DEFINITION

The advancement of minimally invasive techniques in spinal surgery, specifically percutaneous pedicle screw fixation, has reduced approach-related morbidity.

These techniques have been shown to be advantageous in patients with spine tumors and deformities and have become increasingly applicable for managing complex spinal trauma, including thoracolumbar trauma.

The goals of treatment of traumatic spine fracture remain the same whether an open or percutaneous approach is used: stabilize the spine to facilitate rehabilitation; enhance neurologic recovery; and prevent neurologic deterioration, delayed pain, and postoperative deformity.

 

 

ANATOMY

 

Traditional open posterior surgical approaches can result in extensive soft tissue damage, muscle denervation, and ischemia, with subsequent paraspinal muscular atrophy and decreased strength.

 

In addition, open approaches can lead to increased blood loss, protracted postoperative pain, and higher infection rates.

 

In contrast, minimally invasive procedures involve less extensile and thus less disruptive dissection. Important relevant anatomy and anatomic landmarks are discussed in following text.

 

PATHOGENESIS

 

The most common mechanisms of traumatic injury to the thoracolumbar spine are motor vehicle accidents, falls from height, and domestic violence.

 

When traumatic injury results in spinal cord injury, the loss of neurologic function is attributed to both a primary and a secondary injury process.

 

The primary injury is sustained when the spinal cord and column absorb energy from the trauma, with resultant spinal deformation and persistent postinjury compression.

 

A cascade of secondary effects ensue, including vascular changes, cell membrane lipid peroxidation, free radical formation, electrolyte shifts, neurotransmitter accumulation, and inflammation. This cascade results in expansion of the initial area of injury in a rostrocaudal fashion, leading to further gray matter loss and white matter degeneration.

 

IMAGING AND OTHER DIAGNOSTIC STUDIES

 

Preoperative advanced imaging is a critical tool for understanding the patient's pathoanatomy and preoperative planning.

 

Commonly, computed tomography (CT) and magnetic resonance imaging (MRI) scans are obtained to assess

bony and spinal cord injury, respectively.

 

Additionally, MRI can be used to assess the competency of the posterior ligamentous structures, which can assist in determining the overall stability of the injury.

 

Using preoperative images as a guide, the fluoroscope can then be precisely rotated in the axial plane to the degree of medial angulation seen on axial view CT or MRI scans at the respective level.

 

NONOPERATIVE MANAGEMENT

 

Thoracolumbar trauma has historically been managed with conservative treatment in the form of traction, casting, and bed rest.

 

However, nonoperative treatment can be complicated by the morbidities associated with prolonged immobilization.

 

With the development of minimally invasive spine surgery (MISS), we have learned that decreased surgical time, decreased blood loss, and a reduction in postoperative surgical site infection can decrease surgical morbidity in

patients with multiple traumatic injuries.3

 

The application of these principles in the setting of spine trauma offers the patient earlier mobilization and rehabilitation.

 

Recent evidence suggests that benefits of MISS include decreased incidence of pneumonia, decreased length of stay in the intensive care unit, shorter number of ventilator-dependent days, and decreased hospital charges.1,2,6

SURGICAL MANAGEMENT

 

Indications for minimally invasive percutaneous pedicle screw fixation continue to be established.

 

Multiple variables are important when considering surgical intervention, including fracture morphology, neurologic involvement, and the status of the posterior ligamentous complex.

 

The Thoracolumbar Injury Classification and Severity Score can be used to help guide the surgeon's decision-making process for operative versus nonoperative fracture management.

 

Once the decision for surgical intervention has been made, the relative indications for minimally invasive techniques include unstable thoracolumbar burst fractures, stableburst fractures for which conservative treatment has failed, flexion-distraction injuries, extension-distraction injuries, unstable sacral fractures requiring lumbopelvic stabilization, and fracture-dislocations.

 

Preoperative Planning

 

Before the surgical procedure, a thorough understanding of the patient's surgical anatomy is essential because traditional

 

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visual and tactile landmarks for pedicular fixation are not present. Thus, without optimal preoperative fluoroscopic visualization, the surgeon must keep in mind the potential risk for screw malposition.

 

In addition, corrective maneuvers for fracture reduction need to be planned. Fracture reduction can be

accomplished with a mini-open technique at the fracture level (FIG 1A), through patient positioning, or with more standardized compression-distraction forces through the pedicular implants.

