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Placement of Percutaneous Thoracic Pedicle Screws Using NeuroNavigation
PEER-REVIEW REPORTS
Placement of Percutaneous Thoracic Pedicle Screws Using NeuroNavigation Udaya K. Kakarla, Andrew S. Little, Steve W. Chang, Volker K. H. Sonntag, Nicholas Theodore
Key words 䡲 Image guidance 䡲 Minimally invasive 䡲 Pedicle screw placement 䡲 Percutaneous 䡲 Spinal instrumentation 䡲 Thoracic spine neuronavigation Abbreviations and Acronyms CT: Computed tomography From the Division of Neurological Surgery, Barrow Neurological Institute, St. Joseph’s Hospital and Medical Center, Phoenix, Arizona, USA To whom correspondence should be addressed: Nicholas Theodore, M.D. [E-mail: [email protected]] Citation: World Neurosurg. (2010) 74, 6:606-610. DOI: 10.1016/j.wneu.2010.03.028 Supplementary digital content online Journal homepage: www.WORLDNEUROSURGERY.org Available online: www.sciencedirect.com 1878-8750/$ - see front matter © 2010 Elsevier Inc. All rights reserved.
INTRODUCTION Recent advances in neuronavigation have revolutionized the field of craniospinal surgery (2, 4, 7, 8). The use of intraoperative image acquisition has augmented existing neuronavigational protocols, which relied on images obtained preoperatively. Intraoperative neuronavigation provides real-time feedback about surgical anatomy for precise and accurate execution of the surgical procedure. It has been successfully used for spinal instrumentation and craniospinal fixation (4, 5). Iso-C C-arm (Siremobil Iso-C 3D, Siemens Medical Solutions; Erlangen, Germany) provides an accurate three-dimensional volume from multiple fluoroscopic images acquired in the axial plane centered over an isocentric point. Thoracic pedicle screw fixation is technically challenging because of the complexity of the spinal anatomy involved and the proximity of critical neurovascular structures. Percutaneous placement is further complicated by the obscuration of normal surgical landmarks by soft tissue. Percutaneous posterior spinal instrumentation has the potential benefits of minimizing operative exposure and
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䡲 BACKGROUND: Percutaneous thoracic pedicle screw fixation is challenging because of the complexity of the spinal anatomy and obscuration of normal surgical landmarks by soft tissue. We report a novel percutaneous technique in which intraoperative Iso-C C-arm navigation was used to treat complex thoracic spinal fractures. 䡲 METHODS: Between March and September 2007, percutaneous thoracic pedicle screw fixation was performed with the assistance of intraoperative Iso-C C-arm fluoroscopy in six patients (two males, four females; mean age ⴝ 33 years, range ⴝ 16-61 years) with unstable thoracic fractures. The accuracy of pedicle screw placement was assessed by postoperative computed tomography and graded according to the method of Youkilis et al. 䡲 RESULTS: Five patients had unstable acute traumatic fractures and one had an osteoporotic burst fracture. Altogether, 19 spinal segments (range ⴝ 2-4/patient) were fixated using 37 pedicle screws. Pedicle screw misplacement was grade II in 16% and grade III in 3%. None of the patients had neurologic consequences due to screw misplacement, and none required conversion to an open procedure or revision of hardware. There was one wound infection. 䡲 CONCLUSION: Percutaneous thoracic pedicle screw fixation with intraoperative neuronavigation for the stabilization of complex spinal fractures is feasible and associated with acceptable rates of accuracy and morbidity.
muscle dissection, blood loss, and hospital stays. To date, percutaneous thoracic techniques have relied on intraoperative fluoroscopy or preoperatively obtained imaging for navigation. Fluoroscopy is limited by visualization of the pedicle, which may be difficult in obese or osteoporotic patients. Neuronavigation using previously acquired images is limited by the anatomic shifts that can occur during positioning of the patient and in unstable fractures. We present the first technical description of the placement of percutaneous thoracic pedicle screws with the assistance of neuronavigation performed with images acquired intraoperatively and discuss surgical nuances to improve accuracy of placement.
years; range ⫽ 16-61 years) were treated for unstable thoracic spine fractures using the technique described here (Table 1). Five patients had traumatic fractures and one had an osteoporotic burst fracture. No patient presented with a neurologic deficit. Three patients demonstrated instability in an external orthotic brace before internal fixation.
METHODS AND MATERIALS
Equipment The Iso-C system (Siremobil Iso-C 3D) has been well described by Hott et al. (4). Briefly, the equipment consists of a modified C-arm computed tomography (CT) system with a 15-
Patient Population Between March and June 2007, six patients (two males, four females; mean age ⫽ 33
Patient Selection Patients were candidates for percutaneous pedicle screw placement if they sustained unstable thoracic fractures without spinal cord compression or if they required supplementation of an anterior construct.
