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Procedure 37 | Minimally Invasive Exposure Techniques of the Lumbar Spine 349
n
The use of an expandable tubular retractor system allows a more generous
exposure but has the trade off of increased tissue dissection and soft tissue
creep.
• Secure docking of the retractor against the spine can minimize soft tissue
creep, which obscures visibility of the spine (Khoo et al, 2002; Tafazal and
Sell, 2004).
• Because the angular movement of surgical tools is reduced in longer tubular
retractors, the shortest retractor that reaches from the skin to the spine should
be used.
• Fluoroscopic confirmation of tubular retractor position should be obtained
before commencing with surgery.
• The position of the tubular retractor can be adjusted to optimized access to
the region of interest.
n
Although the instruments used for minimally invasive spine surgery (MISS)
procedures are similar to those used with traditional open procedures, longer,
bayoneted instruments are useful to ensure that visualization is not obscured
by the surgeon’s hands.
• The surgeon generally operates with a suction instrument in one hand and a
working instrument (e.g., Kerrison rongeur or curette) in the opposite, dominant hand (Figure 37-5) (Seldomridge and Phillips, 2005).
• In most cases, only minimal assistance is required from a surgical assistant
to retract the nerve root when working in the ventral aspect of the spinal
canal.
n
“Wanding” of the tubular retractor is an important technique that allows access
outside the initial surgical exposure.
• Wanding is performed by loosening the attachment between the retractor
and the operating table and angling the tubular retractor to the new position
(Figure 37-6).
• By wanding, it is generally possible to reach both sides of the spine canal at
two adjacent vertebral levels through a single skin incision.
FIGURE 37-5 FIGURE 37-6
350 Procedure 37 | Minimally Invasive Exposure Techniques of the Lumbar Spine
n
In addition to direct visualization through the retractor, tactile “feel” is also an
important skill for the MIS spinal surgeon to develop and use.
n
In the event of a dural laceration, direct suture repair is the authors’ preferred
treatment strategy for most tears (Bosacco et al, 2001). However, others have
reported successful management of minor dural tears by the use of sealants
without direct repair, as long as there is no tendency for nerve rootlet
extravasation.
n
G E N E RA L C O N T R O V E R S I E S
• The need for a direct repair of “stable”
dural lacerations in an MIS procedure is
often debated by experts in the field.
The risk of dural cutaneous fistula, resulting from the small “dead space” in the
wound, is reduced with an MIS exposure compared with an open surgical
procedure.
Procedure
Step 1
n
An MIS approach offers an excellent option for correcting localized spinal canal
stenosis or treating herniated lumbar disks.
n
Simple decompressive surgery is generally straightforward and is an appropriate
starting point for the novice MISS surgeon.
• It is important to remember that, although MISS decompressions use a
smaller skin incision, the same adequate decompression must be achieved to
have a good clinical outcome.
• In the case of a disk herniation, any free fragments should be localized on
S T E P 1 P EA R L S
• Avoid using an overly large diameter
tubular retractor for decompressive
procedures, because this will push the
surgeon away from the midline.
• The authors prefer to use a 14- to
18-mm diameter tube (outer diameter)
for diskectomies and an 18- to 20-mm
tube for stenosis decompression.
• Leave the ligamentum flavum intact
during drilling of bone to protect the
dura.
S T E P 1 P IT FA L L S
• Ensure an adequate plane over the
dura, and watch the dura carefully
during the resection of bone to avoid
an iatrogenic dural tear.
preoperative imaging studies (recent MRI) relative to the pedicles and the
disk space.
• Working through a simple laminotomy, the disk fragment can be removed
and the compromised neural elements decompressed.
• With spinal stenosis, the location of the obstruction within the spinal canal
should be clearly defined before surgery and confirmed by direct visualization
of the decompressed neural elements before completing the procedure.
n
A bilateral lumbar decompression or “laminoplasty” technique can be used to
address bilateral stenosis through a single unilateral skin incision.
• With the laminoplasty technique, a wide hemilaminectomy is performed first,
after which a medial facet resection can be done to decompress the ipsilateral
side of the spinal canal.
• The tube is then angled toward the contralateral side of the spinal canal
(using the wanding technique outlined previously), and the spinous process
and contralateral lamina are undercut (using a high-speed drill) to provide
access to the contralateral side of the spinal canal (Figure 37-7).
