Analysis of Intraoperative Cone-Beam Computed Tomography Combined With Image Guidance for Lateral Lumbar Interbody Fusion

Analysis of Intraoperative Cone-Beam Computed Tomography Combined With Image Guidance for Lateral... Abstract BACKGROUND Minimally invasive lateral lumbar interbody fusion (LLIF) is traditionally performed with biplanar fluoroscopy. Recent literature demonstrates that intraoperative cone-beam computed tomography combined with spinal navigation can be safely utilized for localization and cage placement in LLIF. OBJECTIVE To evaluate the accuracy and safety of cage placement using spinal navigation in LLIF, as well as to evaluate the radiation exposure to surgeon and staff during the procedure. METHODS The authors performed a retrospective analysis of a prospectively acquired database of patients undergoing LLIF with image-based navigation performed from April 2014 to July 2016 at a single institution. The medical records were reviewed, and data on clinical outcomes, cage accuracy, complications, and radiation exposure were recorded. All patients underwent a minimum 30-d clinical follow-up to assess intraoperative and short-term complications associated with their LLIF. RESULTS Sixty-three patients comprising 117 spinal levels were included in the study. There were 36 (57.1%) female and 27 (42.9%) male patients. Mean age was 62.7 yr (range 24-79 yr). A mean 1.9 (range 1-4) levels per patient were treated. Cages were placed in the anterior or middle of 115 (98.3%) disc spaces. Image-guided cage trajectory was accurate in 116/117 levels (99.1%). In a subgroup analysis of 18 patients, mean fluoroscopy time was 11.7 ± 9.7 s per level. Sixteen (25.4%) patients experienced a complication related to approach. CONCLUSION Use of intraoperative cone-beam computed tomography combined with spinal navigation for LLIF results in accurate and safe cage placement as well as significantly decreased surgeon and staff radiation exposure. Image-guided surgery, Intraoperative cone-beam computed tomography, Lateral lumbar interbody fusion, LLIF, Minimally invasive surgery, O-arm, Radiation exposure ABBREVIATIONS ABBREVIATIONS BMI body mass index CT computed tomography FT fluoroscopy time iCBCT intraoperative cone-beam computed tomography IGN image-guided navigation LLIF lateral lumbar interbody fusion MI minimally invasive Minimally invasive (MI) techniques for lateral lumbar interbody fusion (LLIF) have the ability to improve disc height and provide indirect neural decompression. Compared to posterior interbody techniques, the lateral approach limits damage to dorsal spinal elements and is now commonly used to treat symptomatic degenerative disk disease, spondylolisthesis, and scoliosis.1-5 In performing the LLIF, fluoroscopic guidance and neuromonitoring are used to ensure the accuracy of cage placement and prevent lumbosacral plexus injury.6,7 The necessary use of fluoroscopy leads to increased radiation exposure to the patient, surgeon, and staff. In addition, fluoroscopic guidance does not guarantee ideal cage position. Previous studies have reported the feasibility, safety, and accuracy of using intraoperative cone-beam computed tomography (iCBCT) and image-guided navigation (IGN) for LLIF.8,9 The objective of this study was to evaluate complications, accuracy, radiographic results, and radiation exposure with the use of iCBCT and IGN in LLIF. METHODS With institutional board approval, a retrospective analysis of the electronic medical records was performed for patients who underwent LLIF with the use of iCBCT (O-arm, Medtronic, Inc., Minneapolis, Minnesota) for 3D image acquisition in conjunction with the StealthStation guidance system (Medtronic, Inc., Minneapolis, Minnesota) for spinal navigation. From April 2014 to July 2016, 63 consecutive patients who underwent IGN-assisted LLIF were included in the analysis. Surgical Technique The surgical technique in IGN-assisted LLIF has been detailed extensively in previous studies.8,9 Briefly, the patient is placed in the lateral decubitus position on a flat radiolucent table. Axillary and flank rolls are placed. Tape secures the patient to the table at multiple points to allow tilting of the table, if needed (Figure 1A). Width of the sterile field ensures access to the anterior or posterior superior iliac spine; we typically favor the anterior. A stab incision is made and an iliac pin is impacted into bone to attach the IGN system reference frame (Figure 1B). Additional drapes are placed over the surgical field to maintain sterility prior to introduction of the iCBCT unit. A 3D image of the targeted spine levels is then obtained and autoregistered to the IGN system. A single image acquisition is typically adequate for up to 4 spinal levels. If more than 4 spinal levels are treated, 2 3D image acquisitions are obtained. FIGURE 1. View largeDownload slide A, Patient in the right lateral decubitus position on a flat radiolucent table. B, Reference frame attached to pin embedded in the anterior superior iliac spine. FIGURE 1. View largeDownload slide A, Patient in the right lateral decubitus position on a flat radiolucent table. B, Reference frame attached to pin embedded in the anterior superior iliac spine. The navigated initial dilator is then used to demarcate the skin incision (Figure 2). After incision, the retroperitoneal space is entered using the standard muscle-splitting technique. The navigated dilator, equipped with a nerve stimulator, is advanced through the psoas muscle and into the disc space via IGN (Figure 3). No fluoroscopy is used. After anchoring the dilator in the disc space, sequential dilation is performed with placement of an expandable retractor. The retractor blades are expanded and positioning is confirmed using the navigated initial dilator to demarcate the boundaries of the retractor blades in relationship to the disc space. Visual identification of the disc space confirms the accuracy of navigation. A variety of navigation instruments (ie, Cobb elevator, rotating shaver, and trial spacer) are used to perform discectomy, contralateral annular release, and cage sizing. The appropriately sized cage is then impacted into the disc space using IGN (Figure 4). We do advocate using fluoroscopy, if there is any concern for accuracy, especially in deformity cases. FIGURE 2. View largeDownload slide A, Navigated initial dilator. B, The navigated initial dilator (blue projection) with a virtual extension (yellow projection) is moved along the skin until an orthogonal trajectory into the mid-disc space is determined, which becomes the center of the skin incision. FIGURE 2. View largeDownload slide A, Navigated initial dilator. B, The navigated initial dilator (blue projection) with a virtual extension (yellow projection) is moved along the skin until an orthogonal trajectory into the mid-disc space is determined, which becomes the center of the skin incision. FIGURE 3. View largeDownload slide Using image guidance, the initial dilator (blue projection) is advanced through the psoas muscle and subsequently