DEFINITION

Minimally invasive transforaminal lumbar interbody fusion (MIS TLIF) is a modification of the Wiltse exposure for decompression and interbody fusion of the motion segment using specialized retractor and instrumentation systems and fluoroscopic guidance to minimize the surgical corridor.

Standard TLIF is a well-established technique for decompression and fusion of a vertebral motion segment that uses a midline exposure to perform a unilateral facetectomy and exposure of Kambin triangle to access the disc space for interbody fusion.

TLIF, in comparison to standard posterolateral fusion, allows for improved fusion rates, indirect decompression via restoration of intervertebral disc height, and anterior column support without the need for an anterior retroperitoneal/transperitoneal exposure. The increased risk of neurologic injury to the exiting and traversing nerve roots with TLIF must be weighed against these advantages.

MIS TLIF, in comparison to standard open TLIF, is performed through small paramedian incisions and is

typically coupled with minimally invasive posterior (ie, facet) fusion and instrumentation.1 Typically, formal posterolateral fusion is not done; consequently, MIS TLIF relies heavily on the interbody fusion for avoidance of pseudarthrosis and successful outcomes.

MIS TLIF has been shown to have less blood loss, earlier postoperative recovery, and decreased rates of infection in comparison to standard surgery.1,2,4 MIS TLIF may potentially have improved long-term outcomes as a result of the preservation of important musculotendinous attachments and the maintenance

of integrity of the dorsolumbar fascia.3

MIS TLIF is much more reliant on fluoroscopic imaging guidance in comparison to standard TLIF, thus there is increased radiation exposure to the surgeon, staff, and patient. The amount of radiation exposure lessens with surgeon experience. Navigation with fluoroscopic or computed tomography (CT) imaging may allow for decreased radiation exposure to the surgeon and staff.

 

ANATOMY

Paraspinal Anatomy

 

The lumbar multifidus muscle is a key stabilizer of the lumbar spine.4

 

 

Largest and most medial of the deep lumbar paraspinal musculature

 

Originates from the spinous process and inserts on the superior articular process of the vertebra one to two levels caudally (FIG 1)

 

Designed for short, powerful movements with maximum force generated during lumbar flexion to optimize its ability to stabilize the lumbar spine motion segments during movement

 

Detachment of the multifidus tendon with traditional midline laminectomy compromises multifidus function.

 

A paramedian approach, in contrast, preserves the multifidus tendon attachments.

 

Discectomy

 

Kambin triangle is an anatomic safe corridor to the intervertebral disc space bounded medially by the dural tube/traversing nerve root, laterally by the exiting nerve root, and caudally by the pedicle (FIG 2).

 

 

 

FIG 1 • The multifidi are the deepest and most medial of the lumbar paraspinal musculature. They originate from the spinous process and insert on the superior articular process of the vertebra one to two levels caudally. They are unique among the lumbar paraspinal muscles in that they generate a significant amount of force despite their limited excursion. These characteristics suggest that they play a key role in motion segment stability.

 

 

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FIG 2 • Kambin triangle is a safe corridor to the disc space bounded medially by the traversing nerve root, superiorly by the exiting nerve root, and inferiorly by the pedicle.

 

 

Exposure of Kambin triangle is accomplished by facetectomy. In the technique we described, a total facetectomy is performed. The inferior articular process is removed; however, the pars is maintained (to protect the dorsal root ganglion on cage insertion). The superior articular process is removed up to the cranial aspect of the pedicle.

 

The exiting nerve root hugs the medial and inferior border of its associated pedicle. The sensitive dorsal root ganglion typically lies inferior to the pedicle.

 

Pedicle Screw Placement

 

Percutaneous pedicle screw placement requires understanding the topographic anatomy of the posterior elements as well as the radiographic projection of the pedicle on various radiographic views.

 

The anatomic starting point for pedicle screw placement is typically at the intersection of a horizontal line that bisects the transverse process and a vertical line at or just lateral to the lateral aspect of the pars. The upslope of the facet-transverse process junction is a palpable anatomic landmark.

 

 

The more lateral the starting point, the more medial angulation is needed. This can be problematic in a patient with a narrow pelvis as the posterior iliac crests can limit the ability to medialize pedicle screw tracts.