WORLD NEUROSURGERY, DOI:10.1016/j.wneu.2010.03.028
PEER-REVIEW REPORTS UDAYA K. KAKARLA ET AL.
PERCUTANEOUS PEDICLE SCREWS
Table 1. Clinical Summary of the Six Patients Screw Error Patient
Age (Years)/Sex
Presentation
Findings
Intervention
No. of Screws
Grade II
Grade III
Complications/ New Deficits
1
47/F
Auto Ped/Central Cord/ GCS 15; UE 2/5; LE 3-4/5
T8 chance Fx, T9 facet Fx
C3-6 laminectomy and fusion/T7-T10 PSF
4
0
0
None
2
61/F
Back pain with new LE tingling; LE strength 4/5
T11 osteoporotic burst Fx with conus compression
T11 Corpectomy; T9-L1 PSF
8
1
1
None
3
16/M
Motorcycle crash
T8 comp Fx; T9 burst Fx; unstable in TLSO
T7-T10 PSF
5
0
0
None
4
31/F
MVA
T9 burst; C7 comp Fx; T2-3 Fx; unstable in TLSO
T8-T10 PSF
4
1
0
None
5
17/F
MVA ejection
Hangman’s Fx/T3 Fx dislocations
T1-T5 PSF; C1-C3 fusion
8
2
1
None
6
26/M
Motorcycle crash; GCS 15; No deficits
L1 compression – chance Fx; facet distraction
T11-L2 PSF
8
1
Infection
C, cervical; F, female; Fx, fracture; GCS, Glasgow Coma Scale; LE, lower extremities; L, lumbar; M, male; MVA, motor vehicle accident; PSF, pedicle screw fixation; T, thoracic; TLSO, thoracolumbosacral orthosis; UE, upper extremities
or 23-cm image intensifier and orbital drive. During 3-D image acquisition, the motorized C-arm moves continuously around 190 degrees of rotation acquiring 50 to 100 projection images of fluoroscopy at equidistant angles. A high-resolution 3-D image data set (resolution ⬍ 0.5 mm) is reconstructed using the precisely known rotation geometry, and the images are displayed using slice-image techniques (multiplanar reconstruction) or surface-shaded displays. For navigation during posterior spinal procedures, the reference frame is placed on the spinous process of the adjacent vertebral body. The mean time from scan acquisition until the images are reconstructed and available for navigation is about 5 minutes.
Instrumentation For spinal instrumentation, a Horizon Longitude system (Sofamor-Danek, Medtronic; Minneapolis, MN, USA) was used in all cases. Briefly, the system consists of cannulated pedicle screws with screw extenders, allowing screws to be placed into the pedicles. A rod inserter helps guide a rod over the pedicle screws through the slots in the pedicle screw extenders. This maneuver also helps reduce the rod into the screw heads before the screws are locked.
view. A 2-cm midline incision was made Data and Outcome Analysis one level above the rostral spinal level to Operative time and complications were be instrumented. recorded. Intraoperative Iso-C was not Subperiosteal dissection was performed performed after the screws were placed to expose the spinous process. A reference because artifact from the metal is often arc was firmly attached to the midline spisignificant. Instead, all patients undernous process. With the reference arc in went postoperative CT to assess pedicle range, Iso-C C-arm images were acquired screw accuracy. Accuracy was graded acand 3-D volume images were reconcording to the method of Youkilis et al. structed. The instrumentation tools were (8): Grade I is screw placement within the synchronized with the neuronavigation to pedicle without cortical violation. Grade provide live feedback in all II is a cortical violation of planes of the spine. The acculess than 2 mm. Grade III is a racy of the navigation was cortical violation beyond 2 checked by verifying the bony mm. The grading was perlandmarks before any definiformed by an independent Video available at tive surgical maneuvers were physician who was not inWORLDNEUROSURGERY.org performed. volved in the care of the patients, and the results are A 1-cm incision was made presented here. 2-3 mm lateral to the surface mark made for the pedicles. An image-guided drill guide was placed over the pedicle entrance point, and the desired trajectory was achieved based on Operative Technique (Video) live navigation. A K-wire was advanced into Patients were positioned in the prone pothe pedicle using a pneumatic drill. This step sition on a Jackson radiolucent table. The was repeated until K-wires were placed in all arms were tucked on the patient’s side. pedicles of interest in a caudal-to-cephalad Somatosensory evoked potentials and direction. The pedicles were tapped over the motor evoked potentials were monitored. K-wire with care taken to avoid advancing the The Iso-C C-arm was used to mark the K-wire during this step. Cannulated pedicle pedicles of the thoracic levels on the surscrews attached to screw extenders were inface of the skin using the anteroposterior
WORLD NEUROSURGERY 74 [6]: 606-610, DECEMBER 2010
www.WORLDNEUROSURGERY.org
607
PEER-REVIEW REPORTS UDAYA K. KAKARLA ET AL.