into the disc space. FIGURE 3. View largeDownload slide Using image guidance, the initial dilator (blue projection) is advanced through the psoas muscle and subsequently into the disc space. FIGURE 4. View largeDownload slide A, The cage is impacted into the disc space utilizing navigation. B, Lateral fluoroscopic image showing the cage positioned in the disc space, consistent with image guidance. FIGURE 4. View largeDownload slide A, The cage is impacted into the disc space utilizing navigation. B, Lateral fluoroscopic image showing the cage positioned in the disc space, consistent with image guidance. Outcome Assessment All patients underwent a minimum 30-d clinical follow-up to assess intraoperative and short-term complications associated with their LLIF. All approach-related complications were captured. Lower extremity sensory and motor functions were evaluated postoperatively and at each follow-up visit. All medical complications during the 30-d postoperative period were recorded. Complications from additional posterior procedures—ie, percutaneous pedicle screw fixation—were considered separate from LLIF and not included in this study. All neurologic complications (numbness and weakness) were followed until last documented clinic visit. Radiographic Assessment All patients underwent postoperative computed tomography (CT) or iCBCT to determine cage positioning. Additionally, postoperative X-rays were obtained for all patients (Figure 5). Accuracy was assessed by comparing the projected navigated cage location with intraoperative fluoroscopy images after cage placement (Figure 4). The location of each cage within the disc space was graded based on the grading system previously described.8 In this system, the disc space is divided into 4 quarters in the sagittal plane, and cage position is recorded as number 1 to 4 (from anterior to posterior). FIGURE 5. View largeDownload slide A, Preoperative and B, Postoperative lateral X-rays of patient with L4-5 spondylolisthesis who underwent LLIF with image-guided navigation. FIGURE 5. View largeDownload slide A, Preoperative and B, Postoperative lateral X-rays of patient with L4-5 spondylolisthesis who underwent LLIF with image-guided navigation. Radiation Exposure Intraoperative fluoroscopy time (FT) was obtained from a subgroup of 18 consecutive patients for whom data were available. The remaining patients comprised those treated earlier in our experience, in which FT data included fluoroscopy usage for the posterior approach as well as the lateral approach, so their data could not be analyzed. Because there was no comparison group, the FT of IGN-assisted LLIF was compared with the published literature involving FT with traditional fluoroscopic-guided LLIF. In addition, a correlation analysis was performed with FT and fusion levels as well as FT and body mass index (BMI). Statistical Analysis Descriptive statistics were utilized for the analysis of patient, surgical, and radiographic characteristics. All statistical analyses were performed using GraphPad Prism version 6 software (GraphPad, Inc., San Diego, California). RESULTS Patient demographics and detailed procedural data were listed in Table 1. A total of 63 patients and 117 spinal levels were included in this study. Thirty-six patients (57.1%) were female and 27 (42.9%) were male, with a mean age of 62.7 yr (range 24-79 yr). A mean of 1.9 ± 1.0 levels were fused per patient (range 1-4 levels), and most cases (51 cases; 81.0%) were approached from the left side. Mean BMI was 31.6 (range 19.8-47.1). Thirteen patients were categorized as normal weight (BMI < 25.0) and 11 were overweight (BMI 25.0-29.9). The remaining patients had obesity, with 18 having class I obesity (BMI 30.0-34.9), 14 having class II obesity (BMI 35.0-39.9), and 6 having class III obesity (BMI ≥ 40.0). All patients only required 1 scan with iCBCT for navigation. Indications for surgery included degenerative kyphoscoliosis, adult idiopathic scoliosis, stenosis, spondylolisthesis, tumor, degenerative disc disease, adjacent segment disease, or pseudoarthrosis. TABLE 1. Patient Demographics and Procedural Data Patients 63 Number of levels fused 117 Mean levels fused 1.9 ± 1.0 Mean age (range) 62.7 (24-79) BMI (range) 31.6 (19.8-47.1) Male (%) 27 (42.9) Female (%) 36 (57.1) Levels involved (%)  T12-L1 2 (1.7)  L1-L2 12 (10.3)  L2-L3 28 (23.9)  L3-L4 40 (34.2)  L4-L5 35 (29.9) Indication (%)  Degenerative scoliosis 24 (38.1)  Adjacent segment disease 16 (25.4)  Spondylolisthesis 11 (17.5)  Pseudoarthrosis 4 (6.3)  Postlaminectomy kyphoscoliosis 2 (3.2)  Degenerative disc disease 2 (3.2)  Idiopathic scoliosis 2 (3.2)  Tumor 1 (1.6)  Flat back syndrome 1 (1.6) Patients 63 Number of levels fused 117 Mean levels fused 1.9 ± 1.0 Mean age (range) 62.7 (24-79) BMI (range) 31.6 (19.8-47.1) Male (%) 27 (42.9) Female (%) 36 (57.1) Levels involved (%)  T12-L1 2 (1.7)  L1-L2 12 (10.3)  L2-L3 28 (23.9)  L3-L4 40 (34.2)  L4-L5 35 (29.9) Indication (%)  Degenerative scoliosis 24 (38.1)  Adjacent segment disease 16 (25.4)  Spondylolisthesis 11 (17.5)  Pseudoarthrosis 4 (6.3)  Postlaminectomy kyphoscoliosis 2 (3.2)  Degenerative disc disease 2 (3.2)  Idiopathic scoliosis 2 (3.2)  Tumor 1 (1.6)  Flat back syndrome 1 (1.6) View Large TABLE 1. Patient Demographics and Procedural Data Patients 63 Number of levels fused 117 Mean levels fused 1.9 ± 1.0 Mean age (range) 62.7 (24-79) BMI (range) 31.6 (19.8-47.1) Male (%) 27 (42.9) Female (%) 36 (57.1) Levels involved (%)  T12-L1 2 (1.7)  L1-L2 12 (10.3)  L2-L3 28 (23.9)  L3-L4 40 (34.2)  L4-L5 35 (29.9) Indication (%)  Degenerative scoliosis 24 (38.1)  Adjacent segment disease 16 (25.4)  Spondylolisthesis 11 (17.5)  Pseudoarthrosis 4 (6.3)  Postlaminectomy kyphoscoliosis 2 (3.2)  Degenerative disc disease 2 (3.2)  Idiopathic scoliosis 2 (3.2)  Tumor 1 (1.6)  Flat back syndrome 1 (1.6) Patients 63 Number of levels fused 117 Mean levels fused 1.9 ± 1.0 Mean age (range) 62.7 (24-79) BMI (range) 31.6 (19.8-47.1) Male (%) 27 (42.9) Female (%) 36 (57.1) Levels involved (%)  T12-L1 2 (1.7)  L1-L2 12 (10.3)  L2-L3 28 (23.9)  L3-L4 40 (34.2)  L4-L5 35 (29.9) Indication (%)  Degenerative scoliosis 24 (38.1)  Adjacent segment disease 16 (25.4)  Spondylolisthesis 11 (17.5)  Pseudoarthrosis 4 (6.3)  Postlaminectomy kyphoscoliosis 2 (3.2)  Degenerative disc disease 2 (3.2)  Idiopathic scoliosis 2 (3.2)  Tumor 1 (1.6)  Flat back syndrome 1 (1.6) View Large Complications All cases of LLIF with IGN were performed successfully, except 1 level (L1-L2) that was aborted due to violation of the endplate, which occurred during disc space preparation without navigated instruments. Sixteen patients (25.4%) encountered approach-related complications; 9 had mild transient hip weakness, 3 had transient hip/thigh numbness, and 4 had persistent mild hip/thigh numbness at last follow-up. No patients had persistent weakness at last follow-up. “Mild weakness” was defined as 4/5 or 4+/5 strength based on Medical Research Council criteria. Two patients had superficial wound infections, while another patient