- Email: [email protected]
Neuromonitoring in minimally invasive spine surgery
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P I N E
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27 (2015) 214–216
Available online at www.sciencedirect.com
www.elsevier.com/locate/semss
Neuromonitoring in minimally invasive spine surgery Sreeharsha V. Nandyala, MDa, Hamid Hassanzadeh, MDb, and Kern Singh, MDc,n a
Department of Orthopaedic Surgery, Harvard University, Boston, MA Department of Orthopaedic Surgery, University of Virginia, Charlottesville, VA c Department of Orthopaedic Surgery, Rush University Medical Center, 1611 W Harrison St 400, Chicago, IL 60612 b
abstract Major advances have been made in the implant technology, navigation, and imaging used in minimally invasive spine surgery. In addition, improvements in neuromonitoring protocols have improved the safety of these less invasive interventions, which are often characterized by limited direct visualization of the vital neurovascular elements. This review discusses the current practice of neuromonitoring as it relates to two commonly performed minimally invasive spine surgical procedures: the transpsoas lateral access approach and the percutaneous pedicle screw placement. & 2015 Elsevier Inc. All rights reserved.
1.
Introduction
The implementation of minimally invasive techniques in spine surgery has enabled surgeons to lessen the surgical footprint. During the last decade, advancements in access technology, imaging, and navigation have expanded the breadth of applications for minimally invasive spine surgery (MISS). This progress has enabled surgeons to use less invasive approaches for the management of complex degenerative conditions, deformity, trauma, and malignancies. MISS has shown comparable outcomes to traditional open procedures, leading to its popularity among spine surgeons.1–5 MISS aims to mitigate the drawbacks associated with open techniques, including extensive soft tissue injury that potentiates instability, blood loss, and greater use of hospital resources.4,5 In addition, MISS also represents an area of long-term cost containment.6 Improvements in procedural times, duration of hospital stay, and postoperative pain not only advance patient care but may also reduce the financial burden of spine surgery.6 As the evolution of MISS continues, the safety of these less invasive techniques must be scrutinized. Neuromonitoring n
Corresponding author. E-mail address: [email protected] (K. Singh).
http://dx.doi.org/10.1053/j.semss.2015.04.006 1040-7383/& 2015 Elsevier Inc. All rights reserved.
plays an integral part in mitigating the risk of neurologic injury during MISS. The small incisions limit visualization of the intricate neural and vascular elements. Therefore, the surgeon must rely extensively on preoperative and intraoperative imaging to identify the patient's unique anatomy. Neuromonitoring enables the surgeon to assess for nerve proximity and make appropriate adjustments in positioning and implant placement in the absence of direct visualization. This review describes the current state of neuromonitoring in two commonly performed minimally invasive spine procedures: the transpsoas lumbar approach and percutaneous pedicle screw fixation.
2.
Transpsoas lumbar approach
The transpsoas approach to the lumbar spine is used in MISS as part of the direct lateral interbody fusion and eXtreme Lateral Interbody Fusion (NuVasive Inc., San Diego, CA) techniques. The lateral approach has major advantages over anterior or posterior interbody fusion techniques because of its ability to avoid the substantially greater collateral tissue
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damage that is associated with the more conventional anterior and posterior approaches. In addition, there is limited potential for vascular, ureteral, sexual, and bowel injuries.7 The transpsoas approach is characterized by dissection through the psoas muscle body to access the lumbar disk space. The lumbar plexus is at risk for injury primarily during the dissection. In particular, the genitofemoral and lateral femoral cutaneous nerves are most likely to incur neural insults.7 The ventral nerve roots can also be compromised during the transpsoas approach, retraction of the psoas muscle, and endplate preparation. Furthermore, vascular injury can ensue because direct visualization of the retroperitoneal vessels is not feasible with this technique.8 To account for these limitations, “safe zones” have been suggested to mitigate the risk for neurovascular compromise.8 The surgeon must be cognizant of the ventral-todorsal migration of the vasculature from level L1 to L5.8 Concomitantly, the ventral nerve roots traverse anteriorly from level L1 to L5,8 and the safe zone narrows as a function of the disk's diameter in the lumbar spine. The L4–L5 level has the greatest risk for neurovascular injury because the nerve roots are located most