Long fusion to the pelvis with S2-alar-iliac screws can induce changes in pelvic incidence in adult spinal deformity patients: analysis of predictive factors in a retrospective cohort

Decrease in pelvic incidence after adult spinal deformity surgery is a predictive factor for progression of hip joint osteoarthritis

BACKGROUND

This study aimed to evaluate the association between spinopelvic alignment parameters and hip osteoarthritis progression after spinal alignment correction surgery for adult spinal deformity, focusing on the preoperative to postoperative change in spinopelvic alignment.

METHODS

This retrospective study enrolled 100 adult spinal deformity patients (196 hip joints) who underwent spinal fusion surgery, after excluding four joints with previous total hip arthroplasty. Acetabular roof obliquity (ARO), center edge angle (CE) and Kellgren and Lawrence (KL) grade were measured in the hip joint. Spinopelvic alignment parameters were measured preoperatively and 1-month postoperatively and the changes (Δ) during this period were calculated. Patients were followed-up for ≥ 5 years and factors associated with KL grade progression at 5-years postoperatively were determined by logistic regression analysis.

RESULTS

In the analysis with all cases, KL grade progressed in 23 joints. Logistic regression analysis revealed age (OR: 1.098, 95% CI: 1.007-1.198, p = 0.019), ARO (OR: 1.176, 95% CI: 1.01-1.37, p = 0.026), and Δ PI (OR: 0.791, 95% CI: 0.688-0.997, p < 0.001) as parameters significantly associated with KL grade progression. On the other hand, in the analysis limited to 185 cases with 1-month postoperative KL grade of 0, KL grade progressed in 13 joints. Logistic regression analysis revealed PI-LL (OR: 1.058, 95% CI: 1.001-1.117, p = 0.04), ΔPI (OR: 0.785, 95% CI: 0.649-0.951, p < 0.001), and ΔCobb (OR: 1.127, 95% CI: 1.012-1.253, p = 0.009) as parameters significantly associated with progression.

CONCLUSIONS

Both the overall and limited analyzes of this study identified preoperative to postoperative change in PI as parameters affecting the hip osteoarthritis progression after spinal fusion surgery. Decrease in PI might represent preexisting sacroiliac joint laxity. Patients with this risk factor should be carefully followed for possible hip osteoarthritis progression.

Preoperative supine pelvic incidence predicts standing pelvic incidence following S2AI fixation in patients with adult spinal deformity: a prospective study

STUDY DESIGN

A prospective study.

OBJECTIVE

The aim of this study was to investigate the PI change in different postures and before and after S2‑alar‑iliac (S2AI) screw fixation, and to investigate whether pre-op supine PI could predict post-op standing PI. Previous studies have reported PI may change with various positions. Some authors postulated that the unexpected PI change in ASD patients could be due to sacroiliac joint laxity, S2-alar-iliac (S2AI) screw placement, or aggressive sagittal cantilever technique. However, there was a lack of investigation on how to predict post-op standing PI when making surgical strategy.

METHODS

A prospective case series of ASD patients undergoing surgical correction with S2AI screw placement was conducted. Full-spine X-ray films were obtained at pre-op standing, pre-op supine, pre-op prone, as well as post-op standing postures. Pelvic parameters were measured. Spearman correlation analysis was used to determine relationships between each parameter.

RESULTS

A total of 83 patients (22 males, 61females) with a mean age of 58.4 ± 9.5 years were included in this study. Pre-op standing PI was significantly lower than post-op standing PI (p = 0.004). Pre-op prone PI was significantly lower than post-op standing PI (p = 0.001). By contrast, no significant difference was observed between pre-op supine and post-op standing PI (p = 0.359) with a mean absolute difference of 2.2° ± 1.9°. Correlation analysis showed supine PI was significantly correlated with post-op standing PI (r = 0.951, p < 0.001).

CONCLUSION

This study revealed the PI changed after S2AI screw fixation. The pre-op supine PI can predict post-op standing PI precisely, which facilitates to provide correction surgery strategy with a good reference for ideal sagittal alignment postoperatively.