 

The more medial the starting point, the greater the risk of facet violation.

 

The radiographic starting point for pedicle screw placement is typically at the lateral aspect of the radiographic

pedicle. At the low lumbar spine, because of medial pedicle angulation, an anatomic starting point may be preferred, which may not necessarily coincide with the lateral aspect of the radiographic pedicle.

 

The radiographic pedicle correlates with the anatomic isthmus of the pedicle for hourglass-shaped pedicles. In the lower lumbar spine, where the pedicles are more cylindrical (ie, without an isthmus) and medially angulated, the anatomic correlate of the radiographic pedicle is less clear.

 

Pedicles are oriented sagittally at the thoracolumbar junction and angulate progressively medial as one moves caudally. At S1, the pedicles typically project more than 20 degrees medial.

 

PATIENT HISTORY AND PHYSICAL FINDINGS

 

Earlier postoperative recovery with MIS TLIF is advantageous in elderly patients.

 

Patients with severe osteoporosis are not ideal candidates for MIS TLIF because of the difficulty in avoiding endplate violation and subsequent graft subsidence.

 

MIS TLIF is challenging in obese patients because of the difficulty in obtaining good radiographic imaging and the difficulty in manipulating instruments through a long working corridor. The advantages in terms of postoperative recovery, however, are most apparent in obese patients as the difference in the extent of soft tissue dissection between MIS and standard techniques is greatest.

 

MIS TLIF can be a useful consideration in patients with previous midline surgery as dissection through scar tissue can be avoided. However, scar tissue from intracanal epidural bleeding at levels adjacent to previous surgery can complicate the exposure of Kambin triangle, and extension of previous pedicle screw instrumentation can be challenging.

 

IMAGING AND OTHER DIAGNOSTIC STUDIES

 

Pedicles should be evaluated radiographically prior to surgery to ensure that pedicle screw placement is feasible. If not, alternative means of fixation should be considered (eg, spinous process plate fixation).

 

A narrow pelvis (decreased distance between the posterior iliac crests) can make medial angulation of lower lumbar pedicle screws challenging. A more medial starting point with a straightforward pedicle screw trajectory or alternative means of fixation may need to be considered in these situations.

 

CT and magnetic resonance imaging (MRI) axial sections can be used to identify pedicle screw starting points and to approximate screw diameters and lengths.

 

Nerve root anomalies can be identified on preoperative imaging and, if unilateral, should prompt consideration for MIS TLIF exposure on the contralateral side. Alternative techniques that do not require nerve root retraction can also be considered (eg, standard posterolateral fusion without interbody, anterior fusion through an anterior, or lateral retroperitoneal exposure with posterior MIS fusion and instrumentation, etc).

 

TLIF, in general, should be pursued with care at the level of the cord or conus medullaris as the risk of significant neurologic injury is increased.

 

SURGICAL MANAGEMENT

 

Indications

 

 

One or two level lumbar pathology in the presence of the following:

 

 

 

Spinal stenosis with instability (eg, degenerative or isthmic spondylolisthesis) Symptomatic degenerative disc disease

 

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Relative contraindications

 

 

 

High-grade spondylolisthesis (Meyerding grade 3 or 4) Severe osteoporosis

 

Nerve root anomalies

 

There are multiple methods of performing an MIS TLIF. The different techniques are similar with respect to the decompression and discectomy but can differ with respect to the method used for distraction of the disc space, the fusion technique used to supplement the interbody fusion, and the instrumentation used for stabilization of the motion segment.

 

 

The technique we described involves subtotal discectomy using interbody spacer trials to sequentially distract the disc space and contralateral facet fusion with bilateral pedicle screw placement.

 

Other methods using alternative techniques can be equally successful in properly selected patients.

 

 

The disc space can be distracted via the pedicle screws.

 

Posterior interlaminar or posterolateral bone graft can be used to supplement the interbody fusion.

 

Alternative means of posterior instrumentation/stabilization include unilateral pedicle screw placement, unilateral pedicle screw placement with a contralateral facet screw, unilateral pedicle screw placement with a spinous process plate, and isolated spinous process plate fixation.

