Kyphoplasty is currently a treatment option for. Safety and efficacy of balloon kyphoplasty at 4 or more levels in a single anesthetic session

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1 CLINICAL ARTICLE J Neurosurg Spine 28: , 2018 Safety and efficacy of balloon kyphoplasty at 4 or more levels in a single anesthetic session Alan C. Wang, BS, 1 and Daniel K. Fahim, MD 1,2 1 Department of Neurosurgery, Oakland University William Beaumont School of Medicine, Rochester; and 2 Michigan Head & Spine Institute, Southfield, Michigan OBJECTIVE In this case series, the authors evaluated the safety of balloon kyphoplasty at 4 or more vertebral levels in a single anesthetic session. The current standard is that no more than 3 levels should be cemented at one time because of a perceived risk of increased complications. METHODS A retrospective chart review was performed for 19 consecutive patients who underwent 4-level balloon kyphoplasty between July 1, 2011, and December 31, Outcomes documented included kyphoplasty-associated complications and incidences of subsequent vertebral fracture. RESULTS Nineteen patients aged 22 to 95 years (mean 66.1 years, median 66 years; 53% male, 47% female) had 4 or more vertebrae cemented during the same procedure (mean 4.6 levels [62 thoracic, 29 lumbar]). No postoperative anesthetic complication, infection, extensive blood loss, symptomatic cement leakage, pneumothorax, or new-onset anemia was observed. Five patients experienced new compression fracture within a mean of 278 days postoperatively. One patient with metastatic cancer suffered bilateral pulmonary embolism 19 days after surgery, but no evidence of cement in the pulmonary vasculature was found. CONCLUSIONS In this case series, kyphoplasty performed on 4 or more vertebral levels was not found to increase risk to patient safety, and it might decrease unnecessary risks associated with multiple operations. Also, morbidity associated with leaving some fractures untreated because of an unfounded fear of increased risk of complications might be decreased by treating 4 or more levels in the same anesthetic session. KEY WORDS kyphoplasty; safety; vertebral compression fractures; 4 or more levels; surgical technique Kyphoplasty is currently a treatment option for patients with vertebral compression fractures after failure of conservative treatment, such as oral analgesic medications or external bracing. This procedure involves creating a cavity in the vertebral bodies with a balloon and injecting cement to restore height and reduce kyphosis, whereas vertebroplasty involves only the injection of cement to prevent further loss of vertebral height and alleviate pain. 16 Previous randomized controlled studies found that vertebroplasty was not more effective than placebo alone, but subsequent studies discovered significant improvement with kyphoplasty. 3 14,19,20 The current standard in the literature is that no more than 3 vertebral levels should be cemented at one time. 1 This guideline purports an increased risk of complications associated with multilevel kyphoplasty, including a theoretical risk of anemia, especially in elderly patients, because of the role of the vertebrae in hematopoiesis. 1,17 For patients with more than 3 vertebral compression fractures, abiding by this guideline would necessitate multiple procedures and multiple exposures to the risk of anesthetics. Treating only a few of a patient s many painful fractures can leave him or her with ongoing pain, which can result in decreased ambulation and increased bed rest and therefore increase the patient s risk of developing additional spine fractures related to low bone density, deep vein thrombosis (DVT), pneumonia, atelectasis, and decubitus ulcers. 15,18 Many of these patients are of advanced age and undernourished and might have cancer ABBREVIATIONS BMI = body mass index; DVT = deep vein thrombosis; ME = morphine equivalent; PE = pulmonary embolism; VNRS = verbal numerical rating scale. SUBMITTED March 24, ACCEPTED August 2, INCLUDE WHEN CITING Published online January 26, 2018; DOI: / SPINE J Neurosurg Spine Volume 28 April 2018 AANS 2018, except where prohibited by US copyright law