Can Pelvic Incidence Change After Lumbo-Pelvic Fixation for Adult Spine Deformity, and Would the Change be Affected by the Type of Pelvic Fixation?

STUDY DESIGN

Retrospective review.

OBJECTIVE

To assess the change in pelvic incidence (PI) after lumbo-pelvic fixation and the differential impact of the type of pelvic fixation: S2-alar-iliac screws (S2AI) versus Iliac screws (IS) on postoperative PI.

SUMMARY OF BACKGROUND DATA

Recent studies suggest that changes occur to the previously assumed fixed PI after spino-pelvic fixation.

METHODS

Adult spine deformity (ASD) patients who underwent spino-pelvic fixation with≥4 levels of fusion were included. Preoperative and postoperative PI, lumbar lordosis (LL), thoracic kyphosis, pelvic tilt, sacral slope, PI-LL mismatch, and the Sagittal Vertical Axis (SVA) were analyzed on EOS imaging. A significant PI change was established at≥6°. Patients were categorized based on the type of pelvic fixation (S2AI vs. IS).

RESULTS

One-hundred-forty-nine patients were included. Of these, 77(52%) had a>6° change in their PI postoperatively. In patients with high preoperative PI (>60°), 62% had a significant PI change compared with 33% of patients with normal PI (40°-60°) and 53% in patients with low PI (<40°; P =0.01). PI was likely to decrease in patients with high baseline PI (>60°) and to increase in patients with low baseline PI (<40°). Patients with a significant PI change had a higher PI-LL. Patients in the S2AI group (n=99) and those in the IS group (n=50) were comparable at baseline. In the S2AI group, 50 (51%) patients had>6° change in their PI compared with 27(54%) patients in the IS group( P =0.65). In both groups, patients with high preoperative PI were more prone to significant postoperative changes ( P =0.02 in IS, P =0.01 in S2AI).

CONCLUSION

PI changed significantly in 50% of patients postoperatively, especially in those with high/low preoperative PI and those with severe baseline sagittal imbalance. This occurs similarly in patients with S2AI and those with IS screws. Surgeons should keep in mind these anticipated changes while planning ideal LL, as this impacts postoperative PI-LL mismatch.

LEVEL OF EVIDENCE

4.

How Does Spino-Pelvic Fixation Affect Post-Operative Compensatory Mechanisms in Adult Spinal Deformity?

STUDY DESIGN

Retrospective single-center multi-surgeon cohort study.

OBJECTIVES

Compare the post-operative changes in the compensatory mechanisms of the sagittal balance according to the type of pelvic fixation: S2-Alar-iliac screws (S2AI) vs iliac screws (IS) in patients with Adult spine deformity (ASD).

METHODS

ASD patients who underwent spino-pelvic fixation and remained with a PI-LL >10° mismatch post-operatively were included. Pre-operative and 1-year-follow-up PI, Lumbar lordosis (LL), pelvic tilt (PT), sacral slope (SS), thoracic kyphosis (TK), femur obliquity angle (FOA), knee flexion angle (KFA) and ankle flexion angle (AFA) were analyzed on EOS imaging. Patients were categorized based on their pelvic fixation type (S2AI vs IS), and the pre-operative to 1-year-post-operative changes (ΔX°) in the compensatory mechanisms were compared between groups.

RESULTS

Patients with S2AI (n = 53) and those with IS (n = 26) screws were comparable at baseline. ΔSS averaged 9.87° in the S2AI compared to 13.2° in the IS (P = .001), whereas the ΔKFA reached 6.01° in the S2AI as opposed to 3.06° in the IS (P = .02). The ΔPT was comparable between both groups (6.35°[S2AI group] vs 5.21°[ISgroup], P = .42). ΔTK, ΔLL, ΔFOA and ΔAFA were comparable between both groups.

