Comparison of Consecutive, Interval, and Skipped Pedicle Screw Techniques in Moderate Lenke Type 1 Adolescent Idiopathic Scoliosis

Comparison of Consecutive, Interval, and Skipped Pedicle Screw Techniques in Moderate Lenke Type 1 Adolescent Idiopathic Scoliosis

Accepted Manuscript Comparison of consecutive, interval, and skipped pedicle screw techniques in moderate Lenke type 1 adolescent idiopathic scoliosis...

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Accepted Manuscript Comparison of consecutive, interval, and skipped pedicle screw techniques in moderate Lenke type 1 adolescent idiopathic scoliosis Ming Luo, M.Med, Mingkui Shen, M.Med, Wengang Wang, M.D, Lei Xia, M.D PII:

S1878-8750(16)31212-8

DOI:

10.1016/j.wneu.2016.11.064

Reference:

WNEU 4874

To appear in:

World Neurosurgery

Received Date: 2 September 2016 Revised Date:

10 November 2016

Accepted Date: 12 November 2016

Please cite this article as: Luo M, Shen M, Wang W, Xia L, Comparison of consecutive, interval, and skipped pedicle screw techniques in moderate Lenke type 1 adolescent idiopathic scoliosis, World Neurosurgery (2016), doi: 10.1016/j.wneu.2016.11.064. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Title Page Title:

moderate Lenke type 1 adolescent idiopathic scoliosis

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Author names and affiliations:

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Comparison of consecutive, interval, and skipped pedicle screw techniques in

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Ming Luo, M.Med, Institute of Spinal Deformity, the First Affiliated Hospital of Zhengzhou University, Zhengzhou, Henan 450052, P. R. China. E-mail: [email protected]

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Mingkui Shen, M.Med, Institute of Spinal Deformity, the First Affiliated Hospital of Zhengzhou University, Zhengzhou, Henan 450052, P. R. China.

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E-mail: [email protected]

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Ming Luo and Mingkui Shen contributed equally to this work

Wengang Wang, M.D, Institute of Spinal Deformity, the First Affiliated Hospital of Zhengzhou University, Zhengzhou, Henan 450052, P. R. China. E-mail: [email protected]

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Corresponding author: Lei Xia, M.D, Institute of Spinal Deformity, the First Affiliated Hospital of Zhengzhou University, Zhengzhou, Henan 450052, P. R. China.

Highest academic degrees for all authors:

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E-mail: [email protected]

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Ming Luo, M.Med; Mingkui Shen, M.Med; Wengang Wang, M.D; Lei Xia, M.D

Departmental and institutional affiliations for all authors: Institute of Spinal Deformity, the First Affiliated Hospital of Zhengzhou University,

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Zhengzhou, Henan 450052, P. R. China.

Key words:

adolescent idiopathic scoliosis, consecutive pedicle screw, interval pedicle screw,

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skipped pedicle screw

Abbreviations list:

Scoliosis Research Society-22, SRS-22; adolescent idiopathic scoliosis, AIS; main thoracic, MT

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Abstract Objective To compare perioperative, radiographic and Scoliosis Research Society (SRS)-22

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outcomes of consecutive, interval, and skipped pedicle screw techniques in patients with moderate Lenke type 1 adolescent idiopathic scoliosis (AIS).

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Methods

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We retrospectively reviewed 65 consecutive moderate Lenke type 1 AIS patients at a single institution, using all-pedicle screw constructs with a minimum of 2-years follow-up. In the consecutive group (C group, n=22), pedicle screws were instrumented at consecutive levels bilaterally. In the interval group (I group, n=18),

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pedicle screws were placed at every level on the concave side while skipping levels on the convex side. In the skipped group (S group, n=25), pedicle screws were instrumented by skipping levels bilaterally. Perioperative, radiographic and SRS-22

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measurements were analysed with a one-way ANOVA.

Results

No significant differences were found in length of hospital stay, fused levels, coronal correction, and SRS-22 scores among the three groups. Increased surgery time was found in the C group compared to the I and S groups (P=0.001 and P=0.005, respectively). Decreased blood loss and blood transfusions were found in the S group compared to the C group (P=0.04 and P=0.047, respectively). Decreased implant 3

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were found in the S group compared to the C and I groups (P< 0.001 and

P=0.03, respectively).

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Conclusions Consecutive, interval, and skipped pedicle screw techniques all provide satisfactory deformity correction and SRS-22 outcomes with few complications. With better

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perioperative outcomes, interval and skipped pedicle screw techniques are the more

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cost-effective options for patients with moderate Lenke type 1 AIS.

