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28 Minimally Invasive Posterior Lumbar Fusion Techniques
Fig. 28.6 Osteotomy cuts. Artist’s illustration demonstrating the osteotomy cuts (dashed lines) made with the
drill to disarticulate the inferior articulate process and the
lamina of L4 (purple shading). The first osteotomy cut is
made across the pars interarticularis just beneath the L4
pedicle screw. The second cut is made at the base of the
spinous process, undercutting the spinous process and
drilling the contralateral lamina. Upon completion of
these two osteotomy cuts, the entire segment can be disarticulated. Then the superior articular process of L5 and the
L5 lamina (green shading) is drilled and disarticulated,
offering a generous transforaminal corridor into the disc
space (Used with permission from Barrow Neurological
Institute, Phoenix, Arizona)
379
Fig. 28.7 Expanded Kambin’s triangle for MIS TLIF.
Artist’s illustration depicts the triangle (dashed line)
formed by the exiting root, the traversing root, and the
superior endplate of the caudal vertebral body. Completion
of the laminectomy and facetectomy creates the transforaminal corridor into the disc space. Kambin’s triangle is
classically defined by the boundaries of the superior endplate of the inferior vertebral body, the lateral aspect of the
superior articulating facet, and the exiting superior nerve
root (Used with permission from Barrow Neurological
Institute, Phoenix, Arizona)
points of the ligamentum flavum and resect those
insertion points with a Kerrison rongeur. An en
bloc resection of the ligamentum flavum then
becomes possible and ensures a widely decompressed thecal sac and nerve roots. Typically,
some ligamentum remains over the exiting nerve
root, which is resected to clearly visualize the
location of the exiting nerve root. Completing
that exposure ensures that the boundaries of an
expanded Kambin’s triangle may be clearly
delineated (Fig. 28.7). The medial aspect of the
Kambin’s triangle (the height) is classically
defined by the lateral aspect of the superior articular process [13]. However, in a transforaminal
approach, the entire facet (along with the lamina
and pars interarticularis) has been removed,
which moves the medial aspect of Kambin’s triangle to the lateral aspect of the dural edge and
the traversing root. The expanded Kambin’s triangle is a more relevant anatomical triangle to
define the transforaminal corridor.
The resection of the ligamentum flavum allows
for ready access to the disc space. Little, if any,
retraction of the traversing or exiting nerve root is
needed to access the disc space at this point. A
complex venous network is typically found in the
vicinity of the pedicle and overlying the disc
space. It is worthwhile to cauterize that venous
network before incising the disc space.
Step Four: Discectomy
After completion of the
preemptive cauterization of the epidural veins in
the vicinity of the pedicle and disc space, a No.
11 blade on a bayoneted knife handle is used to
perform a generous annulotomy. Large Kerrison
rongeurs may be used to enlarge the annulotomy
as far medial and as far lateral as the exposure
will allow. A series of downward-angled curettes,
straight curettes, and straight and forward-angled
pituitary rongeurs are used to remove the disc
material. In many cases, there is a far-lateral
component to the disc extrusion that will require
removal. Inspection around and under the exiting
nerve root identifies disc material that may have
migrated into the axilla or under the nerve root.
Paddle distractors are inserted into the disc space
380
L.M. Tumialán
and used to restore disc height, facilitating preparation of the endplates. The goals of the discectomy are to remove as much of the disc material
as possible, to remove the cartilaginous endplate,
and to prepare a bleeding cortical endplate without violating it. Concern about violating the cortical endplate has prompted the author to avoid
cutting interbody paddles and to use only blunt
paddles to restore height. It is important to note
that this is the author’s preference and that some
surgeons routinely use shavers as part of their
disc preparation.
After 15 min of dedicated disc removal and
endplate preparation, a point of diminishing
returns is reached. If less than that amount of
time is spent, the surgeon may not have optimized the environment for fusion. Spending
more than that amount of time may not offer any
more advantage toward achieving arthrodesis.