 

Preoperative Planning

 

Patients should be evaluated for the following:

 

 

Osteoporosis

 

 

Potential issues with bone healing (nicotine use, diabetes mellitus, etc) Previous surgery and the potential for epidural scarring

 

 

Obesity and retractor blade depth requirements Need for contralateral decompression

 

 

 

FIG 3 • Room setup. A. The C-arm should come from the side opposite the surgeon. B. This allows the C-arm to

be easily moved to the side (wagged), allowing the surgeon access to the surgical exposure. It can be easily brought back into position to expedite frequent imaging.

 

 

Imaging should be evaluated for the following:

 

 

 

Mobility of the motion segment Extent and nature of canal stenosis

 

 

Determines cranial/caudal extent of decompression Need for osteophyte removal at the contralateral recess

 

 

Nerve root anomalies—best seen on T1-weighted axial imaging Pedicle orientation, diameters, and pedicle screw lengths

Positioning

 

Patients are positioned prone on a radiolucent spine table. We prefer to position our patients using a Wilson frame attachment for the Jackson table to aid exposure of the interlaminar window and distraction of the motion segment. With release of the disc space and careful attention to the radiographic alignment, we have not found inadvertent fusion in kyphosis to be an issue.

 

Upper limbs are carefully positioned to avoid iatrogenic injury (eg, brachial plexus palsy, ulnar nerve compression, rotator cuff tendinitis).

 

 

Extension of the hips aids in obtaining lordotic alignment of the motion segment. Flexion of the knees reduces root tension for the lower lumbar levels.

 

Room setup (FIG 3)

 

 

C-arm from opposite side of TLIF

 

 

This is a key point. With the C-arm coming in from the opposite side of the exposure, the C-arm base can be locked, and the boom can be “wagged” in and out of the field. This allows for frequent imaging and decreases the need for the surgeon to step out of the surgical field. This is especially critical in the initial phases of the learning curve when frequent imaging is prudent.

 

 

 

 

Table mount on opposite side of TLIF at level of hip Light source on same side of TLIF

 

Imaging

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Consistent terms for intraoperative fluoroscopic imaging help in obtaining reproducible imaging. We use the following:

 

Push in/out

 

Lean or tilt north/south (ie, toward the head/toward the feet)

 

 

 

Rainbow over/under Move north/south Wag north/south

 

Properly aligned anteroposterior (AP) and lateral images are crucial for the MIS TLIF technique. The best

method for identifying the “perfect” image, in our opinion, is to sequentially image from “imperfect” to “perfect” back to “imperfect.”

 

TECHNIQUES

Patient Positioning and Planning Incision Sites

 

AP positioning

 

The C-arm should start in a direct upright position (“90-90”).

 

The table should be rotated (“airplaned”) until a perfectly rotated image is obtained. The C-arm should then be tilted until level endplates are obtained. The C-arm should not be rainbowed.

 

A properly aligned AP image of the vertebral body should show the superior endplate as a single, dense line. The pedicles should be symmetric and located just below the superior endplate. The spinous process should be in the midline (although this can be misleading in the presence of scoliosis because of deformity of the spinous processes) (TECH FIG 1A).

 

 

 

TECH FIG 1 • A. A perfect AP image of the vertebra should have the spinous process in the midline; the pedicles should be symmetric and just inferior to the superior endplate; and the superior endplate should be a single, dense line. The inferior vertebra (L4) in this image is a perfect AP image. The superior vertebra (L3) in this image is rotated; note the asymmetric pedicles. B. After a perfect AP image is obtained of the surgical levels, the midline is marked. Parallel lines 4 cm lateral to the midline are marked. Paramedian incisions (2.5 cm) will be made on these paramedian lines, with the midpoint of these incisions at a point in line with the disc space (on lateral imaging). C. The point in line with the disc space marks the midpoint of the 2.5-cm paramedian skin incision.

 

 

A horizontal line at the back marking the disc space can be used to guide the orientation of the C-arm for a properly aligned lateral image.

 

A properly aligned lateral image should show the superior endplate as a single, dense line. The pedicles should be superimposed.

 

For discs with significant angulation to a vertical plumb line (eg, L5-S1), the patient can be placed into reverse Trendelenburg to ease access to the disc.

 

Planning incisions

 

Mark the center line on a properly aligned AP image (TECH FIG 1B).