PERCUTANEOUS PEDICLE SCREWS
Figure 1. A 16-year-old boy after motorcycle crash. (A) Sagittal CT showed a fracture of the T9 vertebral body and loss of alignment. (B) MRI with STIR signal changes in T9 vertebral body. Axial CTs of T7 (C) shows perfect or Grade I screw placement at all levels, at T8 (D), and at T9 (E). (F) Postoperative photograph showing excellent wound healing at 6 weeks. Used with permission from Barrow Neurological Institute.
serted into the pedicles over the K-wires under image guidance, after which the K-wires were removed. At this point, an optional 3D spin can be performed to verify the accuracy of pedicle screw placement. However, the image quality is often degraded as a result of significant metallic artifact. The reference arc was removed, and a rod was inserted into the pedicle screw heads percutaneously through the slots of the screw extenders. An anteroposterior fluoroscopic image was used to verify adequate rod placement on the screw heads. The rods were reduced into the screw heads and locked into place using an antitorque device. The fascia was closed in the midline incision, and all
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www.SCIENCEDIRECT.com
paramedian incisions were closed subcutaneously.
RESULTS Six patients underwent successful thoracic spinal fixation using the technique described above (Table 1). No patients required conversion to an open procedure. Thirty-seven pedicle screws were placed to stabilize a total of 19 spinal segments. Seven screws (19%) showed cortical violation of the pedicle (Table 1). Six screws (16%) were grade II misplacements, and one (3%) was grade III. None of the patients showed neurologic deficits as a result of pedicle screw
misplacement, and none of the pedicle screws were revised. Intraoperative somatosensory evoked potential and motor evoked potentials were stable during all procedures. One patient developed a superficial wound infection, which was treated with debridement and antibiotics.
CASE ILLUSTRATIONS Case 1 (see operative video) A 16-year-old boy crashed his motorcycle and was admitted as a Level 1 trauma with a Glasgow Coma Scale score of 10T. There was no evidence of spinal cord injury. He had fractures of the T8 and T9 vertebral
WORLD NEUROSURGERY, DOI:10.1016/j.wneu.2010.03.028
PEER-REVIEW REPORTS UDAYA K. KAKARLA ET AL.
PERCUTANEOUS PEDICLE SCREWS
Figure 2. A 61-year-old woman with back pain and paraparesis. (A) Sagittal CT showed a chronic T11 burst fracture associated with loss of height. (B) Sagittal T2-weighted MRI showed increased signal suggesting an acute component of the fracture. (C) Sagittal CT after anterior corpectomy with cage reconstruction demonstrated restoration of height and alignment. (D) Coronal CT after percutaneous pedicle screw placement. (E) Axial CTs demonstrated grade II misplacement at L1 of right pedicle screw and (F) Grade III placement of left pedicle screw at L1. Used with permission from Barrow Neurological Institute.
bodies (Figure 1A and B). He was placed in an external orthotic brace but was unstable on upright and supine x-rays. He underwent posterior internal fixation from T7 to T10 with no cortical surface violation (Figure 1C-E). He remained neurologically intact and was discharged to a rehabilitation facility. At his 6-week follow-up visit, his wounds had healed well (Figure 1F) and he reported no pain. Case 2 A 61-year-old woman with history of systemic lupus erythematosus and chronic ste-
roid use sought treatment for worsening back pain, lower extremity tingling, and urinary retention. CT and magnetic resonance imaging of the lumbar spine showed an acute and chronic osteoporotic burst fracture of the T11 vertebral body that compromised the spinal canal (Figure 2A and B). She underwent a thoracotomy for a T11 corpectomy with placement of an expandable cage and plate (Figure 2C). Given her poor bone quality, she underwent posterior fixation from T9-L1 to prevent failure of the anterior construct (Figure 2D). Postoperative imaging revealed that two screws had
WORLD NEUROSURGERY 74 [6]: 606-610, DECEMBER 2010
been misplaced (Figure 2E and F) with no clinical significance. She recovered well and was discharged to a rehabilitation facility in a thoracolumbosacral orthosis.
DISCUSSION Pedicle screw fixation of the thoracic spine is used to stabilize fractures and to correct spinal deformities. The procedure is technically demanding because the pedicles are small and adjacent to the lungs and great vessels. Until now, appropriate screw placement re-
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PEER-REVIEW REPORTS UDAYA K. KAKARLA ET AL.