Interbody Phase
Step One: Ensure a Complete Discectomy The
operating microscope is rolled out, the fluoroscope is rolled back in, and the bed is rotated to
the neutral position. Angled interbody curettes are
then used to ensure that the disc space has been
optimally prepared. These curettes are graduated
and their placement within the interbody should
easily reveal the capacity to reach 40 mm across
the disc space, which is compatible with rotating
a large interbody spacer into the disc space. If
there is any resistance in passing the angled interbody curette to 40 mm, it is wise to continue to
work within the disc space to prepare it. That
additional investment in time will pay immediate
dividends when the interbody spacer is placed.
Step Two: Interbody Trials The size of the
last paddle distractor should be the size of the
first interbody trial placed into the disc space.
Typically, the dimensions of Kambin’s triangle
allow for the trial to be placed without the need
for retraction of either the exiting or traversing
root. The tip of the trial is placed into the annulotomy, and the trajectory is set by obtaining a
lateral fluoroscopic image (Fig.
28.8). The
interbody is then tapped into the disc space.
Sizing the interbody space by tactile feel is
purely subjective. The trialing should continue
until the interbody trial wedges into the disc
space and requires a slap hammer to remove.
Such a fit will result in an ideally sized interbody spacer that has an exceedingly low likelihood of migration and high likelihood of
achieving an arthrodesis. If the trial can be dislodged without a slap hammer, the interbody is
too small, which may lead to pseudarthrosis or
migration of the interbody.
Step Three: Placement of the Interbody
With
the size of the interbody selected, morcellized
bone graft is packed into the disc space through a
funnel. It is important not to overpack the disc
space in a manner that will affect placement of
the interbody. A down-sloping interbody curette
can be used to distribute the graft into the anterior
third of the disc space.
The preference of the author is to use a curved
interbody spacer that is rotated into the disc space
to occupy as much surface area as possible and
engage the apophyseal ring. The largest interbody spacers currently available are 36 mm in
length, which when rotated into the disc space
will occupy that same dimension in width.
Similar to the trialing process, the tip of the
interbody is placed into the annulotomy, and a
lateral fluoroscopic image is taken to confirm an
ideal trajectory into the disc space (Fig. 28.9).
The interbody is inserted with an oblique trajectory across the disc space parallel to the endplates. Once the posterior aspect of the interbody
has cleared the posterior margin of the disc space,
the rotation of the interbody can begin. The interbody is rotated and advanced until it reaches the
anterior half of the disc space. When a final AP
fluoroscopic image demonstrates that the interbody is well centered in the disc space, the rods
may be placed onto the tulip heads of the pedicle
screws and the construct compressed. Once satisfied with the position of the implant and the
lordosis, the set screws are tightened according to
the manufacturer’s recommendations (Fig.
28.9).
Compression of the pedicle screws on the rod
achieves two key objectives: restoration of seg-
28 Minimally Invasive Posterior Lumbar Fusion Techniques
381
Fig. 28.8 Trialing the interbody. (a) Lateral fluoroscopic
image demonstrating placement of the interbody into the
annulotomy and establishing the ideal trajectory into the
disc space. (b) The ideal-sized trial wedge, once it is
Fig. 28.9 Fluoroscopy
sequence of curved
interbody spacer
placement. (a) Lateral
fluoroscopic image
demonstrating initial
insertion of the
interbody in an oblique
trajectory into the disc
space. (b) After the
spacer has cleared the
posterior margin of the
disc space, rotation of
the interbody begins. (c)
The interbody is rotated
into position to occupy
the anterior half of the
disc space. (d) AP image
with the interbody in the
geometric center of the
disc space (Used with
permission from Barrow
Neurological Institute,
Phoenix, Arizona)
moved into position, requires the use of a slap hammer to
remove. When this criterion has been met, the interbody
can be placed (Used with permission from Barrow
Neurological Institute, Phoenix, Arizona)
mental lordosis and loading of the interbody
spacer. It is important when performing TLIF to
avoid loss of lumbar lordosis [
9]. This is avoided
by placing the largest interbody that is appropriate for the interbody space in the anterior half of
the disc space under compression preventing the
loss of lordosis identified in the literature. Also,
compression loads the interbody spacer, reducing
the risk of migration. Migration of the interbody
is a complication that is often described in the
literature; it is prevented by optimizing the interbody graft endplate interface [14]. Compression
382
L.M. Tumialán
Fig. 28.10 L3–L4 facet cyst and degenerative disc disease. (a) Sagittal T2-weighted MR image demonstrating
disruption of the interspinous process ligament. The
increased signal intensity between the spinous processes
suggests instability of the segment that would be confirmed on flexion-extension studies. The facet cyst caus-
loads the bone graft against the endplates, thereby
optimizing an environment for fusion by embracing the principles of Wolff’s law.