anteriorly, whereas the retroperitoneal vessels are positioned posteriorly.9 Park et al.9 showed that neural tissue was most at risk in 25% of approaches at the L5 level compared with 5% at the L2–L3 and L3–L4 levels. The genitofemoral nerve is at most risk at the L3–L4 level, where it emerges from within the psoas muscle body and traverses on the ventral surface.7 Direct visualization during dissection, along with concurrent neuromonitoring, is advocated to prevent genitofemoral nerve injury.8,9 Meralgia paresthetica may ensue if there is stretch injury of the lateral femoral cutaneous nerve.8,9 This injury can be caused by excessive finger dissection and retractor pressure on the iliac crest. Therefore, neuromonitoring during the dissection and limiting retraction time can be instrumental in preventing this complication. Ahmadian et al.7 performed a systematic review of the literature to analyze lumbar plexopathies after lateral transpsoas procedures. They concluded that there is substantial underreporting of the postoperative nerve injury rate.7 In addition, the literature lacks a standardized classification for the clinical findings associated with postoperative nerve injury after a transpsoas approach.7 Therefore, some investigators developed a diagnostic paradigm for lumbar plexopathy.3,7 Neuromonitoring during the transpsoas approach should be used with free-run electromyography (EMG) or triggered EMG (tEMG) and somatosensory evoked potentials of the upper and lower extremities.10 tEMG monitors the proximity to the nerve within the muscle belly; the stimulus magnitude lessens with close proximity. This information provides the surgeon with real-time feedback for making appropriate adjustments during the dissection. There is considerable debate regarding whether a monopolar or bipolar probe should be used.10 With a monopolar probe, the current flows circumferentially from the tip probe, so eliciting a response depends on the proximity of the nerve from probe.10 A bipolar probe is used for precise localization of the nerves because the current runs between the two poles. In general, a
27 (2015) 214–216
215
monopolar probe is more sensitive than a bipolar probe for identifying a nerve.10 Upper- and lower-extremity somatosensory evoked potentials are paramount for preventing nerve stretch injury secondary to surgical malpositioning.10 In the upper extremity, malpositioning may potentiate the development of a brachial plexus injury.10 To detect intrapsoas nerves, some of the lateral interbody fusion technique systems come with a proprietary continuous, free-run EMG that is referred to as a “directional EMG.”10 The dilator electrodes can be rotated to assess for the proximity to neural structures. Uribe et al.11 showed that this directional EMG monitoring technique has decreased the rates of postoperative paresthesia from 30% to o1% for transpsoas lumbar procedures.
3.
Percutaneous pedicle screw placement
In an effort to preserve the posterior musculature and maintain spinal stability, percutaneous pedicle screw fixation was introduced as a less invasive technique for internal fixation.12 Percutaneous fixation is associated with reduced postoperative pain, blood loss, and hospital resource use.12 Oh et al.13 showed that the accuracy of percutaneous pedicle screw fixation is comparable to that of open screw placement, and in a literature review, Uribe et al.11 reported that the use of EMG maximized the safety of percutaneous pedicle screw placement. However, there are major limitations with this technique, including a steep learning curve and dependence on intraoperative imaging and therefore, radiation exposure.14 Percutaneous pedicle screws are placed over a guidewire within a cannulated pedicle through a small incision. A pedicle access needle is passed under fluoroscopic guidance to cannulate the pedicle and to place the guidewire. EMG stimulation is typically used to monitor percutaneous screw placement.15,16 Access needles can have an electrified awl that provides continuous EMG stimulation.15 Wood and Mannion17 showed that a pedicle access needle stimulation threshold of 45 mA was associated with favorable outcomes. After cannulation, the guidewire should be insulated to prevent current shunting and tested using tEMG. The pedicle access needle is then removed, and a tap is threaded over the guidewire. The tap will generate threads within the pedicle to facilitate pedicle screw placement.17 Threading of the pedicle may violate the cortical wall, so the tap should be insulated and tested with tEMG.15 Ozgur et al.16 have suggested that the guidewire or the tap trajectories should be repositioned if EMG thresholds are o10 mA. A pedicle screw is then advanced into the threaded pedicle, and tEMG should be used to assess for accurate placement. EMG is typically used concomitantly with intraoperative imaging or navigation to ensure appropriate placement of the percutaneous pedicle screw.
4.