 

Mark two parallel paramedian lines approximately 4 cm lateral to the center line.

 

Using lateral imaging, mark the point in line with the disc space on the paramedian skin markings (TECH FIG 1C).

 

This point will be the center of a 3-cm incision.

• Exposure of the Ipsilateral Transforaminal Lumbar Interbody Fusion Target Site

   

  The skin incision is made with a no. 11 blade followed by a fascial incision in line with skin incision. Finger dissection proceeds along the interval between the multifidus and longissimus to the lateral aspect of the facet joint (TECH FIG 2A,B).

   

  The multifidus tendinous attachments at the target facet joint are released with a Cobb elevator using Carm for localization. Because the facet joints at the lower lumbar levels are in close proximity due to the lordotic alignment of the lower lumbar

   

   

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  spine, it is easy to inadvertently release the tendons from the wrong facet joint. This leads to increased bleeding and increased muscle creep and can be avoided by careful fluoroscopic localization prior to tendon release.

   

   

   

  TECH FIG 2 • A. After the skin is incised, the paraspinal fascia is incised in line with the skin incision. B.

  Finger dissection then proceeds between the multifidus and longissimus muscles to the lateral aspect of

  the facet joint. C,D. After the multifidus tendinous attachments are released from the facet joint, dilators are used to expand the surgical corridor and encircle the facet joint. E,F. The retractor should be medially angulated and positioned in line with the disc space. G,H. The key anatomic landmarks are the base of the spinous process medially and the facet joint line laterally. The amount of retractor blade distraction should be sufficient to visualize these landmarks but should be minimized as much as possible to avoid muscle creep. I. We prefer retractors with gaps between the retractor blades (as opposed to tube retractor systems) as they allow angulation of instruments within the working corridor.

   

   

  Release of the tendinous attachments at the facet joint allows the serial dilator tubes to “surround” the facet joint (TECH FIG 2C,D). Twisting the dilators as they are placed aids in the release of the tendinous attachments.

   

  Blade lengths are measured at the lateral aspect of the dilator tube, and the retractor with appropriately sized blades is placed over the dilators. Rotating the retractors back and forth as they are placed over the dilating tubes can be helpful—similar to the twisting motion used when pulling a tight ring off of one's finger.

   

  The retractor blades should be positioned so that they are in line with the disc space and are directed medially toward the facet joint and base of the spinous process (TECH FIG 2E,F).

   

   

   

  Key landmarks (TECH FIG 2G,H) Medially: base of spinous process Laterally: facet joint line

   

  Minimizing retractor opening decreases amount of muscle creep.

   

  We prefer retractors with gaps between the retractor blades, which allows for angulation of instrumentation (TECH FIG 2I).

• Facetectomy and Contralateral Decompression

 

Paraspinal muscle fibers within the surgical field are gently cauterized to expose the base of the spinous process and the facet joint.

 

The facet joint line is identified (TECH FIG 3A,B).

 

The cranial limit of bony resection is sufficient to allow the residual pars to be in line with the inferior endplate of the cranial vertebra (TECH FIG 3C).

 

The ligamentum flavum is maintained for protection of the dural tube during removal of the inferior articular process.

 

 

 

TECH FIG 3 • A,B. The facet joint line (yellow circle) is a key anatomic landmark demarcating the lateral extent of exposure. The burr is used to remove bone from the inferolateral edge of the inferior articular process to the base of the spinous process (yellow arrows). C. The inferior articular process and pars is resected, leaving a residual amount of pars sufficient to protect the dorsal root ganglion. Bone cranial to the pedicle (superior articular process) is completely resected. D. A thorough contralateral decompression can be performed via a unilateral exposure with appropriate angulation of the retractor. E,F. The retractor is angulated and bone resected from the base of the spinous process to allow adequate visualization of the contralateral lateral recess for decompression.

 

 

Ligamentum flavum is released with a curved curette and resected with Kerrison rongeurs to expose the dural tube.

 

 

The contralateral ligamentum flavum and joint capsule are resected to achieve contralateral decompression (TECH FIG 3D). Additional bone at the base of the spinous process can be removed if more access is needed to the contralateral side. The angulation of the retractor is the key to obtaining a surgical corridor that allows access to the contralateral lateral recess (TECH FIG 3E,F). Alternatively, contralateral exposure can be used to decompress the contralateral lateral recess.

