Download Kramer DL, Booth RE, Albert TJ, Balderston RA. Posterior Lumbar

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David L. Kramer, M.D.
Robert E. Booth.Jr.. M.D.
Todd J. Albert, M.D.
Richard A. Balderston, M.D.
173
174 •
SURGICAL APPROACHES TO THE SPINE
The posterior midline approach to the lumbar spine is the most frequently used approach in
surgery of the spine. It is an extensile approach that provides access to the posterior bony
arch and pedicles of the spine, the underlying spinal cord, and the intervertebral disks.
Accordingly, it is an approach well suited for posterior decompression of the spinal cord and
exploration of exiting nerve roots in degenerative conditions of central and foraminal spinal
stenosis. It allows unilateral or bilateral access to herniated disks. Intradural and extradural
tumors may be exposed. When indicated, this approach may provide lateral exposure of the
tran sverse processes for onlay in-situ bone grafting, as well as identification of the dorsal
entry site of the cortical cylinder of the pedicle for biopsy of the vertebral body or for
placement of bone screws used with instrumentation for posterior lumbar fusion.
Anatomy
The anatomy of the lumbar spine is well established. The lumbar vertebrae consist of
relatively large vertebral bodies with blunt posterior arch structures. The superior articular
facet s are directed dorsomedially and lie anterolateral to the inferior articular facets of the
more cephalad lumbar vertebra. As such, • in degenerative conditions of the spine, it is
primari ly the superior articular facet that is responsible for lateral foraminal stenosis and the
inferior articular facet that is responsible for central spinal stenosis (Figure I I - I).
Articular process
Ligamentum flavum
Inferior
•
Superior
•
•
~.
•
Cauda equina
•
-
Nerve
,- r I . /
-
/l / / 1 1, (/
i
V<.
Figure 11 -1. Inferior and sup erior articular process. The anterior margin of th e superior
articular process lies just posterior to th e neuroforamen.
POSTERIO R LUMBAR APPROACH •
175
The pedicle is the cortical cylinder that connects the anterior vertebral body to its
posterior bony arch. These cortical cylinders increase in diameter from LI through L5. The
axis of the pedicle create s an angle with the midline that also increases from approxim ately
7 degrees at LI to 17 degrees at L5. The sagittal intervals between the pedicles, the
intervertebral foramen, are elliptic al conduits with vertical diameter 12 to 19 mm in height,
through which pass the spinal nerve, artery, vein, and branches of the sinuvertebral nerve
( Figure 11 - 2).
Several ligaments support and stabilize the bony contour of the lumbar spine (Figure
11 - 3). The supraspinous ligament is a continuous collection of collagen fibers runni ng along
the dorsal aspect of the spinous proce sses that add posterior column support and stabilize the
cantilevered vertebral bodie s anteriorly. The spinous processes are further stabilized to one
another by the segmentally developed interspinous ligaments. The intertransverse ligament is
also a segmental structure that is best developed in the lumbar spine and creates a fibrous
sling between the transverse processes. The ligamentum ftavum is a strong, elastic structure
that originates on the ventral surface of a cephalad lamina and inserts on the superior lip of
the next caudal lamina. Its resilient and elastic nature allows it to remain taut with lumbar
extension and thereby avoid infolding with subsequent compression on the cord. The anterior longitudin al ligament consists of longitudinal bands of collagen fibers that run along the
Disk
Spinal nerve
Sinuvertebral nerve and artery
~~~~--- Ped i c l e
• Figure 11-2. Anatomy of th e interverte b ra l forame n in rela tio n to th e d isk a nd pedicles. The
two st ructu res passing ve nt ral to th e spi na l ne rve are th e sinuve rte b ral ne rve and th e artery. The
other vessels are ve ins.
176 •
SURGICAL APPROACHES TO THE SPINE
Intervertebral foramen
Ligamentum
--.. .--.. .J
f1avum ..........