quired wide exposure of the spinal anatomy, extensive use of fluoroscopy, or both. The rate of misplacement of thoracic pedicle screws is estimated to be 15%-25% using traditional landmarks and fluoroscopy (8). The goal of image guidance is to improve the accuracy of screw placement as demonstrated in cadaveric studies comparing CT image guidance to conventional open laminoforaminotomy (1, 3, 6) and in large clinical studies (5, 8). Youkilis et al. (8) placed 266 thoracic pedicle screws in 65 patients using wide exposure for landmarks coupled with image guidance. Their misplacement rate was 8.6%. In a study comparing two image-guidance systems for the placement of thoracic pedicle screws, Lekovic et al. (5) reported unintended perforations by 8.7% of the screws when using Fluoro-nav and by 5.3% when using Iso-C. This difference was not statistically significant. Minimally invasive techniques in spinal surgery have become increasingly popular. Their theoretical advantages are decreased morbidity related to decreased blood loss and muscle dissection, less postoperative pain, and a decreased need for rehabilitation. In a feasibility and safety study, Ringel et al. (7) placed percutaneous posterior pedicle screws in the thoracic and lumbar spine using fluoroscopy in 104 patients. Cortical violation occurred in 13% of the 488 pedicle screws placed. Nine patients underwent a repeat operation for misplaced screws. Of these, two patients developed neurologic symptoms as a result of misplacement. Percutaneous techniques coupled with image guidance offers an ideal combination of increased accuracy and decreased morbidity. To our knowledge, the current report is first to evaluate at the feasibility of this approach in as many as four motion segments. This technique was used only in patients requiring posterior internal fixation as determined by the senior author
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PERCUTANEOUS PEDICLE SCREWS
(N.T.). Cortical violations occurred in 19% of the cases with no clinical sequellae or revisions. This rate is slightly higher than that reported by Youkilis et al. (8) and Lekovic et al. (5). This difference could be attributed to several factors. The patient population was small, and a learning curve must be expected when new surgical techniques are used. Accuracy should improve with experience as we have already noticed in these first six cases. Based on our limited experience with this new technique and large experience using image guidance for open spinal instrumentation, we offer the following caveats to improve accuracy of screw placement and to avoid frustration during the procedure. 1. Avoid leaning on the patient or pushing hard on the spine while placing the Kwire. These movements could affect the reference arc and decrease accuracy. 2. Placing the K-wires in a caudal-to-cranial direction avoids the wires obstructing navigation. 3. Rods should be inserted in a cranial-tocaudal direction to decrease the chance of accidental insertion into the spinal canal. 4. The surgeon should always be prepared to convert to an open procedure if necessary. 5. Image quality with Iso-C image guidance is poor and less reliable in morbidly obese patients.
CONCLUSION
REFERENCES 1. Austin MS, Vaccaro AR, Brislin B, Nachwalter R, Hilibrand AS, Albert TJ: Image-guided spine surgery: a cadaver study comparing conventional open laminoforaminotomy and two image-guided techniques for pedicle screw placement in posterolateral fusion and nonfusion models. Spine 27:2503-2508, 2002. 2. Foley KT, Gupta SK: Percutaneous pedicle screw fixation of the lumbar spine: preliminary clinical results. J Neurosurg (Spine 1) 97:7-12, 2002. 3. Hart RA, Hansen BL, Shea M, Hsu F, Anderson GJ: Pedicle screw placement in the thoracic spine: a comparison of image-guided and manual techniques in cadavers. Spine 30:E326-E331, 2005. 4. Hott JS, Deshmukh VR, Klopfenstein JD, Sonntag VK, Dickman CA, Spetzler RF, Papadopoulos SM: Intraoperative Iso-C C-arm navigation in craniospinal surgery: the first 60 cases. Neurosurgery 54:1131-1136, 2004. 5. Lekovic GP, Potts EA, Karahalios DG, Hall G: A comparison of two techniques in image-guided thoracic pedicle screw placement: a retrospective study of 37 patients and 277 pedicle screws. J Neurosurg Spine 7:393-398, 2007. 6. Mirza SK, Wiggins GC, Kuntz C, York JE, Bellabarba C, Knonodi MA, Chapman JR, Shaffrey CI: Accuracy of thoracic vertebral body screw placement using standard fluoroscopy, fluoroscopic image guidance, and computed tomographic image guidance: a cadaver study. Spine 28:402-413, 2003. 7. Ringel F, Stoffel M, Stuer C, Meyer B: Minimally invasive transmuscular pedicle screw fixation of the thoracic and lumbar spine. Neurosurgery 59: ONS361-ONS366, 2006. 8. Youkilis AS, Quint DJ, McGillicuddy JE, Papadopoulos SM: Stereotactic navigation for placement of pedicle screws in the thoracic spine. Neurosurgery 48: 771-778, 2001.
received 01 February 2010; accepted 13 March 2010
Percutaneous image-guided pedicle screw fixation of the thoracic spine is technically feasible in patients who require posterior fixation without decompression. Further work is necessary to determine if the technique will improve patient outcomes.
Citation: World Neurosurg. (2010) 74, 6:606-610. DOI: 10.1016/j.wneu.2010.03.028 Journal homepage: www.WORLDNEUROSURGERY.org Available online: www.sciencedirect.com 1878-8750/$ - see front matter © 2010 Elsevier Inc. All rights reserved.