developed a psoas abscess (treated with percutaneous drainage). One developed asymptomatic myositis ossificans. No spinal canal invasion, visceral injury, or large vessel violation was observed. Medical complications included 3 patients with perioperative myocardial infarctions, 1 patient who developed Miller-Fisher acute intermittent demyelinating polyneuropathy, 2 patients with uncomplicated ileus, 1 patient with transient urinary retention, and 1 patient with perioperative pneumonia (Table 2). TABLE 2. Medical and Surgical Complications Approach-related  Transient hip weakness 9  Persistent hip weakness 0  Transient thigh numbness 3  Persistent thigh numbness 4 Medical  Myocardial infarction 3  Ileus 2  Miller-Fisher acute intermittent demyelinating polyneuropathy 1  Transient urinary retention 1  Pneumonia 1 Wound  Psoas abscess 1  Superficial wound infection 2 Approach-related  Transient hip weakness 9  Persistent hip weakness 0  Transient thigh numbness 3  Persistent thigh numbness 4 Medical  Myocardial infarction 3  Ileus 2  Miller-Fisher acute intermittent demyelinating polyneuropathy 1  Transient urinary retention 1  Pneumonia 1 Wound  Psoas abscess 1  Superficial wound infection 2 View Large TABLE 2. Medical and Surgical Complications Approach-related  Transient hip weakness 9  Persistent hip weakness 0  Transient thigh numbness 3  Persistent thigh numbness 4 Medical  Myocardial infarction 3  Ileus 2  Miller-Fisher acute intermittent demyelinating polyneuropathy 1  Transient urinary retention 1  Pneumonia 1 Wound  Psoas abscess 1  Superficial wound infection 2 Approach-related  Transient hip weakness 9  Persistent hip weakness 0  Transient thigh numbness 3  Persistent thigh numbness 4 Medical  Myocardial infarction 3  Ileus 2  Miller-Fisher acute intermittent demyelinating polyneuropathy 1  Transient urinary retention 1  Pneumonia 1 Wound  Psoas abscess 1  Superficial wound infection 2 View Large Radiographic Results Among all 117 LLIF levels treated using IGN, only 1 level encountered imprecise trajectory during cage insertion, resulting in 99.1% accuracy. Cage placement was reconfirmed by postoperative X-ray or CT images. Of 117 cages, 44 (37.6%) were placed within the anterior disc space in quarters 1 and 2, and 71 (60.7%) were placed in the middle of the disc space in quarters 2 and 3. Two cages (1.7%) were placed within the posterior disc space in quarters 3 and 4 (Table 3). TABLE 3. Radiographic Results IGN accuracy (%) 116/117 (99.1) Cage placement (%)  1-2 44 (37.6)  2-3 71 (60.7)  3-4 2 (1.7) IGN accuracy (%) 116/117 (99.1) Cage placement (%)  1-2 44 (37.6)  2-3 71 (60.7)  3-4 2 (1.7) View Large TABLE 3. Radiographic Results IGN accuracy (%) 116/117 (99.1) Cage placement (%)  1-2 44 (37.6)  2-3 71 (60.7)  3-4 2 (1.7) IGN accuracy (%) 116/117 (99.1) Cage placement (%)  1-2 44 (37.6)  2-3 71 (60.7)  3-4 2 (1.7) View Large Fluoroscopy Time Table 4 details FT of the IGN LLIF procedures. Eighteen patients were included, with mean BMI of 32.9 ± 6.8, and mean levels fused of 1.5 ± 0.6. Mean FT was 16.6 ± 14.4 s (range 2-48 s) per case. Mean FT per level was 11.7 ± 9.7 s. TABLE 4. Patient Fluoroscopy Time Patient BMI Levels Fluoroscopy time (s) 1 25 1 2 2 32.8 2 2 3 43.8 2 3 4 37.1 1 3 5 37.1 1 3 6 24.6 2 14 7 32.7 1 15 8 36.7 1 17 9 35.4 1 20 10 27.8 2 24 11 41.3 1 26 12 44.4 1 3 13 34.2 1 31 14 34.2 2 36 15 24.8 2 38 16 19.8 2 48 17 29.4 1 5 18 31.2 3 9 Patient BMI Levels Fluoroscopy time (s) 1 25 1 2 2 32.8 2 2 3 43.8 2 3 4 37.1 1 3 5 37.1 1 3 6 24.6 2 14 7 32.7 1 15 8 36.7 1 17 9 35.4 1 20 10 27.8 2 24 11 41.3 1 26 12 44.4 1 3 13 34.2 1 31 14 34.2 2 36 15 24.8 2 38 16 19.8 2 48 17 29.4 1 5 18 31.2 3 9 View Large TABLE 4. Patient Fluoroscopy Time Patient BMI Levels Fluoroscopy time (s) 1 25 1 2 2 32.8 2 2 3 43.8 2 3 4 37.1 1 3 5 37.1 1 3 6 24.6 2 14 7 32.7 1 15 8 36.7 1 17 9 35.4 1 20 10 27.8 2 24 11 41.3 1 26 12 44.4 1 3 13 34.2 1 31 14 34.2 2 36 15 24.8 2 38 16 19.8 2 48 17 29.4 1 5 18 31.2 3 9 Patient BMI Levels Fluoroscopy time (s) 1 25 1 2 2 32.8 2 2 3 43.8 2 3 4 37.1 1 3 5 37.1 1 3 6 24.6 2 14 7 32.7 1 15 8 36.7 1 17 9 35.4 1 20 10 27.8 2 24 11 41.3 1 26 12 44.4 1 3 13 34.2 1 31 14 34.2 2 36 15 24.8 2 38 16 19.8 2 48 17 29.4 1 5 18 31.2 3 9 View Large DISCUSSION As MI techniques in spine surgery continue to develop, there is an increasing interest in safety given the radiation exposure associated with these procedures. Specifically, there is a growing body of evidence for the concern of increased radiation exposure to the surgical team in MI spine procedures.10-13 The increased radiation exposure risk noted with MI spine procedures, as well as concerns for the long-term harm of workplace radiation exposure, has led to the development of new techniques to reduce radiation exposure to the surgical team.12,14,15 iCBCT allows for the acquisition of high-quality intraoperative 3D images while generating lower radiation dosage than that of a traditional CT scan.16-18 A previous study by Costa et al17 estimated that each scan of the iCBCT for thoracolumbar procedures corresponds to 2.52 mSv of radiation exposure to the patient. This is significantly lower than the patient radiation exposure from a lumbar spine CT, estimated to range between 7.5 and 10 mSv. The iCBCT unit has been successfully utilized in various neurosurgical applications including spinal instrumentation, tumor resection, and scoliosis correction.19-22 Procedural indications in the present study are similar to those described previously for LLIF. Accuracy of pedicle screw placement has been shown to be superior to C-arm fluoroscopy when directly compared.22,23 Although setup time is longer when utilizing iCBCT, the overall operative time is similar.14 When examining surgical team radiation exposure in fluoroscopic-guided MI-transforaminal lumbar interbody fusion compared to that of iCBCT, there is an evidence of increased radiation exposure noted in the fluoroscopic group.11,13 A study by Taher et al24 investigated FT in traditional MI-LLIF. They included 18 patients with 43 total levels fused (mean 2.4 ± 0.8 levels), with an average FT of 88.7 ± 36.8 s. In the present investigation, we found a mean of 11.7 s per level, as opposed to 37.0 s per level, which is the calculated value from the mean FT divided by mean levels fused in the Taher et al study. This suggests a 3-fold decrease in FT with the use of iCBCT with IGN, which results in significantly reduced radiation to the surgeon and operating room staff. Although the use of IGN has the potential to minimize radiation exposure, we do not advocate eliminating the use of fluoroscopy in navigated LLIF procedures. Especially in cases of deformity, spot fluoroscopic images should be obtained periodically to confirm accuracy. Given that the lumbar plexus lies in the dorsal portion of the psoas muscle,25 traditional MI-LLIF procedures are reported to have risk of severe sensory or motor nerve injury, especially at more caudal levels, despite the use of neuromonitoring.26-30 An advantage of IGN is that the trajectory through the psoas muscle can