Conclusion
MISS aims to reduce the surgical footprint associated with spinal intervention. However, the safety of less invasive
216
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I N E
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R G
techniques must be closely evaluated before widespread implementation. Neuromonitoring during the transpsoas lumbar approach is paramount in preventing injury to the lumbar plexus. In addition, tEMG is integral to ensure optimal percutaneous screw placement. Additional efforts should be made to establish standardized stimulation thresholds for suspected neural injury and a consistent classification system for neural injury, which is essential for comparing findings between studies.
27 (2015) 214–216
7.
8.
9.
r e f e r e n c e s 10. 1. Brodano GB, Martikos K, Lolli F, et al. Transforaminal lumbar interbody fusion in degenerative disc disease and spondylolisthesis grade I: minimally invasive versus open surgery. J Spinal Disord Tech. 2013. http://dx.doi.org/10.1097/BSD.000000 0000000034 [Epub ahead of print Oct 16]. 2. Lau D, Terman SW, Patel R, La Marca F, Park P. Incidence of and risk factors for superior facet violation in minimally invasive versus open pedicle screw placement during transforaminal lumbar interbody fusion: a comparative analysis. J Neurosurg Spine. 2013;18(4):356–361. 3. Rihn JA, Gandhi SD, Sheehan P, et al. Disc space preparation in transforaminal lumbar interbody fusion: a comparison of minimally invasive and open approaches. Clin Orthop Relat Res. 2014;472(6):1800–1805. 4. Seng C, Siddiqui MA, Wong KPL, et al. Five-year outcomes of minimally invasive versus open transforaminal lumbar interbody fusion: a matched-pair comparison study. Spine. 2013; 38(23):2049–2055. 5. Wong AP, Smith ZA, Stadler JA III, et al. Minimally invasive transforaminal lumbar interbody fusion (MI-TLIF): surgical technique, long-term 4-year prospective outcomes, and complications compared with an open TLIF cohort. Neurosurg Clin N Am. 2014;25(2):279–304. 6. Singh K, Nandyala SV, Marquez-Lara A, et al. A perioperative cost analysis comparing single-level minimally invasive and
11.
12. 13.
14.
15.
16.
17.
open transforaminal lumbar interbody fusion. Spine J. 2014; 14(8):1694–1701. Ahmadian A, Deukmedjian AR, Abel N, Dakwar E, Uribe JS. Analysis of lumbar plexopathies and nerve injury after lateral retroperitoneal transpsoas approach: diagnostic standardization. J Neurosurg Spine. 2013;18(3):289–297. Guerin P, Obeid I, Gille O, et al. Safe working zones using the minimally invasive lateral retroperitoneal transpsoas approach: a morphometric study. Surg Radiol Anat. 2011; 33(8):665–671. Park DK, Lee MJ, Lin EL, Singh K, An HS, Phillips FM. The relationship of intrapsoas nerves during a transpsoas approach to the lumbar spine: anatomic study. J Spinal Disord Tech. 2010;23(4):223–228. Jahangiri FR, Sherman JH, Holmberg A, Louis R, Elias J, VegaBermudez F. Protecting the genitofemoral nerve during direct/ extreme lateral interbody fusion (DLIF/XLIF) procedures. Am J Electroneurodiagnostic Technol. 2010;50(4):321–335. Uribe JS, Vale FL, Dakwar E. Electromyographic monitoring and its anatomical implications in minimally invasive spine surgery. Spine. 2010;35(suppl 26):S368–S374. Michael KW, Boden SD. Intraoperative neuromonitoring in spine surgery. Contemp Spine Surg. 2012;13(8):1–7. Oh HS, Kim JS, Lee SH, Liu WC, Hong SW. Comparison between the accuracy of percutaneous and open pedicle screw fixations in lumbosacral fusion. Spine J. 2013; 13(12):1751–1757. Sclafani JA, Kim CW. Complications associated with the initial learning curve of minimally invasive spine surgery: a systematic review. Clin Orthop Relat Res. 2014;472(6): 1711–1717. Isley MR, Zhang XF, Balzer JR, Leppanen RE. Current trends in pedicle screw stimulation techniques: lumbosacral, thoracic, and cervical levels. Neurodiagn J. 2012;52(2):100–175. Ozgur BM, Berta S, Khiatani V, Taylor WR. Automated intraoperative EMG testing during percutaneous pedicle screw placement. Spine J. 2006;6(6):708–713. Wood M, Mannion R. A comparison of CT-based navigation techniques for minimally invasive lumbar pedicle screw placement. J Spinal Disord Tech. 2011;24(1):E1–E5.