WORLD NEUROSURGERY, DOI:10.1016/j.wneu.2010.03.028
Placement of Percutaneous Thoracic Pedicle Screws Using NeuroNavigation Udaya K. Kakarla, Andrew S. Little, Steve W. Chang, Volker K. H. Sonntag, Nicholas Theodore
Key words 䡲 Image guidance 䡲 Minimally invasive 䡲 Pedicle screw placement 䡲 Percutaneous 䡲 Spinal instrumentation 䡲 Thoracic spine neuronavigation Abbreviations and Acronyms CT: Computed tomography From the Division of Neurological Surgery, Barrow Neurological Institute, St. Joseph’s Hospital and Medical Center, Phoenix, Arizona, USA To whom correspondence should be addressed: Nicholas Theodore, M.D. [E-mail: [email protected]] Citation: World Neurosurg. (2010) 74, 6:606-610. DOI: 10.1016/j.wneu.2010.03.028 Supplementary digital content online Journal homepage: www.WORLDNEUROSURGERY.org Available online: www.sciencedirect.com 1878-8750/$ - see front matter © 2010 Elsevier Inc. All rights reserved.
INTRODUCTION Recent advances in neuronavigation have revolutionized the field of craniospinal surgery (2, 4, 7, 8). The use of intraoperative image acquisition has augmented existing neuronavigational protocols, which relied on images obtained preoperatively. Intraoperative neuronavigation provides real-time feedback about surgical anatomy for precise and accurate execution of the surgical procedure. It has been successfully used for spinal instrumentation and craniospinal fixation (4, 5). Iso-C C-arm (Siremobil Iso-C 3D, Siemens Medical Solutions; Erlangen, Germany) provides an accurate three-dimensional volume from multiple fluoroscopic images acquired in the axial plane centered over an isocentric point. Thoracic pedicle screw fixation is technically challenging because of the complexity of the spinal anatomy involved and the proximity of critical neurovascular structures. Percutaneous placement is further complicated by the obscuration of normal surgical landmarks by soft tissue. Percutaneous posterior spinal instrumentation has the potential benefits of minimizing operative exposure and
606
www.SCIENCEDIRECT.com
䡲 BACKGROUND: Percutaneous thoracic pedicle screw fixation is challenging because of the complexity of the spinal anatomy and obscuration of normal surgical landmarks by soft tissue. We report a novel percutaneous technique in which intraoperative Iso-C C-arm navigation was used to treat complex thoracic spinal fractures. 䡲 METHODS: Between March and September 2007, percutaneous thoracic pedicle screw fixation was performed with the assistance of intraoperative Iso-C C-arm fluoroscopy in six patients (two males, four females; mean age ⴝ 33 years, range ⴝ 16-61 years) with unstable thoracic fractures. The accuracy of pedicle screw placement was assessed by postoperative computed tomography and graded according to the method of Youkilis et al. 䡲 RESULTS: Five patients had unstable acute traumatic fractures and one had an osteoporotic burst fracture. Altogether, 19 spinal segments (range ⴝ 2-4/patient) were fixated using 37 pedicle screws. Pedicle screw misplacement was grade II in 16% and grade III in 3%. None of the patients had neurologic consequences due to screw misplacement, and none required conversion to an open procedure or revision of hardware. There was one wound infection. 䡲 CONCLUSION: Percutaneous thoracic pedicle screw fixation with intraoperative neuronavigation for the stabilization of complex spinal fractures is feasible and associated with acceptable rates of accuracy and morbidity.
muscle dissection, blood loss, and hospital stays. To date, percutaneous thoracic techniques have relied on intraoperative fluoroscopy or preoperatively obtained imaging for navigation. Fluoroscopy is limited by visualization of the pedicle, which may be difficult in obese or osteoporotic patients. Neuronavigation using previously acquired images is limited by the anatomic shifts that can occur during positioning of the patient and in unstable fractures. We present the first technical description of the placement of percutaneous thoracic pedicle screws with the assistance of neuronavigation performed with images acquired intraoperatively and discuss surgical nuances to improve accuracy of placement.
years; range ⫽ 16-61 years) were treated for unstable thoracic spine fractures using the technique described here (Table 1). Five patients had traumatic fractures and one had an osteoporotic burst fracture. No patient presented with a neurologic deficit. Three patients demonstrated instability in an external orthotic brace before internal fixation.
METHODS AND MATERIALS
Equipment The Iso-C system (Siremobil Iso-C 3D) has been well described by Hott et al. (4). Briefly, the equipment consists of a modified C-arm computed tomography (CT) system with a 15-
Patient Population Between March and June 2007, six patients (two males, four females; mean age ⫽ 33
Patient Selection Patients were candidates for percutaneous pedicle screw placement if they sustained unstable thoracic fractures without spinal cord compression or if they required supplementation of an anterior construct.