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Text Introduction

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Adolescent idiopathic scoliosis (AIS) afflicts 1–3% adolescents at the danger age of 10–16 years, and the pathogenesis continues to be obscure.1 The Lenke type 1 curve was the most prevalent type of AIS with a morbidity rate of 40%, and it could be

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defined as a structural main thoracic (MT) curve, with the proximal thoracic and

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thoracolumbar/ lumbar curves being nonstructural.2 The MT curve was the specific region being fused for Lenke type 1 AIS.3

The correlation of implant density and deformity correction in AIS has not reached a consensus. Clements et al. reviewed 292 AIS cases and reported a

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significant correlation between implant density and curve correction.4 Larson et al. reviewed 584 patients with Lenke type 1 AIS, and improved curve correction was found in the high-density group (69%) compared to the low-density group (66%).5 studied 49 patients with Lenke type 1 AIS and no correlation

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However, Quan et al.

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was observed between coronal correction and the number of pedicle screws.6 Yang et al. evaluated 58 Lenke type 1 AIS cases and reported that increasing the implant density did not improve radiographic outcomes.7 Bharucha et al. evaluated 91 patients with Lenke type 1 AIS and no significant correlation was found between implant density and tridimensional corrections.8 In addition, Min et al. reviewed 48 patients with thoracic AIS with a minimal 10-year follow-up and concluded that an implant density of 50% was enough to obtain a stable correction and high patient satisfaction.9 5

ACCEPTED MANUSCRIPT The potential risk of implant malposition, neurological injury, increased surgery time and implant costs, related to pedicle screw placement, should be seriously considered. Diab et al. reviewed 1,301 consecutive surgical cases of AIS and

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concluded that the overall neural complication rate was 0.69%.10 The higher number of implanted pedicle screws would increase the risk of neurologic complications. If proven an effective, stable, and safe pedicle screw technique with fewer pedicle

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screws in moderate Lenke type 1 AIS would have significant benefits.

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The purpose of this study was to compare perioperative, radiographic and Scoliosis Research Society (SRS)-22 outcomes among consecutive, interval, and skipped pedicle screw techniques in patients with moderate Lenke type 1 AIS.

Patients and Groups

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Materials and methods

The operation notes and radiographs of consecutive AIS patients were retrospectively

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reviewed in a single institution including those who underwent single stage posterior

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spinal fusion with all-pedicle screw construct from January 2008 to April 2014. Selection criteria: (1) Lenke type 1 AIS; (2) moderate MT curve range from 40–

70°; (3) single stage posterior spinal fusion with an all-pedicle screw construct; (4) absence of thoracoplasty; and (5) a minimum 2-year follow-up with perioperative, radiological, and functional records using the simplified Chinese version of the SRS-22 Questionnaire. 11,12 Exclusion

criteria:

(1)

patients

diagnosed 6

with

early-onset

scoliosis,

ACCEPTED MANUSCRIPT neuromuscular scoliosis, and Lenke type 2-6 AIS; (2) severe AIS with a Cobb angle of MT curve more than 70°; (3) hybrid instrumentation constituted of hooks and wires; or (4) a history of Smith-Petersen osteotomy, pedicle subtraction osteotomy, vertebral

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column resection, or vertebral column decancellation technique being performed. Patients were assigned to three groups according to different pedicle screw techniques. In the consecutive group (C group, Fig. 1), pedicle screws were

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instrumented at consecutive levels bilaterally. In the interval group (I group, Fig. 2),

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pedicle screws were placed at every level on the concave side while skipping levels on the convex side. In the skipped group (S group, Fig. 3),four screws in the two most distal vertebrae for distal foundation and two screws in the most proximal vertebra for proximal foundation were routinely inserted, and every other or every second vertebra

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was instrumented bilaterally in the intermediate region.

Fig. 1. Consecutive pedicle screw technique. Pre-operation: a) anteroposterior and b)

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lateral radiographs. Latest follow-up: c) anteroposterior and d) lateral radiographs.

Fig. 2. Interval pedicle screw technique. Pre-operation: a) anteroposterior and b) lateral radiographs. Latest follow-up: c) anteroposterior and d) lateral radiographs.

Fig. 3. Skipped pedicle screw technique. Pre-operation: a) anteroposterior and b) lateral radiographs. Latest follow-up: c) anteroposterior and d) lateral radiographs.