M I N
S
P I N E
SU
R G
27 (2015) 214–216
Available online at www.sciencedirect.com
www.elsevier.com/locate/semss
Neuromonitoring in minimally invasive spine surgery Sreeharsha V. Nandyala, MDa, Hamid Hassanzadeh, MDb, and Kern Singh, MDc,n a
Department of Orthopaedic Surgery, Harvard University, Boston, MA Department of Orthopaedic Surgery, University of Virginia, Charlottesville, VA c Department of Orthopaedic Surgery, Rush University Medical Center, 1611 W Harrison St 400, Chicago, IL 60612 b
abstract Major advances have been made in the implant technology, navigation, and imaging used in minimally invasive spine surgery. In addition, improvements in neuromonitoring protocols have improved the safety of these less invasive interventions, which are often characterized by limited direct visualization of the vital neurovascular elements. This review discusses the current practice of neuromonitoring as it relates to two commonly performed minimally invasive spine surgical procedures: the transpsoas lateral access approach and the percutaneous pedicle screw placement. & 2015 Elsevier Inc. All rights reserved.
1.
Introduction
The implementation of minimally invasive techniques in spine surgery has enabled surgeons to lessen the surgical footprint. During the last decade, advancements in access technology, imaging, and navigation have expanded the breadth of applications for minimally invasive spine surgery (MISS). This progress has enabled surgeons to use less invasive approaches for the management of complex degenerative conditions, deformity, trauma, and malignancies. MISS has shown comparable outcomes to traditional open procedures, leading to its popularity among spine surgeons.1–5 MISS aims to mitigate the drawbacks associated with open techniques, including extensive soft tissue injury that potentiates instability, blood loss, and greater use of hospital resources.4,5 In addition, MISS also represents an area of long-term cost containment.6 Improvements in procedural times, duration of hospital stay, and postoperative pain not only advance patient care but may also reduce the financial burden of spine surgery.6 As the evolution of MISS continues, the safety of these less invasive techniques must be scrutinized. Neuromonitoring n
Corresponding author. E-mail address: [email protected] (K. Singh).
http://dx.doi.org/10.1053/j.semss.2015.04.006 1040-7383/& 2015 Elsevier Inc. All rights reserved.
plays an integral part in mitigating the risk of neurologic injury during MISS. The small incisions limit visualization of the intricate neural and vascular elements. Therefore, the surgeon must rely extensively on preoperative and intraoperative imaging to identify the patient's unique anatomy. Neuromonitoring enables the surgeon to assess for nerve proximity and make appropriate adjustments in positioning and implant placement in the absence of direct visualization. This review describes the current state of neuromonitoring in two commonly performed minimally invasive spine procedures: the transpsoas lumbar approach and percutaneous pedicle screw fixation.
2.
Transpsoas lumbar approach
The transpsoas approach to the lumbar spine is used in MISS as part of the direct lateral interbody fusion and eXtreme Lateral Interbody Fusion (NuVasive Inc., San Diego, CA) techniques. The lateral approach has major advantages over anterior or posterior interbody fusion techniques because of its ability to avoid the substantially greater collateral tissue
SE
M I N
SP
I N E
S
U R G
damage that is associated with the more conventional anterior and posterior approaches. In addition, there is limited potential for vascular, ureteral, sexual, and bowel injuries.7 The transpsoas approach is characterized by dissection through the psoas muscle body to access the lumbar disk space. The lumbar plexus is at risk for injury primarily during the dissection. In particular, the genitofemoral and lateral femoral cutaneous nerves are most likely to incur neural insults.7 The ventral nerve roots can also be compromised during the transpsoas approach, retraction of the psoas muscle, and endplate preparation. Furthermore, vascular injury can ensue because direct visualization of the retroperitoneal vessels is not feasible with this technique.8 To account for these limitations, “safe zones” have been suggested to mitigate the risk for neurovascular compromise.8 The surgeon must be cognizant of the ventral-todorsal migration of the vasculature from level L1 to L5.8 Concomitantly, the ventral nerve roots traverse anteriorly from level L1 to L5,8 and the safe zone narrows as a function of the disk's diameter in the lumbar spine. The L4–L5 level has the greatest risk for neurovascular injury because the nerve roots are located most anteriorly, whereas the retroperitoneal vessels are positioned posteriorly.9 Park et al.9 showed that