Illustrative Case
History
A 48-year-old woman presented with progressive, worsening axial back pain and radicular
right-leg pain.
Physical Examination
On examination, the patient demonstrated
absence of a right patellar reflex and 4−/5
strength of the right quadriceps.
Radiographic Imaging
MR imaging of the lumbar spine demonstrated
disruption of the interspinous process ligament,
widened facets, and a facet cyst compressing the
traversing nerve root of L4 (Fig. 28.10). Flexionextension studies revealed instability of the segment (Fig. 28.11). At the time of presentation, her
ing central stenosis can be seen. (b) Axial T2-weighted
MR image revealing the facet cyst to the right, resulting in
compression of the traversing nerve root of L4. There is
increased signal within the facet joints bilaterally (Used
with permission from Barrow Neurological Institute,
Phoenix, Arizona)
Oswestry Disability Index score was 43, her VAS
pain score for the leg was 8, and her VAS pain
score for the back was 5.
Treatment
The patient was taken for an L3–L4 MIS TLIF
with a right transforaminal approach. With the
patient positioned on a Jackson table, two incisions were planned 3.5 cm from midline over the
L3–L4 segment. After the level was confirmed
with a lateral fluoroscopic image, the incisions
were made, and cautery was used to divide the
fascia. Sequential dilatation was performed over
the L3–L4 facets on the left and right sides.
Pedicle screw entry points were directly exposed,
and the pedicles were instrumented as described
above. Under the operating microscope, a drill
was used to undercut the spinous process at the
junction of the lamina and spinous process.
Another osteotomy cut was made just inferior to
the L3 pedicle screw, extending to the base of the
spinous process. After both of these osteotomy
cuts, the inferior articular process and lamina
were dissected from the ligamentum flavum and
removed. The superior articular process of L4 was
then removed. The L4 nerve root and thecal sac
were decompressed completely with resection of
28 Minimally Invasive Posterior Lumbar Fusion Techniques
383
Fig. 28.11 Flexion and extension radiographs. (a) The
lateral flexion study demonstrates not only the anterior
translation of the L3 vertebral body on L4 but also boneon- bone contact of the inferior aspect of the L3 on the
superior aspect of L4 at the anterior aspect of the disc
space. (b) The lateral extension study demonstrates ana-
the ligamentum flavum and the facet cyst. The L3
nerve root was then exposed with resection of the
lateral ligamentum flavum.
A complete discectomy was performed, the cartilaginous endplate was removed, and the cortical
endplate was prepared. A 12 × 36-mm interbody
spacer with autograft and allograft was rotated into
the midline of the disc space, and rods were placed
atop the tulip heads of the pedicle screws.
Compression restored the segmental lordosis and
the set screws were tightened. The access ports
were removed and the incisions closed.
Outcome
The patient was discharged the following morning with some incisional discomfort, but with
complete resolution of her right radicular leg
pain. After 1 month, the patient returned to work
and was off all narcotic pain medication with a
weight-carrying restriction of 25 pounds. By the
second postoperative month, she was at work
without restrictions or limitations. At her 6-month
postoperative follow-up, her Oswestry Disability
Index score was 11, and her postoperative VAS
pain scores for leg and back were 0 and 2, respec-
tomical alignment of the L3 and L4 vertebral bodies.
