The cortical bone trajectory (CBT) screw technique

Transcription

1 CLINICAL ARTICLE J Neurosurg Spine 28:57 62, 2018 Cortical bone trajectory screw fixation versus traditional pedicle screw fixation for 2-level posterior lumbar interbody fusion: comparison of surgical outcomes for 2-level degenerative lumbar spondylolisthesis Hironobu Sakaura, MD, PhD, 1 Toshitada Miwa, MD, PhD, 1 Tomoya Yamashita, MD, 2 Yusuke Kuroda, MD, 1 and Tetsuo Ohwada, MD 1 1 Department of Orthopaedic Surgery, Kansai Rosai Hospital, Amagasaki, Hyogo; and 2 Department of Orthopaedic Surgery, Osaka Rosai Hospital, Sakai, Osaka, Japan OBJECTIVE The cortical bone trajectory (CBT) screw technique is a new nontraditional pedicle screw (PS) insertion method. However, the biomechanical behavior of multilevel CBT screw/rod fixation remains unclear, and surgical outcomes in patients after 2-level posterior lumbar interbody fusion (PLIF) using CBT screw fixation have not been reported. Thus, the purposes of this study were to examine the clinical and radiological outcomes after 2-level PLIF using CBT screw fixation for 2-level degenerative lumbar spondylolisthesis (DS) and to compare these outcomes with those after 2-level PLIF using traditional PS fixation. METHODS The study included 22 consecutively treated patients who underwent 2-level PLIF with CBT screw fixation for 2-level DS (CBT group, mean follow-up 39 months) and a historical control group of 20 consecutively treated patients who underwent 2-level PLIF using traditional PS fixation for 2-level DS (PS group, mean follow-up 35 months). Clinical symptoms were evaluated using the Japanese Orthopaedic Association (JOA) scoring system. Bony union was assessed by dynamic plain radiographs and CT images. Surgery-related complications, including symptomatic adjacentsegment disease (ASD), were examined. RESULTS The mean operative duration and intraoperative blood loss were 192 minutes and 495 ml in the CBT group and 218 minutes and 612 ml in the PS group, respectively (p < 0.05 and p > 0.05, respectively). The mean JOA score improved significantly from 12.3 points before surgery to 21.1 points (mean recovery rate 54.4%) at the latest follow-up in the CBT group and from 12.8 points before surgery to 20.4 points (mean recovery rate 51.8%) at the latest follow-up in the PS group (p > 0.05). Solid bony union was achieved at 90.9% of segments in the CBT group and 95.0% of segments in the PS group (p > 0.05). Symptomatic ASD developed in 2 patients in the CBT group (9.1%) and 4 patients in the PS group (20.0%, p > 0.05). CONCLUSIONS Two-level PLIF with CBT screw fixation for 2-level DS could be less invasive and result in improvement of clinical symptoms equal to those of 2-level PLIF using traditional PS fixation. The incidence of symptomatic ASD and the rate of bony union were lower in the CBT group than in the PS group, although these differences were not significant. KEY WORDS 2-level degenerative lumbar spondylolisthesis; cortical bone trajectory screw technique; traditional pedicle screw technique; 2-level posterior lumbar interbody fusion; clinical outcome; fusion status The cortical bone trajectory (CBT) screw technique is a new nontraditional pedicle screw (PS) insertion method. 16 The CBT screw was reported to have 1.71 times higher insertion torque than the traditional PS in vivo. 8 Several biomechanical analyses found that the CBT screw/rod construct has favorable mechanical properties. 1,14 Moreover, by reducing the length of incisions of the superior facet joints and paraspinal muscles, screw insertion through a caudomedial starting point could lead to less-invasive posterior lumbar fusion surgery. With respect ABBREVIATIONS ASD = adjacent-segment disease; CBT = cortical bone trajectory; DS = degenerative lumbar spondylolisthesis; EBL = estimated intraoperative blood loss; JOA = Japanese Orthopaedic Association; PLIF = posterior lumbar interbody fusion; PS = pedicle screw. SUBMITTED September 30, ACCEPTED May 17, INCLUDE WHEN CITING Published online November 10, 2017; DOI: / SPINE AANS 2018, except where prohibited by US copyright law J Neurosurg Spine Volume 28 January

