Adult spinal deformity, including degenerative scoliosis,

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1 SPINE Volume 41, Number 10, pp ß 2016 Wolters Kluwer Health, Inc. All rights reserved DEFORMITY Risk Assessment of Lumbar Segmental Artery Injury During Lateral Transpsoas Approach in the Patients With Lumbar Scoliosis Yoichiro Takata, MD, PhD, Toshinori Sakai, MD, PhD, Fumitake Tezuka, MD, Kazuta Yamashita, MD, Mitsunobu Abe, MD, Kosaku Higashino, MD, PhD, Akihiro Ngamachi, MD, PhD, and Koichi Sairyo, MD, PhD Study Design. A retrospective study using 27 contrastenhanced multi-planar computed tomography scans of subjects with lumbar scoliosis. Objective. To assess the risk of injury of lumbar segmental arteries during transpsoas approach in patients with lumbar scoliosis. Summary of Background Data. Although lumbar interbody fusion using big intervertebral cage through transpsoas approach has a big advantage to correct coronal and sagittal deformity in patients with spinal deformity, the risk for injury of lumbar segmental artery is always concerned. Methods. The abdominal-contrast enhanced multi-planar computed tomography scans of 27 subjects with lumbar scoliosis with over 158 of Cobb angle were retrospectively reviewed. The coronal views through the posterior one third of the intervertebral discs were reviewed. The cranio-caudal intervals of the adjacent segmental arteries at each intervertebral level were measured. The recommended working space for the lateral transpsoas approach using extreme lateral interbody fusion retractor is 24 mm in the cranio-caudal direction. The cutoff value for an intersegmental Cobb angle that would estimate a cranio-caudal interval of less than 24 mm was determined using a receiver operating characteristic curve. Results. The average interval between the cranio-caudal lumbar segmental arteries on the concave side was significantly shorter than that on the convex side (29.9 vs mm, From the Department of Orthopedics, Tokushima University, Tokushima, Japan. Acknowledgment date: October 8, Acceptance date: October 27, The manuscript submitted does not contain information about medical device(s)/drug(s). No funds were received in support of this work. No relevant financial activities outside the submitted work. Address correspondence and reprint requests to Yoichiro Takata, Department of Orthopedics, Tokushima University, Kuramoto Tokushima, Tokushima , Japan; yoichiro76@gmail.com DOI: /BRS P < 0.05). The differences in the intervals between the convex and concave sides were correlated with the corresponding intersegmental Cobb angle (r ¼ 0.65, P < 0.05). Receiver operating characteristic curve analysis revealed that cutoff value for the best prediction of an interval less than 24 mm was 14.58, with a specificity of 94.3% and sensitivity of 71.4%. Conclusion. This study demonstrated that female patients with lumbar scoliosis with an intersegmental Cobb angle higher than would be at high risk for potential injury to the lumbar artery during a transpsoas approach for extreme lateral interbody fusion from the concave side. Key words: complication, lumbar segmental artery, scoliosis, transpsoas approach, vascular injury, extreme lateral interbody fusion. Level of Evidence: 4 Spine 2016;41: Adult spinal deformity, including degenerative scoliosis, is a common cause of coronal and sagittal imbalance, which affects common activities of daily living such as standing and walking. Transpsoas lateral lumbar interbody fusion, also known as extreme lateral interbody fusion (XLIF), is a minimally invasive technique that can correct spinal deformities in the coronal and sagittal plane by using a large intervertebral cage. The application of the XLIF technique to the treatment of adult scoliosis was first reported by Diaz et al. 1 Recently, this technique has become widely used, and the clinical results of XLIF in the treatment of spinal deformity have been reported. 1 5 Although the complication rate of XLIF for spinal deformity is lower than that of posterior open reconstruction using a long construct, 6 some complications of XLIF have been reported. Minor postoperative complications of XLIF include muscle weakness in hip flexion as well as groin and thigh paresthesias, with an incidence of 2% to 30% These symptoms typically resolve over time. In the treatment of lumbar scoliosis using XLIF, the discs are usually approached from the concave side. 11 Due to May 2016