Degeneration of the disc space is demonstrated by the
degree of collapse relative to the segments above and
below (Used with permission from Barrow Neurological
Institute, Phoenix, Arizona)
tively. At 1-year follow-up, the patient demonstrated radiographic evidence of interbody fusion
(Fig. 28.12).
Technical Pearls
Instrumentation Phase
• Fluoroscopy: You may feel tempted to rely more
on fluoroscopy than on direct visualization to
determine a pedicle screw entry point. Such
reliance will increase radiation exposure during
this procedure without increasing the accuracy
of pedicle screw placement. The advantage of a
mini-open approach is that it allows direct visualization of the pedicle screw entry point.
Percutaneous placement of pedicle screws mandates fluoroscopy at every step. Direct visualization of the anatomy does not. The mentality
for fluoroscopy in a mini-open approach should
be to confirm the entry point that you have
already determined to be ideal for a pedicle
screw. After the junction of the pars interarticularis, inferior lateral facet, and transverse process has been unequivocally visualized, the use
of fluoroscopy should be reserved only for con-
384
Fig.
28.12 Postoperative
radiographs at 1-year
follow-up. (a) AP
radiograph
demonstrating a
well-centered interbody
spacer and converging
pedicle screws. (b)
Lateral neutral
radiograph
demonstrating
restoration of the lumbar
lordosis and disc height
compared to
preoperative studies.
Lateral radiographs (c,
flexion; d, extension)
demonstrating the
absence of motion of the
vertebral bodies and the
stability of the segment.
Arthrodesis can be
appreciated immediately
behind the interbody
spacer and within the
spacer (Used with
permission from Barrow
Neurological Institute,
Phoenix, Arizona)
L.M. Tumialán
firming the entry point itself. The emphasis
should be on exposing the anatomy.
• Pedicle probing: Probing the pedicle is a purely
tactile feedback process. Use of a mallet completely eliminates that feedback loop. A mallet
will easily force the tip of the pedicle probe
through a cortical wall, resulting in a breach.
Resist any urge to ask for a mallet when encountering resistance while probing a pedicle.
Instead, when resistance is encountered, begin
softly probing less medially or more medially
until the tip of the pedicle probe finds its way
into the unmistakable trove of cancellous bone.
• Tapping and placing pedicle screws: Use the
minimal access port as a reference point; spe-
cifically, register the position of the pedicle
probe within the port. That position will be the
same for the tap and the pedicle screw.
Incorporating the relative position within the
port will further decrease the need for fluoroscopy and will increase the efficiency of the
procedure.
Decompression Phase
• Maintain the ligamentum flavum intact for as
long as possible. Instead of a piecemeal resection, strive for an en bloc resection. Such an
approach mitigates the risk of a cerebrospinal
28 Minimally Invasive Posterior Lumbar Fusion Techniques
385
fluid leak and minimizes the action of the
Kerrison rongeur.
• Extending the bone work caudally to the caudal pedicle screw into the lamina below
achieves comprehensive foraminotomy and
exposes the insertion of the ligamentum
flavum.
• Conjoined root: Removal of the facet, lamina,
and ligamentum flavum reveals an unmistakable continuation of the dura between the exiting and traversing root. The dura drapes over
the entire disc space. When such an anatomical circumstance is encountered, it is no longer feasible to access the disc space, and
placement of an interbody through that corridor is not an option. Such an anatomical circumstance is not common, but it is important
to recognize. The author has encountered this
situation on only three occasions in more than
500 TLIFs. At this point, there are two options.
The first is to proceed to the contralateral facet
and expose the disc space on that side to determine whether a viable transforaminal corridor
will allow access to the disc space. The second
option is to proceed with a posterolateral
fusion. In reality, the access and visibility for
a posterolateral fusion are far superior with a
paramedian mini-open approach. The absence
of an interbody means that the arthrodesis will
rely entirely on the posterolateral fusion.
