Perspectives Commentary on: Accuracy of Pedicle Screw Placement in the Thoracic and Lumbosacral Spine Using a Conventional Intraoperative FluoroscopyGuided Technique: A National Neurosurgical, Education and Training Center Analysis of 1236 Consecutive Screws by Nevzati et al. World Neurosurg 82: 866-871.E2, 2014
Accurate Pedicle Screw Placement—A Perspective Statement Carter S. Gerard and Richard G. Fessler
T
he article, “Accuracy of Pedicle Screw Placement in the Thoracic and Lumbosacral Spine Using a Conventional Intraoperative Fluoroscopy-Guided Technique: A National Neurosurgical Education and Training Centre Analysis of 1236 Consecutive Screws”, is a welcome addition to the accumulating literature evaluating the safety and accuracy of pedicle screw placement in patients undergoing posterior thoracic and lumbar instrumentation. In addition, it extends our analysis of fluoroscopically guided placement to the “training” scenario. Since the first report in 1959 by Boucher (1), pedicle screw instrumentation has gradually gained popularity and is now the nearly exclusive form of fixation in the thoracic and lumbar spine. The success of this technology stems in part from the ability of pedicle screws to stabilize all 3 columns of the spine. This results in biomechanical superiority and improved fusion rates when compared with previous technique such as hooks and rods or sublaminar wiring (5). In addition to improved rigidity, pedicle screws are generally regarded as a safe technique when performed by an experienced surgeon. Although complication rates of pedicle screw placement are low, serious injury may result from misdirected screws due to the proximity of the intended trajectory to vital structures. To further limit the potential risk to patients, multiple technologies have been applied to ensure accurate pedicle screw placement. Recent efforts to improve screw placement are vast, including neuromonitoring with screw stimulation, robotic guidance, and the increasingly common intraoperative guidance. Although all of these adjuncts have been reported to decrease screw breach rates, much controversy remains as to the true clinical value of each. The risk reduction offered by additional technology often requires added time in the operating room, additional costs, and may expose the patient to even greater
Key words Accuracy - Lumbar spine - Pedicle screw - Screw misplacement - Spinal fusion - Thoracic spine -
Abbreviations and Acronyms 2D: 2-dimensional CT: Computerized tomography
WORLD NEUROSURGERY 83 [5]: 747-749, MAY 2015
levels of radiation. Therefore, to intelligently use the rapidly expanding armamentarium of assistive devices and to understand the considerable body of literature dedicated to this subject, it is vital to clearly define what constitutes accurate placement and how that might translate to better clinical outcomes. An accurately placed screw will engage the posterior, middle, and anterior column, yet remaining in the cortices of the pedicle. There are multiple classification systems, most notably the Gertzbein classification (4) and subsequent variations, which have aided in defining pedicle screw accuracy. Using the Gertzbein classification, Nevzati et al. (8) demonstrated that those patients with spinal canal violation of >4 mm were at risk for neurological deficits (4). By describing the scale of misplacement Nevzati et al. (8) have shown that greater risk of injury is associated with greater magnitudes of erroneous placement. Although such results seem intuitive, the systematic description of screw misplacement has been essential for communication and improvement of current techniques. The traditional technique of freehand pedicle screw placement, using visual identification of anatomic landmarks alone, has previously been reported to have a misplacement rate of as high as 29% (2). This has led to the more common method of pedicle screw placement with a freehand technique and the assistance of intraoperative fluoroscopy. The freehand technique with intraoperative fluoroscopy requires the surgeon to understand the anatomic nuances of each pedicle to ensure effective screw placement. This becomes increasingly challenging in the thoracic spine or in any situation where the anatomy is altered. Nevertheless, large series have shown this technique to be safe with high levels of accuracy. Parker et al. (9) published a series that analyzed the accuracy of 6816 consecutive screws placed in the
Department of Neurological Surgery, Rush University Medical Center, Chicago, Illinois, USA To whom correspondence should be addressed: Carter S. Gerard, M.D. [E-mail: [email protected]] Citation: World Neurosurg. (2015) 83, 5:747-749. http://dx.doi.org/10.1016/j.wneu.2014.09.016
www.WORLDNEUROSURGERY.org
747
PERSPECTIVES