be more easily adjusted, if needed, based on neuromonitoring compared to fluoroscopic guidance. In this study, 16 patients (25.4%) encountered approach-related complications, which is comparable to previous non-navigated LLIF studies.31,32 However, most of these complications were transient hip discomfort or mild thigh weakness, which could be considered expected consequences of the trans-psoas LLIF procedure. More importantly, there was no severe motor or sensory deficiency. For patients with persistent mild numbness, it is possible that follow-up was not of sufficient length for improvement given the 30-d minimum follow-up in this study. Our mean follow-up time was 8.8 mo (range 3-14). These results suggest that IGN-assisted LLIF along with neuromonitoring is a safe procedure, with 99.1% accuracy in navigated trajectory. A ventrally placed LLIF cage can provide improved segmental lordosis, although the achievement of indirect decompression relies more on posterior disc height.33,34 Thus, the ideal position for LLIF cage placement should be within the anterior to middle portion of the disc space, a location that this report demonstrates can be achieved in most cases with IGN. Of the 117 levels treated with navigation, 115 (98.3%) cages were positioned within the anterior to middle disc space. Due to rotational scoliosis, 1 patient had 2 cages placed in the posterior quadrant because of the technical difficulty in accessing the anterior portion of the disc space. Regarding accuracy, the projected cage location on IGN was compared to a fluoroscopic image after cage placement and found to be consistent. Of note, for multilevel cases, the superior-most disc level is treated first, followed by the next distal level, to minimize the loss of accuracy with placement of the cage, given that the reference frame is anchored in the anterior superior iliac spine. Of note, IGN did not produce submillimeter accuracy. Particularly in multilevel cases, there was up to an estimated 2 to 3 mm error. This level of precision, however, was adequate for cage placement. Limitations There were several limitations to this study. It is a retrospective analysis, with all the accompanied biases involved. Further, there was only a subgroup of 18 patients available for radiation exposure analysis. The generalizability of this study is reliant on individual surgeon experience with the LLIF procedure and spinal navigation. However, in our experience of working with other surgeons, the learning curve seems relatively steep. CONCLUSION iCBCT and IGN can be used to decrease fluoroscopic use while maintaining accuracy and safety during LLIF procedures. Future investigations with larger sample sizes are needed to compare the radiation exposure between navigated LLIF and traditional LLIF procedures. Disclosures Paul Park is a consultant for and receives royalties from Globus. He is also a consultant for Medtronic, Zimmer-Biomet, and NuVasive. The other authors have no personal, financial, or institutional interest in any of the drugs, materials, or devices described in this article. REFERENCES 1. Malham GM , Parker RM , Goss B , Blecher CM , Ballok ZE . Indirect foraminal decompression is independent of metabolically active facet arthropathy in extreme lateral interbody fusion . Spine (Phila Pa 1976) . 2014 ; 39 ( 22 ): E1303 - E1310 . Google Scholar CrossRef Search ADS PubMed 2. Anand N , Baron EM , Khandehroo B , Kahwaty S . 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Br J Neurosurg . 2016 ; 30 ( 6 ): 658 - 661 . Google Scholar CrossRef Search ADS PubMed 24. Taher F , Hughes AP , Sama AA et al. 2013 Young Investigator Award winner: how safe is lateral lumbar interbody fusion for the surgeon? A prospective in vivo radiation exposure study . Spine (Phila Pa 1976) . 2013 ; 38 ( 16 ): 1386 - 1392 . Google Scholar CrossRef Search ADS PubMed 25. Uribe JS , Arredondo N , Dakwar E , Vale FL . Defining the safe working zones using the minimally invasive lateral retroperitoneal transpsoas approach: an anatomical study . J Neurosurg Spine . 2010 ; 13 ( 2 ): 260 - 266 . Google Scholar CrossRef Search ADS PubMed 26. 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 . Google Scholar CrossRef Search ADS PubMed 27. Houten JK , Alexandre LC , Nasser R , Wollowick AL . Nerve injury during the transpsoas approach for lumbar fusion . J Neurosurg Spine . 2011 ; 15 ( 3 ): 280 - 284 . Google Scholar CrossRef Search ADS PubMed 28. Uribe JS , Isaacs RE , Youssef JA et al. Can triggered electromyography monitoring throughout retraction predict postoperative symptomatic neuropraxia after XLIF? Results from a prospective multicenter trial . Eur Spine J . 2015 ; 24 ( suppl 3 ): 378 - 385 . Google Scholar CrossRef Search ADS PubMed 29. Cahill KS , Martinez JL , Wang MY , Vanni S , Levi AD . Motor nerve injuries following the minimally invasive lateral transpsoas approach . J Neurosurg Spine . 2012 ; 17 ( 3 ): 227 - 231 . Google Scholar CrossRef Search ADS PubMed 30. Lykissas MG , Aichmair A , Hughes AP et al. Nerve injury after lateral lumbar interbody fusion: a review of 919 treated levels with identification of risk factors . Spine J . 2014 ; 14 ( 5 ): 749 - 758 . Google Scholar CrossRef Search ADS PubMed 31. Joseph JR , Smith BW , La Marca F , Park P . Comparison of complication rates of minimally invasive transforaminal lumbar interbody fusion and lateral lumbar interbody fusion: a systematic review of the literature . Neurosurg Focus . 2015 ; 39 ( 4 ): E4 . Google Scholar CrossRef Search ADS PubMed 32. Lehmen JA , Gerber EJ . MIS lateral spine surgery: a systematic literature review of complications, outcomes, and economics . Eur Spine J . 2015 ; 24 ( suppl 3 ): 287 - 313 . Google Scholar CrossRef Search ADS PubMed 33. Kepler CK , Huang RC , Sharma AK et al. Factors influencing segmental lumbar lordosis after lateral transpsoas interbody fusion . Orthop Surg . 2012 ; 4 ( 2 ): 71 - 75 . Google Scholar CrossRef Search ADS PubMed 34. Park SJ , Lee CS , Chung SS , Kang SS , Park HJ , Kim SH . The ideal cage position for achieving both indirect neural decompression and segmental angle restoration in lateral lumbar interbody fusion (LLIF) [published online June 27, 2016] . Clin Spine Surgery . 2017 ; 30 ( 6 ): E784 - E790 . Google Scholar CrossRef Search ADS COMMENT The authors provide a detailed review of their series of 63 patients treated with lateral lumbar interbody fusion (LLIF) using intraoperative cone-beam CT combined with image guidance (iCBCT). They provide assessment of the accuracy and safety of using iCBT and assess the radiation exposure to the surgeon and staff. They were able to successfully complete all but 1 procedure (1 case was aborted due to endplate violation). Their overall complication rate appears to be comparable to previously reported series of LLIF cases. Application of iCBCT resulted in 99% of their cases with appropriate cage placement based on CT assessment. Importantly, they also demonstrated a significant reduction in radiation exposure to the surgeon and staff with the use of iCBCT. Minimally invasive spine procedures have traditionally been associated with relatively high levels of radiation exposure to the surgeon and operating room staff. Efforts to reduce this exposure are important and should be made a priority. The authors have provided favorable data in support of iCBCT as an option to significantly reduce radiation exposure without compromising accurate localization and cage placement in LLIF. Justin S. Smith Charlottesville, Virginia Copyright © 2017 by the Congress of Neurological Surgeons This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/about_us/legal/notices) http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Operative Neurosurgery Oxford University Press