 

Achieving biologic fusion is challenging in multilevel traumatic cases, and the benefit of doing so is not entirely clear. If necessary, the fusion procedure can be performed in a staged fashion through a standardized midline

approach when the patient is physiologically stable (“damage control”).

 

Alternatively, in cases in which anterior reconstruction or decompression is indicated, fusion can be achieved anteriorly with stabilization performed posteriorly with minimally invasive percutaneous pedicle screw placement.

 

Other options for achieving fusion include the use of a posterior cannula through a midline posterior approach to the facet joint. FIG 1B shows a hybrid approach to facet fusion, combining percutaneous fixation and a mini-open technique.

 

Positioning

 

The operative setup and positioning for minimally invasive spine procedures are the same as for conventional open posterior procedures.

 

 

 

FIG 1 • A. The mini-open technique is used to achieve biologic fusion in addition to percutaneous pedicle screw placement. B. Patient with spine trauma being treated with a minimally invasive technique.

 

 

The patient is positioned prone on a radiolucent table, with care being taken to pad the entire body in a systematic fashion.

 

Ensure that the eyes are well protected, the cervical spine is in a neutral position, the arms are positioned in 90 degrees of abduction and 90 degrees of elbow flexion, the bony prominences are well padded, and vital structures and distal extremities are protected from incidental injury during the operation. Additionally, the abdomen must be free of compression to improve venous return.

 

Approach

 

Percutaneous pedicle instrumentation can be performed by one of four methods: true anteroposterior (AP) targeting, Magerl (or owl's eye) technique, image-guided navigation, and biplanar fluoroscopy.

 

We describe the first two methods because these are the authors' preferred techniques for the following reasons:

 

 

By using only a true AP view, the setup is more time efficient.

 

Sterility is maintained when not alternating between AP and lateral views.

 

Two surgeons can operate simultaneously on both sides, thereby reducing procedure time and radiation exposure. However, this technique might not be feasible for every patient. Obesity, severely deformed anatomy, and osteopenia are factors that might preclude acceptable imaging of vertebral landmarks.

 

 

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TECHNIQUES

Fluoroscopic Imaging

When performing MISS, fluoroscopic imaging is essential. Therefore, the surgeon must be able to obtain a clear image and identify each vertebral body that requires treatment in both the AP and lateral views.

After the patient is positioned, the surgeon should obtain a true AP view with the center of the x-ray beam parallel to the superior endplate of the vertebra. This will produce a single superior endplate shadow as the anterior and posterior margins are superimposed on each other.

 

TECH FIG 1 • True AP (A) and lateral (B) view fluoroscopic images obtained before commencing percutaneous needle placement.

 

Furthermore, the pedicle shadows should be just inferior to the superior endplate shadow and the spinous process will lie equidistant between the pedicles (TECH FIG 1).

Pedicle Starting Points

After a true AP fluoroscopy view is obtained, the surgeon defines the starting points on the patient's skin by placing a Kirschner wire (K-wire) longitudinally over the lateral border of the pedicles on either side of the spine.

This position is marked, and the K-wire is then placed transversely across the pedicles of each targeted vertebra.

A second line is marked to intersect the first two longitudinal lines.

Next, skin incisions are marked 1 cm lateral to the intersection of the skin marks. This accounts for the divergent trajectory of the pedicles and helps to better align the skin and fascial incisions with the bony target (TECH FIG 2).

 

 

 

 

 

TECH FIG 2 • Preoperative skin markings show the minimally invasive screw starting points.

True Anteroposterior View Method

 

The skin and fascia are incised, and the muscular tissues are dissected bluntly until the transverse process is palpated. Jamshidi needles are inserted into the incisions and are docked at the correct starting point for each pedicle.

 

This point is the intersection of the lateral border of the upgoing facet, the midline of the transverse process, and the upslope of the pars interarticularis.

 

A true AP view image is obtained to verify this location, and the needle tip should overlie the midlateral wall of the pedicle. If the pedicle is imagined to be a clock face, this is the 3 o'clock position for the patient's right pedicle and the 9 o'clock position for the patient's left pedicle.

 

The craniocaudal direction of the needle can be simultaneously verified on fluoroscopy. Once the proper position of the Jamshidi needle is confirmed, it is tapped with a mallet to penetrate a few millimeters into the cortex.

 

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At that time, the needle shaft can be realigned to be parallel to the superior vertebral endplate.