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ACCEPTED MANUSCRIPT Surgical Technique One senior surgeon from a single institution performed all surgeries. The all-pedicle screw constructs (Stryker Xia, WeGo SINO, and WeGo UPASS) were used, consisting

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of pedicle screws and dual titanium rods. After anatomical exposure of the spine, pedicle screws were instrumented using a free hand technique. In the C group, pedicle screws were inserted at consecutive

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levels bilaterally. In the I group, pedicle screws were inserted at every level on the

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concave side while skipping levels on the convex side. In the S group, four screws in the two most distal vertebrae for distal foundation and two screws in the most proximal vertebra for proximal foundation were routinely inserted, and every other or every second vertebra was instrumented bilaterally in the intermediate region.

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Correction manoeuvres were the same among the three groups. After insertion of the concave rod, simple rod rotation was performed by distraction and compression. The transverse processes and vertebral plate were decorticated thoroughly, and allograft

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bone material was placed for fusion.

Perioperative, Radiographic and SRS-22 Outcomes Measurements Perioperative measurements included the patient age, gender, surgery time, intraoperative blood loss, total blood transfusions, length of hospital stay, implant costs, fused levels, number of pedicle screws, and cross-links. Screw density was calculated from fused levels and the number of screws. Screw density was defined as the number of pedicle screws per vertebrae implanted.8 A 8

ACCEPTED MANUSCRIPT maximum 2.0-implant density implied that two pedicle screws were placed in each vertebra bilaterally, from the upper-instrumented vertebra to the lower-instrumented vertebra.

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Radiographic measurements included the patients’ Lenke type, lumbar spine modifier, thoracic sagittal profile, Risser sign grade, Cobb levels of MT curve, Cobb angle of MT curve, Cobb angle of convex-Bending, vertebral rotation (Nash-Moe),

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apical vertebra translation, thoracic trunk shift, thoracic kyphosis (T5–T12), lumbar

operation) and latest follow-up.

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lordosis (T12–S1) at the time of pre-operation, early post-operation (2 weeks after

The flexibility index, MT correction rate, change values of the MT curve, and loss values of the MT curve were calculated from above radiographic measurements.

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Functional outcome measurements were assessed with the simplified Chinese version of SRS-22 Questionnaire at pre-operation and the latest follow-up. Complications of

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the perioperative and follow-up periods were recorded.

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Statistical Analysis

All data were collected and analysed using SPSS 21.0 for Windows (SPSS Inc, Chicago, IL, USA). For multiple comparisons across the three groups, a one-way ANOVA was adopted if the distributions of the data conformed to normality and there was equality of variances; if not, a Kruskal-Wallis rank sum test was used. Further analysis was performed with Bonferonni’s test. A P value of <0.05 was considered statistically significant. 9

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Results The baseline characteristics of the three groups of patients are presented in Table 1. Sixty-five consecutive moderate Lenke type 1 AIS patients with 43 females and 22

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males were carefully reviewed. The latest follow-up averaged 2.9 years (range 2–7 years). In the C group, there were 13 female and 9 male patients, and the age at surgery was 14.5±2.0 years. The lumbar spine modifiers were 13A, 4B, and 5C, and

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the thoracic sagittal profile was 2 hypokyphosis, 15 normal, and 5 hyperkyphosis. In

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the I group, there were 14 female and 4 male patients, and the age at surgery was 13.9±2.3 years. The lumbar spine modifiers were12A, 2B, and 4C, and the thoracic sagittal profile was 3 hypokyphosis, 13 normal, and 2 hyperkyphosis. In the S group, there were 16 female and 9 male patients, and the age at surgery was 14.8±2.3 years.

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The lumbar spine modifiers were 18A, 3B, and 4C, and the thoracic sagittal profile was 3 hypokyphosis, 19 normal, and 3 hyperkyphosis.

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Table1. The baseline characteristics of the three groups

Except for a significant difference in the thoracic trunk shift between the I and S

groups (P=0.01), there were no significant differences among the three groups in terms of age, riser sign, Cobb levels of the MT curve, Cobb angle of the MT curve, Cobb angle of convex-Bending, MT flexibility, vertebral rotation, apical vertebra translation, thoracic kyphosis, and lumbar lordosis. The perioperative outcomes of the three groups of patients are presented in Table 10

ACCEPTED MANUSCRIPT 2. No significant differences were observed among the three groups in terms of hospital stay and fused levels. Successively decreasing values of the number of pedicle screws (20.8, 17.2, and 14.5, respectively) and screw density (2.0, 1.6, and 1.3,

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respectively) were recorded in the C, I and S groups. Increased surgery time was found in the C group compared to the I and S groups (P=0.001 and P=0.005, respectively). Decreased blood loss and blood transfusions, but increased cross-links

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were found in the S group compared to the C group (P=0.04, P=0.047, and P=0.02,

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respectively). Decreased implant costs were found in the S group compared to the C and I groups (P< 0.001 and P=0.03, respectively).