Analysis of Intraoperative Cone-Beam Computed Tomography Combined With Image Guidance for Lateral Lumbar Interbody Fusion

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Oxford University Press
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Copyright © 2017 by the Congress of Neurological Surgeons
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2332-4252
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2332-4260
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10.1093/ons/opx176
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Abstract

Abstract BACKGROUND Minimally invasive lateral lumbar interbody fusion (LLIF) is traditionally performed with biplanar fluoroscopy. Recent literature demonstrates that intraoperative cone-beam computed tomography combined with spinal navigation can be safely utilized for localization and cage placement in LLIF. OBJECTIVE To evaluate the accuracy and safety of cage placement using spinal navigation in LLIF, as well as to evaluate the radiation exposure to surgeon and staff during the procedure. METHODS The authors performed a retrospective analysis of a prospectively acquired database of patients undergoing LLIF with image-based navigation performed from April 2014 to July 2016 at a single institution. The medical records were reviewed, and data on clinical outcomes, cage accuracy, complications, and radiation exposure were recorded. All patients underwent a minimum 30-d clinical follow-up to assess intraoperative and short-term complications associated with their LLIF. RESULTS Sixty-three patients comprising 117 spinal levels were included in the study. There were 36 (57.1%) female and 27 (42.9%) male patients. Mean age was 62.7 yr (range 24-79 yr). A mean 1.9 (range 1-4) levels per patient were treated. Cages were placed in the anterior or middle of 115 (98.3%) disc spaces. Image-guided cage trajectory was accurate in 116/117 levels (99.1%). In a subgroup analysis of 18 patients, mean fluoroscopy time was 11.7 ± 9.7 s per level. Sixteen (25.4%) patients experienced a complication related to approach. CONCLUSION Use of intraoperative cone-beam computed tomography combined with spinal navigation for LLIF results in accurate and safe cage placement as well as significantly decreased surgeon and staff radiation exposure. Image-guided surgery, Intraoperative cone-beam computed tomography, Lateral lumbar interbody fusion, LLIF, Minimally invasive surgery, O-arm, Radiation exposure ABBREVIATIONS ABBREVIATIONS BMI body mass index CT computed tomography FT fluoroscopy time iCBCT intraoperative cone-beam computed tomography IGN image-guided navigation LLIF lateral lumbar interbody fusion MI minimally invasive Minimally invasive (MI) techniques for lateral lumbar interbody fusion (LLIF) have the ability to improve disc height and provide indirect neural decompression. Compared to posterior interbody techniques, the lateral approach limits damage to dorsal spinal elements and is now commonly used to treat symptomatic degenerative disk disease, spondylolisthesis, and scoliosis.1-5 In performing the LLIF, fluoroscopic guidance and neuromonitoring are used to ensure the accuracy of cage placement and prevent lumbosacral plexus injury.6,7 The necessary use of fluoroscopy leads to increased radiation exposure to the patient, surgeon, and staff. In addition, fluoroscopic guidance does not guarantee ideal cage position. Previous studies have reported the feasibility, safety, and accuracy of using intraoperative cone-beam computed tomography (iCBCT) and image-guided navigation (IGN) for LLIF.8,9 The objective of this study was to evaluate complications, accuracy, radiographic results, and radiation exposure with the use of iCBCT and IGN in LLIF. METHODS With institutional board approval, a retrospective analysis of the electronic medical records was performed for patients who underwent LLIF with the use of iCBCT (O-arm, Medtronic, Inc., Minneapolis, Minnesota) for 3D image acquisition in conjunction with the StealthStation guidance system (Medtronic, Inc., Minneapolis, Minnesota) for spinal navigation. From April 2014 to July 2016, 63 consecutive patients who underwent IGN-assisted LLIF were included in the analysis. Surgical Technique The surgical technique in IGN-assisted LLIF has been detailed extensively in previous studies.8,9 Briefly, the patient is placed in the lateral decubitus position on a flat radiolucent table. Axillary and flank rolls are placed. Tape secures the patient to the table at multiple points to allow tilting of the table, if needed (Figure 1A). Width of the sterile field ensures access to the anterior or posterior superior iliac spine; we typically favor the anterior. A stab incision is made and an iliac pin is impacted into bone to attach the IGN system reference frame (Figure 1B). Additional drapes are placed over the surgical field to maintain sterility prior to introduction of the iCBCT unit. A 3D image of the targeted spine levels is then obtained and autoregistered to the IGN system. A single image acquisition is typically adequate for up to 4 spinal levels. If more than 4 spinal levels are treated, 2 3D image acquisitions are obtained. FIGURE 1. View largeDownload slide A, Patient in the right lateral decubitus position on a flat radiolucent table. B, Reference frame attached to pin embedded in the anterior superior iliac spine. FIGURE 1. View largeDownload slide A, Patient in the right lateral decubitus position on a flat radiolucent table. B, Reference frame attached to pin embedded in the anterior superior iliac spine. The navigated initial dilator is then used to demarcate the skin incision (Figure 2). After incision, the retroperitoneal space is entered using the standard muscle-splitting technique. The navigated dilator, equipped with a nerve stimulator, is advanced through the psoas muscle and into the disc space via IGN (Figure 3). No fluoroscopy is used. After anchoring the dilator in the disc space, sequential dilation is performed with placement of an expandable retractor. The retractor blades are expanded and positioning is confirmed using the navigated initial dilator to demarcate the boundaries of the retractor blades in relationship to the disc space. Visual identification of the disc space confirms the accuracy of navigation. A variety of navigation instruments (ie, Cobb elevator, rotating