 

The shaft of the Jamshidi needle is then marked 2 cm above the skin to track the depth of penetration into the pedicle. The depth is confirmed by checking the preoperative imaging studies and measuring the length of the pedicle at each level.

 

Then, with the needle shaft parallel to the endplate on the true AP view and with 10 to 12 degrees of lateral to medial angulation, the needle is tapped to the depth of the mark on the shaft.

 

 

 

TECH FIG 3 • A. The Jamshidi needle being advanced into the pedicle. B. AP view fluoroscopic image confirms appropriate placement of the Jamshidi needles within the pedicles.

 

 

The tip of the needle should be at the base of the pedicle, anterior to the posterior wall (TECH FIG 3). A blunt-tipped guidewire is driven through the needle into the cancellous bone and advanced 10 to 15 mm past the tip of the needle.

 

The needle is removed as the guidewire is held in position, the pedicle is tapped, and a cannulated pedicle screw is placed. A true lateral view radiograph can be used to confirm the appropriate depth of the screw. All the aforementioned steps are performed at each vertebral level to be instrumented.

• Magerl, or Owl's Eye, Technique

   

  This method involves a fluoroscopic view along the axis of the pedicle. To obtain the owl's eye (or en face) view, the x-ray beam is positioned directly in line with the pedicle axis.

   

  First, a true AP view of the vertebra of interest is obtained. The C-arm is then rotated until the x-ray beam is parallel to the pedicle (typically 10 to 30 degrees oblique to the true AP view) (TECH FIG 4).

   

  Once a proper view has been obtained, the skin incision should be made directly over the pedicle.

   

  Placement of the Jamshidi needle, K-wire exchange, and pedicle cannulation or screw placement should then be performed in the same manner as with other techniques.

   

  Intermittent lateral view fluoroscopic images or preoperative images can aid in determining the depth of instrument positioning.

   

  Obtaining an en face view of the S1 pedicle is achieved in a slightly different manner. Because the pedicle is not cylindrical at the S1 level, only the medial wall is visible on its projection.

   

  The surgeon must first align the C-arm in the sagittal plane such that the superior sacral endplate appears as a single line. The C-arm is then rotated axially to obtain the maximum resolution of the medial pedicle wall.

   

  As with the lumbar spine, determination of the medial angulation of the pedicle can be aided with preoperative axial view CT or MRI scans.

   

   

   

  TECH FIG 4 • Fluoroscopic image shows the Magerl technique of screw insertion.

• Rod Placement

   

  A few basic principles allow the successful and efficient percutaneous placement of rods. Of primary importance is screw positioning, with special attention paid to align the screw heads in the coronal and sagittal planes.

   

  Screw depth is determined by advancing the screws to a position at which they meet slight resistance against the lateral border of the facet joint.

   

  The tops of the screw extensions and cannulae should demonstrate a smooth transition between levels and symmetric angulation.

   

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  The tops of the screw extensions can be used to assess rod contouring in the appropriate coronal and sagittal planes.

   

  Once contoured, the rod should be inserted in a cranial to caudal manner because of the protective, shingling effect of the thoracic and lumbar lamina.

   

   

  An example of the workflow for rod insertion during a multilevel procedure is as follows: First, rod length is estimated and precontoured before passage.

   

  Second, to maximize sensory feedback, a two-handed technique should be used (TECH FIG 5). The

  surgeon's dominant hand is placed on the rod holder, and the nondominant hand remains free to manipulate the screw heads.

   

  TECH FIG 5 • A-C. Three different angles and stages of rod placement and passage and technique.

   

  While pushing the rod, the surgeon can rotate each screw head to allow passage. To confirm successful placement, the surgeon can attempt to rotate the screw heads.

  If rotation of the screw head is possible, the rod passage must be reattempted.

  Alternatively, the surgeon can use another instrument, such as a screwdriver, for tactile feedback as the rod passes through each screw head.

   

   

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  PEARLS AND PITFALLS

  • The owl's eye technique can provide an excellent view of the pedicle, but certain disadvantages are associated with the technique.

  • First, this technique precludes working simultaneously on either side of the patient, requiring realignment of the C-arm twice per level. This increases radiation exposure to the patient and the surgical team.

  • Second, this technique is associated with a higher rate of medial pedicle wall violation, likely secondary to the more medial starting position of the pedicle screws. Because the spinal canal is not well visualized with the en face projection, a medial violation might not be recognized. Therefore, it is critical that pedicle cannulation is started in a lateral position at the junction of the transverse process and facet.