CONCLUSION

The type of pelvic fixation impacts significantly the post-operative compensatory mechanisms in patients with ASD. Patients with S2AI screws are more likely to compensate their remaining post-operative PI-LL mismatch through their knees and less likely through their pelvis compared to patients with IS, despite similar changes in PT. This could be explained by an increased SI joint laxity in ASD patient and the lower resistance of the iliac connectors to the junctional mechanical stresses, allowing for sacro-iliac joint motion in patients with IS.

Bilateral psoas release for long standing hip-spine syndrome: surgical technique and case report

Background

Severe positive sagittal malalignment can potentially lead to shortening and contracture of the psoas and joint capsule in a flexed spinopelvic position. The utilization of bilateral psoas release to supplement sagittal spinal deformity correction in the same hospitalization was not reported in the literature.

Case presentation

A 66-year-old patient presented with a 5-year history of severe global spinal deformity (sagittal vertical axis 220 mm, 60° spinopelvic mismatch) that did not improve on supine radiographs, and a modified Thomas test with more than 30° flexion contracture of bilateral hips. A 3-stage operation utilizing posterior spinal column osteotomies, anterior lumbar interbody fusion, and bilateral psoas releases was performed.

Outcome

Her postoperative alignment significantly improved and she was pleased with her new posture and the ability to stand up straight.

Conclusions

This report is the first to demonstrate safe and substantial correction of severe spinal deformities associated with bilateral hip flexion contracture in 1 hospitalization.

Modified unilateral iliac screw fixation with partial reduction in the treatment of high-grade spondylolisthesis at L5/S1 in adult patients: introduction of key technique, report of clinical outcomes and analysis of spinopelvic parameters

BACKGROUND

Management of high-grade spondylolisthesis (HGS) remains challenging. Spinopelvic fixation such as iliac screw (IS) was developed to deal with HGS. However concerns regarding constructs prominence and increased infection-related revision surgery have complicated it's use. We aim to introduce the modified iliac screw (IS) technique in treating high-grade L5/S1 spondylolisthesis and it's clinical and radiological outcomes.

METHODS

Patients with L5/S1 HGS who underwent modified IS fixation were enrolled. Pre- and postsurgical upright full spine radiographs were obtained to analyze sagittal imbalance, spinopelvic parameters, pelvic incidence-lumbar lordosis mismatch (PI-LL), slip percentage, slip angle (SA), and lumbosacral angle (LSA). Visual analogue scale (VAS), Oswestry disability index (ODI) were evaluated pre- and postoperatively for clinical outcomes assessment. Estimated blood loss, operating time, perioperative complications and revision surgery were documented.

RESULTS

From Jan 2018 to March 2020, 32 patients (15 males) with mean age of 58.66 ± 7.77 years were included. The mean follow-up period was 49 months. The mean operation duration was 171.67 ± 36.66 min. At the last follow-up: (1) the VAS and ODI score were significantly improved (p < 0.05), (2) PI increased by an average of 4.3°, the slip percent, SA and LSA were significantly improved (p < 0.05), (3) four patients (16.7%) with global sagittal imbalance recovered a good sagittal alignment, PI-LL within ± 10° was observed in all patients. One patient experienced wound infection. One patient underwent a revision surgery due to pseudoarthrosis at L5/S1.

CONCLUSION

The modified IS technique is safe and effective in treating L5/S1 HGS. Sparing use of offset connector could reduce hardware prominence, leading to lower wound infection rate and less revision surgery. The long-term clinical affection of increased PI value is unknown.

A Comprehensive Analysis of the Behavior of Pelvic Incidence After Different Posterior Spinal Procedures in Elderly Patients With Spinal Deformity

STUDY DESIGN

A retrospective case-control study.

OBJECTIVE

To evaluate the behavior of pelvic incidence (PI) after different posterior spinal procedures in elderly patients with adult spinal deformity (ASD), to determine the potential associated factors with the variability in PI after spinal surgery and to comprehensively analyze its mechanisms.