2 lumbar scoliosis, each interval of the adjacent lumbar segmental arteries on concave side is expected to be shorter than that on the convex side. Injury to the lumbar segmental artery is an important risk during the transpsoas lateral approach to the spine. However, no reports have described the anatomical considerations for lumbar segmental arteries in scoliosis patients. The purpose of this study was to assess the risk of lumbar segmental artery injury during the lateral transpsoas approach in patients with lumbar scoliosis. MATERIALS AND METHODS An institutional review board exemption was obtained for the review of imaging studies, the indications for the studies, and the official computed tomography (CT) reports. We reviewed the anterior-posterior abdominal standing radiographs of 475 consecutive subjects (279 males, 196 females; average age, 67.1 years; range, years), who underwent abdominal contrast-enhanced multi-planar CT scans for the purpose of creating surgical plans for colon cancer. Of 475 subjects, we selected 27 subjects with lumbar scoliosis with a coronal Cobb angle greater than 158 (8 males, 19 females; average age, 75.7 years; range, years) (Table 1). We retrospectively reviewed the abdominal contrast-enhanced multi-planar CT scans of these 27 subjects. Subjects with a history of abdominal or lumbar surgery were excluded from the analysis. The CT-scan data were transferred to the computer software AquariusNET ver. 1.6 (TeraRecon, San Mateo, CA). The axial and sagittal planes were adjusted to reproduce the true anterior-posterior and lateral views during the XLIF procedure, respectively (Figure 1A). The coronal views through the posterior one third of the intervertebral discs in L1-L2, L2-L3, L3-L4, and L4-L5 were reviewed (Figure 1B). The cranio-caudal intervals of the adjacent segmental arteries at each intervertebral level, excluding the L4-L5 level, were measured, because the lumbar segmental arteries of L5 were not enhanced in 24 of the 27 (88.9%) subjects. The relationship between this interval and each intersegmental Cobb angle was analyzed. The recommended working space for the lateral transpsoas approach for the XLIF retractor is 24 mm in the cranio-caudal direction (Figure 2A, B). The cutoff value for an intersegmental Cobb angle that would estimate a cranio-caudal interval of less than 24 mm was determined using a receiver operating characteristic (ROC) curve. Statistical analysis including Pearson correlation coefficient, t test, chi-squared test, and ROC analysis were performed with SPSS Statistics version 22.0 (IBM Corp. Armonk, NY). RESULTS A statistically significant female predominance of lumbar scoliosis was observed (Table 1). The lumbar curvature showed right convexity in 13 subjects and left convexity in 14 subjects. The apex of the convexity was located at L1- L2 in 3 subjects, at L2-L3 in 10 subjects, and at L3-L4 in 14 subjects. The average Cobb angle was 23.48, and each intersegmental Cobb angle was 6.88, 8.48, 6.48, and 6.48 in L1-L2, L2-L3, L3-L4, and L4-L5, respectively. The average interval between the cranio-caudal lumbar segmental arteries on the concave side was significantly shorter than that on the convex side (29.9 vs mm, P < 0.05). The intervals on the concave side at L1-L2 and L2-L3 were significantly shorter in female subjects than the corresponding ones in male subjects (Table 2). The differences in the intervals between the convex and concave sides were correlated with the corresponding intersegmental Cobb angle (r ¼ 0.65, P < 0.05) (Figure 3). The cranio-caudal intervals of the adjacent segmental arteries on the concave side were less than 24 mm at seven intervertebral levels in five female subjects (Table 1). None of the male subjects showed a cranio-caudal interval less than 24 mm. ROC curve analysis (Figure 4) demonstrated that the intersegmental Cobb angle showed good prediction of the interval between the cranio-caudal segmental arteries, with an area under curve (AUC) of 0.8. Its cutoff value for the best prediction of an interval less than 24 mm was 14.58, with a specificity of 94.3% and sensitivity of 71.4%. DISCUSSION XLIF is widely used to treat the adult spinal deformity surgery. This technique has many benefits, such as reduced postoperative pain, short hospital stay, less intraoperative blood loss, early ambulation. A laterally inserted large footprint cage with a lordotic angle provides strong correction of coronally tilted lumbar segments and decreases lumbar lordosis. 12,13 The major complications of XLIF include visceral perforation, 3,14 major vascular injury, kidney laceration, 18 retroperitoneal hematoma, 19 and iatrogenic lumbar artery pseudoaneurysm. 20 Delayed retroperitoneal hematoma following lumbar arterial injury can be life threatening. In our study, the interval between adjacent TABLE 1. Characteristics of Subjects Male Female P n ¼ 279 n ¼ 196 No. of subjects without scoliosis <0.05 No. of subjects with Cobb angle > No. of subjects with <24 mm interval 0 5 (7 levels) Chi-squared test. Spine 881