2 H. Sakaura et al. to comparative studies of posterior lumbar interbody fusion (PLIF) surgery using CBT screw fixation and PLIF using traditional PS fixation, reports on only 2 studies have been published so far. 5,15 Kasukawa et al. 5 reported very short-term outcomes of transforaminal lumbar interbody fusion in a small number of patients and no clinical outcomes. We recently reported clinical and radiological outcomes after single-level PLIF with CBT screw fixation compared with those after single-level PLIF using traditional PS fixation in a larger patient population. 15 However, no reports concerning surgical outcomes of 2-level PLIF using CBT screw fixation have been published. Thus, the purposes of this study were to examine clinical and radiological outcomes after 2-level PLIF with CBT screw fixation for 2-level degenerative lumbar spondylolisthesis (DS) and to compare them with those after 2-level PLIF using traditional PS fixation for 2-level DS. Methods Patients In Kansai Rosai Hospital, DS is defined as a greater than 3-mm anterior vertebral slip demonstrated on a lateral radiograph of a patient in the neutral position. 15 All patients included in this comparative study had suffered from both low-back pain and neurogenic intermittent claudication as a result of 2-level DS before surgery and were considered for surgery because of the unresponsiveness of symptoms to conservative treatment, such as medication and/or epidural block. Twenty-two consecutive patients (4 men, 18 women) with 2-level DS underwent 2-level PLIF with CBT screw fixation between November 2011 and September 2013 at Kansai Rosai Hospital and were followed up for at least 2 years after surgery (CBT group). The mean age of the patients at the time of surgery was 70.7 years (range years). Fused levels were L2 4 in 1 patient, L3 5 in 18 patients, and L4 S1 in 3 patients. The mean duration of follow-up was 39.4 months (range months). A historical control group comprised 20 consecutive patients (6 men, 14 women) in whom 2-level PLIF using traditional PS fixation for 2-level DS between August 2009 and October 2011 was performed by the same surgeons who conducted the surgeries in the CBT group, and these patients were followed up for at least 2 years after surgery (PS group). The mean age of the patients at the time of surgery was 68.3 years (range years). Fused levels were L2 4 in 1 patient, L3 5 in 17 patients, L4 6 in 1 patient, and L4 S1 in 1 patient. The mean duration of follow-up was 35.4 months (range months). Every patient in the 2 groups underwent a followup examination at 3, 6, and 12 months after surgery and once per year thereafter. We found no significant differences between the groups in terms of sex, age at the time of surgery, fused levels, and follow-up duration (Table 1). Our study protocol was approved by the institutional review board of Kansai Rosai Hospital, and informed consent was obtained from each participant. Surgical Procedure We limited the length/extent of incisions of the facet joints and paraspinal muscles supradjacent to the fused TABLE 1. Demographic characteristics of the CBT and PS groups Characteristic CBT Group PS Group No. of patients Sex, male/female ratio 4:18 6:14 Age at surgery in yrs (mean ± SD) 70.7 ± ± 9.6 Duration of follow-up in mos (mean ± SD) 39.4 ± ± 11.4 segment as much as possible in the CBT group. 15 However, in the PS group, we incised paraspinal muscles and facet joints supradjacent to the fused segment to place the traditional PSs. 15 In both groups, adequate posterior neural decompression was performed. After enough intervertebral disc material was removed, 2 carbon fiber reinforced polyetheretherketone cages filled with local bone graft were inserted into the intervertebral space, and local bone blocks were inserted lateral or medial to the cages. 15 In the CBT group, the fused segments were stabilized using CBT screws and rods. Our CBT screws were inserted by hand with neither intraoperative image guidance nor a navigation system, 15 according to the method advocated by Matsukawa et al. 9 (Fig. 1). In contrast, in the PS group, the fused areas were fixed using traditional PSs and rods inserted by hand (Fig. 2). 15 Each patient in both groups wore a lumbosacral orthosis for 3 months after surgery. Clinical and Radiological Evaluations As factors that reflect surgical invasiveness, surgery duration and estimated intraoperative blood loss (EBL) were examined. 