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Table2. The perioperative outcomes of the three groups

The radiographic outcomes of early post-operation and the latest follow-up are presented in Table 3. Consecutive, interval, and skipped pedicle screw techniques all

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achieved satisfactory deformity correction and the final MT curves were 15.3°, 18.8°,

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and 19.2°, respectively. No significant differences were found among the three groups in the Cobb angle of the MT curve, change values of the MT curve, correction rate of the MT curve, loss of the MT curve, apical vertebra translation, thoracic trunk shift, thoracic kyphosis, and lumbar lordosis, including early post-operation and the latest follow-up.

Table3. The radiographic outcomes of the three groups 11

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The functional assessments with the SRS-22 Questionnaire are presented in Table 4. There were no significant differences in the scores of function/activity, pain,

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self-image, mental health, and satisfaction among the three groups in terms of pre-operation and latest follow-up.

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Table4. The SRS-22 questionnaire of the three groups of patients

Complications were recorded during the follow-up period after surgery. In the C group, one patient underwent surgical revision for a distal adding-on phenomenon, and one patient had a superficial infection treated with antibiotics. One patient in the I

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group had an implant malposition, and one pedicle screw in T9 was removed. In the S group, one patient had poor wound healing and a vacuum sealing drainage device was

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used.

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Discussion

The definition of consecutive, interval, and skipped pedicle screw techniques has

not come to agreement. In Li and Tao’s studies, the consecutive placement was defined as pedicle screws placed at every level on the concave side while skipping levels on the convex side, and interval placement was defined as pedicle screws instrumented by skipping levels bilaterally.13,14 Ketenci et al. defined consecutive placement as pedicle screws inserted at consecutive levels bilaterally, and interval 12

ACCEPTED MANUSCRIPT placement as pedicle screws inserted at every level on the concave side while skipping levels on the convex side.15 In Morr’s study the definition of consecutive placement was the same as Ketenci’s, but skipped placement was defined as pedicle

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screws instrumented at every level on the concave side while skipping levels on the convex side. 16 Hwang et al. defined skipped pedicle screw fixation as pedicle screws inserted by skipping levels bilaterally.17 In this study, the definition of consecutive,

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interval, and skipped pedicle screw fixation were the same as Ketenci and

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Hwang’s.15,17

This study performed a multiple comparison of radiographic and SRS-22 outcomes among the three surgical strategies and no significant differences were found. Some studies have compared consecutive versus interval and interval versus

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skipped pedicle screw fixations, and similar conclusions were reported. A study by Li et al. involved 30 patients with Lenke type 1 AIS, and concluded that consecutive and interval pedicle screw placements were equally effective for major curve correction

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(15.5° versus 15.8°).13 Morr et al. reported a matched cohort of 40 patients with

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Lenke type 1 AIS, and both consecutive and skipped pedicle screw fixation provided excellent coronal correction and SRS-22 scores (96 versus 94.3; P = 0.34).16 Min et al. reviewed 48 patients with thoracic AIS with a minimal 10-year follow-up and concluded that an implant density of 50% was enough to obtain a stable correction and high patient satisfaction.9 In addition, biomechanical studies suggested that consecutive pedicle screw fixation might put excess force on pedicles without achieving much improvement in tridimensional corrections.18,19 13

ACCEPTED MANUSCRIPT The interval pedicle screw technique was particular as the pedicle screws were placed at every level on the concave side, but not at the convex side. Navéaux et al. analysed the implant distribution in 279 AIS patients and found that only

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instrumentation at the concave side, particularly at the apical region, was associated with curve correction.20 In addition, Liu et al. evaluated 77 patients with a main thoracic curve and reported that high screw density on the concave side could provide

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better thoracic kyphosis restoration.21 Sudo et al. analysed 64 patients with Lenke

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type 1 AIS and concluded that a change in thoracic kyphosis was significantly correlated with screw density at the concave side (r=0.351) but not at the convex side (r=0.144).22 In this study, reduced surgery time was found in the I group compared to the C group (I group: 283.1 min; C group: 359.5 min, P=0.001) due to fewer pedicle

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screws implanted. Although no significant differences were observed in blood loss and implant costs between the C and I groups, the mean values of blood loss (I group: 935.2 ml; C group: 1120.0 ml) and implant costs (I group: $ 12706.5; C group:

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$ 14907.8) were smaller in the I group compared to the C group, which was also

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especially valuable to the AIS patients. Therefore, the interval pedicle screw technique would be a good choice for hypokyphosis AIS patients. The skipped pedicle screw technique achieved considerably preferable

perioperative outcomes. Decreased blood loss and blood transfusions were found in the S group compared to the C group (P=0.04 and P=0.047, respectively). Decreased implant costs were found in the S group compared to the C and I groups (P< 0.001 and P=0.03, respectively). Other studies reported homologous conclusions. Tsirikos et 14

ACCEPTED MANUSCRIPT al. reviewed 212 AIS patients and increased surgery time and intra-operative blood loss were observed in the consecutive pedicle screw group, and implant costs were reduced by 35% in the interval group.23 Larson et al. explored the national all-payer

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hospital inpatient database in the US and analysed the annual costs for AIS patients. By changing the high-density screw pattern to low-density, the total cost of AIS surgery in the US would effectively be reduced by $11 million to $20 million.24

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Increased cross-links were found in the S group compared to the C group

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(P=0.02), and this might affect the correction outcomes. However, Dhawale et al. compared 75 AIS patients over a 2-year follow-up and concluded that there were no differences in the maintenance of correction, SRS scores, and complications with or without cross-linking posterior segmental instrumentation in AIS patients.25 In

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addition, a total of 500 patients (377 cross-link and 123 non–cross-link) were included in Garg’s study, and there did not appear to be significant clinical or radiographic outcome differences in patients with AIS based on the use of cross-links.26 Therefore,

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the increased cross-links in the S group in our study might not have affected the

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correction outcomes as a confounding factor. Although there have been many studies comparing the efficacy of consecutive

versus interval and interval versus skipped pedicle screw techniques, to our limited knowledge, no formal studies had performed multiple comparisons on the three pedicle screw techniques. As the high cost of AIS surgery is closely related to the expensive pedicle screws,27,28 implant costs account for a large proportion of hospital expenses for AIS surgery.29 Using fewer pedicle screws indicated a reduction of 15

ACCEPTED MANUSCRIPT hospital expenses and risk of neurologic complications. This study supportes the use of interval and skipped pedicle screw techniques as more cost-effective options for moderate Lenke type 1 AIS patients. We believe this conclusion would provide

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significant benefits for both spinal surgeons and moderate Lenke type 1 AIS patients. Some limitations should not be ignored in this study. First, as a retrospective study, AIS patients were not randomly assigned to different pedicle screw techniques.

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The evidence level was limited compared to an RCT, and further RCTs are needed.

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Second, the relatively small sample size and short follow-up time were underpowered to find more significant differences, and a longer follow-up study should be performed to assess the maintenance of deformity correction. Third, the assessment of vertebral rotation using CT was lacking, because the financial costs and exposure to

Conclusion

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ionizing radiation are important considerations that limited the clinical use of CT.

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This study performed a multiple comparison of consecutive, interval, and skipped

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pedicle screw techniques in patients with moderate Lenke type 1 AIS. The three surgical techniques all provide satisfactory deformity correction and SRS-22 outcomes with few complications. With better perioperative outcomes, interval and skipped pedicle screw techniques are more cost-effective options for patients with moderate Lenke type 1 AIS.

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Acknowledgements: All the authors were directly involved in the whole process; therefore, it is disclosed

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that all the authors contributed equally towards the research.

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Funding sources: The authors declare that they have no funding.

Conflict of interest:

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None of the authors has any potential conflict of interest.

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Figure Legends: :

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Fig. 1. Consecutive pedicle screw technique. Pre-operation: a) anteroposterior and b) lateral radiographs. Latest follow-up: c) anteroposterior and d) lateral radiographs.

Fig. 2. Interval pedicle screw technique. Pre-operation: a) anteroposterior and b) lateral radiographs. Latest follow-up: c) anteroposterior and d) lateral radiographs.

Fig. 3. Skipped pedicle screw technique. Pre-operation: a) anteroposterior and b) 17

ACCEPTED MANUSCRIPT lateral radiographs. Latest follow-up: c) anteroposterior and d) lateral radiographs.

1.

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References Weinstein SL, Dolan LA, Cheng JC, et al. Adolescent idiopathic scoliosis. Lancet

2008;371:1527-1537. 2.

Lenke LG, Betz RR, Harms J, et al. Adolescent idiopathic scoliosis: a new classification to

determine extent of spinal arthrodesis. J Bone Joint Surg Am 2001;83-a:1169-1181. 3.

