lumbosacral junction. A: Posterior approach to the lumbosacral junction demonstrating laminae, ligamentum flavum, and facet joint
capsules. B: Unilateral flavectomy, laminotomy, and approach for discectomy after retraction of the S1
nerve root. C: Extensive facetectomy to demonstrate the transforaminal “window” for access to the disc
space. D: Posterolateral fusion with pedicle screws and rods after wide destabilizing facetectomy at the
lumbosacral junction.
L5S1 Disc
the superior articular facet are decorticated, before bone
grafting and fusion procedures. For this reason decortication should be deferred until as late as possible in the procedure. Minor degrees of initial bleeding can occur with
dissection around the S1 posterior foramen. This is best
controlled with bipolar diathermy.
Attempts to coagulate the posterior branch of the segmental vessels, lateral to the pars interarticularis, threaten
the posterior primary rami that accompany these vessels.
At L4 and L5 these nerves do not have cutaneous sensory
function (4), but the damage has implications for muscle
function.
In unilateral posterior lumbosacral approaches effective retraction can be obtained with a Taylor pointed
retractor, placed lateral to the facet joint, and retained by
a weight and chain.
Bilateral approaches obtain best visualization with T ravers (straight) or Adson (curved) self-retainers. Difficulty
with retraction is alleviated by pro ximal and distal release
of the erector spinae from the midline structures. Careful
use of self-retaining retractors and hand-held retractors
gives adequate exposure to all posterior structures. Powerful crank type retractors can give wide exposure to the
posterior structures, but can damage the paraspinal muscles, particularly if the retractor blades are forced hard up
against the posterior iliac crest laterally. Muscle atrophy,
weakness, and electromyographic changes occur following surgery, and these changes should be minimized
(5–7). The crank retractor bulk can also limit access to
the correct oblique pathway for pedicle screw placement
at L5 and S1 (Fig. 21-3).
As an alternative to bilateral multifidus dissection off
the spinous process and laminae for decompressive procedures, a unilateral multifidus strip combined with a
spinous process osteotomy (at the base) allows midline
access for decompression. This approach may limit mus-
CHAPTER 21/SURGICAL APPROACHES TO THE LUMBOSACRAL JUNCTION / 231
FIG. 21-3. Magnetic resonance imaging scan (axial) of the
lumbosacral junction of an achondroplastic dwarf presenting
for decompression of spinal stenosis. Note that the posterior
iliac crests are very medial, causing herniation of the
paraspinal muscle mass posteriorly. A posterior approach to
this level is technically difficult because of muscle bulk and
difficulty with retraction owing to the iliac crests. A limited
amount of muscle excision may be required to access the
spinal canal.
cle damage, preserve midline structures, and improve
cosmesis, yet risks problems from spinous process
nonunion, and cannot be applied if bilateral wider posterolateral exposure is needed (8).
and to allow access to the L5-S1 disc space to provide a
working channel for interbody dissection and surgery.
More proximal and lateral dissection is required if the L5
root needs decompression under the pars interarticularis,
such as when there is a pars defect filled with hypertrophic fibrocar tilage in association with a spondylolysis
or spondylolisthesis (Fig. 21-2).
Once inside the canal it is essential to appreciate the
position of the roots and dura at all times. A small layer
of fat may cover the dura dorsally. The dural sac and traversing S1 root are medial to any working zone for discectomy or interbody work. The exiting L5 root has
passed superiorly and laterally to the lumbosacral disc. If
pathology about the exiting L5 root requires treatment at
the lumbosacral junction, it is both superior and lateral to
the flavectomy site for entry to the lumbosacral canal.
Epidural veins may be bountiful to the lateral and anterior regions of the canal, adjacent to the medial wall of
the pedicle, and also to the posterior intervertebral body
of L5 and S1. The vertebral body venous plexus communicates with the epidural veins anterior to the dural sac.
The most effective way to prevent troublesome venous
bleeding is to carefully position the patient before
surgery, leaving the abdomen free from pressure, thereby
avoiding engorgement of the epidural plexus.
If epidural venous bleeding is troublesome during
canal dissection, careful packing with Gelfoam soaked in
thrombin or with neurosurgical patties is useful. Larger
veins may be cauterized with bipolar diathermy after
careful retraction of neural structures. Occasional venous
ooze from a cut bone at the edge of a laminectomy field
may require the use of bone wax.
SPINAL CANAL DISSECTION AT THE
LUMBOSACRAL JUNCTION
Entry to the spinal canal at the lumbosacral junction
requires removal of the ligamentum flavum on one or
both sides of the midline. This can be achieved with
either cautious sharp dissection in the midline or detachment of the ligamentum flavum at its periphery (easiest
distally) using a small curved sharp curette. Once the
epidural space is opened, it is explored and expanded
with a dissector. A Kerrison up-cutting rongeur can be
used to remove the ligamentum flavum and display the
epidural space from the midline out to the facet joint.