neural tissue was most at risk in 25% of approaches at the L5 level compared with 5% at the L2–L3 and L3–L4 levels. The genitofemoral nerve is at most risk at the L3–L4 level, where it emerges from within the psoas muscle body and traverses on the ventral surface.7 Direct visualization during dissection, along with concurrent neuromonitoring, is advocated to prevent genitofemoral nerve injury.8,9 Meralgia paresthetica may ensue if there is stretch injury of the lateral femoral cutaneous nerve.8,9 This injury can be caused by excessive finger dissection and retractor pressure on the iliac crest. Therefore, neuromonitoring during the dissection and limiting retraction time can be instrumental in preventing this complication. Ahmadian et al.7 performed a systematic review of the literature to analyze lumbar plexopathies after lateral transpsoas procedures. They concluded that there is substantial underreporting of the postoperative nerve injury rate.7 In addition, the literature lacks a standardized classification for the clinical findings associated with postoperative nerve injury after a transpsoas approach.7 Therefore, some investigators developed a diagnostic paradigm for lumbar plexopathy.3,7 Neuromonitoring during the transpsoas approach should be used with free-run electromyography (EMG) or triggered EMG (tEMG) and somatosensory evoked potentials of the upper and lower extremities.10 tEMG monitors the proximity to the nerve within the muscle belly; the stimulus magnitude lessens with close proximity. This information provides the surgeon with real-time feedback for making appropriate adjustments during the dissection. There is considerable debate regarding whether a monopolar or bipolar probe should be used.10 With a monopolar probe, the current flows circumferentially from the tip probe, so eliciting a response depends on the proximity of the nerve from probe.10 A bipolar probe is used for precise localization of the nerves because the current runs between the two poles. In general, a
27 (2015) 214–216
215
monopolar probe is more sensitive than a bipolar probe for identifying a nerve.10 Upper- and lower-extremity somatosensory evoked potentials are paramount for preventing nerve stretch injury secondary to surgical malpositioning.10 In the upper extremity, malpositioning may potentiate the development of a brachial plexus injury.10 To detect intrapsoas nerves, some of the lateral interbody fusion technique systems come with a proprietary continuous, free-run EMG that is referred to as a “directional EMG.”10 The dilator electrodes can be rotated to assess for the proximity to neural structures. Uribe et al.11 showed that this directional EMG monitoring technique has decreased the rates of postoperative paresthesia from 30% to o1% for transpsoas lumbar procedures.
3.
Percutaneous pedicle screw placement
In an effort to preserve the posterior musculature and maintain spinal stability, percutaneous pedicle screw fixation was introduced as a less invasive technique for internal fixation.12 Percutaneous fixation is associated with reduced postoperative pain, blood loss, and hospital resource use.12 Oh et al.13 showed that the accuracy of percutaneous pedicle screw fixation is comparable to that of open screw placement, and in a literature review, Uribe et al.11 reported that the use of EMG maximized the safety of percutaneous pedicle screw placement. However, there are major limitations with this technique, including a steep learning curve and dependence on intraoperative imaging and therefore, radiation exposure.14 Percutaneous pedicle screws are placed over a guidewire within a cannulated pedicle through a small incision. A pedicle access needle is passed under fluoroscopic guidance to cannulate the pedicle and to place the guidewire. EMG stimulation is typically used to monitor percutaneous screw placement.15,16 Access needles can have an electrified awl that provides continuous EMG stimulation.15 Wood and Mannion17 showed that a pedicle access needle stimulation threshold of 45 mA was associated with favorable outcomes. After cannulation, the guidewire should be insulated to prevent current shunting and tested using tEMG. The pedicle access needle is then removed, and a tap is threaded over the guidewire. The tap will generate threads within the pedicle to facilitate pedicle screw placement.17 Threading of the pedicle may violate the cortical wall, so the tap should be insulated and tested with tEMG.15 Ozgur et al.16 have suggested that the guidewire or the tap trajectories should be repositioned if EMG thresholds are o10 mA. A pedicle screw is then advanced into the threaded pedicle, and tEMG should be used to assess for accurate placement. EMG is typically used concomitantly with intraoperative imaging or navigation to ensure appropriate placement of the percutaneous pedicle screw.
4.