lumbar and thoracic spine with freehand technique consisting of anatomic landmarks, lateral fluoroscopy, and screw stimulation. Surgical indications included of pathologies with the most common being degenerative/deformity (51.2%), spondylolisthesis (23.7%), tumor (22.7%), and trauma (11.3%). After surgery, all patients were evaluated with a computerized tomography (CT) scan to assess screw placement. Misplaced screws were then defined by any breach that resulted in >25% of the screw diameter outside of the bone. Using this metric, Parker et al. (9) reported a total of 117 (1.7%) misplaced screws in 87 (9%) patients. As expected, the analysis showed a higher breach rate in the thoracic compared with the lumbar spine, with T4 and T6 at highest risk. Yet, of the patients with misplaced hardware, only 8 (0.8%) of the 964 required revision surgery due to misplaced hardware (9). In their article Nevzati et al. (8) report a series involving fluoroscopically assisted freehand technique in the setting of a teaching institution where hardware was placed by trainees under the direct supervision of attending surgeons. They retrospectively analyzed 1236 consecutively placed pedicle screws in a total of 273 patients. Using a variation of the Gertzbein classification, the degree of cortical violation, and therefore screw misplacement, was classified as minor (4 mm or the entire screw diameter). In their series, they identified 247 (20%) misplacement screws, of which 47 (3.8%) were classified as severe (>4 mm). Consistent with previous studies, the series identified the risk of misplacement to be significantly higher in the thoracic spine at 33.3% versus 18.9% in the lumbar spine. An uncomfortably high number of patients, 23 (8.4%), would ultimately require revision surgery due to misplaced hardware. Their candid analysis of the data serves as a valuable reminder to all surgeons that despite the excellent results reported in the literature, accurate freehand placement of pedicle screw remains challenging and is a skill that develops with time and practice. The article again illustrates how the variable anatomy of the spine, thoracic versus lumbar, offers unique risks that must be recognized and mitigated. The rapid development of percutaneous techniques has allowed spine surgeons to accurately place pedicle screws with a minimal exposure using a variety of imaging modalities including 2-dimensional (2D) non-navigated fluoroscopy, 2-D and 3-D computer-assisted technique fluoroscopic navigation, and CT guidance. Smith et al. (10) reported a series of 601 percutaneous pedicle screws placed in the lumbar spine with the assistance of 2D non-navigated fluoroscopy. Analysis of postoperative CT scans revealed a pedicle breach rate of 6.2%. They went on to
REFERENCES 1. Boucher HH: A method of spinal fusion. J Bone Joint Surg Br 41-B:248-259, 1959.
2. Castro WH, Halm H, Jerosch J, Malms J, Steinbeck J, Blasius S: Accuracy of pedicle screw placement in lumbar vertebrae. Spine 21: 1320-1324, 1996.
748
www.SCIENCEDIRECT.com
show a complication rate of 1.3% with no patients requiring revision surgery (10). The successful transition of stereotactic techniques from cranial surgery to the spine has enhanced our ability to safely place pedicle instrumentations. Guided pedicle screw placement with intraoperative fluoroscopy and CT have also shown favorable results with some recent studies reporting accuracy rates of 96%e97% (3, 6, 7). The development of 3D fluoroscopy (O-arm) has alleviated many of the limitations associated with the initial systems based on preoperative images such as movement from prone positioning or spinal manipulation. Although intraoperative guidance is not appropriate in every scenario, it has been shown to be valuable for cases where the risk of pedicle breach is greatest, especially in the thoracic spine (11). Although the technology is improving daily, there remain notable costs and limitations that must be considered. Initial use of the systems will certainly result in longer operating times as the staff and surgeon become accustomed to the technology. While this improves, the early delays can be considerable. Cases that span multiple levels may require repeated imaging, exposing patients to a significant amount of radiation. Furthermore, unlike a fixed cranium, the spine is a relatively mobile structure. Therefore, care must be taken after manipulation of the spine as the presented images may be spurious. For this reason, the surgeon must possess a solid understanding of the anatomy to continuously verify the fidelity of the stereotactic coordinates. Despite these hindrances, computer-assisted guidance has a role in spinal surgery and is certain to have a wider application in the future. Pedicle screws are currently the gold standard for stabilization of the thoracic and lumbar spine. The complication rate associated with pedicle screw misplacement is low, yet the results of an aberrant trajectory may be disastrous. Large series have reported high levels of accuracy for a variety of techniques including fluoroscopically assisted freehand technique, 2D nonguided fluoroscopy, and with various types of intraoperative guidance. However, regardless of the technique there remains wide variability in the skill and experience of the individual surgeon. The accuracy rates offered by experienced surgeons is comparable with intraoperative guidance and avoids the added time, radiation, and cost. Regardless of the methods used for pedicle screw placement, there is no technologic substitute, as demonstrated by Nevzati et al. (8), for practice and familiarity with the procedure. Furthermore, it is imperative to recognize the qualities that might increase the risk of screw misplacement such as instrumentation in the thoracic spine or aberrant anatomy. Once the potential hazards are identified the surgeon must take added measures to ensure accurate screw placement and a satisfactory result for his or her patient.