METHODS

Elderly patients underwent long fusion to sacrum with and without pelvic fixation were assigned to Group L+P and Group L-P, respectively. In Group L-P, those with severe sagittal deformity were selected as Group A. 20 elderly patients with severe sagittal deformity underwent short lumbar fusion were included as Group B. The following radiographic parameters were evaluated: thoracic kyphosis (TK), thoracolumbar kyphosis (TLK), lumbar lordosis (LL), PI-LL, sagittal vertical axis (SVA), T1 pelvic angle (TPA), and pelvic parameters. PI changing more than 5° (△PI > 5°) was considered as substantially changed.

RESULTS

For the whole cohort and in Group L+P, PI were not substantially changed (△PI ≤ 5°) after surgery. Besides the severer sagittal malalignment in patients with △PI > 5° in Group L-P, relatively larger mean age, greater proportion of female and lower preoperative PI were found than those in patients with △PI ≤ 5°. 70.8% of patients had substantial increase of PI in Group A, while only 10% of patients had in Group B (P < 0.001).

CONCLUSION

PI behaves differently under different conditions in elderly ASD patients. Besides severe sagittal deformity, aging, female and low preoperative PI are also the potential risk factors of PI increasing after long fusion to sacrum.

Dynamic change of pelvic incidence after long fusion to pelvis with S2-alar-iliac screw: a 2-year follow-up study

INTRODUCTION

Pelvic incidence (PI) is a key morphological parameter that reflects the relation between the sacrum and iliac wings. It is well accepted that PI remains constant after reaching maturity. However, recent studies indicated that PI might be altered after lumbosacral fusion. Additionally, it remains uncertain on the long-term influence of long fusion to pelvis with S2-alar-iliac screw on PI in patients with adult spinal deformity (ASD).

STUDY DESIGN

A retrospective study.

OBJECTIVE

To investigate whether and how PI would change during the follow-up in ASD patients who underwent S2AI fixation and to identify factors associated with the change in PI.

METHODS

We retrospectively reviewed all ASD patients who underwent spinal surgery using S2AI screws between November 2014 and January 2017 at our institution. Patients with minimum follow-up of two years were included. The following sagittal radiographic parameters were measured: PI, Lumbar lordosis (LL), pelvic tilt (PT), PI-LL, sagittal vertical axis (SVA) at pre-op, post-op and 2-year follow-up. According to the changes in PI at immediate post-operation, patients were classified into two groups; Group A: Changes of PI less than or equal 5° and Group B: Changes of PI greater than 5°.

RESULTS

A total of 82 ASD patients (Group A: 32, Group B: 50; mean age of 53.5 ± 12.6 years) with a mean follow-up period of 30.2 ± 9.2 months were included in this study. At immediate post-operation, Group A showed no significant change in PI (45.7° ± 11.4° to 45.3° ± 11.2°, p = 0.749); while Group B had a significant decrease in PI (51.6° ± 14.5° to 40.9° ± 14.0°, p < 0.001). At the last follow-up, 48% patients (24/50) in Group B had a significant increase in PI (32.8° ± 6.4° to 45.8° ± 11.2°, p < 0.001). Intergroup analysis showed that ΔPI, post-op PI, post-op PT and age were significantly different between both groups. In addition, pre-op PI, post-op PI, post-op PT, post-op PI-LL were significantly correlated with ΔPI at last follow-up. Also, logistic regression analysis showed that post-op PI was the associated risk factor (OR = 0.865, p = 0.024) for PI-LL mismatch.

CONCLUSION

Our study showed that PI decreased in more than half of ASD patients immediately after spinal surgery using S2AI screws. Approximately 48% of them were able to recover during the 2-year follow-up. Lower pre-op PI, post-op PI and PT were found to be strongly associated with the return of PI. Thus, these current findings indicated that patients with a high PI at pre-operation should not be over-corrected to avoid PI-LL mismatch postoperatively.

Use of iliac screw associated with more correction of lumbar lordosis than S2-alar-iliac screw for adult spinal deformity

Background

To date, there is a paucity of reports clarifying the change of spinopelvic parameters in patients with adult spinal deformity (ASD) who underwent long segment spinal fusion using iliac screw (IS) and S2-alar-iliac screw (S2AI) fixation.