15 Clinical symptoms were evaluated before surgery and at the latest follow-up visit using the Japanese Orthopaedic Association (JOA) scoring system for assessment of the results of treatment for low-back pain 19 by Sakaura et al. 15 In brief, the JOA score consists of the rating of subjective symptoms (low-back pain, leg pain and/or tingling, and neurogenic intermittent claudication), clinical signs (performance on straight-leg-raising test, sensory disturbance, and motor deficit), restriction of activities of daily living, and urinary bladder function. Thus, the total JOA score in healthy populations is 29 points (Table 2). The rate of postoperative improvement in the JOA score over that before surgery (recovery rate) was calculated by the following formula: postoperative recovery rate (%) = (postoperative score - preoperative score)/(29 - preoperative score) 100. Bony union was evaluated at the latest follow-up examination by the first author (H.S.). A solid bony union was defined as when osseous continuity between the vertebra and the grafted bone was achieved on multiplanar reconstruction CT images, with neither loosening of the PSs nor motion at the fused segments according to flexion and extension lateral radiographs. 15 Bony union status was classified as union in situ (a solid fusion without loss of graft height), collapsed union (a solid fusion with 2-mm cages and/or grafted bone block subsidence into the adjacent vertebral body), or nonunion (according to previously reported criteria 18 ). Regarding perioperative complications, the patients medical records were examined. Symptomatic adjacent- 58 J Neurosurg Spine Volume 28 January 2018

3 Two-level PLIF with CBT screw fixation FIG. 1. A 56-year-old woman underwent 2-level (L4 5 and L5 S1) PLIF using CBT screws and rods for L4 5 DS. Radiographs were obtained 5 days after surgery. Left: Anteroposterior view. Right: Lateral view of the patient in the neutral position. FIG. 2. A 71-year-old woman underwent 2-level (L4 5 and L5 S1) PLIF using traditional PSs and rods for L4 5 DS. Radiographs were obtained 5 days after surgery. Left: Anteroposterior view. Right: Lateral view of the patient in the neutral position. segment disease (ASD) was diagnosed when clinical symptoms such as low-back pain, leg pain, and neurogenic intermittent claudication became exacerbated again during postoperative follow-up and the responsible lesions adjacent to the fused level were also confirmed with MR imaging of the lumbar spine. 15 Statistical Analysis The unpaired t-test, Mann-Whitney U-test, Wilcoxon signed-rank test, Kruskal-Wallis test, and Fisher exact probability test were used for statistical analysis with JMP software (SAS Institute), as appropriate. A p value of < 0.05 was considered significant. Results Clinical Results The mean operative duration in the CBT group was 192 ± 30 minutes (range minutes), which was significantly shorter than that in the PS group (218 ± 49 minutes; range minutes; p < 0.05). The mean EBL was 495 ± 386 ml (range ml) in the CBT group and 612 ± 424 ml (range ml) in the PS group; the EBL was less in the CBT group than in the PS group, although we found no significant difference between the groups. The mean JOA score improved significantly from 12.3 points before surgery to 21.1 points at the latest follow-up (mean recovery rate 54.4%) in the CBT group and from 12.8 points before surgery to 20.4 points at the latest follow-up (mean recovery rate 51.8%) in the PS group (Table 3). No significant differences were found in the JOA scores before surgery and at the latest follow-up or in its recovery rate between the 2 groups (Table 3). Bony Union Status In the CBT group, union in situ was achieved at 32 of the 44 segments in all 22 patients. A collapsed union occurred at 8 segments in 8 patients, and nonunion was found at 4 segments in 4 patients. Thus, solid bony union was achieved at 40 of the 44 segments (fusion rate 90.9%) in all 22 patients. In the PS group, union in situ was achieved at 30 of the 40 segments in 18 of the 20 patients. A collapsed union occurred at 8 segments in 6 patients, and nonunion was found at 2 segments in 2 patients. Solid bony union was achieved at 38 of the 40 segments (fusion rate 95.0%) in all 20 patients. Although the fusion rate was higher in the PS group than in the CBT group, we found no significant difference between the 2 groups (Table 4). No patients in either group with pseudarthrosis have undergone additional surgery so far, because they have not developed any symptoms (severe low-back pain, leg pain, or neurogenic intermittent claudication resulting from nonunion) that necessitate revision surgery. Surgery-Related Complications Intraoperative and early postoperative complications occurred in 2 patients (9.1%) in the CBT group, and these perioperative complications occurred in 3 patients (15.0%) in the PS group (Table 5). The incidence of these perioperative complications was higher in the PS group than in the CBT group, but no significant difference between the groups was found. Only 2 patients (9.1%) in the CBT group developed symptomatic ASD (Table 5). One patient had developed a vertebral compression fracture at the vertebra cephalad J Neurosurg Spine Volume 28 January