Lenke LG, Betz RR, Clements D, et al. Curve prevalence of a new classification of operative

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adolescent idiopathic scoliosis: does classification correlate with treatment? Spine (Phila Pa 1976) 2002;27:604-611. 4.

Clements DH, Betz RR, Newton PO, et al. Correlation of scoliosis curve correction with the

5.

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number and type of fixation anchors. Spine (Phila Pa 1976) 2009;34:2147-2150.

Larson AN, Polly DW, Jr., Diamond B, et al. Does higher anchor density result in increased curve

correction and improved clinical outcomes in adolescent idiopathic scoliosis? Spine (Phila Pa 1976) 2014;39:571-578. 6.

Quan GM, Gibson MJ. Correction of main thoracic adolescent idiopathic scoliosis using pedicle

screw instrumentation: does higher implant density improve correction? Spine (Phila Pa 1976) 2010;35:562-567.

Yang S, Jones-Quaidoo SM, Eager M, et al. Right adolescent idiopathic thoracic curve (Lenke 1 A

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Bharucha NJ, Lonner BS, Auerbach JD, et al. Low-density versus high-density thoracic pedicle

screw constructs in adolescent idiopathic scoliosis: do more screws lead to a better outcome? Spine J 9.

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pedicle screw instrumentation: results of 48 patients with minimal 10-year follow-up. Eur Spine J

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2013;22:345-354.

10. Diab M, Smith AR, Kuklo TR. Neural complications in the surgical treatment of adolescent idiopathic scoliosis. Spine (Phila Pa 1976) 2007;32:2759-2763. 11. Cheung KM, Senkoylu A, Alanay A, et al. Reliability and concurrent validity of the adapted Chinese version of Scoliosis Research Society-22 (SRS-22) questionnaire. Spine (Phila Pa 1976) 2007;32:1141-1145.

12. Qiu G, Qiu Y, Zhu Z, et al. Re-evaluation of reliability and validity of simplified Chinese version of SRS-22 patient questionnaire: a multicenter study of 333 cases. Spine (Phila Pa 1976) 2011;36:E545-550. 13. Li M, Shen Y, Fang X, et al. Coronal and sagittal plane correction in patients with Lenke 1 adolescent idiopathic scoliosis: a comparison of consecutive versus interval pedicle screw placement. J Spinal Disord Tech 2009;22:251-256. 14. Tao F, Zhao Y, Wu Y, et al. The effect of differing spinal fusion instrumentation on the occurrence 18

ACCEPTED MANUSCRIPT of postoperative crankshaft phenomenon in adolescent idiopathic scoliosis. J Spinal Disord Tech 2010;23:e75-80. 15. Ketenci IE, Yanik HS, Demiroz S, et al. Three-Dimensional Correction in Patients With Lenke 1 Adolescent Idiopathic Scoliosis: Comparison of Consecutive Versus Interval Pedicle Screw Instrumentation. Spine (Phila Pa 1976) 2016;41:134-138. 16. Morr S, Carrer A, Alvarez-Garcia de Quesada LI, et al. Skipped versus consecutive pedicle screw constructs for correction of Lenke 1 curves. Eur Spine J 2015;24:1473-1480.

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17. Hwang CJ, Lee CK, Chang BS, et al. Minimum 5-year follow-up results of skipped pedicle screw fixation for flexible idiopathic scoliosis. J Neurosurg Spine 2011;15:146-150.

18. Wang X, Aubin CE, Robitaille I, et al. Biomechanical comparison of alternative densities of pedicle screws for the treatment of adolescent idiopathic scoliosis. Eur Spine J 2012;21:1082-1090.

19. Salmingo RA, Tadano S, Fujisaki K, et al. Relationship of forces acting on implant rods and degree of scoliosis correction. Clin Biomech (Bristol, Avon) 2013;28:122-128.

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20. Le Naveaux F, Aubin CE, Larson AN, et al. Implant distribution in surgically instrumented Lenke 1 adolescent idiopathic scoliosis: does it affect curve correction? Spine (Phila Pa 1976) 2015;40:462-468. 21. Liu H, Li Z, Li S, et al. Main thoracic curve adolescent idiopathic scoliosis: association of higher rod

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stiffness and concave-side pedicle screw density with improvement in sagittal thoracic kyphosis restoration. J Neurosurg Spine 2015;22:259-266.

22. Sudo H, Abe Y, Kokabu T, et al. Correlation analysis between change in thoracic kyphosis and multilevel facetectomy and screw density in main thoracic adolescent idiopathic scoliosis surgery. Spine J 2016;16:1049-1054.