Methods

A retrospective review of consecutive patients who underwent deformity correction surgery for ASD between 2013 and 2017 was performed. Patients were divided into two groups based on whether IS or S2AI fixation was performed. All radiographic parameters were measured preoperatively, immediately postoperatively, and the last follow-up. Demographics, intraoperative and clinical data were analyzed between the two groups. Additionally, the cohort was subdivided according to the postoperative change in pelvic incidence (PI): subgroup (C) was defined as change in PI ≥5° and subgroup (NC) with change < 5°. In subgroup analyses, the 2 different types of postoperative change of PI were directly compared.

Results

A total of 142 patients met inclusion criteria: 111 who received IS and 31 received S2AI fixation. The IS group (65.6 ± 26°, 39.8 ± 13.8°) showed a significantly higher change in lumbar lordosis (LL) and upper lumbar lordosis (ULL) than the S2AI group (54.4 ± 17.9°, 30.3 ± 9.9°) (p < 0.05). In subgroup (C), PI significantly increased from 53° preoperatively to 59° postoperatively at least 50% of IS cohort, with a mean change of 5.8° (p < 0.05). The clinical outcomes at the last follow-up were significantly better in IS group than in S2AI group in terms of VAS scores for back and leg. The occurrence of sacroiliac joint pain and pelvic screw fracture were significantly greater in S2AI group than in IS group (25.8% vs 9%, p < 0.05) and (16.1% vs 3.6%, p < 0.05).

Conclusions

Compared with the S2AI technique, the IS technique usable larger cantilever force demonstrated more correction of lumbar lordosis, and possible increase in pelvic incidence. Further study is warranted to clarify the clinical impaction of these results.

Position-related Change of Pelvic Incidence Depends on the Nonfused Sacroiliac Joint in Patients with Degenerative Spinal Diseases

STUDY DESIGN

A retrospective cross-sectional study.

OBJECTIVE

This study aims to determine whether the sacroiliac (SI) joint motion correlated to pelvic incidence (PI) change from standing to supine position in patients with degenerative spinal diseases.

SUMMARY OF BACKGROUND DATA

PI was found an unstable parameter after adolescence as the fixed nature of PI was challenged by several studies. The SI joint has been shown to have some motion, age-related degenerative changes of cartilage and SI ligaments contribute to SI joint instability.

METHODS

The study contains both specimen study and radiographic study. One human specimen was acquired, on which PI was measured with different sacrum-ilium positions. In radiographic study, patients with old thoracolumbar fracture, lumbar disc herniation, stenosis, and spondylolisthesis were included. Ankylosing spondylitis (AS) patients were also included as control group. PI was measured on standing x-rays and scanogram of computed tomography images in supine position.

RESULTS

Specimen study result revealed that SI motion would lead to the change of PI with fixed pelvic thickness. In radiographic study, 101 patients with different etiology and 30 AS patients were included. After stratifying into different age groups, standing PI was significantly larger than supine PI in each age groups (P = 0.002, <0.001, and <0.001, respectively). In patients with degenerative diseases, PI was significantly larger on standing position than that on supine position. ΔPI showed no significant difference across etiologies. However, in AS patients, standing PI and supine PI revealed no significant difference (P = 0.528).

CONCLUSION

Mobile SI joint may be the cause of increased PI in the aging spine. The dynamic change of PI is etiology-independent if the SI joint was not fused. Older patients have greater position-related change of PI.Level of Evidence: 4.

Change in pelvic incidence between the supine and standing positions in patients with bilateral sacroiliac joint vacuum signs

OBJECTIVE

Pelvic incidence (PI) is a commonly utilized spinopelvic parameter in the evaluation and treatment of patients with spinal deformity and is believed to be a fixed parameter. However, a fixed PI assumes that there is no motion across the sacroiliac (SI) joint, which has been disputed in recent literature. The objective of this study was to determine if patients with SI joint vacuum sign have a change in PI between the supine and standing positions.