Interspinous
ligament - ----f:
':f:+-'- I
Supraspinous
ligament
(I I
•
.' f"AS:;
e(e1
Posterior
longitudinal ligament
•
Figure 11-3. Ligaments of the lumbar spine .
ventral surface of the spine from the skull to the sacrum. This broad anterior ligament is
intimately related to the periosteum of the anterior vertebral bodies and loosely adherent to
the intervening intervertebral disks. In contrast to this, the posterior longitudinal ligament is
a thick but narrow band of fibrous tissue that runs along the posterior aspect of the vertebral
bodies. Unlike the anterior longitudinal ligament, this ligament actually bowstrings over the
vertebral bodies and has its strongest attachments at the level of the disk as it extends out
laterally through the intervertebral foramen. This cruciform pattern may account for the
observation that most disk herniations are lateral to this strong midline strap.
Nucleus pulposus
•
Annulus fibrosis
•
..p
,•
A5f1{j:~
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Figure 11-4. Disk showing annulus fibrosis and nucleus pulposus.
POSTERIOR LUMBAR APPROACH •
~",-,!'--------
171
L3 pedicle
L3-4 herniated disk
~..::'~;:---
'.~'"'£'------
L3 spina l nerve
L4 pedicle
L4 spinal nerve
~'_</!,;r.-'l-----
'\."-"'~--
•
L5 pedicle
L5 spinal nerve
Figure 11 - 5. Lumbar nerv e roots w ith L3-4 hern iated disk.
The intervertebral disk compri ses the outer annulus fibrosis, a series of concentric
fibrous lamellae running oblique to the long axis, and the inner nucleu s pulposus, comp osed
primaril y of water, type II coll agen , and proteoglycan . The nucleus pulposus responds as a
visco us fluid under pressure and as such acts to resist and redistribut e axial co mpressive
forces within the spine. In contrast, the annulus function s to resist tension from horizontal
pressure that has been redirected by the nucleus in response to axial load (Figure 11-4).
The annulus also resists torsional stress as well as stress created by the angular vertebral
separation that permits lumbar flexion and exten sion.
Neural structures in the lumbar spine follow fairl y con sistent anatomic patterns. The
co nus medularis is usuall y found between L I and L2, below which the spinal cord continues
as a collection of nerve roots collectively referred to as the cauda equina. The nerve roots of
the cauda equina descend within the canal to exit beneath their respectively named pedicles
( Figure 11-5). For example, the L4 nerve root descend s posteriorl y over the L3-4 disk
before it turns laterall y to exit beneath the L4 pedicle through the L4-5 foram en.
Blood supply to the lumbar vertebral elements and muscles is derived from a modified
seg mental system of vessels called the iliolumbar system. As opposed to the thoracic spine ,
where segmental blood flow come s off the aorta (which ends at L4), the segmental blood
flow in the lumbar spine originates from branches of the fourth lumbar arter y, the middle
sacral artery, the internal iliac arter y, and the iliolumbar artery (Figure 11 - 6). Dorsal
178 •
SURG IC A L APPROACHES TO THE SPINE
- - - --Aorta
,
-
-
-
Musculocutaneous
branch of third lumbar
artery
L4 ----~
Right 4th lumbar - - - - segmental artery
Muscular branch to
posterior abdominal wall
./_.-----:~
Common iliac
artery - / .L..._
/
,..,
c~---
Middle sacral artery
-=::::- ~
I
(
Internal iliac .:....---~
artery
Iliolumbar artery
External iliac - - - - ,
artery
Anterior (visceral)
division of internal
iliac artery
)
(
Sacrum
Superior and inferior
gluteal arteries
•
Posterior division of
internal iliac artery
Figure 11-6. Drawing of t he d istributio n and m ajor variations of the sacroiliolumbar system of arteries that supply the
vertebrae and the ir a sso ciated structu res inferior to the fourth lum b ar verte bra.
branches of this system reach the paraspinal mu scles by ascending in the interval between
the face t joints, just lateral to the pars interarticularis. It is this segme ntal vessel that is often
encountered whil e dissecting within the soft tissue lateral to the pars ( Figure 11 - 7).