4 H. Sakaura et al. TABLE 2. JOA scoring system for assessing the results of treatment for low-back pain to the fused level by 15 months after surgery, and it had healed with conservative treatment by 18 months after surgery. The other patient developed lumbar spinal canal stenosis at the cephalad segment adjacent to the fused areas by 41 months after surgery. So far, her symptoms have been alleviated with conservative treatment. In the PS group, 4 patients (20.0%) developed symptomatic ASD. All 4 patients developed lumbar spinal canal stenosis at the cephalad segment adjacent to the fused areas. The time period between the initial surgery and the onset of symptomatic ASD ranged from 19 to 36 months (mean 25 months). Two of the 4 patients (10.0% overall) underwent additional surgery for symptomatic ASD because of unresponsiveness to conservative treatment (Table 5). The incidence of symptomatic ASD was approximately 2 times higher in the PS group than in the CBT group, although no significant difference between the 2 groups was found. Discussion As a new nontraditional PS insertion method, a CBT TABLE 3. Clinical outcomes in the CBT and PS groups Group Item JOA Score Before Surgery Final Follow-Up Possible Scores Subjective symptoms (9 points) Low-back pain 3, 2, 1, 0 Leg pain &/or tingling 3, 2, 1, 0 Gait (neurogenic intermittent claudication) 3, 2, 1, 0 Clinical signs (6 points) Performance on straight-leg-raising test 2, 1, 0 Sensory disturbance 2, 1, 0 Motor deficit 2, 1, 0 Restriction of activities of daily living (14 points) Turn over while lying 2, 1, 0 Standing 2, 1, 0 Washing 2, 1, 0 Leaning forward 2, 1, 0 Sitting (~1 hr) 2, 1, 0 Lifting or holding heavy object 2, 1, 0 Walking 2, 1, 0 Urinary bladder function 0, 3, 6 Total* 29 to 6 * The total JOA score of a healthy person is 29 points. JOA Score Recovery Rate at Final Follow-Up (%) CBT 12.3 ± ± 4.1* 54.4 ± 18.4 PS 12.8 ± ± 6.2* 51.8 ± 29.0 Values are presented as the mean ± SD. * Scores are significantly higher than before surgery (Wilcoxon signed-rank test, p < 0.001). TABLE 4. Fusion status of the CBT and PS groups Group Total No. of Segments Union Type (no. of segments) In Situ Collapsed Nonunion CBT PS screw technique was advocated recently by Santoni et al. 16 In their cadaveric study, the CBT screw was shown to provide a 30% increase in uniaxial yield pullout load relative to that of the traditional PS. In addition, the insertion torque during CBT screwing in vivo was reported to be 1.71 times higher than that of traditional pedicle screwing. 8 Regarding the biomechanical behavior of a CBT screw/rod construct, a CBT screw/rod construct reportedly provides about the same stability as a traditional PS rod construct. 14 It has been reported that a CBT screw/rod construct provides resistance to craniocaudal toggling displacement that is significantly superior to that of a traditional PS rod construct. 1 Furthermore, using a caudomedial starting point of the CBT screw could lead to less-invasive posterior lumbar fusion surgery by reducing the length/extent of incisions of the supradjacent facet joints and paraspinal muscles. The risk of supradjacent facet violation by the screw could also be reduced by using a caudomedial starting point and a caudocephalad- and mediolateral-directed path for the CBT screw. Only 2 reports from comparative studies of PLIF surgery using CBT screw fixation or traditional PS fixation have been published. 5,15 Kasukawa et al. 5 reported the very short-term results of single-level transforaminal lumbar interbody fusion in a small number of the patients but did not evaluate the clinical status in a larger population of patients. In contrast, we recently reported the minimum 2-year clinical and radiological outcomes of patients after single-level PLIF with CBT screw fixation compared with those after single-level PLIF using traditional PS fixation. 15 However, the biomechanics of multilevel CBT screw/rod fixation have not yet been investigated, and no reports concerning surgical outcomes of patients after 2-level PLIF with CBT screw fixation have been published. To our knowledge, ours is the first inves- TABLE 5. Surgery-related complications in the CBT and PS groups Complication Group (no. [%] of patients) CBT, n = 22 PS, n = 20 Intraop Dural laceration 1 (4.5) 0 (0.0) Misplacement of PS 0 (0.0) 1 (5.0) Postop Symptomatic hematoma 0 (0.0) 1 (5.0) Delayed wound healing 1 (4.5) 0 (0.0) Deep wound infection 0 (0.0) 1 (5.0) Symptomatic ASD 2 (9.1) 4 (20.0) Additional surgery for ASD 0 (0.0) 2 (10.0) 60 J Neurosurg Spine Volume 28 January 2018