 

Discectomy

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The retractor blades are maintained in line with the disc space but are redirected laterally toward Kambin triangle (TECH FIG 4A,B).

 

The superior articular process is removed up to the cranial aspect of the pedicle. Care must be taken to remove all bone cranial to the pedicle within the corridor used for interbody cage placement. Residual bone (typically at the lateral aspect of the superior articular process cranial to the pedicle) will cause the larger size cages to migrate medially into the traversing nerve root. When all bone cranial to the pedicle has been removed, retraction of the dural tube is not typically necessary for safe cage placement.

 

The dural tube should be released from the posterior vertebral body to allow the traversing nerve root to move out of the way of the spacers/cage. This is especially important in revision settings when the dural

tube is commonly adherent to the posterior vertebral bodies as a result of previous epidural bleeding and scarring and thus at increased risk for injury.

 

The disc within Kambin triangle is exposed.

 

Epidural veins are cauterized with bipolar electrocautery. The location of the traversing and exiting nerve roots should be assessed at all times to prevent inadvertent neural injury.

 

A horizontal slit annulotomy is made with a no. 15 blade scalpel and is subsequently opened with a rotary shaver.

 

 

 

TECH FIG 4 • A. The retractor is then redirected to Kambin triangle for discectomy and endplate preparation. B. Note the difficult to access areas for discectomy: the ipsilateral lateral disc space and the contralateral posterior disc space. C. An osteotome can be used to remove the posterosuperior osteophyte from the caudal level to ease access to the disc space.

 

 

Posterior disc osteophytes are removed with rongeurs or osteotomes. Removal of the posterior lips can ease access to the disc space (TECH FIG 4C). We typically maintain the posterosuperior lip to decrease the chance for impingement of the exiting nerve root by the cage and the chance for cage migration posteriorly.

 

Subtotal discectomy and endplate preparation is accomplished using a combination of straight and angled curettes and rasps.

 

Smooth rotating paddle sizers and spacer trials can be used to dilate and release disc space. We prefer to avoid use of the rotary shaver, especially in osteoporotic bone, because of the risk of endplate

violation.

 

Fluoroscopic guidance can be used to ensure thorough discectomy. The most commonly missed portions of the disc are the ipsilateral lateral disc and the contralateral posterior disc.

 

Concave endplates can make discectomy challenging unless posterior osteophytes/lips are removed and/or the curettes are appropriately bent to accommodate the concavity.

 

Thorough release of the disc space and restoration of disc height aids in reduction of spondylolisthesis.

 

 

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• Cage Selection and Insertion

   

  Trial spacers are sequentially trialed until good purchase is obtained. Undersizing the cage can increase the stress on posterior instrumentation, risking failure. Oversizing the cage risks endplate compromise and subsequent graft subsidence.

   

  Options for cage selection include oblique and banana-shaped cages.

   

  Oblique cages are easier to insert but can have suboptimal purchase in the presence of concave endplates if the implant is not appropriately contoured.

   

  Banana-shaped cages are more difficult to place but are more biomechanically sound. They are less likely to migrate posteriorly.

   

  Bulleted cages (a modification for ease of insertion) should be used with caution as violation of the anterior annulus is possible with aggressive insertion.

   

   

   

  TECH FIG 5 • A. Expandable cage options are inserted at a contracted height to allow safer entry into the disc space with less chance for impingement of the traversing and exiting nerve roots. B. The cage is then expanded in the interbody space to restore disc height and obtain interbody cage purchase. C.

  Maintaining the pars protects the exiting nerve root and dorsal root ganglion during cage insertion.

   

   

  A recent innovation is an expandable oblique cage that allows for cage insertion at a contracted height to minimize the risk of nerve root impingement, with the ability to expand once inserted into the disc space (TECH FIG 5A,B).

   

  Bone graft is packed anteriorly within the disc space. A combination of local autograft bone together with allograft bone graft extender is used to fill the disc space.

   

  The cage is inserted with care taken to avoid impingement of both the traversing and exiting nerve root. The residual pars protects the exiting nerve root during cage insertion (TECH FIG 5C).