WORLD NEUROSURGERY, DOI:10.1016/j.wneu.2010.03.028
PEER-REVIEW REPORTS UDAYA K. KAKARLA ET AL.
PERCUTANEOUS PEDICLE SCREWS
Table 1. Clinical Summary of the Six Patients Screw Error Patient
Age (Years)/Sex
Presentation
Findings
Intervention
No. of Screws
Grade II
Grade III
Complications/ New Deficits
1
47/F
Auto Ped/Central Cord/ GCS 15; UE 2/5; LE 3-4/5
T8 chance Fx, T9 facet Fx
C3-6 laminectomy and fusion/T7-T10 PSF
4
0
0
None
2
61/F
Back pain with new LE tingling; LE strength 4/5
T11 osteoporotic burst Fx with conus compression
T11 Corpectomy; T9-L1 PSF
8
1
1
None
3
16/M
Motorcycle crash
T8 comp Fx; T9 burst Fx; unstable in TLSO
T7-T10 PSF
5
0
0
None
4
31/F
MVA
T9 burst; C7 comp Fx; T2-3 Fx; unstable in TLSO
T8-T10 PSF
4
1
0
None
5
17/F
MVA ejection
Hangman’s Fx/T3 Fx dislocations
T1-T5 PSF; C1-C3 fusion
8
2
1
None
6
26/M
Motorcycle crash; GCS 15; No deficits
L1 compression – chance Fx; facet distraction
T11-L2 PSF
8
1
Infection
C, cervical; F, female; Fx, fracture; GCS, Glasgow Coma Scale; LE, lower extremities; L, lumbar; M, male; MVA, motor vehicle accident; PSF, pedicle screw fixation; T, thoracic; TLSO, thoracolumbosacral orthosis; UE, upper extremities
or 23-cm image intensifier and orbital drive. During 3-D image acquisition, the motorized C-arm moves continuously around 190 degrees of rotation acquiring 50 to 100 projection images of fluoroscopy at equidistant angles. A high-resolution 3-D image data set (resolution ⬍ 0.5 mm) is reconstructed using the precisely known rotation geometry, and the images are displayed using slice-image techniques (multiplanar reconstruction) or surface-shaded displays. For navigation during posterior spinal procedures, the reference frame is placed on the spinous process of the adjacent vertebral body. The mean time from scan acquisition until the images are reconstructed and available for navigation is about 5 minutes.
Instrumentation For spinal instrumentation, a Horizon Longitude system (Sofamor-Danek, Medtronic; Minneapolis, MN, USA) was used in all cases. Briefly, the system consists of cannulated pedicle screws with screw extenders, allowing screws to be placed into the pedicles. A rod inserter helps guide a rod over the pedicle screws through the slots in the pedicle screw extenders. This maneuver also helps reduce the rod into the screw heads before the screws are locked.
view. A 2-cm midline incision was made Data and Outcome Analysis one level above the rostral spinal level to Operative time and complications were be instrumented. recorded. Intraoperative Iso-C was not Subperiosteal dissection was performed performed after the screws were placed to expose the spinous process. A reference because artifact from the metal is often arc was firmly attached to the midline spisignificant. Instead, all patients undernous process. With the reference arc in went postoperative CT to assess pedicle range, Iso-C C-arm images were acquired screw accuracy. Accuracy was graded acand 3-D volume images were reconcording to the method of Youkilis et al. structed. The instrumentation tools were (8): Grade I is screw placement within the synchronized with the neuronavigation to pedicle without cortical violation. Grade provide live feedback in all II is a cortical violation of planes of the spine. The acculess than 2 mm. Grade III is a racy of the navigation was cortical violation beyond 2 checked by verifying the bony mm. The grading was perlandmarks before any definiformed by an independent Video available at tive surgical maneuvers were physician who was not inWORLDNEUROSURGERY.org performed. volved in the care of the patients, and the results are A 1-cm incision was made presented here. 2-3 mm lateral to the surface mark made for the pedicles. An image-guided drill guide was placed over the pedicle entrance point, and the desired trajectory was achieved based on Operative Technique (Video) live navigation. A K-wire was advanced into Patients were positioned in the prone pothe pedicle using a pneumatic drill. This step sition on a Jackson radiolucent table. The was repeated until K-wires were placed in all arms were tucked on the patient’s side. pedicles of interest in a caudal-to-cephalad Somatosensory evoked potentials and direction. The pedicles were tapped over the motor evoked potentials were monitored. K-wire with care taken to avoid advancing the The Iso-C C-arm was used to mark the K-wire during this step. Cannulated pedicle pedicles of the thoracic levels on the surscrews attached to screw extenders were inface of the skin using the anteroposterior
WORLD NEUROSURGERY 74 [6]: 606-610, DECEMBER 2010
www.WORLDNEUROSURGERY.org
607
PEER-REVIEW REPORTS UDAYA K. KAKARLA ET AL.