The muscles of the lumbar spine may be divided into three layers: superfic ial, middle,
and dee p (Figure II - 8). The superfic ial layer consists primaril y of muscles related to the
shoulde r girdle: the latissimus dorsi, trapeziu s, and serratus posterior. As such, these muscles
are innervated by peripheral nerves taking their ori gin within the brachial plexus. The
intermediate layer consists of long, lon gitudinal muscle masses ex tending over several motion segments. Taken together, these are referred to as the erector spinae (fro m lateral to
medial: iliocostalis, longissimus, spinalis). The deep layer is the only layer composed of true
spinal muscles, in that they are innervated and have origins and insertion s at each spinal
POSTERIOR LUMBAR APPROA CH •
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Dorsal branch
Lumbar branch
Laminar branch
M--
•
-
Segmental lumbar arte ry
Figure 11-7. Distribution of segmental a rtery as it passes near the facet joint and the par s
inte rarticularis .
level. The muscles that make up this layer are the multifidi , rotatores, levatores, and
intertransversarii.
Surgical Approach
Proper positionin g of the patient IS the crucia l first step in minimi zing total blood loss
during the posterior lumbar approach. By ensuring that the abdomen is allowed to hang free,
intra-abdominal pressure is kept at a minimum, thereby redu ~ing spinal venous pressure and
decreasing subsequent bleeding. Several frames exist that allow such decompr ession of the
abdomen and free exc ursion of the chest ( Figure 11- 9). The criticism of these frames is that
they tend to increase lumb ar lordosis, making laminotom y and lateral recess decompression
somew hat more difficult. Thi s position of relative hyperextension, however, reproduces the
axial compressio n of the neural elements. If the spine is effectively decompressed in this
extended positio n, relief of radicular symptoms may be expected when the patient is erect.
When kneeling frames are used, care should be taken to thoroughly pad all bony prominences (k nees, anterior tibiae, elbows) and abduction of the arms should not exceed 90
degrees to the trunk axis .
The length of the incision is determin ed by palpation of the spinous processes of the
appropriate levels. The skin incision is made in the midline directly over these spinous
180 •
SURGICAL APPROACHES TO THE SPINE
- - - Latissimus dorsi
External abdominal
oblique muscle -------l~,
- -- Thoracolumbar
fascia
Iliac crest - - - - - - Gluteal anastomosis
to gluteus medius
muscle - - -- - -
Gluteus maximus
-
+!
-------f1.~f'----f,
A
Spinalis
Erector
spinae
------;''-::f'----:;R!:--rr~
..~~
Lon gissimus --+-J!'-7'....,.,..----:;~"::;
~~
Iliocostalis
- - ' M -,f'--;''--, "'~ ""'""'
;r--
- Serratus posterior
inferior
Transversus abdominis - -2 =
muscle and aponeurosis
-
•
B
•
•
(
t
Figure 11-8. Muscle layers of lumbar sp ine . A Superficia l layer. B, Intermed ia te layer.
POSTERIOR LUMBAR APPROACH •
181
__- - Rotatores brevis
' - - - - - Rotator es longus
- - - - Latera l intertransversar ii
Transversus
abdominis muscle
and aponeurosis
Multifidus
r-- - - Quadratus lumborum
--F-----""'.f.~B!i'H j'1.'i
~~t7:,_f_;_1F--_,_'_"T--
Intersp inalis lumborum
c
•
Figure 11-8 Continued C, Deep layer.
processes afte r infiltratin g the skin with I : 100,000 epinephrine solution (usually with 0.25%
Marcaine). Dissection is carried down throu gh the subcutaneo us adipose tissue, eith er
sharply or with electroca utery, to the level of the lumb odorsal fascia . Thi s thick fascial layer,
clea rly see n in the anatomic speci men (Figure 11 -10), is composed of the fasc ial extension
of the latissimu s dorsi, the quadratus lumb orum , and the trapezius and envelops the underlying erec tor spinae muscles. The deep fibers of the lumb odorsal fascia coa lesce with the
periosteum of the spinous processes and lamin ae med ially and with the fasc ia of the psoas
anteriorly . By performing a subperiostea l dissection along the spinous processes, one can , for
the most part, preserve this muscle envelope and avo id violation of the intramu scular
vessels. The tip of the spinous processes has a bulb ous shape. Accordingly, dissection with
the elevator or ca utery must be directed initially dorsally to go under the edge and thus
avoi d dissecting into the paraspinou s musculature. Thi s is the first obstacle to be addre ssed
in the posterior approac h, because meticulou s hemostasis is required to prevent the slow,
persis tent bleeding, poolin g within the depth s of the wound , that may plague the surge on for
the rema inder of the surgical procedure. Avoi dance of straying into the muscles may be
faci litated by ge ntle' lateral retraction of the erector spinae muscles with a Cobb ele vator,
thereby de lineating under tension the origin of the deeper segmental muscles (i.e ., multifidi)
as they originate off the interspinous ligaments (Figure 11 - II ). Th is subperios teal dissect ion
is carr ied in a distal to proximal direction as the paraspinous muscles originate ob liquely on
the midline inters pinous ligament. Instrum ents passed from ca udad to cep halad will stay in
the subperiosteal plane, thus avo iding further muscle bleedi ng.