The extent of dissection within the canal is determined
by the pathology. Flavectomy alone gives adequate access
to most posterolateral disc herniations. Partial laminectomy of either L5 proximally or S1 distally may be
required for migrated disc fragments. Medial facetectomy is required where facet hypertrophy causes lateral
recess stenosis at the entrance to the nerve root canal.
Facetectomy can be performed with either rongeurs or
osteotomes. Occasionally, more radical or complete facetectomy is required to decompress the L5-S1 foramen
PARASA GITTAL APPRO A CH T O THE
LUMBOSACRAL JUNCTION
Wiltse described the parasagittal approach to the lumbar spine (9), primarily for intertransverse fusion. It is
particularly advantageous if surgery involves only posterolateral fusion without canal exploration. At the lumbosacral junction, in the presence of a high-grade
spondylolisthesis, it can be very difficult to find and display the L5 transverse process in its forw ard slipped position. The Wiltse approach allows direct dissection on to
the posterolateral structures with the minimum of muscle
dissection (Fig. 21-4). Pedicle screws can be placed without excessive muscle retraction, a particularly helpful
step at L5 where the pedicle is obliquely directed (10).
This approach is also useful to treat the relativel y uncommon far lateral disc herniation at L5-S1 and for excision
of anomalous transverse processes that articulate with the
sacrum and cause pain (Fig. 21-5) (11,12).
The approach is longitudinal and parasagittal between
the multifidus muscle g roup medially and sacrospinalis
laterally. Skin incision options include a midline longitudinal skin incision approach with bilateral parasagittal
232 /SECTION IV/SURGERY
L5 Transverse
Process
Ala of
Sacrum
Superior Sacral Facet
A B
FIG. 21-4. Diagrammatic approach of the Wiltse parasagittal approach to the spine. A: The Wiltse
parasagittal approach demonstrating the lateral aspects of the superior articular facets and the L5 transverse process and ala of the sacrum. B: Removal of the intertransverse membrane demonstrates the
nerve root and the site of a far lateral (extraforaminal) disc prolapse.
fascial incisions two fingers breadth lateral to the midline; bilateral skin parasagittal incisions over the intermuscular interval; and a transverse skin incision at the
lumbosacral junction with vertical fascial incisions over
the parasagittal muscle interval. Bone graft may be harvested through any of the skin incisions by subcutaneous
dissection. The latter incision may be cosmetic, avoiding
a longitudinal lower lumbar incision.
The intermuscular interval is 2 to 3 centimeters lateral
to the midline, and allows a direct approach to the lateral
aspect of the superior articular facets of L5 and S1 and
the transverse process of L5 and the ala of the sacrum.
The lateral border of the L5 pars interarticularis is tra-
L5 Nerve Root
Extraforaminal
Disc Herniation
versed by the posterior primary ramus of L5 and the posterior branch of the segmental vessels. The latter frequently require coagulation.
The parasagittal approach gives excellent visualization
of the posterolateral fusion bed and the lateral superior
articular facet and the transverse process. Far lateral disc
herniations may be resected after the intertransverse
membrane is removed from its attachment to the adjacent
transverse processes. The L5 nerve root traverses
obliquely over the posterolateral aspect of the disc before
forming a lumbosacral trunk.
This parasagittal approach can be used to access the
spinal canal with multifidus retraction, hemilaminectomy
on the surgical side, and then dissection beneath the lamina on the contralateral side so as to perform medial facetectomy and root decompression on that contralateral side
(13).
A posterolateral approach lateral to iliocostalis has
been described as an alternative approach to the far lateral disc prolapse (14). This approach develops a plane
between iliocostalis and the flank muscles, and then follows the most lateral branch of the posterior primary rami
down to the nerve root in the foramen. It is an approach
perhaps more useful in the proximal lumbar spine, above
the posterior iliac crest, yet has been used at L5-S1.
FIG. 21-5. Axial magnetic resonance imaging scan of a right
far lateral disc prolapse (arrow) at the lumbosacral junction
causing L5 root symptoms. This herniation can be approached surgically via a Wiltse parasagittal approach with
minimal bone resection. Attempts to approach this from
within the canal require destabilizing facet joint excision.
ANTERIOR APPROACHES TO THE
LUMBOSACRAL JUNCTION
Anterior approaches to the lumbosacral junction require an approach between the great vessels to the lumbosacral disc. Retraction of the iliac arteries and veins
laterally gives the broad expanse of the lumbosacral disc,
with only the median sacral artery and the presacral autonomic nerves coursing inferiorly across the lumbosacral
disc. Decisions as to the approach to this disc depend on