Meticulous bilateral exposure of the entire
transverse process of the rostral and caudal
vertebrae, along with decortication of the
entire posterior face of the transverse process
with generous amounts of morcellized bone
graft spanning from transverse process to
transverse process, will optimize an environment for arthrodesis, despite the absence of an
interbody.
Interbody Phase
• Always create the most generous annulotomy
that the Kambin’s triangle will allow before
beginning the trialing process. Opening the
annulotomy with a 4-mm Kerrison rongeur
medially up to the lateral aspect of the thecal
sac and laterally at least to the midpedicular
line will vastly facilitate access to the disc
space and placement of the interbody.
• Removing the posterior scallop of the disc
space with either a box-cutting chisel or a
standard osteotome will facilitate placement
of the ideal interbody that will address the
mismatch in height at the center of the disc
space and the posterior margin of the disc
space. A No. 4 Kerrison rongeur can also be
used to level out the scallop.
Complications and Strategies for Avoidance
Complications may arise at three distinct intervals in this type of operation: surgical phase,
early postoperative phase, and late postoperative
phase.
Surgical
Cerebrospinal fluid leak, errant placement of
instrumentation, and suboptimal decompression
are the three leading complications that can occur
during surgery. The risk of a cerebrospinal fluid
leak can be mitigated by performing the instrumentation first, which prevents the need for
wielding sharp instruments, such as a tap, with
the neural elements exposed. When instrumentation is performed before the decompression, the
neural elements are kept safe by the bony elements. Furthermore, accomplishing as much of
the bone work as possible while keeping the ligamentum flavum intact prevents an errant pass of
an instrument or drill. In that manner, the neural
elements are protected by the ligamentum flavum
until it becomes time for the decompression with
the resection of the ligamentum. Every effort
should be made to complete all drilling before
exposure of the neural elements.
A suboptimal decompression results in a
symptomatic patient immediately after surgery. It
is rarely necessary to perform bilateral decompression, to include bilateral facetectomies, in
order to adequately address the extent of com-
386
L.M. Tumialán
pression of the neural elements. However, bilateral decompression may be necessary in patients
who have bilateral facet arthropathy resulting in
bilateral severe foraminal narrowing. Such a
complication may be avoided by detailed history
taking, examination, and careful review of the
T1-weighted parasagittal MR images.
Early Postoperative Phase
The most common early postoperative phase
complication is migration of the interbody graft
[14], which may occur for two reasons. First, an
undersized graft may have been placed at the
time of surgery; second, violation of the cortical
endplate may have occurred. It is vital to sense a
firm placement of the interbody trial. As noted
previously, it should require a slap hammer to
dislodge the trial from its position before considering the height to be appropriate. A curved interbody rotated into position is much less likely to
migrate, especially under compression. The
action of compression further engages the graft
endplate interface. Bullet-shaped grafts may
extrude along the same path they were inserted.
A curved graft rotated into position is much less
likely to do so.
difficult, in the process of removing the disc material and preparing the endplate, you may appreciate entire sheets of the cartilaginous endplates
coming out of the disc space. With regard to the
tactile feel, you should have the unmistakable feel
of rasping against cortical endplate as compared
to cartilaginous endplate. The endplate preparation phase should never be rushed. Time invested
in this phase of the operation will mitigate the risk
of this late complication.
Finally, adjacent segment degeneration may
be difficult to avoid altogether because it is an
element of the natural history of lumbar disc
degeneration. However, certain measures can be
taken to mitigate that risk. Minimizing the extent
of exposure is the first measure. The advantage of
a minimally invasive approach is the capacity to
perform a procedure without the wide exposures
that weaken muscle and cause inadvertent injury
to surrounding structures. The second measure is
respecting the integrity of the facet capsule at the
rostral level. While it is essential to expose the
inferior and lateral aspects of the rostral facet to
visualize the pedicle screw entry point, that exposure does not require violating the facet capsule.