shaver, and trial spacer) are used to perform discectomy, contralateral annular release, and cage sizing. The appropriately sized cage is then impacted into the disc space using IGN (Figure 4). We do advocate using fluoroscopy, if there is any concern for accuracy, especially in deformity cases. FIGURE 2. View largeDownload slide A, Navigated initial dilator. B, The navigated initial dilator (blue projection) with a virtual extension (yellow projection) is moved along the skin until an orthogonal trajectory into the mid-disc space is determined, which becomes the center of the skin incision. FIGURE 2. View largeDownload slide A, Navigated initial dilator. B, The navigated initial dilator (blue projection) with a virtual extension (yellow projection) is moved along the skin until an orthogonal trajectory into the mid-disc space is determined, which becomes the center of the skin incision. FIGURE 3. View largeDownload slide Using image guidance, the initial dilator (blue projection) is advanced through the psoas muscle and subsequently into the disc space. FIGURE 3. View largeDownload slide Using image guidance, the initial dilator (blue projection) is advanced through the psoas muscle and subsequently into the disc space. FIGURE 4. View largeDownload slide A, The cage is impacted into the disc space utilizing navigation. B, Lateral fluoroscopic image showing the cage positioned in the disc space, consistent with image guidance. FIGURE 4. View largeDownload slide A, The cage is impacted into the disc space utilizing navigation. B, Lateral fluoroscopic image showing the cage positioned in the disc space, consistent with image guidance. Outcome Assessment All patients underwent a minimum 30-d clinical follow-up to assess intraoperative and short-term complications associated with their LLIF. All approach-related complications were captured. Lower extremity sensory and motor functions were evaluated postoperatively and at each follow-up visit. All medical complications during the 30-d postoperative period were recorded. Complications from additional posterior procedures—ie, percutaneous pedicle screw fixation—were considered separate from LLIF and not included in this study. All neurologic complications (numbness and weakness) were followed until last documented clinic visit. Radiographic Assessment All patients underwent postoperative computed tomography (CT) or iCBCT to determine cage positioning. Additionally, postoperative X-rays were obtained for all patients (Figure 5). Accuracy was assessed by comparing the projected navigated cage location with intraoperative fluoroscopy images after cage placement (Figure 4). The location of each cage within the disc space was graded based on the grading system previously described.8 In this system, the disc space is divided into 4 quarters in the sagittal plane, and cage position is recorded as number 1 to 4 (from anterior to posterior). FIGURE 5. View largeDownload slide A, Preoperative and B, Postoperative lateral X-rays of patient with L4-5 spondylolisthesis who underwent LLIF with image-guided navigation. FIGURE 5. View largeDownload slide A, Preoperative and B, Postoperative lateral X-rays of patient with L4-5 spondylolisthesis who underwent LLIF with image-guided navigation. Radiation Exposure Intraoperative fluoroscopy time (FT) was obtained from a subgroup of 18 consecutive patients for whom data were available. The remaining patients comprised those treated earlier in our experience, in which FT data included fluoroscopy usage for the posterior approach as well as the lateral approach, so their data could not be analyzed. Because there was no comparison group, the FT of IGN-assisted LLIF was compared with the published literature involving FT with traditional fluoroscopic-guided LLIF. In addition, a correlation analysis was performed with FT and fusion levels as well as FT and body mass index (BMI). Statistical Analysis Descriptive statistics were utilized for the analysis of patient, surgical, and radiographic characteristics. All statistical analyses were performed using GraphPad Prism version 6 software (GraphPad, Inc., San Diego, California). RESULTS Patient demographics and detailed procedural data were listed in Table 1. A total of 63 patients and 117 spinal levels were included in this study. Thirty-six patients (57.1%) were female and 27 (42.9%) were male, with a mean age of 62.7 yr (range 24-79 yr). A mean of 1.9 ± 1.0 levels were fused per patient (range 1-4 levels), and most cases (51 cases; 81.0%) were approached from the left side. Mean BMI was 31.6 (range 19.8-47.1). Thirteen patients were categorized as normal weight (BMI < 25.0) and 11 were overweight (BMI 25.0-29.9). The remaining patients had obesity, with 18 having class I obesity (BMI 30.0-34.9), 14 having class II obesity (BMI 35.0-39.9), and 6 having class III obesity (BMI ≥ 40.0). All patients only required 1 scan with iCBCT for navigation. Indications for surgery included degenerative kyphoscoliosis, adult idiopathic scoliosis, stenosis, spondylolisthesis, tumor, degenerative disc disease, adjacent segment disease, or pseudoarthrosis. TABLE 1. Patient Demographics and Procedural Data Patients 63 Number of levels fused 117 Mean levels fused 1.9 ± 1.0 Mean age (range) 62.7 (24-79) BMI (range) 31.6 (19.8-47.1) Male (%) 27 (42.9) Female (%) 36 (57.1) Levels involved (%)  T12-L1 2 (1.7)  L1-L2 12 (10.3)  L2-L3 28 (23.9)  L3-L4 40 (34.2)  L4-L5 35 (29.9) Indication (%)  Degenerative scoliosis 24 (38.1)  Adjacent segment disease 16 (25.4)  Spondylolisthesis 11 (17.5)  Pseudoarthrosis 4 (6.3)  Postlaminectomy kyphoscoliosis 2 (3.2)  Degenerative disc disease 2 (3.2)  Idiopathic scoliosis 2 (3.2)  Tumor 1 (1.6)  Flat back syndrome 1 (1.6) Patients 63 Number of levels fused 117 Mean levels fused 1.9 ± 1.0 Mean age (range) 62.7 (24-79) BMI (range) 31.6 (19.8-47.1) Male (%) 27 (42.9) Female (%) 36 (57.1) Levels involved (%)  T12-L1 2 (1.7)  L1-L2 12 (10.3)  L2-L3 28 (23.9)  L3-L4 40 (34.2)  L4-L5 35 (29.9) Indication (%)  Degenerative scoliosis 24 (38.1)  Adjacent segment disease 16 (25.4)  Spondylolisthesis 11 (17.5)  Pseudoarthrosis 4 (6.3)  Postlaminectomy kyphoscoliosis 2 (3.2)  Degenerative disc disease 2 (3.2)  Idiopathic scoliosis 2 (3.2)  Tumor 1 (1.6)  Flat back syndrome 1 (1.6) View Large TABLE 1. Patient Demographics and Procedural Data Patients 63 Number of levels fused 117 Mean levels fused 1.9 ± 1.0 Mean age (range) 62.7 (24-79) BMI (range) 31.6 (19.8-47.1) Male (%) 27 (42.9) Female (%) 36 (57.1) Levels involved (%)  T12-L1 2 (1.7)  L1-L2 12 (10.3)  L2-L3 28 (23.9)  L3-L4 40 (34.2)  L4-L5 35 (29.9) Indication (%)  Degenerative scoliosis 24 (38.1)  Adjacent segment disease 16 (25.4)  Spondylolisthesis 11 (17.5)  Pseudoarthrosis 4 (6.3)  Postlaminectomy kyphoscoliosis 2 (3.2)  Degenerative disc disease 2 (3.2)  Idiopathic scoliosis 2 (3.2)  Tumor 1 (1.6)  Flat back syndrome 1 (1.6) Patients 63 Number of levels fused 117 Mean levels fused 1.9 ± 1.0 Mean age (range) 62.7 (24-79) BMI (range) 31.6 (19.8-47.1) Male (%) 27 (42.9) Female (%) 36 (57.1) Levels involved (%)  T12-L1 2 (1.7)  L1-L2 12 (10.3)  L2-L3 28 (23.9)  L3-L4 40 (34.2)  L4-L5 35 (29.9) Indication (%)  Degenerative scoliosis 24 (38.1)  Adjacent segment disease 16 (25.4)  Spondylolisthesis 11 (17.5)  Pseudoarthrosis 4 (6.3)  Postlaminectomy kyphoscoliosis 2 (3.2)  Degenerative disc disease 2 (3.2)  Idiopathic scoliosis 2 (3.2)  Tumor 1 (1.6)  Flat back syndrome 1 (1.6) View Large Complications All cases of LLIF with IGN were performed successfully, except 1 level (L1-L2) that was aborted due to violation of the endplate, which occurred during disc space preparation without navigated instruments. Sixteen patients (25.4%) encountered approach-related complications; 9 had mild transient hip weakness, 3 had transient hip/thigh numbness, and 4 had persistent mild hip/thigh numbness at last follow-up. No patients had persistent weakness at last follow-up. “Mild weakness” was defined as 4/5 or 4+/5 strength based on Medical Research Council criteria. Two patients had superficial wound infections, while another patient developed a psoas abscess (treated with percutaneous drainage). One developed asymptomatic myositis ossificans. No spinal canal invasion, visceral injury, or large vessel violation was observed. Medical complications included 3 patients with perioperative myocardial infarctions, 1 patient who developed Miller-Fisher acute intermittent demyelinating polyneuropathy, 2 patients with uncomplicated ileus, 1 patient with transient urinary retention, and 1 patient with perioperative pneumonia (Table 2). TABLE 2. Medical and Surgical Complications Approach-related  Transient hip weakness 9  Persistent hip weakness 0  Transient thigh numbness 3  Persistent thigh numbness 4 Medical  Myocardial infarction 3  Ileus 2  Miller-Fisher acute intermittent demyelinating polyneuropathy 1  Transient urinary retention 1  Pneumonia 1 Wound  Psoas abscess 1  Superficial wound infection 2 Approach-related  Transient hip weakness 9  Persistent hip weakness 0  Transient thigh numbness 3  Persistent thigh numbness 4 Medical  Myocardial infarction 3  Ileus 2  Miller-Fisher acute intermittent demyelinating polyneuropathy 1  Transient urinary retention 1  Pneumonia 1 Wound  Psoas abscess 1  Superficial wound infection 2 View Large TABLE 2. Medical and Surgical Complications Approach-related  Transient hip weakness 9  Persistent hip weakness 0  Transient thigh numbness 3  Persistent thigh numbness 4 Medical  Myocardial infarction 3  Ileus 2  Miller-Fisher acute intermittent demyelinating polyneuropathy 1  Transient urinary retention 1  Pneumonia 1 Wound  Psoas abscess 1  Superficial wound infection 2 Approach-related  Transient hip weakness 9  Persistent hip weakness 0  Transient thigh numbness 3  Persistent thigh numbness 4 Medical  Myocardial infarction 3  Ileus 2  Miller-Fisher acute intermittent demyelinating polyneuropathy 1  Transient urinary retention 1  Pneumonia 1 Wound  Psoas abscess 1  Superficial wound infection 2 View Large Radiographic Results Among all 117 LLIF levels treated using IGN, only 1 level encountered imprecise trajectory during cage insertion, resulting in 99.1% accuracy. Cage placement was reconfirmed by postoperative X-ray or CT images. Of 117 cages, 44 (37.6%) were placed within the anterior disc space in quarters 1 and 2, and 71 (60.7%) were placed in the middle of the disc space in quarters 2 and 3. Two cages (1.7%) were placed within the posterior disc space in quarters 3 and 4 (Table 3). TABLE 3. Radiographic Results IGN accuracy (%) 116/117 (99.1) Cage placement (%)  1-2 44 (37.6)  2-3 71 (60.7)  3-4 2 (1.7) IGN accuracy (%) 116/117 (99.1) Cage placement (%)  1-2 44 (37.6)  2-3 71 (60.7)  3-4 2 (1.7) View Large TABLE 3. Radiographic Results IGN accuracy (%) 116/117 (99.1) Cage placement (%)  1-2 44 (37.6)  2-3 71 (60.7)  3-4 2 (1.7) IGN accuracy (%) 116/117 (99.1) Cage placement (%)  1-2 44 (37.6)  2-3 71 (60.7)  3-4 2 (1.7) View Large Fluoroscopy Time Table 4 details FT of the IGN LLIF procedures. Eighteen patients were included, with mean BMI of 32.9 ± 6.8, and mean levels fused of 1.5 ± 0.6. Mean FT was 16.6 ± 14.4 s (range 2-48 s) per case. Mean FT per level was 11.7 ± 9.7 s. TABLE 4. Patient Fluoroscopy Time Patient BMI Levels Fluoroscopy time (s) 1 25 1 2 2 32.8 2 2 3 43.8 2 3 4 37.1 1 3 5 37.1 1 3 6 24.6 2 14 7 32.7 1 15 8 36.7 1 17 9 35.4 1 20 10 27.8 2 24 11 41.3 1 26 12 44.4 1 3 13 34.2 1 31 14 34.2 2 36 15 24.8 2 38 16 19.8 2 48 17 29.4 1 5 18 31.2 3 9 Patient BMI Levels Fluoroscopy time (s) 1 25 1 2 2 32.8 2 2 3 43.8 2 3 4 37.1 1 3 5 37.1 1 3 6 24.6 2 14 7 32.7 1 15 8 36.7 1 17 9 35.4 1 20 10 27.8 2 24 11 41.3 1 26 12 44.4 1 3 13 34.2 1 31 14 34.2 2 36 15 24.8 2 38 16 19.8 2 48 17 29.4 1 5 18 31.2 3 9 View Large TABLE 4. Patient Fluoroscopy Time Patient BMI Levels Fluoroscopy time (s) 1 25 1 2 2 32.8 2 2 3 43.8 2 3 4 37.1 1 3 5 37.1 1 3 6 24.6 2 14 7 32.7 1 15 8 36.7 1 17 9 35.4 1 20 10 27.8 2 24 11 41.3 1 26 12 44.4 1 3 13 34.2 1 31 14 34.2 2 36 15 24.8 2 38 16 19.8 2 48 17 29.4 1 5 18 31.2 3 9 Patient BMI Levels Fluoroscopy time (s) 1 25 1 2 2 32.8 2 2 3 43.8 2 3 4 37.1 1 3 5 37.1 1 3 6 24.6 2 14 7 32.7 1 15 8 36.7 1 17 9 35.4 1 20 10 27.8 2 24 11 41.3 1 26 12 44.4 1 3 13 34.2 1 31 14 34.2 2 36 15 24.8 2 38 16 19.8 2 48 17 29.4 1 5 18 31.2 3 9 View Large DISCUSSION As MI techniques in spine surgery continue to develop, there is an increasing interest in safety given the radiation exposure associated with these procedures. Specifically, there is a growing body of evidence for the concern of increased radiation exposure to the surgical team in MI spine procedures.10-13 The increased radiation exposure risk noted with MI spine procedures, as well as concerns for the long-term harm of workplace radiation exposure, has led to the development of new techniques to reduce radiation exposure to the surgical team.12,14,15 iCBCT allows for the acquisition of high-quality intraoperative 3D images while generating lower radiation dosage than that of a traditional CT scan.16-18 A previous study by Costa et al17 estimated that each scan of the iCBCT for thoracolumbar procedures corresponds to 2.52 mSv of radiation exposure to the patient. This is significantly lower than the patient radiation exposure from a lumbar spine CT, estimated to range between 7.5 and 10 mSv. The iCBCT unit has been successfully utilized in various neurosurgical applications including spinal instrumentation, tumor resection, and scoliosis correction.19-22 Procedural indications in the present study are similar to those described previously for LLIF. Accuracy of pedicle screw placement has been shown to be superior to C-arm fluoroscopy when directly compared.22,23 Although setup time is longer when utilizing iCBCT, the overall operative time is similar.14 When examining surgical team radiation exposure in fluoroscopic-guided MI-transforaminal lumbar interbody fusion compared to that of iCBCT, there is an evidence of increased radiation exposure noted in the fluoroscopic group.11,13 A study by Taher et al24 investigated FT in traditional MI-LLIF. They included 