182 •
SURGICAL APPROACHES TO THE SPINE
• Figure 11-9. Patient on Andrews frame. A, Note abdominal decompression preventing
pressure on inferior vena cava. B, Incision line.
The seco nd obs tacle enco untered during the posterior approac h is the dissection carried
out lateral to the face t joi nts. As ment ioned , this lateral extension is usually req uired only
during the approa ch for fusion using posterol ateral bone graft or pedicl e instrumentati on .
Once the subperiostea l dissection has been carried down to the level of the lamin a, care
must be taken to avo id inad vertent subperiostea l dissection into the facet joi nt. Th is may be
difficult in spondy lart hritic spi nes where face t osteo phytes ca use med ial overha ng of the
PO STERIOR LUMBAR A PPROACH
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• Figure 11 -10. The lumbosacral fascia envelops the underlying ere ctor sp ina e mu scles. The
deep fibers of the fa scia coalesce with the periosteum of the spinou s pro cesses an d lamina
medially and with the fascia of the psoas anteriorly.
•
Figure 11-11 . Sub p e rioste a l dissection of paraspinal mu scl es off the spinous pro c ess and
laminae.
184 •
SURGICAL APPROACHES TO THE SPINE
inferior artic ular process. Once the medial margin of the facet j oint is enco untered, se lfretaining retractors may be placed to enlarge the operative field and to co mpress the
intramuscular vasculature to redu ce hemorrhage. Delin eation of the pars interarti cularis is an
extremely help ful maneuver as it defines the lateralm ost margin of the ca nal bet ween the
pedicles. Subpe riostea l remova l of soft tissue ove rlyi ng the pars is facilit ated by ca refully
cutting down to the bone with a Co bb elevator perpend icul ar to the axis of the pars and then
gently rotati ng the elevator laterally agai nst the bone, swee ping the soft tissue lateral to the
pars. Electrocautery ca n be used with this maneu ver to facilitate the removal of the soft
tissue . In cases of spondylolisthes is or spondylolysis, one must exercise extreme ca ution to
avoid penetration thro ugh a fibrous or dyspla stic pars defect. Add itional brisk bleeding is
often enco untered immediately lateral to the pars, between the facet jo ints. Th is arises from
inadvertent and planned interru ptio n of the seg mental facetal artery previously described.
These vessels may be safely co ntrolled with e1ectoca utery as the neural ele ments pass deep
to the transverse processes and intervenin g intertran sverse ligament. Dissection of the paraspinal muscles off the facet joint s is facilitated by gently retractin g the muscle mass up and
over the intact facet j oint cap sule. By applying lateral tension to the muscle, muscle fiber
origins arising from the jo int ca psule are more clearly delin eated and may be dissected off
under direct visua lization, thereby preserving the facet j oint capsule ( Figure 11-1 2). Preservation of the intact facet jo int is necessary if the surgeo n wis hes to preserve stab ility of the
spine while avo iding fusion of the motion seg ment.
The last obstacle to be ove rcome durin g this approach is the ex pos ure of the transverse
processes . These may be palpated lateral and ju st caud ad to eac h facet jo int. Each facet joi nt
is co mposed of the superior artic ular process of the ca udal vertebra and the inferio r articular
process of the cep halad vertebra. As described ea rlier, the superior articular process of the
caudal vertebra lies antero latera l to the inferior articular process of the ce phalad vertebra.