2 or other medical comorbidities as well, which compounds their risk of developing complications secondary to immobility. Also, patients with many fractured vertebral bodies might be denied the well-documented benefits of kyphoplasty because of the perceived increased risk of treating more than 3 fractures within the same surgery. The purpose of this case series was to examine and evaluate the complications experienced by patients undergoing a 4-level balloon kyphoplasty within the same surgery. It is important to minimize both the procedural and anesthesia-related risks for patients with 4 or more vertebral compression fractures. Also important is to minimize the morbidity and death associated with leaving symptomatic compression fractures untreated. Methods Data on procedures that involved percutaneous balloon kyphoplasty (Medtronic) of 4 or more vertebral levels by the senior author (D.K.F.) at our institution between July 1, 2011, and December 31, 2015, were collected, and the applicable patient charts were reviewed. The following variables were collected: demographic information, indication for procedure, vertebral levels involved, whether the patient was undergoing concurrent radiofrequency tumor ablation, fracture diagnosis, and the presence or absence of metastatic disease, multiple myeloma, or osteoporosis. Operative and postoperative details, including estimated blood loss, cement leakage or extravasation, development of a new radiculopathy, new neurological deficits, new fractures, postoperative DVT, infection, and postoperative anemia, were also gathered. Distance of uninterrupted ambulation, pain scores according to a verbal numerical rating scale (VNRS; 0 [no pain] to 10 [worst pain possible]), and the amount of pain medication in morphine equivalents (MEs) were also documented for patients who underwent the procedure while hospitalized in an inpatient unit. From a practical standpoint, anteroposterior and lateral fluoroscopic images were used for every patient (2 separate c-arm units) to save time by not switching between the anteroposterior and lateral views throughout the procedure. The fluoroscopy units were always positioned to maximize the number of fractured levels that could be visualized at the same time. In our experience, a maximum of 4 lumbar vertebrae or 5 thoracic vertebrae can be visualized at the same time. Whenever all the affected vertebral bodies could be seen within a single field of view (implying adjacent fractures), 1 episode of cement mixing was adequate. The fluoroscopy units were then repositioned for use during treatment of distant fractures. We frequently had adequate time to access and treat the distant fractures without mixing more cement, but we did not hesitate to mix more cement if its consistency was not appropriate for the procedure. Results Of the 189 kyphoplasty operations performed by the senior author over the study time period, 19 (10%) involved 4 or more levels. The patient population (n = 19) was aged between 22 and 95 years (mean 66.1 years, TABLE 1. Patient demographics Demographic Value No. of patients 19 Age in yrs Mean 66.1 Median (range) 66 (22 95) Sex Male 10 Female 9 Follow-up duration in days Mean 459 Median (range) 391 ( ) Oxygen requirement before op (no. of patients 2 (2 L) [via nasal cannula]) BMI in kg/m 2 (mean [range]) 26.9 ( ) median 66 years); 53% were male and 47% were female (Table 1). Patients were followed up for a mean of days (median 391 days, range days). All patients experienced tenderness to palpation over their fracture sites. All patients underwent MRI with a STIR sequence that revealed acute or subacute fractures; patients with any contraindication to MRI had available previous scans for comparison that showed no fracture or bone scans that revealed increased activity consistent with an acute fracture. Because of the severity of their pain while standing or ambulating, all patients were essentially confined to bed rest before surgery. The indication for kyphoplasty was compression fractures of thoracic and lumbar vertebrae related to osteoporosis (n = 8), trauma (n = 1), metastatic disease (n = 6), or multiple myeloma (n = 4) (Fig. 1). Medical comorbidities of the study population included heart disease (7 [36.8%]), heart failure (2 [10.5%]), pulmonary disease (5 [26.3%]), diabetes (3 [15.8%]), hypertension (12 [63.2%]), renal disease (3 [15.8%]), peripheral vascular disease (2 [10.5%]), peripheral arterial disease (1 [5.3%]), hypercholesterolemia (2 [10.5%]), hyperlipidemia (2 [10.5%]), previous DVT (1 [5.3%]), previous pulmonary embolism (PE) (2 [10.5%]), and previous cerebrovascular accident (1 [5.3%]) (Table 2). In addition, 2 patients were receiving a baseline of 2 L of oxygen via nasal cannula. The mean body mass index (BMI) of the patients was 26.9 kg/m 2 (range kg/m 2 ), and 7 patients had a BMI greater than 30 kg/m 2. Three patients were considered morbidly obese. Ten patients had cancer (6 had metastatic malignancies and 4 had multiple myelomas). Patients were administered general endotracheal anesthesia and experienced no cardiac complications, and no patients remained intubated at the completion of the procedure (all patients were extubated without incident at the completion of the procedure). The mean number of levels treated in 1 operation was 4.6 (median 4, range 4 6) (Table 3). There were 62 thoracic vertebrae and 29 lumbar vertebrae treated (Table 3). In this case series, kyphoplasty was performed on 4 vertebral levels in 11 patients, on 5 levels in 5 patients, and on 6 levels in 3 patients (Table J Neurosurg Spine Volume 28 April