   

  If endplate violation occurs and the cage settles into an endplate defect, there is a risk for graft subsidence. In this situation, the cage can be “pushed” to the contralateral side of the disc space using the trial spacers and a second cage can be inserted into the location of the endplate defect to prevent migration of the initial cage back into the defect.

   

  The annulotomy window is sealed with fibrin sealant.

• Pedicle Screw Tract Cannulation

   

  Bilateral pedicle screw placement is the most stable construct. A unilateral construct may be acceptable in a young patient with normal bone density and excellent pedicle screw purchase.

   

  Properly aligned AP images are obtained at the target vertebrae. This is the most crucial step for safe percutaneous pedicle screw placement. We prefer to cannulate all pedicles under AP imaging before moving to lateral imaging.

   

  A Jamshidi needle is docked at the appropriate starting point at the lateral margin of the pedicle. The anatomic starting point identified through palpation should match the radiographic starting point on imaging. If not, ensure that true AP imaging has been obtained (TECH FIG 6A).

   

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  The needle is gently tapped to seat the needle tip into the bone. A line is drawn on the needle shaft 20 mm above the skin. This represents the length of the pedicle, from the starting point to the base of the pedicle.

   

  The needle is aligned parallel to the endplate and held in the appropriate amount of mediolateral angulation for the level being performed. The needle is advanced toward the medial border of pedicle using gentle taps with the mallet. The tip should be just medial to the medial border of the pedicle when the 20-mm mark reaches the skin. On lateral imaging, the tip should be just past the posterior vertebral line (TECH FIG 6B).

   

  Oblique imaging (bull's-eye imaging) is useful and is especially helpful for cannulating medially angulated L5 and S1 pedicles and checking for medial and lateral breaches.

   

  Starting with the AP view, the C-arm is angulated 15 degrees in the axial plane (rainbowed) to line the beam up with the pedicle axis.

   

   

   

  TECH FIG 6 • A. Jamshidi needles are docked on the radiographic pedicle starting points and their positions checked on AP fluoroscopy. B. Traversing the pedicle with a Jamshidi needle radiographically requires an understanding of the anatomic correlates to radiographic imaging findings. Once the Jamshidi needle has approached the medial pedicle wall on AP imaging, it should be just ventral to the posterior vertebral body wall on lateral imaging. C. Uncontrolled advancement of the guidewire risks catastrophic vascular or visceral injury. Grasping the guidewire with a needle driver 5 to 10 mm above the Jamshidi needle followed by gentle tapping of the needle driver allows for controlled insertion of the guidewire.

   

   

  The needle should be advanced down the center of the radiographic pedicle, keeping the needle shaft in line with the C-arm beam.

   

  Guidewires are placed after ensuring that there is an adequate fascial incision to accommodate placement of the pedicle screw (muscle/fascia can become entrapped underneath the head of the pedicle screw).

  Guidewires are inserted past the tip of the Jamshidi needle into “crunchy” cancellous bone. If the bone is too hard to manually insert the guidewire, a needle driver clamped to the guidewire 5 mm above the top of the Jamshidi needle can be gently tapped with a mallet (TECH FIG 6C). After checking guidewire positioning on lateral imaging, screw lengths can be determined.

   

  00

• Tapping and Insertion of Screws

   

  Cannulas are used to dilate the muscle around the guidewire.

   

  The pedicle is tapped over the guidewire. We typically undertap by 1 mm. Tapping should be done under fluoroscopic imaging to prevent potentially catastrophic advancement of the guidewire.

   

  The tap can be tested for pedicle breach with triggered electromyography.

   

  Threshold values (8 to 10 mA) should prompt placement of a screw with the same diameter as the tap to avoid breaching the pedicle.

   

  Electrodiagnostic evidence of pedicle breach should prompt careful radiographic assessment of the pedicle screw tract with AP and oblique imaging. Redirecting the guidewire or aborting screw placement should be considered if there is concern for pedicle breach.