23. Tsirikos AI, Subramanian AS. Posterior spinal arthrodesis for adolescent idiopathic scoliosis using pedicle screw instrumentation: does a bilateral or unilateral screw technique affect surgical outcome?

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J Bone Joint Surg Br 2012;94:1670-1677.

24. Larson AN, Polly DW, Jr., Ackerman SJ, et al. What would be the annual cost savings if fewer screws were used in adolescent idiopathic scoliosis treatment in the US? J Neurosurg Spine 2016;24:116-123.

25. Dhawale AA, Shah SA, Yorgova P, et al. Effectiveness of cross-linking posterior segmental

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instrumentation in adolescent idiopathic scoliosis: a 2-year follow-up comparative study. Spine J 2013;13:1485-1492.

26. Garg S, Niswander C, Pan Z, et al. Cross-Links Do Not Improve Clinical or Radiographic Outcomes

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of Posterior Spinal Fusion With Pedicle Screws in Adolescent Idiopathic Scoliosis: A Multicenter Cohort Study. Spine Deformity 2015;3:338-344. 27. Roach JW, Mehlman CT, Sanders JO. "Does the outcome of adolescent idiopathic scoliosis surgery justify the rising cost of the procedures?". J Pediatr Orthop 2011;31:S77-80. 28. Martin CT, Pugely AJ, Gao Y, et al. Increasing hospital charges for adolescent idiopathic scoliosis in the United States. Spine (Phila Pa 1976) 2014;39:1676-1682. 29. Kamerlink JR, Quirno M, Auerbach JD, et al. Hospital cost analysis of adolescent idiopathic scoliosis correction surgery in 125 consecutive cases. J Bone Joint Surg Am 2010;92:1097-1104.

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ACCEPTED MANUSCRIPT Table1. The baseline characteristics of the three groups C Group

I Group

S Group

P(C vs. I)

P(C vs. S)

P(I vs. S)

Modifiers (A/B/C)

13/4/5 2/15/5 13/9 14.5±2.0 2.9±1.4 7.5±1.2 53.2±9.9 30.6±8.1 42.5±11.0 1.7±0.6 33.3±19.0 18.5±8.3 29.0±16.9 -56.2±12.0

12/2/4 3/13/2 14/4 13.9±2.3 2.4±1.6 7.5±1.8 55.1±9.1 30.5±10.2 45.1±13.9 1.8±0.6 36.5±16.7 12.0±8.3 24.0±12.0 -56.4±9.9

18/3/4 3/19/3 16/9 14.8±2.3 2.5±1.6 7.5±1.0 54.0±9.5 31.6±11.3 42.1±13.1 1.8±0.7 39.3±14.6 21.8±16.2 23.8±12.4 -52.0±7.5

0.43 0.28 1.00 0.54 0.98 0.51 0.81 0.55 0.10 0.27 0.98

0.60 0.34 0.96 0.77 0.71 0.90 0.71 0.23 0.34 0.21 0.13

0.19 0.85 0.96 0.72 0.70 0.43 0.91 0.59 0.01 0.96 0.16

Age (y) Riser sign Cobb levels of MT MT Cobb (°) convex-Bending Cobb (°) Flexibility (%) VR (Nash-Moe) AVT (mm) TTS (mm) TK (T5–T12) LL (T12–S1)

SC

Gender (F/M)

M AN U

TSP (−1/N/+1)

RI PT

Variable

AC C

EP

TE D

TSP indicates thoracic sagittal profile; a minus sign, hypokyphosis; N, normal; a plus sign, hyperkyphosis; F, female; M, male; MT, main thoracic; VR, vertebral rotation; AVT, apical vertebra translation; TTS, thoracic trunk shift; TK, thoracic kyphosis; LL, lumbar lordosis.

ACCEPTED MANUSCRIPT Table2. The perioperative outcomes of the three groups C Group

I Group

S Group

P (C vs. I)

P (C vs. S)

P (I vs. S)

Surgery time (min)

359.5±87.3 1120.0±465.1 699.8±432.0 20.1±3.5 14907.8±4841.6 10.4±2.1 20.8±4.2 2.0±0.0 0.3±0.6

283.1±53.2 935.2±362.8 519.5±333.5 19.3±3.8 12706.5±5160.5 10.7±2.4 17.2±3.9 1.6±0.1 0.6±0.8

301.6±56.4 882.4±317.3 488.0±294.9 19.1±3.5 9855.1±2583.1 11.3±1.5 14.5±2.5 1.3±0.2 0.8±0.9