METHODS

A retrospective chart review identified patients with a standing radiograph, supine radiograph, and CT scan encompassing the SI joints within a 6-month period. Patients were grouped according to their SI joints having either no vacuum sign, unilateral vacuum sign, or bilateral vacuum sign. PI was measured by two independent reviewers.

RESULTS

Seventy-three patients were identified with an average age of 66 years and a BMI of 30 kg/m2. Patients with bilateral SI joint vacuum sign (n = 27) had an average absolute change in PI of 7.2° (p < 0.0001) between the standing and supine positions compared to patients with unilateral SI joint vacuum sign (n = 20) who had a change of 5.2° (p = 0.0008), and patients without an SI joint vacuum sign (n = 26) who experienced a change of 4.1° (p = 0.74). ANOVA with post hoc Tukey test showed a statistically significant difference in the change in PI between patients with the bilateral SI joint vacuum sign and those without an SI joint vacuum sign (p = 0.023). The intraclass correlation coefficient between the two reviewers was 0.97 for standing PI and 0.96 for supine PI (p < 0.0001).

CONCLUSIONS

Patients with bilateral SI joint vacuum signs had a change in PI between the standing and supine positions, suggesting there may be increasing motion across the SI joint with significant joint degeneration.

Can pelvic incidence change after spinal deformity correction to the pelvis with S2-alar-iliac screws?

PURPOSE

Pelvic incidence (PI) is assumed to be fixed, yet studies have reported PI changes after long fusions to the pelvis. In a cohort of ASD patients undergoing surgery with S2-alar-iliac (S2AI) screws, we sought to: (1) report the magnitude of PI changes, and (2) evaluate subsequent pelvic parameter changes.

METHODS

A retrospective case series of ASD patients undergoing surgical correction with S2AI screw placement and sagittal cantilever correction maneuvers was conducted. Patients were categorized based on preoperative PI: High-PI (H-PI) (PI ≥ 60°); Normal-PI (N-PI) (60° > PI > 40°); Low-PI (L-PI) (PI ≤ 40°). PI was measured preoperatively and immediately postoperatively. A significant PI change was established a priori at ≥ 6.0. PI, pelvic tilt (PT), lumbar lordosis (LL), and PI-LL mismatch were analyzed.

RESULTS

In 68 patients (82.3% female, ages 22-75 years), the average change in PI was 4.6° ± 3.1, and 25 (36.8%) had a PI change ≥ 6.0° with breakdown as follows: H-PI 12 (66.7%) patients, 9 (25.87%) patients, and 4 (33.3%) patients. Of 25 patients with PI changes, 10 (14.7%) had a PI increase and 15 (22.1%) had a PI decrease. Significant improvements were seen in PT, LL, PI-LL mismatch in all patients with a PI change ≥ 6.0°, in addition to both subgroups with an increase or decrease in PI.

CONCLUSIONS

PI changes of ≥ 6.0° occurred in 36.8% of patients, and H-PI patients most commonly experienced PI changes. Despite PI alterations, pelvic parameters significantly improved postoperatively. These results may be explained by sacroiliac joint laxity, S2AI screw placement, or aggressive sagittal cantilever techniques.

Comparative tomographic study of the iliac screw and the S2-alar-iliac screw in children

OBJECTIVES

The recent advancements in spine fixation aid in the treatment of complex spinal pathologies. Both the iliac screw (IS) and the S2-alar-iliac (S2AI) screw provide adequate stability in the fixation of complex lumbosacral spine pathologies, leading to a significant increased rate of using these techniques in the daily practice of the spine surgeons. This study aims to analyze, describe, and compare the insertion and positioning parameters of the S2AI screw and IS techniques in children without spinal deformities.

METHODS

An observational retrospective study was conducted at a university hospital in 2018, with 25 computed tomography (CT) images selected continuously. Mann-Whitney-Shapiro-Wilk tests were performed. The reliability of the data was assessed using the intraclass correlation. The data were stratified by age group only for Pearson's correlation analysis.