3. Dinesh SK, Tiruchelvarayan R, Ng I: A prospective study on the use of intraoperative computed tomography (iCT) for image-guided placement of thoracic pedicle screws. Br J Neurosurg 26: 838-844, 2012. 4. Gertzbein SD, Robbins SE: Accuracy of pedicular screw placement in vivo. Spine 15:11-14, 1990. 5. Kim YJ, Lenke LG, Cho SK, Bridwell KH, Sides B, Blanke K: Comparative analysis of pedicle screw
versus hook instrumentation in posterior spinal fusion of adolescent idiopathic scoliosis. Spine 29:2040-2048, 2004. 6. Lee M-H, Lin MH-C, Weng H-H, Cheng WC, Tsai YH, Wang TC, Yang JT: Feasibility of intraoperative computed tomography navigation system for pedicle screw insertion of the thoracolumbar spine. J Spinal Disord Tech 26:E183-E187, 2013.
WORLD NEUROSURGERY, http://dx.doi.org/10.1016/j.wneu.2014.09.016
PERSPECTIVES
7. Ling JM, Dinesh SK, Pang BC, Chen MW, Lim HL, Louange DT, Yu CS, Wang CME: Routine spinal navigation for thoraco-lumbar pedicle screw insertion using the O-arm three-dimensional imaging system improves placement accuracy. J Clin Neurosci 21:493-498, 2014. 8. Nevzati E, Marbacher S, Soleman J, Perrig WN, Diepers M, Khamis A, Fandino J: Accuracy of pedicle screw placement in the thoracic and lumbosacral spine using a conventional intraoperative fluoroscopy-guided technique: a national neurosurgical education and training centre analysis of 1236 consecutive screws. World Neurosurg 82:866-871.e2, 2014. 9. Parker SL, McGirt MJ, Farber SH, Amin AG, Rick AM, Suk I, Bydon A, Sciubba DM,
Wolinsky JP, Gokaslan ZL, Witham TF: Accuracy of free-hand pedicle screws in the thoracic and lumbar spine: analysis of 6816 consecutive screws. Neurosurgery 68:170-178, 2011. 10. Smith ZA, Sugimoto K, Lawton CD, Fessler RG: Incidence of lumbar spine pedicle breach following percutaneous screw fixation: a radiographic evaluation of 601 screws in 151 patients. J Spinal Disord Tech 27:358-363, 2014.
Conflict of interest statement: Carter Gerard has no potential conflict of interest to disclose. Richard Fessler receives royalties from DePuy-Synthes, Medtronic, and Stryker, none of which are related to the content of this manuscript. He is a consultant to DePuy-Synthes. Citation: World Neurosurg. (2015) 83, 5:747-749. http://dx.doi.org/10.1016/j.wneu.2014.09.016 Journal homepage: www.WORLDNEUROSURGERY.org Available online: www.sciencedirect.com
11. Waschke A, Walter J, Duenisch P, Reichart R, Kalff R, Ewald C: CT-navigation versus fluoroscopy-guided placement of pedicle screws at the thoracolumbar spine: single center experience of 4,500 screws. Eur Spine J 22:654-660, 2013.