The transverse process may be identi fied by follow ing the base of the superior articular
process out latera lly. The pedicl e may also be located directly anterior to the base of the
superior artic ular process. One ca n easily see how the anatomy of the facet jo int serves as
an important guide for understandin g the three-dimensional anatomy of the spine (Figure
11-13). A Cobb eleva tor may then be gently applied to the dorsomedial aspec t of the
transverse process, and a gentle lateral swee ping motion will facilitate definition of the upper
and lower borders of the process. Electroca utery may then be used to subperiostea lly dissect
the segmentally arising muscles (intertra nsve rsarii, rotatores, levatore s) off the bony process.
Care must be taken to avo id excessive downward force again st the process because it is
eas i l~ fractured. All attempts must be made to preser ve the intertransverse ligament , because
it serves to define the safe bound ary anterior to which injur y to the nerve roots, vasc ular
structures, and retroperitoneal space may take place. Th is ligament also serves as a fibro us
sling on which to place bone graft for an intertra nsve rse process fusion ( Figure 11-14).
Once sufficient lateral exposure has been obtained, the lateral gutters may be tamp onaded
with thro mbin-moistened sponges and attention may be turn ed to carry ing out the procedure
at hand.
In the case of decomp ressive lamin ectomy, attention is directed to the midline inter val
between the ligamentum flavum and the superio r edge of the lamina definin g the ca udal
extent of the decompression. Th is is most readily acco mplished using a medi um-sized
(2 mm) curved curet with a gentle swee ping motion agai nst the superior lamin ar edge
( Figure 11- 15). The curet must be supported with two hand s to avoi d inadvertent penetr ation of the ligamentum, which , ow ing to its seg mental origin , may be quit e thin where it
meets (but does not fuse) with its homologue in the midlin e. Onc e the ca udal insertio n of
the ligamentum has been taken dow n and entry into the ca nal has bee n accomplished,
Kerrison ronge urs may be placed ca refu lly within the ca nal, taking care to mai ntai n contact
of the boot of the instr ument with the undersurface of the lamina. In the even t that any
resis tance is encountered with the Kerrison rongeur , a Pen field dissector may be used to
POSTERIOR LUMBAR APPROACH •
185
A
Erector spinae
B
•
Cauda equina
Psoas
Figure 11- 12. A and B, The paraspinal musculature is dissected off the facet capsules under tension. thereby exposing the
tran sverse processes laterally.
186 •
SURG ICAL APPROACHES TO THE SPINE
.
',
Transverse process
;'
,
Ii
.»
..j ! '
Superior articular process
•
Figure 11 -13. Three-dimensional model of superior arti cular process in relati on ship to the
transverse p roc ess, the pedicle , the disk, and the exiting nerve root.
gently release any sublaminar adhesions. In this fashion, a central trough may be created
across the levels to be excised in a caudad to cephalad direction (Figure 11 -16). This
trough may then be widened using Kerrison rongeurs angled caudad and laterally toward the
lateral recess . Care must alway s be taken to keep the angle of the Kerrison rongeur parallel
with the dura to avoid inadvertent trapping of the dura within the teeth of the instrument. By
proceed ing in this fashion, the lateral recesses may be decompressed of facetal osteophytes
and hypertrophy of the ligamentum as it extends out laterally toward the foramen .
If fusion with pedicle instrumentation is desired, one must first identify the axis of the
pedicle. The dorsal entry site to the cortical cylinder of the pedicle is identified at a point
formed by the intersection of a line bisecting the transverse process in the coronal plane
with a perpendicular line ju st lateral to the base of the superior articular process in the
parasagi ttal plane (Figure 11 -17). Entry to the pedicle is made with a bur or awl. As
descri bed, the angle created by the axis of the pedicle relative to the midline increa ses as
one procee ds from Ll to L5.
Unilateral laminotomy for diskectomy is carried out with an approach similar to that
used for lumbar laminectomy, although the dissection is carried out only on one side of the
interspi nous ligament. With this approach, one can limit the size of the initial skin incision .