RESULTS

The mean age was 11.7 years (4.5 SD). The mean IS length was 106.63 mm (4.59 SD). The mean length of the S2AI screw was 104.13 mm (4.22 SD). The mean skin distance from the IS entry point was 28.13 mm (4.27 SD) and that for the S2AI screw was 39.96 mm (4.54 SD).

CONCLUSIONS

Through CT, the S2AI screw trajectory was observed to have a greater bone thickness and skin distance than the IS. There was a linear correlation between age and screw length for both techniques. A similar relationship was observed between skin distance and age for the S2AI screw technique. In children, the S2AI screw technique presents advantages such as greater cutaneous coverage and implant thickness than the IS technique.

Sequential correction technique to avoid postoperative global coronal decompensation in rigid adult spinal deformity: a technical note and preliminary results

PURPOSE

This study aims to evaluate this new sequential correction technique for preventing postoperative coronal imbalance.

METHODS

Adult Spinal deformity (ASD) patients were stratifies into two types: primary thoracolumbar/lumbar (TL/L) curve with compensatory lumbosacral (LS) curve (Type I) and primary LS curve with compensatory TL/L curve (Type II): for Type I patients: correction of major TL/L curve and one- or two-level segmental rod installed at the convexity of the TL/L curve, L4-S1 TLIF to correct fractional curve and a short rod installed on the contralateral side and installation of long rods; for Type II patients: horizontalize L4 and L5, short rod installation at the convexity of the LS curve, distraction of curve with regional rod and installation of long rods. ASD patients were enrolled with inclusion criteria: with pre-op TL/L Cobb angle more than 30°, with pelvic fixation and with UIV over T10. Radiographic parameters were analyzed.

RESULTS

Twenty-one patients were recruited (14 patients Type I and 7 Type II patients). Both Cobb angle and coronal offset were significantly improved after surgery. In Type I patients, Cobb angle was improved from 50.48° to 26.91° and coronal offset from 2.94 to 0.95 cm; in Type II patients, Cobb angle was improved from 61.42° to 28.48° and coronal offset from 2.82 to 1.38 cm. In the 10 patients with baseline coronal imbalance, 9 were corrected to coronal balance after surgery.

CONCLUSION

The sequential correction technique allows decomposing the complex correction surgery into several steps, and each step focuses only on one task. It can also reduce the difficulty of rod installation due to the separated maneuvers and multi-rod system.

LEVEL OF EVIDENCE

IV These slides can be retrieved under Electronic Supplementary Material.

Comparative tomographic study of the S2-alar-iliac screw versus the iliac screw

AIMS

Iliac screws and S2-alar-iliac screws provide adequate mechanical stability for the fixation of lumbosacral spine pathologies, which has led to a significant increase in the use of these techniques in the routine practice of spine surgeons. However, studies on the ideal technical positioning for both techniques are limited.

STUDY DESIGN

This is an observational, retrospective, analytical descriptive study.

OBJECTIVE

To analyze, describe and compare the insertion and positioning parameters of the S2-alar-iliac and iliac screw techniques in adult patients without spinal deformities.

METHODS

The present study comprises a retrospective analysis of lumbosacral computed tomography images selected continuously in 2016 from 25 patients at a university hospital. Mann-Whitney-Shapiro-Wilk tests were performed. Data reliability was assessed using intraclass correlation.

RESULTS

The mean length of the iliac screw was greater than that of the S2-alar-iliac screw, and the S2-alar-iliac screw sat 20.5 mm deeper than the iliac screw. The mean of the greatest bone thickness for the iliac screw was 20.72 mm; that of the S2-alar-iliac screw was 23.24 mm. The mean distance from the iliac screw entry point to the skin was 32.46 mm, and the mean distance from the S2-alar-iliac screw entry point to the skin was 52.87 mm.

CONCLUSION

The trajectory of the S2-alar-iliac screws studied via computed tomography was greater in terms of bone thickness and deeper relative to the skin compared with the iliac screws. The S2-alar-iliac technique may have desirable clinical advantages in terms of the diameter of the screws and reduced protrusion when used in adults. These slides can be retrieved from Electronic supplementary material.