3 FIG. 1. Number of patients who underwent 4-, 5-, or 6-level kyphoplasty to treat vertebral compression fractures related to osteoporosis, metastatic malignancy, multiple myeloma, or trauma. 4). Nine patients had only thoracic vertebral fractures, 2 patients had only lumbar vertebral fractures, 1 patient had lumbar and sacral fractures, and 7 patients had thoracic and lumbar fractures (Table 5). As illustrated in Fig. 2, T-9 and T-11 were the vertebral levels treated most often in this case series. Moreover, 6 (31.6%) patients had only adjacent fractures, 2 (10.5%) patients had fractures at distant sites, and 11 (57.9%) patients had both adjacent and distant fractures treated. Surgery was performed a mean of 48.6 days (median 36 days, range days) (Table 3) after the compression fracture was first diagnosed with imaging (MRI or CT); this period provided time for an appropriate trial of nonoperative treatment measures (oral analgesics, nonsteroidal antiinflammatory medications, and external bracing), which is consistent with guidelines in the literature that recommend operating on a fracture 3 weeks after diagnosis and trial of nonoperative measures. 2 Four patients underwent kyphoplasty less than 3 weeks after MRI or CT fracture diagnosis. These patients were completely nonresponsive to nonoperative measures and were essentially bedbound after experiencing the inciting trauma. Preoperative and postoperative imaging, including MRI with a STIR sequence for a patient who underwent L1 5 kyphoplasty, is shown in Fig. 3. TABLE 2. Medical comorbidities Comorbidity No. of Patients (%) Heart disease 7 (37) Heart failure 2 (11) Pulmonary disease 5 (26) Diabetes 3 (16) Hypertension 12 (63) Renal disease 3 (16) Peripheral vascular disease 2 (11) Peripheral arterial disease 1 (5) Hypercholesterolemia 2 (11) Hyperlipidemia 2 (11) Previous DVT 1 (5) Previous PE 2 (11) Previous CVA 1 (5) BMI >30 kg/m 2 7 (37) Morbid obesity 3 (16) Metastatic disease 6 (32) Multiple myeloma 4 (21) CVA = cerebrovascular accident. 374 J Neurosurg Spine Volume 28 April 2018

4 TABLE 3. Kyphoplasty characteristics Characteristic Three patients underwent concomitant radiofrequency tumor ablation during their procedure. No postoperative infections occurred. Estimated blood loss was minimal (< 10 ml) for 16 patients, whereas 1 patient lost 25 ml of blood, and 2 patients lost 50 ml of blood (these 2 patients were receiving blood thinners for their concomitant cardiac condition, and to minimize the risk of an adverse thrombotic event, the medications were not discontinued for surgery). The volumes of cement injected were approximately 3 ml in the high thoracic region, 4 ml in the thoracolumbar region, and 6 ml in the low lumbar region. Two instances of cement leakage in 2 patients were noted, but these patients were asymptomatic and experienced no new radiculopathy or other neurological deficits. No cases of pneumothorax were noted. All patients scheduled for outpatient kyphoplasty (n = 10) were discharged from the hospital without complications at the conclusion of the procedure and met discharge criteria. The mean decrease in recorded pain (according to VNRS scores) was 2.5 (n = 4, range 0 4) (Fig. 4). The amount of pain medication recorded decreased a mean of 2.7 MEs; 89% of the patients had no change in their pain medication (n = 10) (Fig. 4). Patients who underwent the procedure while inpatient (n = 9) were returned to their inpatient unit. All the patients were able to ambulate within a few hours of surgery, and they all reported significant improvement in their back pain symptoms. In the 9 hospital inpatients, VNRS pain scores decreased a mean of 5.2 (median 5, range [95% CI ], p = ), from a mean of 7.8 (median 7, range ) to a mean of 2.7 (median 2, range 2 6) on day 2 after the operation (Fig. 4). The need for pain medication was decreased a mean of 11.6 MEs per day (median 0 MEs per day [no change], range increase of 30 to decrease of 69 MEs per day [95% CI 11.2 to 34.4], p = ) from a mean of TABLE 4. Vertebral levels in patients undergoing kyphoplasty No. of Levels Treated No. of Patients