Dissection proceed s to the level of the lumbodorsal fascia . At this point, sharp dissection
throug h this fascial layer proceeds between the spinou s proce sses above and below the
affected level only on the side of the pathology. By subperiosteally sweeping the paraspinal
muscu lature off of the spinous processes and intervening interspinous ligament with a Cobb
elevator, one can gain access to the laminae overlying the disk hern iation . The paras pinal
POSTERIOR LUMBAR APPROACH
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•
187
Figure 11-14. Inte rtransverse process fusion with au togenous bone graft.
musculature is held lateral to the facet joint with a Taylor retractor. As in the case of
decompression for spinal stenosis, the interva l between the superior edge of the caudal
lamina and the ligamentum ftavum is exploited with a small curved curet. Kerrison rongeurs
are then used to create a lamin otomy over lying the disk herniation by resec ting a portion of
the superior edge of the caudal lamin a and the inferior edge of the cep halad lamina (Figure
11 - 18). One must keep in mind that the L5-S I disk is at the level of the interlaminar space;
yet as one prog resses in a cephalad direction, the disk space proportionately is in a more
cep halad position than the interlaminar space. Exposure of the L2-L3 disk space therefore
requires more removal of the L2 lamina beca use the disk is in a more cephalad position
compared with the interlaminar space. Removal of some bone from the medial aspect of the
pars interartic ularis may be necessary to gai n eno ugh lateral expo sure to the underlying disk,
although at least 8 mm of the pars should be left intact to preserve stability. Once again,
preserving the facet capsule is paramount to preserving stability of the motion segment.
Once the lam inotomy is created, the dura and affec ted nerve root may be identified and
gently retracted toward the midline, exposi ng the underlying disk herniation (Figure II - 19).
Closure of the posterior lumbar approach involves reapproximating the paraspinal musculature with interrupted absorbable sutures in an attempt to close the potent ial space created
188 •
SURG IC A L AP PROACHES TO THE SPINE
•
Figure 11-15. Taking down ligamentum flavum with curet.
by the lateral di ssecti on . Th e lumbod or sal fasc ia is then reapproxirnated to itself as the
stre ngth layer in the clo sure. usin g interrupted or runnin g ab sorbable sutures . The subc uta neous layers and skin are then closed in a sta ndard fash ion of the surgeo n's c hoosing.
Complica tions
Co mplicatio ns e nco untered with thi s a pproac h include ( I) identificati on of the wrong le vel.
(2) injury to neural e le me nts, (3) excess ive bleeding. and (4 ) destabilizing the motion
seg me nt. Pre venti on is the key to avoiding eac h of these co mplica tio ns.
Ide ntificatio n of the appropriate le vel can be ens ured by severa l mean s. Th e most
impo rtant ste p is to ca refully ev a luate the preop er ati ve film s. One sho uld determine if there
are any "sacralize d" or " lumbarize d' ver tebrae . Signifi cant ante roli sth eses or ret roli sth eses
must. also be ide ntified. Evaluatio n of spina l dysraphi sm such as spina bifida occ ulta is
cri tic al to avoid pen etrati on of the cana l a nd injury to the neural e le me nts . Th e sacrum is
us ua lly easi ly ide ntifia ble. No moti on bet ween spino us processes is detected whe n o ne sacral
spino us process is moved with a Koch e r cl amp. Tapping on a sacra l lamina also tend s to
POSTERIOR LUMBAR APPROACH
•
189
Figure 11-16. During the laminectomy, a central tro ugh is created in a caudad to cephalad direction (A). The trough is
then widened (8) with the Kerrison rongeur toward the lateral recesses.
•
190 •
SURGIC A L APPROACHES TO THE SPINE
/
·rl'
•
Figure 11-17. Pedicle entry site.
produce a rela tively dull sound when compared with nonfu sed lumbar segments. An intraoperative lateral radiograph should always be obtained with a Kocher clamp on the cephalad
portio n of the spinous process at the level of the pathologic process. A Kocher clamp in this
positio n tend s to be directly posterior to the pedicle at that level and may allow more clear
identification of the marked level.