   

   

   

  TECH FIG 7 • A. The pedicles are tapped with cannulated taps, neuromonitoring is checked, and then screws are inserted. This should be done under lateral imaging to monitor for inadvertent advancement of the guidewire. B. Guidewires should be removed once the screw tip is 5 mm past the posterior vertebral body wall to minimize the chances of the guidewire binding within the screw cannula and inadvertently advancing. Screws should be inserted deep to avoid prominent hardware; the radiographic transverse process can be a useful guide. For multilevel fusions with segmental instrumentation, screws should be inserted to a depth where the polyaxial motion of the screw head is maintained to ease rod insertion and capture.

   

   

  Screws are placed over the guidewire, again, under fluoroscopic imaging to prevent inadvertent guidewire advancement (TECH FIG 7A). The guidewire can be removed once the screw tip is past the posterior vertebral body wall.

   

  Insert screws deep to avoid prominent hardware. The radiographic projection of the transverse process can aid in proper placement with regard to depth (TECH FIG 7B). If two levels are being performed and segmental fixation is desired, care must be taken to properly align screw heights to achieve a smooth contour for rod seating.

• Rod Passage

   

  The rod length is determined with MIS calipers.

   

  If necessary, the rod should be contoured after attachment to its holder to prevent issues with the attachment mechanism.

   

   

   

  TECH FIG 8 • Appropriate length rods are contoured and then introduced into the screw sleeves, reduced into the screw heads, and captured with set screws.

   

   

  The rods are passed under the fascia and through the rod sleeves under lateral fluoroscopic imaging (TECH FIG 8). Entrapment of fascia underneath the screw heads/rod must be avoided as this can result in severe postoperative pain.

   

   

  Confirm rods are seated within the sleeves, visually or with a tester.

   

• Rod Reduction

  01

   

  A rod reducer can be used to reduce the rod to the screw heads. If this is difficult, ensure that polyaxial motion of the screw heads is present. This may necessitate slight backing out of the screw.

   

  Screw caps are placed and compression or distraction can then be performed as needed.

   

   

   

  TECH FIG 9 • Reduction of spondylolisthesis at L4-L5 using rod reduction technique after thorough discectomy and minimally invasive interbody cage placement.

   

   

  The rod sleeves are removed, and a final check for entrapment of the muscle/fascia is done prior to closure.

   

  If reduction of a spondylolisthesis is desired, the rods can be fixed into the caudal vertebrae, and the

   

  pedicle screws from the cranial vertebra can be reduced to the rod. This technique depends on good screw purchase to prevent pullout (TECH FIG 9).

• Closure

  The surgical sites are compressed for 2 to 3 minutes to tamponade muscle bleeders.

  The epidural space is checked. We typically do not find it necessary to use a subfascial drain. Muscle fascia is closed with 0 Vicryl on a tapered needle.

  The surgical sites are compressed again for 2 to 3 minutes. The dermis is closed with 2-0 Vicryl on a tapered needle.

  A topical skin adhesive (eg, Dermabond) is used to seal the skin.

• Incidental Durotomy

  The patient can be placed into Trendelenburg to minimize leakage. A suture repair is performed, if possible.

  If suture repair is not possible, for small durotomies (<5 mm), we have found a layered patch to be effective. A collagen matrix patch (eg, DuraGen) is sealed with fibrin glue (eg, Tisseel). This is repeated with progressively larger collagen matrix patches. We typically use three layers (ie, patch, fibrin glue, second patch, fibrin glue, third patch, fibrin glue).

   

  Cerebrospinal fluid leakage is rarely a problem because of the minimal dead space. Patients are placed supine with the head of bed flat postoperatively for 24 hours.

   

  PEARLS AND PITFALLS
  	Patient ▪ As with all spinal surgery, proper patient selection is the key to successful selection outcomes. Osteoporotic patients, obese patients, and patients with isthmic spondylolisthesis are challenging and should be avoided during the initial learning curve for this minimally invasive technique.     C-arm ▪ The C-arm should be placed on the opposite side of the TLIF exposure to ease placement use of frequent imaging.     Retractor ▪ The angulation of the retractor is the key to obtaining adequate exposure to positioning for perform a contralateral decompression. Removal of the base of the spinous contralateral process can aid in obtaining adequate visualization. decompression     Preservation of ▪ Preserving the pars helps avoid impingement of the exiting nerve root during pars cage placement.     Removal of ▪ Ensuring removal of anterior longitudinal ligament (ALL) bone superolateral to bone the pedicle clears the corridor for cage placement and prevents medial migration superolateral of the cage into the traversing root during insertion. to pedicle     Removal of ▪ Lessens the risk of endplate disruption from discectomy instrumentation and

   

  posterior lip eases graft sizing and placement

   

  Endplate violation

  • Avoid aggressive use of discectomy instruments, especially in osteoporotic patients. If an endplate defect occurs, placement of a second cage may be helpful to avoid graft subsidence.