• During drilling of bone, it is safer to leave the ligamentum flavum intact to
protect the underlying dura.
n
After the bone drilling is complete, the ligamentum flavum should be removed
to allow direct visualization of the nerve roots and decompression of the dura.
Procedure 37 | Minimally Invasive Exposure Techniques of the Lumbar Spine 351
FIGURE 37-7
Step 2
n
Posterolateral (onlay) fusion
• Posterolateral fusion between the transverse processes of adjacent levels can
be achieved, working through a tubular retractor system.
• For in intertransverse (onlay) fusion, an expandable retractor is useful to
expose the entire interval between the transverse processes.
• After docking on the transverse processes, the soft tissues are cleared away
to allow visualization of the underlying bone that is decorticated.
• The interval between the transverse processes is then filled with a suitable
bone graft material, followed by removal of the tubular retractor.
• Take care to avoid violation of the intertransverse membrane, because this
may place the underlying nerve root at risk of injury.
n
Posterior interbody fusion
• A posterior lumbar interbody fusion or transforaminal lumbar interbody fusion
is achieved by removal of an adequate amount of the facet joint so that the
traversing nerve root requires minimal retraction (German and Foley, 2005;
Khoo et al, 2002; Lehman et al, 2005).
• Interbody fusions, theoretically, provide a more favorable fusion environment
compared with the intertransverse space and also allow reconstruction of a
collapsed disk space.
• When performing a minimally invasive TLIF, the skin incision should be placed
at least 4 cm lateral to the midline to allow good access to the contralateral
disk space (Figure 37-8).
• Because a TLIF is a more technical procedure, it should be undertaken by
surgeons who are already experienced with tubular surgical techniques for
lumbar decompression.
352 Procedure 37 | Minimally Invasive Exposure Techniques of the Lumbar Spine
FIGURE 37-8
• The side of the most significant leg pain is generally chosen for a TLIF
exposure.
• With careful protection and retraction of the traversing nerve root, the posterolateral annulus is incised to allow access to the interbody space.
• Curettes and disk shaver instruments are used to perform a thorough
diskectomy.
• The bony end plates must not be violated, because this will encourage bleeding and subsidence of the interbody implant.
• Lateral fluoroscopy should be used to determine the depth of instruments
introduced into the disk space and reduce the change of inadvertent anterior
penetration of the annulus, which can risk a vascular catastrophe.
• The well cleaned out disk space should be sized for the optimal interbody
implant.
• The interbody implant should be packed with an appropriate bone graft
material, and the space around the implant should also be filled with graft
material.
• Great care should be taken to avoid compression of the exiting nerve during
insertion of trials or the interbody fusion device.
• The fusion device should be positioned symmetrically on the AP image and
toward the front of the disk space on the lateral image.
• Palpation should be used to ensure the absence of compression of the exiting
and traversing nerve root at the conclusion of a TLIF procedure.
Procedure 37 | Minimally Invasive Exposure Techniques of the Lumbar Spine 353
S T E P 2 P EA R L S
• Penetration of the end plate during
diskectomy should be avoided by the
careful use of sharp instruments within
the disk space.
• All cartilaginous material must be
removed from the end plates to allow
an optimal chance of achieving fusion.
• Avoid undersizing the interbody
implants during interbody fusion, which
may reduce stability of the construct
and allow migration of the implant.
• Any overhanging bone that reduces the
opening to the disk space should be
removed to allow optimal clearance of
disk material and proper sizing of the
interbody implant.
S T E P 2 P IT FA L L S
• Take great care to avoid violation of the
anterior annulus, which risks a major
vascular injury.
• Be aware that, rarely, a conjoined nerve
root may prevent safe access to the
disk space when performing a TLIF or
PLIF approach. In such a situation, an
alternative fusion method should be
undertaken.
n
Anterior lumbar interbody fusion
• ALIF provides an excellent reconstruction of the disk space and eliminates
the need to operate adjacent to the dural sac, as with a posterior interbody
procedure. This thereby decreases the risk of neural injury or epidural
scarring.
• After ALIF, percutaneous pedicle screws can be placed to achieve a posterior
tension band construct and provide circumferential stability to the fusion
construct.
• A mini-open retroperitoneal approach is preferred for ALIF surgery at the
current time.
• This exposure provides wide access to the intervertebral disk, which can be
thoroughly resected, allowing reconstruction with a large interbody device.
n
Lateral transpsoas interbody fusion
• The lateral transpsoas approach is gaining popularity for fusions above the
L5-S1 level.