Ne ural elements, especially nerve roots , must be identified individually and protected.
The more lateral the dissection, the easier it is to identify the nerve root and retract it so that
the disk may be seen. Realization that the dura may be closely applied, and at time s
adherent to, the undersurface of the ligamentum ftavum inspire s the surgeon to exercise
ex treme caution and meticulous handling of this soft tissue plane.
Excessive bleeding may be avoided by taking several preventi ve measure s throu ghout
the proc edure. Staying strictly subperiosteal during the initial approach through the paraspinal muscle s should ensure a relatively dry exposure of the posterior bony elements.
Identifying the pars interarticularis early in the dissection followed by cauterization of the
segmental facetal artery ju st lateral to the pars will assist in maintaining a dry field durin g
exposure of the transverse processes. A branch of the posterior primary ramus of the lumbar
nerve root tend s to run with the seg mental vess el as it passes adjacent to the facet joint and
pars intera rticularis. As it supplies the para spinal muscul ature in a seg mental fashi on, loss of
some .of these nerve branches tend s not to significantly denervate the muscle. Care must be
taken to avo id penetration of the coronal plane between the tran sverse proce sses, becau se
significant bleedin g may arise in the retroperitoneal space. Exce ssive bleeding may also be
encountered durin g blunt dissection through the epidural venous plexus en route to the disk .
POSTERIO R LUMBAR APPROACH •
•
191
Figure 11 -18. Laminotomy with Kerrison rongeur.
Thi s bleeding may be lessened with proper positioning on a laminectomy frame and with the
use of a spinal anesthetic. If encountered, it may be controlled with Gelfoam and thrombin. soaked cottonoid pattie s. Bipolar Malis electrocautery may also be used with ca ution to
coagulate identifiable venou s bleeding vessel s. Lastly , penetration of the anterior annulu s
fibrosus with an open pituitary rongeur during overzealous resection of the intervertebral
disk may also lead to devastating consequences, such as injury to the adjacent iliac vessel s.
Unless a fusion is part of the preoperative plan, no posterior surgical approac h to the
lumbar spine is likely to improve stability. Accordingly, the surgeon must rely on techn ique
to preserve stabilizing structures wherever possibl e. As emphasized , facet j oint capsules must
be identified and protected. If a unilateral approach to the spine is used, the supraspinous
and interspinous ligaments should also be pre served. The pars interarti cula ris imparts bony
stability between the facet joints. Exces sive resection of the pars durin g lamin ectony ( i.e.,
less than 5 to 8 mm of pars remaining) may result in subsequent fracture , predisposing the
motion segment to a state of instability. If significa nt resection of the pars is requ ired to
achieve a complete decompression of the nerve root, one should incorporate a fusion acro ss
the involved motion segment.
192 •
SURG IC A L A PPROAC HES TO THE SPINE
•
Figure 11-19. Medially retra cted dura with exp osure of disk herniati on .
Conclusi on
The three-dimensional anatomy of the lumbar spine must be clearly understood to be able to
loca te anterior structures when looking at the posterior aspect of the spin e. Th e key to the
pos terior topographic anatomy of the spine is the facet joint. By identifying thi s structure,
one ca n ide ntify the location of the transverse process as well as the und erlying pedicl e. Th e
key to the anatomy within the canal is the pedicle. Identification of the pedicle ori ent s the
surgeon · to the level of the disk and the - position of the exiting nerv e root through its
forame n. Respect for tho se soft tissue and bony elements that contribute to spinal stability is
necessary if one is to successfully approach the posterior aspect of the spine without doin g
harm to the pati en t.
BIB LIOG RAPHY
Hollin gshead W H: An atom y for Surgeo ns, 3rd ed, vo l 3. Philadelphi a. Har per & Row. 1982.
Rauschning, W : Nor ma l and path ologic anato my of the lumb ar roo t canals. Sp ine 12: 1008. 1987.
Rothm an RH. Simeone FA : The Spine, 3rd ed. Phil adelphi a, WB Saund er s, 1992.
Watkin s MB : Postero lateral fusion of the lumbar and lumbosacral spine. J Bone Jo int Surg 35A : 101 4, 1953.