Beginning on the transverse process and working
laterally to medially are the surest ways to prevent inadvertent disruption of the facet capsule.
Late Postoperative Phase
Pseudarthrosis and adjacent-level degeneration
are late complications of this procedure.
Pseudarthrosis and migration of the graft go hand
in hand. Thus, the measures to mitigate the risk of
graft migration or extrusion are the same measures needed to prevent pseudarthrosis. However,
pseudarthrosis may occur in a well-positioned
interbody graft that has not migrated. In those circumstances, the cartilaginous endplate was likely
not completely removed from either the inferior
or superior endplate or both. In that case, the
interbody is wedged between two sheets of cartilaginous endplate that will reliably block bone
growth. The preparation of the endplate is done
by tactile feel, but it also has a visual component.
Although direct visualization of the endplate is
Conclusion
The capacity to reliably and efficiently perform
an MIS TLIF results from the culmination of
skills developed through minimally invasive
microdiscectomies and laminectomies. It is a
difficult operation to embark upon without that
minimally invasive skill set. However, once facility has been achieved with bayoneted instruments
and minimally invasive techniques, the paramedian approach is actually more efficient. The
direct approach to the facet allows for easier
access to the anatomy for instrumentation and
decompression, with less blood loss, less postoperative discomfort, and shorter hospital stays.
The investment in overcoming the learning curve
pays immediate dividends in the management of
degenerative processes of the lumbar spine.
28 Minimally Invasive Posterior Lumbar Fusion Techniques
387
References
1. Foley KT, Smith MM. Microendoscopic discectomy.
Tech. Neurosurg. 1997;3(4): 301–7
2. Cloward RB. The degenerated lumbar disc: treatment
by vertebral body fusion. J Int Coll Surg. 1954;22(4
Sect. 1):375–86. Epub 1954/10/01
3. Harms J, Jeszenszky D. The unilateral, transforaminal approach for posterior lumbar interbody fusion.
Orhtopaedics and Traumatology. 1998;6(2):88–99.
4. Foley KT, Holly LT, Schwender JD. Minimally invasive lumbar fusion. Spine. 2003;28(15 Suppl):S26–35.
Epub 2003/08/05
5. Isaacs RE, Podichetty VK, Santiago P, Sandhu
FA, Spears J, Kelly K, et al. Minimally invasive
microendoscopy- assisted transforaminal lumbar
interbody fusion with instrumentation. J Neurosurg
Spine. 2005;3(2):98–105. Epub 2005/12/24
6. Holly LT, Schwender JD, Rouben DP, Foley
KT. Minimally invasive transforaminal lumbar interbody fusion: indications, technique, and complications.
Neurosurg Focus. 2006;20(3):E6. Epub 2006/04/08
7. O’Toole JE, Eichholz KM, Fessler RG. Surgical site
infection rates after minimally invasive spinal surgery.
J Neurosurg Spine. 2009;11(4):471–6. Epub 2009/11/26
8. Rampersaud YR, Foley KT, Shen AC, Williams S,
Solomito M. Radiation exposure to the spine surgeon
during fluoroscopically assisted pedicle screw insertion. Spine. 2000;25(20):2637–45. Epub 2000/10/18
9. Hsieh PC, Koski TR, O’Shaughnessy BA, Sugrue
P, Salehi S, Ondra S, et al. Anterior lumbar interbody fusion in comparison with transforaminal
lumbar interbody fusion: implications for the restoration of foraminal height, local disc angle, lumbar
lordosis, and sagittal balance. J Neurosurg Spine.
2007;7(4):379–86. Epub 2007/10/16
10. Mummaneni PV, Rodts GE Jr. The mini-open transforaminal lumbar interbody fusion. Neurosurgery.
2005;57(4 Suppl):256–61. discussion -61. Epub
2005/10/20
11. Wong AP, Smith ZA, Nixon AT, Lawton CD,
Dahdaleh NS, Wong RH, et al. Intraoperative and
perioperative complications in minimally invasive
transforaminal lumbar interbody fusion: a review of
513 patients. J Neurosurg Spine. 2015;22(5):487–95.