  • When longer or curved rods are needed, insertion and positioning of these rods can be challenging.

   

   

   

   

  • Precise and careful positioning of the pedicle screws is essential and should not be overlooked. It is important to remain deep to the fascia and to use the rod's bend to steer the tip and facilitate the passage.

     

  • Furthermore, the development of more advanced implant systems has made multilevel procedures easier to perform.

     

  • Determining proper rod length for multilevel constructs can also be challenging. Although most implant manufacturers have equipment to aid in this process, multiple inspections should be performed using lateral view fluoroscopy to confirm that the rod length is correct.

     

  • Percutaneous pedicle fixation of the upper thoracic spine deserves special consideration because of the inherent magnitude of upper thoracic kyphosis.

     

  • Adequate fluoroscopic images might be difficult to obtain because of patient positioning and body habitus.

     

  • To aid in fluoroscopic imaging, placing the patient's head into a skeletal pin headrest and simultaneously flexing the cervical spine and translating the spine anteriorly might facilitate the process.

     

  • Positioning the head in this fashion also enables the rod and the rod holder to be manipulated through the upper screw extensions without maneuvering around the patient's head.

     

  • Percutaneously placed multilevel constructs that cross the thoracolumbar junction can also present a challenge.

     

  • Although the lordotic portion of the rod might pass easily across the thoracic kyphosis, passage of the rod from the upper thoracic region toward the lumbosacral junction generally becomes more difficult as the kyphotic portion of the rod is passed across the thoracic apex.

     

  • Manipulation of the kyphotic portion of the rod into a more coronal plane or a frank lordotic position usually assists the passage of the rod across the thoracic spine. Rod inserters that allow in situ rotation of the rod can help to overcome these challenges.

 

POSTOPERATIVE CARE

 

Standard postoperative care should be delivered to all patients after percutaneous pedicle fixation, including pain control, deep vein thrombosis prophylaxis, and progressive physical therapy.

 

OUTCOMES

The literature evaluating the results of MISS with percutaneous pedicle fixation continues to evolve. Several studies have examined the rates of postoperative surgical infection associated with minimally invasive techniques.

 

 

O'Toole et al5 reported three surgical site infections among 1338 minimally invasive spinal procedures in 1274 patients with a mean age of 55.5 years. The surgical site infection rate was 0.10% for simple decompressive procedures, 0.74% for fusion and/or fixation procedures, and 0.22% overall. The authors compared their rate with the 2% to 6% reported rates in large clinical series of open spinal procedures and concluded that minimally invasive techniques might reduce postoperative wound infections by nearly 10 fold.

 

Rodgers et al8 examined a retrospective cohort of 313 patients treated with minimally invasive extreme lateral interbody fusion and found no surgical site infections.

 

Wang et al10 compared 20 patients with type A thoracolumbar fractures treated with traditional open pedicle screw fixation with 17 patients treated with percutaneous pedicle screw techniques. The authors found that the percutaneously treated cohort had significantly smaller incisions, less estimated blood loss, shorter intraoperative time, decreased lengths of stay, and less postoperative pain.

 

Poelstra et al7 conducted a restrospective review of 10 patients managed with damage control orthopaedics and minimally invasive techniques for unstable thoracolumbar fractures associated with life-threatening injuries.

 

Nonoperative brace treatment was not possible because of fracture type, associated injuries, or body habitus (>300 pounds), and all patients were too hemodynamically unstable to undergo open spinal stabilization.

 

Patients were followed for a minimum of 1 year. Postoperative CT scans confirmed that a total of 82 screws in 10 patients were placed without pedicle breaches. Blood loss was an average of 177 mL, and the average length of surgery from time of incision to transfer of the patient to the intensive care unit was 95 minutes.

 

All patients underwent minimally invasive spinal stabilization within 48 hours after injury, all patients survived their trauma, and no revision surgery was performed.

 

The authors concluded that damage control spinal stabilization via a minimally invasive technique is appropriate for patients who have suffered multisystem trauma and complex unstable spinal injuries. However, further studies are needed to assess whether immediate patient survival and eventual functional outcomes are truly improved with an MISS damage control approach.

 

In a patient with multiple traumatic injuries, minimally invasive spinal fixation might play an important role in allowing early stabilization of thoracolumbar spinal fractures and could consequently minimize the morbidities associated with delayed fixation.