• Advantages of this approach include the absence of required vascular mobilization, the ability to implant a large, mechanically sound interbody implant
and the excellent coronal plane correction that is achieved when dealing with
a spinal deformity.
• A disadvantage of the lateral approach is the potential risk to the lumbar
plexus (Seldomridge and Phillips, 2005).
• Common sequelae of the approach include sensory changes in the region of
the upper thigh and hip flexor pain or weakness that are felt to be approachrelated although generally transient.
• After positioning in the lateral decubitus position, the C-arm is used to localize the central region of the involved disk space.
• A muscle splitting approach is used to access the retroperitoneal space and
psoas muscle.
• The authors prefer to split the psoas between its anterior third and posterior
two thirds to reach the lateral disk.
• Neuromonitoring can be used to localize nerve roots within the psoas muscle.
• Fluoroscopic documentation of correct positioning of the retractor relative to
the disk space is mandatory.
• A thorough diskectomy should be performed.
• An interbody implant that traverses the disk space from lateral apophyseal
ring to lateral apophyseal ring should be chosen.
• The interbody implant and disk space should be packed with an appropriate
graft material.
354 Procedure 37 | Minimally Invasive Exposure Techniques of the Lumbar Spine
Step 3: Instrumentation
n
Minimally invasive spinal instrumentation has been simplified with the advent
of percutaneous cannulated pedicle screw systems.
n
Surgeons should familiarize themselves with the specifics of the instrumentation
system before the procedure.
n
Percutaneous pedicle screw instrumentation begins with obtaining a true AP
fluoroscopic image of the vertebra (Figure 37-9, A).
n
Incisions should be localized about 1 cm lateral to the lateral margin of
the pedicle visualized on the AP image (Figure 37-9, B) (Lehman et al, 2005;
Seldomridge and Phillips, 2005).
n
Preexisting incisions used for a TLIF or PLIF procedure can generally be used for
the placement of pedicle screw fixation.
n
A Jamshidi needle is introduced through the skin incision to dock on the bone
directly over the lateral boarder of the pedicle at the 3 o’clock (right) and 9
o’clock (left) position.
n
After confirming that the tip of the needle is properly positioned (Figure 37-10,
A
), the tip of the needle is seated a few millimeters into the bone with gentle
mallet taps (Figure 37-10, B).
n
The position of the needle tip is again confirmed with AP fluoroscopy.
A
FIGURE 37-9, A-B
B
Procedure 37 | Minimally Invasive Exposure Techniques of the Lumbar Spine 355
n
Next, the needle shaft is marked 20 mm above the skin edge.
n
Holding the needle shaft parallel to the end-plate shadow, with about 10
degrees of lateral to medial angulation, the needle is tapped through the
pedicle, until the mark on the needle shaft reaches the skin edge (at this point,
the needle tip has traversed the isthmus of the pedicle).
n
An AP image is again taken to assess the position of the tip of the needle, which
should lie approximately
1
2
to
of the distance (from medial to lateral) across
2
3
the pedicle (Figure 37-11).
n
A guidewire is inserted through the needle shaft and advanced about 15 mm
into the vertebral body.
n
The Jamshidi needle should advance smoothly as it is tapped through the
pedicle. If hard bone is encountered, the tip of the needle is most likely medial
and striking the cortical surface of the superior articular process. In such an
event, the tip of the needle should be repositioned with a more lateral starting
point to avoid penetration of the facet joint.
n
The guidewire should also encounter cancellous bone at the base of the needle
shaft. This has a characteristic “feel” that should be confirmed by the surgeon
before insertion of the guidewire.
A
FIGURE 37-10, A-B
FIGURE 37-11
B
356 Procedure 37 | Minimally Invasive Exposure Techniques of the Lumbar Spine
n
S T E P 3 P EA R L S
• Obtaining a true AP fluoroscopic image
parallel to the superior end plate of
the vertebral body is paramount for
the success of percutaneous screw
placement.
• By marking the depth of insertion
through the pedicle on the Jamshidi
needle, the surgeon can safely insert
the guidewires without having to
switch multiple times between the AP
and lateral fluoroscopy images.
Guidewires are inserted through the Jamshidi needle (Figure 37-12, A and B).
n
Cannulated instruments, such as awls and taps, are used to prepare the pedicle
for screw insertion.
n
Electromyography can be used to test the tap and ensure that it has not
breeched the cortex (Figure 37-13).
n
Lateral fluoroscopy should be used to monitor the depth of instruments inserted
over the guidewires (Figure 37-14).
n
The guidewire should always be held when passing instruments over it, to
prevent advancement of the guidewire or inadvertent removal.
n
After tapping the pedicle holes with a cannulated tap, the cannulated pedicle
screws can be placed.