Epub 2015/02/24
12. Raynor BL, Lenke LG, Bridwell KH, Taylor BA,
Padberg AM. Correlation between low triggered
electromyographic thresholds and lumbar pedicle
screw malposition: analysis of 4857 screws. Spine.
2007;32(24):2673–8. Epub 2007/11/17
13. Hoshide R, Feldman E, Taylor W. Cadaveric analysis of the Kambin’s triangle. Cureus. 2016;8(2):e475.
Epub 2016/03/24
14. Bakhsheshian J, Khanna R, Choy W, Lawton CD,
Nixon AT, Wong AP, et al. Incidence of graft extrusion
following minimally invasive transforaminal lumbar
interbody fusion. J Clin Neurosci. 2016;24:88–93.
Epub 2015/11/19
Cortical Bone Screw Fixation
Mark Benjamin Frenkel, J.J. Renfrow,
and Charles L. Branch Jr.
Introduction
The cortical bone trajectory (CBT) for lumbar
pedicle screws was first reported in 2009 by
Santoni et al. [1] as an alternative to traditional,
medially directed pedicle screws. Screws placed
using this trajectory, which has a starting point in
the pars interarticularis and is more laterally and
cranially oriented than traditional trajectory pedicle screws (TTS) (Fig. 29.1), have come to be
referred to as cortical bone trajectory screws or
cortical screws (CS). There are numerous benefits to cortical screws compared to pedicle screws,
including less muscle dissection, stronger pullout
strength, and less risk to neural elements. In this
chapter, we discuss the available clinical and biomechanical literature pertaining to cortical
screws and indications for their use and review
the surgical technique of placing cortical screws
in the setting of a midline lumbar fusion.
As a result of the more medial starting point of
the cortical screw trajectory, the tulip head of the
screw is more medially seated than pedicle
screws. This more medially seated head requires
M.B. Frenkel • J.J. Renfrow • C.L. Branch Jr. (*)
Department of Neurosurgery, Wake Forest Baptist
Medical Center, One Medical Center Blvd, Winston
Salem, NC 27157, USA
mfrenkel@wakehealth.edu;
e-mail:
jrenfrow@wakehealth.edu; cbranch@wakehealth.edu
29
less lateral exposure for placement than pedicle
screws and thus can be performed through a
smaller midline incision with less muscular dissection (Fig. 29.2). One radiographic study compared the fat infiltration ratio, which correlates
with muscle damage, of the multifidus muscles at
18-month follow-up in 16 patients who underwent posterior lumbar interbody fusion (PLIF)
with cortical screws compared with patients who
underwent PLIF with pedicle screws. Hung found
that the smaller dissection afforded by the cortical
screws induced significantly less multifidus muscle damage which could theoretically help to prevent the development of adjacent-level disease
[2]. The less invasive properties of cortical screws
could theoretically decrease postoperative pain,
shorten operative duration, and minimize blood
loss, and these outcome measures remain ripe for
future study.
In both healthy and osteoporotic patients, the
subcortical and cortical bone of the pedicle is more
dense than the trabecular bone of the vertebral
body with the greatest fixation being more dependent on its purchase in this denser bone [
cortical bone trajectory was specifically designed
to maximally purchase the higher density cortical
bone of the pedicle [
study examining the density of bone along cortical
screws and pedicle screws pathways in 180 randomly selected patients found that the cortical
screw pathway had a statistically significantly
greater bone density at fixation points compared to
those along a traditional trajectory [4].
1] (Fig. 29.3). A radiographic
3]. The
© Springer International Publishing AG 2017
L.T. Holly, P.A. Anderson (eds.), Essentials of Spinal Stabilization,
DOI 10.1007/978-3-319-59713-3_29
389