 

McHenry et al4 retrospectively reviewed risk factors of respiratory failure in 1032 patients at a level 1 trauma center after operative stabilization of thoracolumbar spinal fractures.

 

They found the following five independent risk factors for respiratory failure: age older than 35 years, Injury Severity Score greater than 25 points, Glasgow Coma Scale score below 12 points, blunt chest injury, and surgical stabilization performed more than 2 days after admission.

 

They concluded that early operative stabilization of thoracolumbar fractures—the only risk factor that can be controlled by the physician—might decrease the risk of respiratory failure in multiply injured patients.

 

COMPLICATIONS

As with any surgical intervention, the benefits of operative stabilization must be weighed against the risks of surgery, especially in a critically ill patient suffering from multiple systemic traumatic injuries.

 

Although the risk of blood loss is less compared with conventional open techniques, care should be coordinated among the entire medical team to optimize preoperative risks in cases of hemodynamic instability, coagulopathy, hypothermia, or elevated serum lactate levels.

Compared with open surgical techniques, postoperative infection rates associated with minimally invasive

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techniques are substantially reduced. Implant malpositioning, loss of reduction, and failure of fusion are other potential pitfalls of minimally invasive techniques that are yet to be determined.

 

 

CONCLUSIONS

The purported benefits of MISS are reduction of blood loss, reduced postoperative pain, lower complication rates, fewer days spent in the hospital, and quicker return to work.

These benefits have been shown to be true when looking at degenerative conditions of the spine treated in this fashion. However, when looking at applying minimally invasive solutions for traumatic injuries of the spine, these benefits are yet to be proven.

The greatest benefit, however, of the minimally invasive procedure in a traumatically injured patient is reduction in the postoperative infection rate. Thus, when a surgeon is deciding whether to use minimally invasive techniques for traumatic thoracolumbar disorders, he or she needs to establish the proper indications for the procedure, offer the procedure for those cases in which it is superior to perform a conventional open procedure, establish revision strategies if the technique is not effective, and minimize complications.

 

 

ACKNOWLEDGMENT

We thank senior editor and writer Dori Kelly, MA, for invaluable assistance with the manuscript.

 

REFERENCES

1. Cengiz SL, Kalkan E, Bayir A, et al. Timing of thoracolomber spine stabilization in trauma patients; impact on neurological outcome and clinical course: a real prospective (rct) randomized controlled study. Arch Orthop Trauma Surg 2008;128(9):959-966.

    

    

2. Croce MA, Bee TK, Pritchard E, et al. Does optimal timing for spine fracture fixation exist? Ann Surg 2001;233(6):851-858.

    

    

3. Kerwin AJ, Frykberg ER, Schinco MA, et al. The effect of early surgical treatment of traumatic spine injuries on patient mortality. J Trauma 2007;63(6):1308-1313.

    

    

4. McHenry TP, Mirza SK, Wang J, et al. Risk factors for respiratory failure following operative stabilization of thoracic and lumbar spine fractures. J Bone Joint Surg Am 2006;88(5):997-1005.

    

    

5. O'Toole JE, Eichholz KM, Fessler RG. Surgical site infection rates after minimally invasive spinal surgery. J Neurosurg Spine 2009;11(4): 471-476.

    

    

6. Pakzad H, Roffey DM, Knight H, et al. Delay in operative stabilization of spine fractures in multitrauma

   patients without neurologic injuries: effects on outcomes. Can J Surg 2011;54(4):270-276.

    

    

7. Poelstra KA, Gelb D, Kane B, et al. The feasibility of damage control spinal stabilization (MISS) in the acute setting for complex 1 thoracolumbar fractures. Presented at the 23rd Meeting of the North American Spine Society; October 14-18, 2008; Toronto, Canada.

    

    

8. Rodgers WB, Cox CS, Gerber EJ. Early complications of extreme lateral interbody fusion in the obese. J Spinal Disord Tech 2010;23(6):393-397.

    

    

9. Scalea TM, Boswell SA, Scott JD, et al. External fixation as a bridge to intramedullary nailing for patients with multiple injuries and with femur fractures: damage control orthopedics. J Trauma 2000;48(4):613-621.

    

    

10. Wang HW, Li CQ, Zhou Y, et al. Percutaneous pedicle screw fixation through the pedicle of fractured vertebra in the treatment of type A thoracolumbar fractures using Sextant system: an analysis of 38 cases. China J Traumatol 2010;13(3):137-145.