WORLD NEUROSURGERY 83 [5]: 747-749, MAY 2015
1878-8750/$ - see front matter ª 2015 Elsevier Inc. All rights reserved.
www.WORLDNEUROSURGERY.org
749
Accurate Pedicle Screw Placement—A Perspective Statement Carter S. Gerard and Richard G. Fessler
T
he article, “Accuracy of Pedicle Screw Placement in the Thoracic and Lumbosacral Spine Using a Conventional Intraoperative Fluoroscopy-Guided Technique: A National Neurosurgical Education and Training Centre Analysis of 1236 Consecutive Screws”, is a welcome addition to the accumulating literature evaluating the safety and accuracy of pedicle screw placement in patients undergoing posterior thoracic and lumbar instrumentation. In addition, it extends our analysis of fluoroscopically guided placement to the “training” scenario. Since the first report in 1959 by Boucher (1), pedicle screw instrumentation has gradually gained popularity and is now the nearly exclusive form of fixation in the thoracic and lumbar spine. The success of this technology stems in part from the ability of pedicle screws to stabilize all 3 columns of the spine. This results in biomechanical superiority and improved fusion rates when compared with previous technique such as hooks and rods or sublaminar wiring (5). In addition to improved rigidity, pedicle screws are generally regarded as a safe technique when performed by an experienced surgeon. Although complication rates of pedicle screw placement are low, serious injury may result from misdirected screws due to the proximity of the intended trajectory to vital structures. To further limit the potential risk to patients, multiple technologies have been applied to ensure accurate pedicle screw placement. Recent efforts to improve screw placement are vast, including neuromonitoring with screw stimulation, robotic guidance, and the increasingly common intraoperative guidance. Although all of these adjuncts have been reported to decrease screw breach rates, much controversy remains as to the true clinical value of each. The risk reduction offered by additional technology often requires added time in the operating room, additional costs, and may expose the patient to even greater
Key words Accuracy - Lumbar spine - Pedicle screw - Screw misplacement - Spinal fusion - Thoracic spine -
Abbreviations and Acronyms 2D: 2-dimensional CT: Computerized tomography
WORLD NEUROSURGERY 83 [5]: 747-749, MAY 2015
levels of radiation. Therefore, to intelligently use the rapidly expanding armamentarium of assistive devices and to understand the considerable body of literature dedicated to this subject, it is vital to clearly define what constitutes accurate placement and how that might translate to better clinical outcomes. An accurately placed screw will engage the posterior, middle, and anterior column, yet remaining in the cortices of the pedicle. There are multiple classification systems, most notably the Gertzbein classification (4) and subsequent variations, which have aided in defining pedicle screw accuracy. Using the Gertzbein classification, Nevzati et al. (8) demonstrated that those patients with spinal canal violation of >4 mm were at risk for neurological deficits (4). By describing the scale of misplacement Nevzati et al. (8) have shown that greater risk of injury is associated with greater magnitudes of erroneous placement. Although such results seem intuitive, the systematic description of screw misplacement has been essential for communication and improvement of current techniques. The traditional technique of freehand pedicle screw placement, using visual identification of anatomic landmarks alone, has previously been reported to have a misplacement rate of as high as 29% (2). This has led to the more common method of pedicle screw placement with a freehand technique and the assistance of intraoperative fluoroscopy. The freehand technique with intraoperative fluoroscopy requires the surgeon to understand the anatomic nuances of each pedicle to ensure effective screw placement. This becomes increasingly challenging in the thoracic spine or in any situation where the anatomy is altered. Nevertheless, large series have shown this technique to be safe with high levels of accuracy. Parker et al. (9) published a series that analyzed the accuracy of 6816 consecutive screws placed in the
Department of Neurological Surgery, Rush University Medical Center, Chicago, Illinois, USA To whom correspondence should be addressed: Carter S. Gerard, M.D. [E-mail: [email protected]] Citation: World Neurosurg. (2015) 83, 5:747-749. http://dx.doi.org/10.1016/j.wneu.2014.09.016
www.WORLDNEUROSURGERY.org
747
PERSPECTIVES