PERCUTANEOUS PEDICLE SCREWS
Figure 1. A 16-year-old boy after motorcycle crash. (A) Sagittal CT showed a fracture of the T9 vertebral body and loss of alignment. (B) MRI with STIR signal changes in T9 vertebral body. Axial CTs of T7 (C) shows perfect or Grade I screw placement at all levels, at T8 (D), and at T9 (E). (F) Postoperative photograph showing excellent wound healing at 6 weeks. Used with permission from Barrow Neurological Institute.
serted into the pedicles over the K-wires under image guidance, after which the K-wires were removed. At this point, an optional 3D spin can be performed to verify the accuracy of pedicle screw placement. However, the image quality is often degraded as a result of significant metallic artifact. The reference arc was removed, and a rod was inserted into the pedicle screw heads percutaneously through the slots of the screw extenders. An anteroposterior fluoroscopic image was used to verify adequate rod placement on the screw heads. The rods were reduced into the screw heads and locked into place using an antitorque device. The fascia was closed in the midline incision, and all
608
www.SCIENCEDIRECT.com
paramedian incisions were closed subcutaneously.
RESULTS Six patients underwent successful thoracic spinal fixation using the technique described above (Table 1). No patients required conversion to an open procedure. Thirty-seven pedicle screws were placed to stabilize a total of 19 spinal segments. Seven screws (19%) showed cortical violation of the pedicle (Table 1). Six screws (16%) were grade II misplacements, and one (3%) was grade III. None of the patients showed neurologic deficits as a result of pedicle screw
misplacement, and none of the pedicle screws were revised. Intraoperative somatosensory evoked potential and motor evoked potentials were stable during all procedures. One patient developed a superficial wound infection, which was treated with debridement and antibiotics.
CASE ILLUSTRATIONS Case 1 (see operative video) A 16-year-old boy crashed his motorcycle and was admitted as a Level 1 trauma with a Glasgow Coma Scale score of 10T. There was no evidence of spinal cord injury. He had fractures of the T8 and T9 vertebral
WORLD NEUROSURGERY, DOI:10.1016/j.wneu.2010.03.028
PEER-REVIEW REPORTS UDAYA K. KAKARLA ET AL.
PERCUTANEOUS PEDICLE SCREWS
Figure 2. A 61-year-old woman with back pain and paraparesis. (A) Sagittal CT showed a chronic T11 burst fracture associated with loss of height. (B) Sagittal T2-weighted MRI showed increased signal suggesting an acute component of the fracture. (C) Sagittal CT after anterior corpectomy with cage reconstruction demonstrated restoration of height and alignment. (D) Coronal CT after percutaneous pedicle screw placement. (E) Axial CTs demonstrated grade II misplacement at L1 of right pedicle screw and (F) Grade III placement of left pedicle screw at L1. Used with permission from Barrow Neurological Institute.
bodies (Figure 1A and B). He was placed in an external orthotic brace but was unstable on upright and supine x-rays. He underwent posterior internal fixation from T7 to T10 with no cortical surface violation (Figure 1C-E). He remained neurologically intact and was discharged to a rehabilitation facility. At his 6-week follow-up visit, his wounds had healed well (Figure 1F) and he reported no pain. Case 2 A 61-year-old woman with history of systemic lupus erythematosus and chronic ste-
roid use sought treatment for worsening back pain, lower extremity tingling, and urinary retention. CT and magnetic resonance imaging of the lumbar spine showed an acute and chronic osteoporotic burst fracture of the T11 vertebral body that compromised the spinal canal (Figure 2A and B). She underwent a thoracotomy for a T11 corpectomy with placement of an expandable cage and plate (Figure 2C). Given her poor bone quality, she underwent posterior fixation from T9-L1 to prevent failure of the anterior construct (Figure 2D). Postoperative imaging revealed that two screws had
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been misplaced (Figure 2E and F) with no clinical significance. She recovered well and was discharged to a rehabilitation facility in a thoracolumbosacral orthosis.