Conclusion
MISS aims to reduce the surgical footprint associated with spinal intervention. However, the safety of less invasive
216
SE
M I N
SP
I N E
SU
R G
techniques must be closely evaluated before widespread implementation. Neuromonitoring during the transpsoas lumbar approach is paramount in preventing injury to the lumbar plexus. In addition, tEMG is integral to ensure optimal percutaneous screw placement. Additional efforts should be made to establish standardized stimulation thresholds for suspected neural injury and a consistent classification system for neural injury, which is essential for comparing findings between studies.
27 (2015) 214–216
7.
8.
9.
r e f e r e n c e s 10. 1. Brodano GB, Martikos K, Lolli F, et al. Transforaminal lumbar interbody fusion in degenerative disc disease and spondylolisthesis grade I: minimally invasive versus open surgery. J Spinal Disord Tech. 2013. http://dx.doi.org/10.1097/BSD.000000 0000000034 [Epub ahead of print Oct 16]. 2. Lau D, Terman SW, Patel R, La Marca F, Park P. Incidence of and risk factors for superior facet violation in minimally invasive versus open pedicle screw placement during transforaminal lumbar interbody fusion: a comparative analysis. J Neurosurg Spine. 2013;18(4):356–361. 3. Rihn JA, Gandhi SD, Sheehan P, et al. Disc space preparation in transforaminal lumbar interbody fusion: a comparison of minimally invasive and open approaches. Clin Orthop Relat Res. 2014;472(6):1800–1805. 4. Seng C, Siddiqui MA, Wong KPL, et al. Five-year outcomes of minimally invasive versus open transforaminal lumbar interbody fusion: a matched-pair comparison study. Spine. 2013; 38(23):2049–2055. 5. Wong AP, Smith ZA, Stadler JA III, et al. Minimally invasive transforaminal lumbar interbody fusion (MI-TLIF): surgical technique, long-term 4-year prospective outcomes, and complications compared with an open TLIF cohort. Neurosurg Clin N Am. 2014;25(2):279–304. 6. Singh K, Nandyala SV, Marquez-Lara A, et al. A perioperative cost analysis comparing single-level minimally invasive and
11.
12. 13.
14.
15.
16.
17.
open transforaminal lumbar interbody fusion. Spine J. 2014; 14(8):1694–1701. Ahmadian A, Deukmedjian AR, Abel N, Dakwar E, Uribe JS. Analysis of lumbar plexopathies and nerve injury after lateral retroperitoneal transpsoas approach: diagnostic standardization. J Neurosurg Spine. 2013;18(3):289–297. Guerin P, Obeid I, Gille O, et al. Safe working zones using the minimally invasive lateral retroperitoneal transpsoas approach: a morphometric study. Surg Radiol Anat. 2011; 33(8):665–671. Park DK, Lee MJ, Lin EL, Singh K, An HS, Phillips FM. The relationship of intrapsoas nerves during a transpsoas approach to the lumbar spine: anatomic study. J Spinal Disord Tech. 2010;23(4):223–228. Jahangiri FR, Sherman JH, Holmberg A, Louis R, Elias J, VegaBermudez F. Protecting the genitofemoral nerve during direct/ extreme lateral interbody fusion (DLIF/XLIF) procedures. Am J Electroneurodiagnostic Technol. 2010;50(4):321–335. Uribe JS, Vale FL, Dakwar E. Electromyographic monitoring and its anatomical implications in minimally invasive spine surgery. Spine. 2010;35(suppl 26):S368–S374. Michael KW, Boden SD. Intraoperative neuromonitoring in spine surgery. Contemp Spine Surg. 2012;13(8):1–7. Oh HS, Kim JS, Lee SH, Liu WC, Hong SW. Comparison between the accuracy of percutaneous and open pedicle screw fixations in lumbosacral fusion. Spine J. 2013; 13(12):1751–1757. Sclafani JA, Kim CW. Complications associated with the initial learning curve of minimally invasive spine surgery: a systematic review. Clin Orthop Relat Res. 2014;472(6): 1711–1717. Isley MR, Zhang XF, Balzer JR, Leppanen RE. Current trends in pedicle screw stimulation techniques: lumbosacral, thoracic, and cervical levels. Neurodiagn J. 2012;52(2):100–175. Ozgur BM, Berta S, Khiatani V, Taylor WR. Automated intraoperative EMG testing during percutaneous pedicle screw placement. Spine J. 2006;6(6):708–713. Wood M, Mannion R. A comparison of CT-based navigation techniques for minimally invasive lumbar pedicle screw placement. J Spinal Disord Tech. 2011;24(1):E1–E5.