lumbar and thoracic spine with freehand technique consisting of anatomic landmarks, lateral fluoroscopy, and screw stimulation. Surgical indications included of pathologies with the most common being degenerative/deformity (51.2%), spondylolisthesis (23.7%), tumor (22.7%), and trauma (11.3%). After surgery, all patients were evaluated with a computerized tomography (CT) scan to assess screw placement. Misplaced screws were then defined by any breach that resulted in >25% of the screw diameter outside of the bone. Using this metric, Parker et al. (9) reported a total of 117 (1.7%) misplaced screws in 87 (9%) patients. As expected, the analysis showed a higher breach rate in the thoracic compared with the lumbar spine, with T4 and T6 at highest risk. Yet, of the patients with misplaced hardware, only 8 (0.8%) of the 964 required revision surgery due to misplaced hardware (9). In their article Nevzati et al. (8) report a series involving fluoroscopically assisted freehand technique in the setting of a teaching institution where hardware was placed by trainees under the direct supervision of attending surgeons. They retrospectively analyzed 1236 consecutively placed pedicle screws in a total of 273 patients. Using a variation of the Gertzbein classification, the degree of cortical violation, and therefore screw misplacement, was classified as minor (4 mm or the entire screw diameter). In their series, they identified 247 (20%) misplacement screws, of which 47 (3.8%) were classified as severe (>4 mm). Consistent with previous studies, the series identified the risk of misplacement to be significantly higher in the thoracic spine at 33.3% versus 18.9% in the lumbar spine. An uncomfortably high number of patients, 23 (8.4%), would ultimately require revision surgery due to misplaced hardware. Their candid analysis of the data serves as a valuable reminder to all surgeons that despite the excellent results reported in the literature, accurate freehand placement of pedicle screw remains challenging and is a skill that develops with time and practice. The article again illustrates how the variable anatomy of the spine, thoracic versus lumbar, offers unique risks that must be recognized and mitigated. The rapid development of percutaneous techniques has allowed spine surgeons to accurately place pedicle screws with a minimal exposure using a variety of imaging modalities including 2-dimensional (2D) non-navigated fluoroscopy, 2-D and 3-D computer-assisted technique fluoroscopic navigation, and CT guidance. Smith et al. (10) reported a series of 601 percutaneous pedicle screws placed in the lumbar spine with the assistance of 2D non-navigated fluoroscopy. Analysis of postoperative CT scans revealed a pedicle breach rate of 6.2%. They went on to
REFERENCES 1. Boucher HH: A method of spinal fusion. J Bone Joint Surg Br 41-B:248-259, 1959.
2. Castro WH, Halm H, Jerosch J, Malms J, Steinbeck J, Blasius S: Accuracy of pedicle screw placement in lumbar vertebrae. Spine 21: 1320-1324, 1996.
748
www.SCIENCEDIRECT.com
show a complication rate of 1.3% with no patients requiring revision surgery (10). The successful transition of stereotactic techniques from cranial surgery to the spine has enhanced our ability to safely place pedicle instrumentations. Guided pedicle screw placement with intraoperative fluoroscopy and CT have also shown favorable results with some recent studies reporting accuracy rates of 96%e97% (3, 6, 7). The development of 3D fluoroscopy (O-arm) has alleviated many of the limitations associated with the initial systems based on preoperative images such as movement from prone positioning or spinal manipulation. Although intraoperative guidance is not appropriate in every scenario, it has been shown to be valuable for cases where the risk of pedicle breach is greatest, especially in the thoracic spine (11). Although the technology is improving daily, there remain notable costs and limitations that must be considered. Initial use of the systems will certainly result in longer operating times as the staff and surgeon become accustomed to the technology. While this improves, the early delays can be considerable. Cases that span multiple levels may require repeated imaging, exposing patients to a significant amount of radiation. Furthermore, unlike a fixed cranium, the spine is a relatively mobile structure. Therefore, care must be taken after manipulation of the spine as the presented images may be spurious. For this reason, the surgeon must possess a solid understanding of the anatomy to continuously verify the fidelity of the stereotactic coordinates. Despite these hindrances, computer-assisted guidance has a role in spinal surgery and is certain to have a wider application in the future. Pedicle screws are currently the gold standard for stabilization of the thoracic and lumbar spine. The complication rate associated with pedicle screw misplacement is low, yet the results of an aberrant trajectory may be disastrous. Large series have reported high levels of accuracy for a variety of techniques including fluoroscopically assisted freehand technique, 2D nonguided fluoroscopy, and with various types of intraoperative guidance. However, regardless of the technique there remains wide variability in the skill and experience of the individual surgeon. The accuracy rates offered by experienced surgeons is comparable with intraoperative guidance and avoids the added time, radiation, and cost. Regardless of the methods used for pedicle screw placement, there is no technologic substitute, as demonstrated by Nevzati et al. (8), for practice and familiarity with the procedure. Furthermore, it is imperative to recognize the qualities that might increase the risk of screw misplacement such as instrumentation in the thoracic spine or aberrant anatomy. Once the potential hazards are identified the surgeon must take added measures to ensure accurate screw placement and a satisfactory result for his or her patient.