Value No. of fractured thoracic vertebrae 62 No. of fractured lumbar vertebrae 29 No. of levels treated in 1 anesthetic session Mean 4.6 Median (range) 4 (4 6) Days btwn MRI-based diagnosis & kyphoplasty Mean 48.6 Median (range) 36 (2 159) No. of patients undergoing simultaneous radiofrequency 3 tumor ablation TABLE 5. Location of vertebral fractures Location of Fracture No. of Fractures (%) Thoracic vertebrae only 9 (47.4) Thoracic & lumbar vertebrae 7 (36.8) Lumbar vertebrae only 2 (10.5) Lumbar & sacral vertebrae 1 (5.3) 78 MEs per day (median 22.5 MEs per day, range MEs per day) on admission and before the procedure to a mean of 66.4 MEs per day (median 15 MEs per day, range MEs per day) after the procedure (Fig. 4). The 1 patient who required additional pain management during the postoperative period initially had a decrease in his pain medication requirement after the kyphoplasty but subsequently required 15 mg of morphine twice daily on postoperative day 9 for distal extremity pain related to documented vasculitis. This pain did not seem related to his previous compression fracture pain or the associated procedure. One patient had undergone no previous physical therapy evaluation, and no data were available to assess changes in ambulation before and after the procedure. Of the 8 inpatients with available ambulation data according to physical therapy documentation, ambulation without interruption was improved by a mean of 92.5 ft (median 80 ft, range ft). No patient experienced regression with ambulation or required additional assistive devices for ambulation after their procedure. Five patients suffered new compression fractures a mean of 278 days after surgery (median 140 days, range days). Four patients suffered 1 new compression fracture. Two of those new fractures were progressive fractures at the level of the previously cemented vertebra, 1 was below a previously cemented vertebra, and 1 was at a remote vertebra. The 1 patient with more than 1 new compression fracture after the kyphoplasty suffered 1 remote compression fracture and 2 compression fractures in between previously cemented vertebrae. Two other complications occurred during the follow-up period. One patient with metastatic cancer was diagnosed with a nondisplaced pathological rib (not correlated with a kyphoplasty-treated level) 2 days after the procedure. Another inpatient with metastatic breast cancer suffered bilateral PE 19 days after surgery; no evidence of cement in the pulmonary vasculature was found (DVT of the lower extremity was diagnosed with ultrasound). None of the patients developed anemia after multilevel kyphoplasty. Of the 19 patients, 13 (68.4%) had anemia before the procedure and continued to have anemia after the surgery. The majority (69.2%) of them were patients with concomitant metastatic cancer. Discussion Although the results of previous randomized controlled trials have cast doubt on the efficacy of vertebroplasty and balloon kyphoplasty, recent literature has revealed it to be safe and effective. 3,10 Randomized controlled studies by J Neurosurg Spine Volume 28 April

5 FIG. 2. Vertebral levels and the frequency at which kyphoplasty was performed on them in our study patients. Clark et al. 4 and Wardlaw et al., 20 as well as multiple retrospective reviews and prospective trials by others, 5 9, 11 14,19 have found that, compared with placebo or conservative medical management, vertebroplasty and kyphoplasty can safely increase vertebral body height, decrease pain, and increase activity levels and improve quality of life in patients with osteoporotic or metastatic compression fractures. To our knowledge, this is the first study to have addressed the safety of performing kyphoplasty at 4 or more vertebral levels in the same anesthetic session. Current guidelines indicate that complications of kyphoplasty can be amplified when more than 3 vertebral levels are treated concurrently. There are purported increased risks of infection, bleeding, local trauma (pneumothorax, fracture of ribs and adjacent vertebra), cement leakage (radiculopathy, canal stenosis, paralysis), PE, and death. 17 We do not believe that any absolute contraindications to multilevel kyphoplasty exist, and we do not believe there to be a maximum number of vertebrae that can be treated at one time. Neither local infections at procedure sites nor excessive blood loss was observed in this case series. Hematoma was associated as an adverse event in 1 of 149 study patients in a previous randomized controlled trial. 20 The 2 patients in our series who experienced cement leakage were asymptomatic and without neurological deficits. In studies of FIG. 3. Images of a patient who underwent L1 5 kyphoplasty. A: Preoperative sagittal CT image. B: Preoperative MRI STIR sequence. C: Postoperative sagittal CT image. 376 J Neurosurg Spine Volume 28 April 2018