5 Two-level PLIF with CBT screw fixation tigation of surgical outcome of patients after 2-level PLIF using CBT screw fixation compared with that after 2-level PLIF with traditional PS fixation. To reduce approach-related trauma during surgery, various less-invasive techniques in spine surgery have been developed over the past decade. 6 As a representative example, a percutaneous PS technique has become widely accepted. 11 However, during PLIF, this technique needs other approaches for PS fixation in addition to a midline approach for posterior decompression and interbody bone grafting. In contrast, PLIF with CBT screw fixation can be performed only via a less-invasive posterior midline approach. 15 In our study, the mean operative duration was significantly shorter in the CBT group than in the PS group. The mean EBL was less in the CBT group than in the PS group, although we found no significant difference between the 2 groups. Mizuno et al. 10 reported that inflammatory marker levels, the creatine kinase level, and the white blood cell count recovered to within their normal range within 1 week after single-level PLIF using CBT screw fixation and that the creatine kinase level was equivalent to that after mini open PLIF reported elsewhere. 10,17 Given these results, it seems that 2-level PLIF with CBT screw fixation could be less invasive than 2-level PLIF with traditional PS fixation. Regarding clinical outcomes, we found no significant difference in the JOA scores before surgery and those at the latest follow-up or in the JOA recovery rates between the 2 groups (mean recovery rates 54.4% [CBT group] and 51.8% [PS group]). From a small clinical case series study, Okuyama et al. reported that the mean recovery rate of the JOA score after 2-level PLIF with traditional PS fixation was 45.3%. 12 Although more follow-up studies in larger patient populations are needed, these results suggest that 2-level PLIF using CBT screw fixation provides clinical outcomes equal to those after 2-level PLIF with traditional PS fixation. The bony union rate was higher in the PS group than in the CBT group. A biomechanical study in cadaveric lumbar specimens found that traditional PS fixation is stiffer than CBT screw fixation during axial rotation with an intact intervertebral disc and that traditional PS fixation is stiffer than CBT screw fixation during lateral bending with transforaminal lumbar interbody support. 14 It has been suggested that micromotion during axial rotation and lateral bending might lead to a lower bony union rate in the CBT group than in the PS group. Therefore, to improve the successful bony union rate in the CBT group, transverse connectors and cages that have increased surface areas might be useful, because they could reduce micromotion during axial rotation and lateral bending. A risk factor for the development of ASD after lumbar fusion surgery is fusion length. 3,4,13 Moreover, the incidence of symptomatic ASD after PLIF is reportedly higher than that after posterolateral lumbar fusion. 13 Thus, a higher incidence of symptomatic ASD is one of the more serious possible problems after 2-level PLIF. However, in this comparative study, the incidence of symptomatic ASD was approximately 2 times higher in the PS group than in the CBT group. This result indicates that PLIF with CBT screw fixation could reduce the incidence of symptomatic ASD by limiting the length/extent of incisions of superior facet joints and paraspinal muscles and possibly reducing the risk of superior facet violation, 15 which could increase biomechanical stress and thus result in destabilization at the supradjacent segment. 