3. Dinesh SK, Tiruchelvarayan R, Ng I: A prospective study on the use of intraoperative computed tomography (iCT) for image-guided placement of thoracic pedicle screws. Br J Neurosurg 26: 838-844, 2012. 4. Gertzbein SD, Robbins SE: Accuracy of pedicular screw placement in vivo. Spine 15:11-14, 1990. 5. Kim YJ, Lenke LG, Cho SK, Bridwell KH, Sides B, Blanke K: Comparative analysis of pedicle screw
versus hook instrumentation in posterior spinal fusion of adolescent idiopathic scoliosis. Spine 29:2040-2048, 2004. 6. Lee M-H, Lin MH-C, Weng H-H, Cheng WC, Tsai YH, Wang TC, Yang JT: Feasibility of intraoperative computed tomography navigation system for pedicle screw insertion of the thoracolumbar spine. J Spinal Disord Tech 26:E183-E187, 2013.
WORLD NEUROSURGERY, http://dx.doi.org/10.1016/j.wneu.2014.09.016
PERSPECTIVES
7. Ling JM, Dinesh SK, Pang BC, Chen MW, Lim HL, Louange DT, Yu CS, Wang CME: Routine spinal navigation for thoraco-lumbar pedicle screw insertion using the O-arm three-dimensional imaging system improves placement accuracy. J Clin Neurosci 21:493-498, 2014. 8. Nevzati E, Marbacher S, Soleman J, Perrig WN, Diepers M, Khamis A, Fandino J: Accuracy of pedicle screw placement in the thoracic and lumbosacral spine using a conventional intraoperative fluoroscopy-guided technique: a national neurosurgical education and training centre analysis of 1236 consecutive screws. World Neurosurg 82:866-871.e2, 2014. 9. Parker SL, McGirt MJ, Farber SH, Amin AG, Rick AM, Suk I, Bydon A, Sciubba DM,
Wolinsky JP, Gokaslan ZL, Witham TF: Accuracy of free-hand pedicle screws in the thoracic and lumbar spine: analysis of 6816 consecutive screws. Neurosurgery 68:170-178, 2011. 10. Smith ZA, Sugimoto K, Lawton CD, Fessler RG: Incidence of lumbar spine pedicle breach following percutaneous screw fixation: a radiographic evaluation of 601 screws in 151 patients. J Spinal Disord Tech 27:358-363, 2014.
Conflict of interest statement: Carter Gerard has no potential conflict of interest to disclose. Richard Fessler receives royalties from DePuy-Synthes, Medtronic, and Stryker, none of which are related to the content of this manuscript. He is a consultant to DePuy-Synthes. Citation: World Neurosurg. (2015) 83, 5:747-749. http://dx.doi.org/10.1016/j.wneu.2014.09.016 Journal homepage: www.WORLDNEUROSURGERY.org Available online: www.sciencedirect.com
11. Waschke A, Walter J, Duenisch P, Reichart R, Kalff R, Ewald C: CT-navigation versus fluoroscopy-guided placement of pedicle screws at the thoracolumbar spine: single center experience of 4,500 screws. Eur Spine J 22:654-660, 2013.
WORLD NEUROSURGERY 83 [5]: 747-749, MAY 2015
1878-8750/$ - see front matter ª 2015 Elsevier Inc. All rights reserved.
www.WORLDNEUROSURGERY.org
749