DISCUSSION Pedicle screw fixation of the thoracic spine is used to stabilize fractures and to correct spinal deformities. The procedure is technically demanding because the pedicles are small and adjacent to the lungs and great vessels. Until now, appropriate screw placement re-
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quired wide exposure of the spinal anatomy, extensive use of fluoroscopy, or both. The rate of misplacement of thoracic pedicle screws is estimated to be 15%-25% using traditional landmarks and fluoroscopy (8). The goal of image guidance is to improve the accuracy of screw placement as demonstrated in cadaveric studies comparing CT image guidance to conventional open laminoforaminotomy (1, 3, 6) and in large clinical studies (5, 8). Youkilis et al. (8) placed 266 thoracic pedicle screws in 65 patients using wide exposure for landmarks coupled with image guidance. Their misplacement rate was 8.6%. In a study comparing two image-guidance systems for the placement of thoracic pedicle screws, Lekovic et al. (5) reported unintended perforations by 8.7% of the screws when using Fluoro-nav and by 5.3% when using Iso-C. This difference was not statistically significant. Minimally invasive techniques in spinal surgery have become increasingly popular. Their theoretical advantages are decreased morbidity related to decreased blood loss and muscle dissection, less postoperative pain, and a decreased need for rehabilitation. In a feasibility and safety study, Ringel et al. (7) placed percutaneous posterior pedicle screws in the thoracic and lumbar spine using fluoroscopy in 104 patients. Cortical violation occurred in 13% of the 488 pedicle screws placed. Nine patients underwent a repeat operation for misplaced screws. Of these, two patients developed neurologic symptoms as a result of misplacement. Percutaneous techniques coupled with image guidance offers an ideal combination of increased accuracy and decreased morbidity. To our knowledge, the current report is first to evaluate at the feasibility of this approach in as many as four motion segments. This technique was used only in patients requiring posterior internal fixation as determined by the senior author
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(N.T.). Cortical violations occurred in 19% of the cases with no clinical sequellae or revisions. This rate is slightly higher than that reported by Youkilis et al. (8) and Lekovic et al. (5). This difference could be attributed to several factors. The patient population was small, and a learning curve must be expected when new surgical techniques are used. Accuracy should improve with experience as we have already noticed in these first six cases. Based on our limited experience with this new technique and large experience using image guidance for open spinal instrumentation, we offer the following caveats to improve accuracy of screw placement and to avoid frustration during the procedure. 1. Avoid leaning on the patient or pushing hard on the spine while placing the Kwire. These movements could affect the reference arc and decrease accuracy. 2. Placing the K-wires in a caudal-to-cranial direction avoids the wires obstructing navigation. 3. Rods should be inserted in a cranial-tocaudal direction to decrease the chance of accidental insertion into the spinal canal. 4. The surgeon should always be prepared to convert to an open procedure if necessary. 5. Image quality with Iso-C image guidance is poor and less reliable in morbidly obese patients.
CONCLUSION
REFERENCES 1. Austin MS, Vaccaro AR, Brislin B, Nachwalter R, Hilibrand AS, Albert TJ: Image-guided spine surgery: a cadaver study comparing conventional open laminoforaminotomy and two image-guided techniques for pedicle screw placement in posterolateral fusion and nonfusion models. Spine 27:2503-2508, 2002. 2. Foley KT, Gupta SK: Percutaneous pedicle screw fixation of the lumbar spine: preliminary clinical results. J Neurosurg (Spine 1) 97:7-12, 2002. 3. Hart RA, Hansen BL, Shea M, Hsu F, Anderson GJ: Pedicle screw placement in the thoracic spine: a comparison of image-guided and manual techniques in cadavers. Spine 30:E326-E331, 2005. 4. Hott JS, Deshmukh VR, Klopfenstein JD, Sonntag VK, Dickman CA, Spetzler RF, Papadopoulos SM: Intraoperative Iso-C C-arm navigation in craniospinal surgery: the first 60 cases. Neurosurgery 54:1131-1136, 2004. 5. Lekovic GP, Potts EA, Karahalios DG, Hall G: A comparison of two techniques in image-guided thoracic pedicle screw placement: a retrospective study of 37 patients and 277 pedicle screws. J Neurosurg Spine 7:393-398, 2007. 6. Mirza SK, Wiggins GC, Kuntz C, York JE, Bellabarba C, Knonodi MA, Chapman JR, Shaffrey CI: Accuracy of thoracic vertebral body screw placement using standard fluoroscopy, fluoroscopic image guidance, and computed tomographic image guidance: a cadaver study. Spine 28:402-413, 2003. 7. Ringel F, Stoffel M, Stuer C, Meyer B: Minimally invasive transmuscular pedicle screw fixation of the thoracic and lumbar spine. Neurosurgery 59: ONS361-ONS366, 2006. 8. Youkilis AS, Quint DJ, McGillicuddy JE, Papadopoulos SM: Stereotactic navigation for placement of pedicle screws in the thoracic spine. Neurosurgery 48: 771-778, 2001.
received 01 February 2010; accepted 13 March 2010
Percutaneous image-guided pedicle screw fixation of the thoracic spine is technically feasible in patients who require posterior fixation without decompression. Further work is necessary to determine if the technique will improve patient outcomes.
Citation: World Neurosurg. (2010) 74, 6:606-610. DOI: 10.1016/j.wneu.2010.03.028 Journal homepage: www.WORLDNEUROSURGERY.org Available online: www.sciencedirect.com 1878-8750/$ - see front matter © 2010 Elsevier Inc. All rights reserved.
WORLD NEUROSURGERY, DOI:10.1016/j.wneu.2010.03.028