6 FIG. 4. Changes in pain (A) and pain medication usage (B) by patients after kyphoplasty. kyphoplasty safety, cement leaks occurred in 8% 33%, but only 0.5% 4% of those patients were symptomatic. 2,17 One patient in our series who did not experience cement leakage developed bilateral PE 19 days after surgery, but no evidence of cement in the pulmonary vasculature was found. Bouza et al. 2 reported a postoperative PE case incidence of 0.9 per 100 and an overall serious complication rate of 11.5%, whereas another study reported that PEs were not associated with kyphoplasty. 20 Other studies on kyphoplasty complications have found that PE develops in 3.5% 23% of patients after surgery, but tachypnea and dyspnea occur in only 1% of affected patients. 17 Local trauma occurs in < 1% of patients, and in this case series, 1 patient had a nondisplaced rib fracture diagnosed 2 days after surgery. 17 Although 5 patients experienced postoperative compression fractures, only 1 instance was within 2 months (43 days) of the kyphoplasty procedure. Many authors consider additional fractures unrelated to kyphoplasty, and one study found that most fractures related to kyphoplasty occur within 2 months of the procedure. 17 Another study on the safety of kyphoplasty found a 20.7% risk of new vertebral fractures after surgery, and this percentage increased with longer follow-up. 2 In our case series, the 4 new compression fractures that occurred more than 2 months after the procedure were more likely a result of the natural progression of disease, age, or osteoporosis and not the procedure, given the length of days after the procedure on average before the next fracture occurred (after we omitted the 1 case that occurred within 2 months). A theoretical increased risk of anemia exists, especially in elderly patients, because of the role of the vertebrae in hematopoiesis. 17 We did not observe such an increase in our case series. However, 13 of the 19 patients had a history of anemia before their procedure, which might have rendered the analysis of their hematopoietic status more complicated. In a meta-analysis by Yuan et al., 21 which included 2 randomized controlled trials, kyphoplasty was associated with significantly greater pain relief, greater improvement in daily function, and a higher quality of life than are conservative nonoperative treatments. As our study revealed, patients fare significantly better when fractures are treated to restore activity, mobility, and function. In treating all vertebral fractures instead of only up to 3 within a single anesthetic session, patients can ambulate and be liberated from function-impairing pain earlier. If only some of their fractures are treated or if some fractures are treated and the patient must return for a second procedure on the remaining vertebral fractures, the patient would still be bedbound because of the pain. Patients who are denied treatment with kyphoplasty because they are perceived to have too many fractures to undergo the procedure continue to suffer from the disabling symptoms of these fractures. More days in bed result in increased risks of DVT, decubitus ulcers, atelectasis, pneumonia, loss of muscle mass, loss of bone density, and other health detriments associated with immobility. 15,18 Treating all the fractures at the same time, regardless of their location in the thoracic or lumbar spine, can decrease the morbidity associated with delaying ambulation and leaving some painful fractures untreated because of an unfounded fear of increased risk of complications associated with treating 4 or more levels within the same anesthetic session. Conclusions In this case series of 19 patients, kyphoplasty performed on 4 or more vertebral levels did not result in an increased risk to patient safety and might have decreased unnecessary risks associated with multiple operations. The morbidity associated with leaving some fractures untreated because of an unfounded fear of increased risk of complications also might have been decreased by treating 4 or more levels within the same anesthetic session. Current guidelines can result in suboptimal treatment recommendations being made to some patients with 4 or more vertebral body compression fractures. These patients could be be inappropriately denied a simple and minimally invasive percutaneous procedure that could be very helpful for treating their symptoms. References 