3 Figure 1. Measurement of the cranio-caudal interval between adjacent lumbar segmental arteries. A, The axial (upper left panel) and sagittal (lower right panel) planes were adjusted to reproduce the intraoperative fluoroscopic images of the extreme lateral interbody fusion procedure. In the coronal plane (left lower panel), the lumbar segmental arteries are enhanced clearly (white arrows). B, Coronal view of multi-planar computed tomography images. The cranio-caudal interval between adjacent lumbar segmental arteries and the intersegmental Cobb angle were measured. lumbar arteries on the concave side was significantly shorter than that on the convex side. Considering the risk of lumbar artery injury, it is important to be very careful when using the transpsoas approach from the concave side for XLIF in a patient with lumbar scoliosis. Thus far, only one study has mentioned the anatomy of neurovascular structures with respect to the minimally invasive lateral approach in patients with lumbar scoliosis, 21 describing magnetic resonance imaging morphometric data on 19 scoliotic levels. Regev et al 21 reported that the safe May 2016

4 Figure 2. A, The cranio-caudal distance of the XLIF retractor is 24 mm. B, Intraoperative fluoroscopic image of installation of the XLIF retractor via the transpsoas approach with the recommended dilatation. XLIF indicates extreme lateral interbody fusion. TABLE 2. Cranio-Caudal Intervals of Adjacent Lumbar Arteries Cranio-Caudal Interval in Concavity Male Female P L1-L2 (mm) <0.05 L2-L3 (mm) <0.05 L3-L4 (mm) ¼0.46 t test. zone for lateral access to the intervertebral disc in the scoliotic group decreased to nearly half as that in the non-scoliotic group due to overlapping of the vena cava or aorta over the vertebral body; however, they did not describe the anatomy of the lumbar segmental arteries. Our study is the first to describe the anatomy of segmental arteries in lumbar scoliosis. Figure 3. The difference in the intervals between the convex and concave sides in relation to each intersegmental Cobb angle, with a superimposed regression line. Figure 4. Receiver operating characteristic curve of the intersegmental Cobb angle for the prediction of the cranio-caudal interval between adjacent segmental arteries in 27 subjects with lumbar scoliosis. Spine 883

5 This study presented a cutoff value of for the intersegmental Cobb angle to predict an interval of less than 24 mm for adjacent segmental arteries in the concave side. Thus, when performing XLIF for patients with scoliosis with an intersegmental Cobb angle more than 14.58, careful intraoperative care is essential for avoiding injury to the lumbar segmental arteries. This study has some limitations. The first limitation is with respect to patient positioning. The CT scans were all performed with the patient in the supine position, whereas direct lateral transpsoas approaches are performed with the patient in the lateral decubitus position. In the decubitus position, the interval of adjacent segmental arteries on the concave side might become longer. The second limitation concerns bodily stature. In our study, all the subjects were Japanese, and female subjects showed shorter intervals on the concave side as compared with male subjects. The cutoff value of the intersegmental Cobb angle might be different in other ethnic populations. In conclusion, this study demonstrated that female patients with lumbar scoliosis with an intersegmental Cobb angle more than would be at high risk for potential injury to the lumbar artery during a transpsoas approach for XLIF from the concave side. Key Points This study analyzed the interval of adjacent lumbar arteries on both the concave and convex sides of lumbar scoliosis to assess the risk of injury to the lumbar segmental arteries in a lateral transpsoas approach for XLIF in patients with lumbar scoliosis. The average distance between cranio-caudal segmental arteries on the concave side was significantly shorter than that on the convex side. The cutoff value of the intersegmental Cobb angle to avoid lumbar segmental artery injury during lateral transpsoas approach using the XLIF retractor was References 1. Diaz R, Phillips F, Pimenta L, et al. XLIF for lumbar degenerative scoliosis: outcomes of minimally invasive surgical treatment out to 3 years postoperatively. Spine J 2006;6:75S. 2. Anand N, Rosemann R, Khalsa B, et al. Mid-term to long-term clinical and functional outcomes of minimally invasive correction and fusion for adults with scoliosis. Neurosurg Focus 2010;28:E6. 3. Tormenti MJ, Maserati MB, Bonfield CM, et al. Complications and radiographic correction in adult scoliosis following combined transpsoas extreme lateral interbody fusion and posterior pedicle screw instrumentation. Neurosurg Focus 2010;28:E7. 4. Dakwar E, Cardona RF, Smith DA, et al. Early outcomes and safety of the minimally invasive, lateral retroperitoneal transpsoas approach for adult degenerative scoliosis. Neurosurg Focus 2010;28:E8. 5. Wang MY, Mummaneni PV. Minimally invasive surgery for thoracolumbar spinal deformity: initial clinical experience with clinical and radiographic outcomes. Neurosurg Focus 2010;28:E9. 6. 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