     

    Pedicle cannulation

  • Properly aligned AP and lateral imaging is crucial to safe pedicle screw placement. Serial imaging going from “imperfect” to “perfect” back to imperfect improves identification of perfect imaging. Oblique imaging is useful for medially angulated pedicles.

 

Inadvertent guidewire advancement

• Images should be taken frequently during tapping and screw placement.

   

  Muscle/fascia entrapment

• Entrapment of muscle/fascia should be checked prior to closure.

 

 

 

POSTOPERATIVE CARE

 

Perioperative antibiotic prophylaxis

 

Patients are mobilized early (ie, day of surgery, if possible).

 

Antispasmodic medications are a useful addition to the postoperative pain control regimen.

 

Oral steroids can be used for postoperative radiculitis. This should be a diagnosis of exclusion; new or unexpected postoperative neurologic symptoms or signs should be investigated with imaging.

02

 

OUTCOMES

The literature supports earlier postoperative recovery, less blood loss, and decreased rates of infection in comparison to standard TLIF. Fusion rates are comparable to open posterior interbody fusion techniques.

 

 

COMPLICATIONS

Infection

The risk of infection with MIS TLIF appears to be decreased in comparison to standard techniques.

Bleeding

Bleeding is rarely enough to require transfusion.

Epidural bleeding can lead to epidural hematoma. Risk of epidural hematoma is minimized with judicious use of subfascial drains.

Nerve injury

Releasing the dural tube from the posterior vertebral body minimizes the risk of injury to the traversing

 

 

nerve root during cage insertion.

Maintaining the pars minimizes the risk of injury to the exiting nerve root during cage insertion.

The procedure may need to be aborted or done on the contralateral side if conjoined or anomalous nerve root anatomy is identified.

New or unexpected postoperative neurologic deficit should be worked up expeditiously. Reexploration to evacuate epidural hematoma and ensure there is no neural entrapment should be considered in the perioperative period as necessary.

Cerebrospinal fluid leakage

Suture is usually not necessary. Most durotomies tend to be small and can be sealed with layered collagen matrix patch and fibrin sealant.

Hardware issues

Graft subsidence can occur with endplate violation and can subsequently lead to pedicle screw failure. Care must be taken to avoid endplate violation, especially with elderly osteoporotic patients.

Pedicle screw breach is possible. Medial breaches may occur more frequently in comparison to standard techniques because of the ease of medial angulation through the paramedian exposure. Accurate radiographic views are crucial. Neuromonitoring is a useful adjunct. Neuromonitoring of the tap does not preclude breach by the screw.

Adjacent segment deterioration

May be minimized in comparison to standard techniques as a result of the preservation of adjacent segment musculotendinous attachments. Compromise of the cranial facet during screw placement must be avoided.

 

REFERENCES

1. Dhall SS, Wang MY, Mummaneni PV. Clinical and radiographic comparison of mini-open transforaminal lumbar interbody fusion with open transforaminal lumbar interbody fusion in 42 patients with longterm followup. J Neurosurg Spine 2008;9(6):560-565.

    

    

2. Karikari IO, Isaacs RE. Minimally invasive transforaminal lumbar interbody fusion: a review of techniques and outcomes. Spine 2010;35(26 suppl):S294-S301.

    

    

3. Kim CW, Garfin SR, Fessler RG. Rationale of minimally invasive spine surgery. In: Herkowitz HN, Garfin SR, Eismont FJ, et al, eds. Rothman-Simeone The Spine, ed 6. Philadelphia: Elsevier Saunders, 2011:998-1006.

    

    

4. McGirt MJ, Parker SL, Lerner J, et al. Comparative analysis of perioperative surgical site infection after minimally invasive versus open posterior/transforaminal lumbar interbody fusion: analysis of hospital billing and discharge data from 5170 patients. J Neurosurg Spine