2,7 Conclusions Similar to our reported clinical and radiological outcomes in patients after single-level PLIF with CBT screw fixation for single-level DS compared with those after single-level PLIF using traditional PS fixation, 15 2-level PLIF with CBT screw fixation for 2-level DS could be less invasive and provide surgical outcomes comparable to those of 2-level PLIF using traditional PS fixation. The incidence of symptomatic ASD and the successful bony union rate were lower in the CBT group than in the PS group, although the differences between the 2 groups were not significant. References 1. Baluch DA, Patel AA, Lullo B, Havey RM, Voronov LI, Nguyen NL, et al: Effect of physiological loads on cortical and traditional pedicle screw fixation. Spine (Phila Pa 1976) 39:E1297 E1302, Cardoso MJ, Dmitriev AE, Helgeson M, Lehman RA, Kuklo TR, Rosner MK: Does superior-segment facet violation or laminectomy destabilize the adjacent level in lumbar transpedicular fixation? An in vitro human cadaveric assessment. Spine (Phila Pa 1976) 33: , Etebar S, Cahill DW: Risk factors for adjacent-segment failure following lumbar fixation with rigid instrumentation for degenerative instability. J Neurosurg 90 (2 Suppl): , Greiner-Perth R, Boehm H, Allam Y, Elsaghir H, Franke J: Reoperation rate after instrumented posterior lumbar interbody fusion: a report on 1680 cases. Spine (Phila Pa 1976) 29: , Kasukawa Y, Miyakoshi N, Hongo M, Ishikawa Y, Kudo D, Shimada Y: Short-term results of transforaminal lumbar interbody fusion using pedicle screw with cortical bone trajectory compared with conventional trajectory. Asian Spine J 9: , Kim CW, Siemionow K, Anderson DG, Phillips FM: The current state of minimally invasive spine surgery. J Bone Joint Surg Am 93: , Kim HJ, Chun HJ, Kang KT, Moon SH, Kim HS, Park JO, et al: The biomechanical effect of pedicle screws insertion angle and position on the superior adjacent segment in 1 segment lumbar fusion. Spine (Phila Pa 1976) 37: , Matsukawa K, Yato Y, Kato T, Imabayashi H, Asazuma T, Nemoto K: In vivo analysis of insertional torque during pedicle screwing using cortical bone trajectory technique. Spine (Phila Pa 1976) 39:E240 E245, Matsukawa K, Yato Y, Nemoto O, Imabayashi H, Asazuma T, Nemoto K: Morphometric measurement of cortical bone trajectory for lumbar pedicle screw insertion using computed tomography. J Spinal Disord Tech 26:E248 E253, Mizuno M, Kuraishi K, Umeda Y, Sano T, Tsuji M, Suzuki H: Midline lumbar fusion with cortical bone trajectory screw. Neurol Med Chir (Tokyo) 54: , Mobbs RJ, Sivabalan P, Li J: Minimally invasive surgery compared to open spinal fusion for the treatment of degenerative lumbar spine pathologies. J Clin Neurosci 19: , 2012 J Neurosurg Spine Volume 28 January

6 H. Sakaura et al. 12. Okuyama K, Chiba M, Suzuki H, Konishi N, Kuroda T, Suzuki T, et al: [Study of PLIF augmented with pedicle screw fixation from the degenerative lumbar spondylolisthesis in two spinal segments.] Rinsho Seikei Geka 32: , 1997 (Jpn) 13. Park P, Garton HJ, Gala VC, Hoff JT, McGillicuddy JE: Adjacent segment disease after lumbar or lumbosacral fusion: review of the literature. Spine (Phila Pa 1976) 29: , Perez-Orribo L, Kalb S, Reyes PM, Chang SW, Crawford NR: Biomechanics of lumbar cortical screw-rod fixation versus pedicle screw-rod fixation with and without interbody support. Spine (Phila Pa 1976) 38: , Sakaura H, Miwa T, Yamashita T, Kuroda Y, Ohwada T: Posterior lumbar interbody fusion with cortical bone trajectory screw fixation versus posterior lumbar interbody fusion using traditional pedicle screw fixation for degenerative lumbar spondylolisthesis: a comparative study. J Neurosurg Spine 25: , Santoni BG, Hynes RA, McGilvray KC, Rodriguez-Canessa G, Lyons AS, Henson MA, et al: Cortical bone trajectory for lumbar pedicle screws. Spine J 9: , Tsutsumimoto T, Shimogata M, Ohta H, Misawa H: Miniopen versus conventional open posterior lumbar interbody fusion for the treatment of lumbar degenerative spondylolisthesis: comparison of paraspinal muscle damage and slip reduction. Spine (Phila Pa 1976) 34: , Yamamoto T, Ohkohchi T, Ohwada T, Kotoku H, Harada N: Clinical and radiological results of PLIF for degenerative spondylolisthesis. J Musculoskelet Res 2: , Yone K, Sakou T, Kawauchi Y, Yamaguchi M, Yanase M: Indication of fusion for lumbar spinal stenosis in elderly patients and its significance. Spine (Phila Pa 1976) 21: , 1996 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: all authors. Acquisition of data: all authors. Analysis and interpretation of data: Sakaura. Drafting the article: Sakaura. Critically revising the article: Sakaura. Reviewed submitted version of manuscript: all authors. Approved the final version of the manuscript on behalf of all authors: Sakaura. Statistical analysis: Sakaura. Study supervision: Ohwada. Correspondence Hironobu Sakaura, Department of Orthopaedic Surgery, Kansai Rosai Hospital, Inabaso, Amagasaki, Hyogo , Japan. sakaura @yahoo.co.jp. 62 J Neurosurg Spine Volume 28 January 2018