L5
L4
A
FIGURE 37-12, A-B
B
FIGURE 37-13 FIGURE 37-14
Procedure 37 | Minimally Invasive Exposure Techniques of the Lumbar Spine 357
S T E P 3 P IT FA L L S
• Guidewires should always be carefully
held when instruments are passed over
them.
n
The rod can then be introduced and locked into place (Figures 37-15 and 37-16).
n
Final AP and lateral fluoroscopy (Figure 37-17) should confirm the fusion con-
struct to be in an acceptable position.
n
The authors prefer to use subcuticular resorbable sutures to close the wound,
resulting in a desirable cosmetic result (Figure 37-18).
FIGURE 37-15
FIGURE 37-16
FIGURE 37-17 FIGURE 37-18
358 Procedure 37 | Minimally Invasive Exposure Techniques of the Lumbar Spine
Postoperative Care and Expected Outcomes
n
Postoperative care is similar to traditional open lumbar surgery. However,
patients generally have less postoperative pain and are able to mobilize earlier
in the postoperative period, compared with open surgery.
n
The authors encourage mobilization and ambulation on the day of surgery and
discharge when patients are comfortable on oral medications.
n
Although all of the complications of open spinal surgery are still applicable to
MIS spinal procedures, certain complications, such as infection and heavy bleeding, are much less frequent with MIS procedures.
n
Optimal long-term outcome depends on proper patient selection and careful,
adequate performance of the operation.
Evidence
Bosacco SJ, Gardner MJ, Guille JT. Evaluation and treatment of dural tears in
lumbar spine surgery: a review. Clin Orthop Relat Res 2001;389:238-47.
Dural lacerations are fortunately not a very common misadventure during
spinal surgery, but neglect can lead to significant complications. This review
addresses their prevalence and treatment options.
German JW, Foley KT. Minimal access surgical techniques in the management of
the painful lumbar motion segment. Spine 2005;30(Suppl):S52-9.
This paper reports good results following minimally invasive spinal fusion
procedures. Although the preliminary data appear promising, long-term studies
are required for critical review.
Jaikumar S, Kim DH, Kam AC. History of minimally invasive spine surgery.
Neurosurgery 2002;51(Suppl):S1-14.
Minimally invasive spine surgery (MISS) appeals to patients because of early
recovery and the cosmetic benefits. Advances in this field are influenced by the
evolving technologies in lasers, endoscopy, and image guidance. Reviewing the
history of MISS is helpful in understanding this emerging technique in spine
surgery.
Khoo LT, Palmer S, Laich DT, Fessler AG. Minimally invasive percutaneous posterior
lumbar interbody fusion. Neurosurgery 2002;51(Suppl):S166-71.
With minimally invasive techniques, a complete posterior lumbar interbody
fusion can be achieved safely with good results. However, the efficacy of these
procedures remains to be validated by further studies.
Lehman RA, Vaccaro AR, Bartagnoli R, Kuklo TR. Standard and minimally invasive
approaches to the spine. Orthop Clin North Am 2005;36:281-92.
Minimal-access retractors and specialized instruments are being designed to
access and treat different spinal pathologies with minimal access surgery. These
minimally invasive procedures are safe and effective, and avoid the surgical
morbidities and disadvantages associated with standard open techniques.
Seldomridge JA, Phillips FM. Minimally invasive spine surgery. Am J Orthop
2005;34:224-32.
This paper reviews the rationale of minimally invasive spine surgery (MISS),
highlighting its benefits and describing common MISS procedures.
Tafazal SI, Sell PJ. Incidental durotomy in lumbar spine surgery: incidence and
management. Eur Spine J 2004;14:287-90.
This paper describes the incidence and sequelae of an accidental dural
laceration as well as the preferred treatment method once a dural tear has
been diagnosed.
Wu RH, Fraser JF, Härtl R. Minimal access versus open transforaminal lumbar
interbody fusion: meta-analysis of fusion rates. Spine 2010;35:2273-81.
A meta-analysis of studies comparing transforaminal lumbar interbody fusion
performed using either traditional techniques or minimally invasive spine
surgery (MISS) demonstrated similar fusion rates, with a trend toward fewer
complications in the MISS group.