1. Anselmetti GC, Bonaldi G, Carpeggiani P, Manfrè L, Masala S, Muto M: Vertebral augmentation: 7 years experience. Acta Neurochir Suppl 108: , Bouza C, López-Cuadrado T, Almendro N, Amate JM: Safety of balloon kyphoplasty in the treatment of osteoporotic vertebral compression fractures in Europe: a meta-analysis of randomized controlled trials. Eur Spine J 24: , Buchbinder R, Osborne RH, Ebeling PR, Wark JD, Mitchell P, Wriedt C, et al: A randomized trial of vertebroplasty for painful osteoporotic vertebral fractures. N Engl J Med 361: , Clark W, Bird P, Gonski P, Diamond TH, Smerdely P, Mc- Neil HP, et al: Safety and efficacy of vertebroplasty for acute painful osteoporotic fractures (VAPOUR): a multicentre, randomised, double-blind, placebo-controlled trial. Lancet 388: , Coumans JVC, Reinhardt MK, Lieberman IH: Kyphoplasty for vertebral compression fractures: 1-year clinical outcomes from a prospective study. J Neurosurg 99 (1 Suppl):44 50, Edidin AA, Ong KL, Lau E, Kurtz SM: Mortality risk for operated and nonoperated vertebral fracture patients in the medicare population. J Bone Miner Res 26: , Fourney DR, Schomer DF, Nader R, Chlan-Fourney J, Suki D, Ahrar K, et al: Percutaneous vertebroplasty and kypho- J Neurosurg Spine Volume 28 April

7 plasty for painful vertebral body fractures in cancer patients. J Neurosurg 98 (1 Suppl):21 30, Hirsch JA, Chandra RV: Resurrection of evidence for vertebroplasty? Lancet 388: , Hulme PA, Krebs J, Ferguson SJ, Berlemann U: Vertebroplasty and kyphoplasty: a systematic review of 69 clinical studies. Spine (Phila Pa 1976) 31: , Kallmes DF, Comstock BA, Heagerty PJ, Turner JA, Wilson DJ, Diamond TH, et al: A randomized trial of vertebroplasty for osteoporotic spinal fractures. N Engl J Med 361: , Klazen CA, Lohle PN, de Vries J, Jansen FH, Tielbeek AV, Blonk MC, et al: Vertebroplasty versus conservative treatment in acute osteoporotic vertebral compression fractures (Vertos II): an open-label randomised trial. Lancet 376: , Lange A, Kasperk C, Alvares L, Sauermann S, Braun S: Survival and cost comparison of kyphoplasty and percutaneous vertebroplasty using German claims data. Spine (Phila Pa 1976) 39: , Ledlie JT, Renfro M: Balloon kyphoplasty: one-year outcomes in vertebral body height restoration, chronic pain, and activity levels. J Neurosurg 98 (1 Suppl):36 42, Lieberman IH, Dudeney S, Reinhardt MK, Bell G: Initial outcome and efficacy of kyphoplasty in the treatment of painful osteoporotic vertebral compression fractures. Spine (Phila Pa 1976) 26: , Liu Z, Tao X, Chen Y, Fan Z, Li Y: Bed rest versus early ambulation with standard anticoagulation in the management of deep vein thrombosis: a meta-analysis. PLoS One 10:e , McCall T, Cole C, Dailey A: Vertebroplasty and kyphoplasty: a comparative review of efficacy and adverse events. Curr Rev Musculoskelet Med 1:17 23, Nieto-Iglesias C, Andrés-Nieto I, Peces-García E, Roca-Amatria G, Ares JDA, Franco-Gay ML, et al: Vertebroplasty and kyphoplasty: techniques, complications, and troubleshooting. Tech Reg Anesth Pain Manage 18:40 48, Parry SM, Puthucheary ZA: The impact of extended bed rest on the musculoskeletal system in the critical care environment. Extrem Physiol Med 4:16, Taylor RS, Taylor RJ, Fritzell P: Balloon kyphoplasty and vertebroplasty for vertebral compression fractures: a comparative systematic review of efficacy and safety. Spine (Phila Pa 1976) 31: , Wardlaw D, Cummings SR, Van Meirhaeghe J, Bastian L, Tillman JB, Ranstam J, et al: Efficacy and safety of balloon kyphoplasty compared with non-surgical care for vertebral compression fracture (FREE): a randomised controlled trial. Lancet 373: , Yuan WH, Hsu HC, Lai KL: Vertebroplasty and balloon kyphoplasty versus conservative treatment for osteoporotic vertebral compression fractures: A meta-analysis. Medicine (Baltimore) 95:e4491, 2016 Disclosures The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper. Author Contributions Conception and design: Fahim. Acquisition of data: Wang. Analysis and interpretation of data: Wang. Drafting the article: Wang. Critically revising the article: Fahim. Reviewed submitted version of manuscript: both authors. Approved the final version of the manuscript on behalf of both authors: Fahim. Statistical analysis: Wang. Administrative/technical/material support: Wang. Study supervision: Fahim. Supplemental Information Previous Presentations A portion of this paper was presented at the 2017 AANS Annual Scientific Meeting, April 22 26, Los Angeles, CA. Correspondence Daniel K. Fahim: Beaumont Hospital, Royal Oak, MI. daniel. fahim@beaumont.edu. 378 J Neurosurg Spine Volume 28 April 2018