18 patients with 43 total levels fused (mean 2.4 ± 0.8 levels), with an average FT of 88.7 ± 36.8 s. In the present investigation, we found a mean of 11.7 s per level, as opposed to 37.0 s per level, which is the calculated value from the mean FT divided by mean levels fused in the Taher et al study. This suggests a 3-fold decrease in FT with the use of iCBCT with IGN, which results in significantly reduced radiation to the surgeon and operating room staff. Although the use of IGN has the potential to minimize radiation exposure, we do not advocate eliminating the use of fluoroscopy in navigated LLIF procedures. Especially in cases of deformity, spot fluoroscopic images should be obtained periodically to confirm accuracy. Given that the lumbar plexus lies in the dorsal portion of the psoas muscle,25 traditional MI-LLIF procedures are reported to have risk of severe sensory or motor nerve injury, especially at more caudal levels, despite the use of neuromonitoring.26-30 An advantage of IGN is that the trajectory through the psoas muscle can be more easily adjusted, if needed, based on neuromonitoring compared to fluoroscopic guidance. In this study, 16 patients (25.4%) encountered approach-related complications, which is comparable to previous non-navigated LLIF studies.31,32 However, most of these complications were transient hip discomfort or mild thigh weakness, which could be considered expected consequences of the trans-psoas LLIF procedure. More importantly, there was no severe motor or sensory deficiency. For patients with persistent mild numbness, it is possible that follow-up was not of sufficient length for improvement given the 30-d minimum follow-up in this study. Our mean follow-up time was 8.8 mo (range 3-14). These results suggest that IGN-assisted LLIF along with neuromonitoring is a safe procedure, with 99.1% accuracy in navigated trajectory. A ventrally placed LLIF cage can provide improved segmental lordosis, although the achievement of indirect decompression relies more on posterior disc height.33,34 Thus, the ideal position for LLIF cage placement should be within the anterior to middle portion of the disc space, a location that this report demonstrates can be achieved in most cases with IGN. Of the 117 levels treated with navigation, 115 (98.3%) cages were positioned within the anterior to middle disc space. Due to rotational scoliosis, 1 patient had 2 cages placed in the posterior quadrant because of the technical difficulty in accessing the anterior portion of the disc space. Regarding accuracy, the projected cage location on IGN was compared to a fluoroscopic image after cage placement and found to be consistent. Of note, for multilevel cases, the superior-most disc level is treated first, followed by the next distal level, to minimize the loss of accuracy with placement of the cage, given that the reference frame is anchored in the anterior superior iliac spine. Of note, IGN did not produce submillimeter accuracy. Particularly in multilevel cases, there was up to an estimated 2 to 3 mm error. This level of precision, however, was adequate for cage placement. Limitations There were several limitations to this study. It is a retrospective analysis, with all the accompanied biases involved. Further, there was only a subgroup of 18 patients available for radiation exposure analysis. The generalizability of this study is reliant on individual surgeon experience with the LLIF procedure and spinal navigation. However, in our experience of working with other surgeons, the learning curve seems relatively steep. CONCLUSION iCBCT and IGN can be used to decrease fluoroscopic use while maintaining accuracy and safety during LLIF procedures. Future investigations with larger sample sizes are needed to compare the radiation exposure between navigated LLIF and traditional LLIF procedures. Disclosures Paul Park is a consultant for and receives royalties from Globus. He is also a consultant for Medtronic, Zimmer-Biomet, and NuVasive. The other authors have no personal, financial, or institutional interest in any of the drugs, materials, or devices described in this article. REFERENCES 1. Malham GM , Parker RM , Goss B , Blecher CM , Ballok ZE . Indirect foraminal decompression is independent of metabolically active facet arthropathy in extreme lateral interbody fusion . Spine (Phila Pa 1976) . 2014 ; 39 ( 22 ): E1303 - E1310 . Google Scholar CrossRef Search ADS PubMed 2. Anand N , Baron EM , Khandehroo B , Kahwaty S . 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Comparison of complication rates of minimally invasive transforaminal lumbar interbody fusion and lateral lumbar interbody fusion: a systematic review of the literature . Neurosurg Focus . 2015 ; 39 ( 4 ): E4 . Google Scholar CrossRef Search ADS PubMed 32. Lehmen JA , Gerber EJ . MIS lateral spine surgery: a systematic literature review of complications, outcomes, and economics . Eur Spine J . 2015 ; 24 ( suppl 3 ): 287 - 313 . Google Scholar CrossRef Search ADS PubMed 33. Kepler CK , Huang RC , Sharma AK et al. Factors influencing segmental lumbar lordosis after lateral transpsoas interbody fusion . Orthop Surg . 2012 ; 4 ( 2 ): 71 - 75 . Google Scholar CrossRef Search ADS PubMed 34. Park SJ , Lee CS , Chung SS , Kang SS , Park HJ , Kim SH . The ideal cage position for achieving both indirect neural decompression and segmental angle restoration in lateral lumbar interbody fusion (LLIF) [published online June 27, 2016] . Clin Spine Surgery . 2017 ; 30 ( 6 ): E784 - E790 . Google Scholar CrossRef Search ADS COMMENT The authors provide a detailed review of their series of 63 patients treated with lateral lumbar interbody fusion (LLIF) using intraoperative cone-beam CT combined with image guidance (iCBCT). They provide assessment of the accuracy and safety of using iCBT and assess the radiation exposure to the surgeon and staff. They were able to successfully complete all but 1 procedure (1 case was aborted due to endplate violation). Their overall complication rate appears to be comparable to previously reported series of LLIF cases. Application of iCBCT resulted in 99% of their cases with appropriate cage placement based on CT assessment. Importantly, they also demonstrated a significant reduction in radiation exposure to the surgeon and staff with the use of iCBCT. Minimally invasive spine procedures have traditionally been associated with relatively high levels of radiation exposure to the surgeon and operating room staff. Efforts to reduce this exposure are important and should be made a priority. The authors have provided favorable data in support of iCBCT as an option to significantly reduce radiation exposure without compromising accurate localization and cage placement in LLIF. Justin S. Smith Charlottesville, Virginia Copyright © 2017 by the Congress of Neurological Surgeons This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/about_us/legal/notices)

Journal

Operative NeurosurgeryOxford University Press

Published: Aug 2, 2017

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