0.001 0.14 0.12 0.45 0.11 0.62 0.002 < 0.001 0.16

0.005 0.04 0.047 0.34 < 0.001 0.12 < 0.001 < 0.001 0.02

0.38 0.66 0.78 0.89 0.03 0.34 0.02 < 0.001 0.42

Blood loss (ml) Blood transfusions (ml) Hospital stay (days) Implant costs ($) Fused levels No. screws

M AN U TE D EP AC C

Cross-links

SC

Screw density

RI PT

Variable

ACCEPTED MANUSCRIPT Table3. The radiographic outcomes of the three groups Variable

C Group

I Group

S Group

P (C vs. I)

P (C vs. S)

P (I vs. S)

0.29 0.62 0.25 0.73 0.25 0.98 0.19

0.20 0.26 0.07 0.66 0.99 0.08 0.34

0.89 0.57 0.59 0.95 0.24 0.09 0.64

0.17 0.57 0.37 0.56 0.79 0.23 0.44 0.92

0.10 0.26 0.09 0.55 0.55 0.86 0.32 0.81

0.88 0.62 0.50 0.98 0.40 0.28 0.88 0.74

MT Cobb (°) Change of MT Cobb (°) Correction rate (%) AVT (mm) TTS (mm) TK (T5–T12) LL (T12–S1)

14.2±7.4 39.4±7.0 75.1±12.0 15.2±9.5 10.1±6.9 23.9±9.2 -45.5±11.3

16.9±8.8 38.2±6.9 70.3±13.6 16.3±10.1 12.9±8.3 23.9±10.5 -49.9±8.1

17.2±7.7 36.8±9.3 68.2±13.0 16.5±9.2 10.1±7.8 18.5±10.9 -48.4±11.4

LATEST FOLLOW-UP

Correction rate (%) Loss of MT Cobb (°) AVT (mm) TTS (mm) TK (T5–T12) LL (T12–S1)

18.8±8.9 36.2±6.8 66.8±14.2 2.0±3.9 13.0±7.6 12.6±6.7 22.6±9.2 -53.9±9.2

19.2±7.6 34.8±10.6 63.8±15.0 2.0±5.1 15.4±9.9 10.0±9.9 22.0±12.8 -53.0±8.2

SC

Change of MT Cobb (°)

15.3±7.5 37.9±9.0 71.0±13.9 1.1±5.3 13.8±9.4 9.6±5.5 25.3±10.0 -53.6±10.3

M AN U

MT Cobb (°)

RI PT

EARLY POST-OPERATION

AC C

EP

TE D

MT indicates main thoracic; AVT, apical vertebra translation; TTS, thoracic trunk shift; TK, thoracic kyphosis; LL, lumbar lordosis.

ACCEPTED MANUSCRIPT Table4. The SRS-22 questionnaire of the three groups of patients Variable

C Group

I Group

S Group

P (C vs. S)

P (I vs. S)

0.63 0.42 0.61 0.78

0.52 0.61 0.72 0.96

0.27 0.74 0.85 0.81

-

-

-

0.92 0.59 0.52 0.72 0.77

0.10 0.85 0.23 0.54 0.91

0.15 0.71 0.07 0.84 0.85

P (C vs. I)

Mental health

3.7±0.3 4.3±0.5 3.2±0.4 3.8±0.4

3.8±0.4 4.4±0.4 3.2±0.5 3.9±0.4

3.7±0.3 4.4±0.4 3.2±0.4 3.8±0.4

Satisfaction

-

-

-

Function/activity Pain Self-image

LATEST FOLLOW-UP

Pain Self-image Mental health

3.9±0.2 4.2±0.3 3.7±0.3 4.0±0.3 4.1±0.5

3.8±0.2 4.3±0.3 3.5±0.3 4.0±0.4 4.0±0.6

AC C

EP

TE D

M AN U

Satisfaction

3.9±0.2 4.3±0.3 3.6±0.3 4.0±0.3 4.0±0.6

SC

Function/activity

RI PT

PRE-OPERATION

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT

Highlights: 1. This study compares three all-pedicle screw techniques (consecutive, interval, and skipped pedicle screw techniques) in moderate Lenke type 1 AIS patients.

RI PT

2. Interval and skipped pedicle screw techniques are more cost-effective options. 3. Consecutive, interval, and skipped pedicle screw techniques all provide

AC C

EP

TE D

M AN U

SC

satisfactory deformity correction and SRS-22 outcomes with few complications.