Elsevier

Spine Deformity

Volume 6, Issue 1, January 2018, Pages 72-78
Spine Deformity

Case Series
S2 Alar Iliac Fixation in Long Segment Constructs, a Two- to Five-Year Follow-up

https://doi.org/10.1016/j.jspd.2017.05.004Get rights and content

Abstract

Study Design

Retrospective review of patients having undergone S2 alar-iliac (S2AI) fixation for long fusions with a minimum two-year follow-up.

Objectives

To report on fusion rates, complications, technique-specific complications of patients having undergone S2AI fixation.

Summary of background data

Sacropelvic fixation continues to be a challenge when performing long fusions to the pelvis. S2AI screws have been found to provide solid biomechanical fixation and have been found to have good clinical results in short-term follow-up for pediatric and adult patients.

Methods

Cases were retrospectively reviewed in patients who had placement of S2AI screws for long fusions with at least a two-year follow-up. Demographic data, complications, and reoperations were reviewed. Complications were broken into minor and major categories similar to previous series on pelvic fixation.

Results

There were 86 cases identified. Minor and major complications occurred in 29% and 24% of patients, respectively, with the majority of minor complications being intraoperative dural tears. Revision surgery for all causes was performed in 23% of the cohort. Fusion rate at L5–S1 for patients without preoperative pseudarthrosis was 95.3%. Preoperative L5–S1 pseudoarthrosis was identified in 20 patients, 17 (95%) of these went onto fusion after one surgery. There was evidence of S2AI screw lucency in 10.4% of cases. However, the majority of these were asymptomatic.

Conclusions

Sacropelvic fixation using the S2AI technique provides safe, durable fixation with low rates of technique-specific complications and limited need for hardware removal. Complication rates in this series were similar to other series on long fusions to the pelvis. Additionally, fusion rates were high at L5–S1 for both patients with and without preoperative L5–S1 pseudarthrosis. It appears that the S2AI technique is a powerful option for patients with previous L5–S1 pseudarthrosis.

Level of Evidence

Level III.

Introduction

Sacral fixation for long fusions to the spine provides an extra point of distal stability, but also places significant strain on caudal fixation. Ending thoracolumbar fusions at S1 may be indicated for degenerative stenosis; however, S1 screws alone may lead to high pseudarthrosis rates with or without loss of sagittal balance [1], [2]. Retrospective studies have shown pseudarthrosis rates as high as 24% in long fusions (greater than four levels) when sacral fixation is used alone [2], [3]. Sacropelvic fixation may be used to enhance stability and avoid complications seen when S1 pedicle screws are used alone as distal fixation. There are several accepted indications for use of supplemental sacropelvic fixation: flat-back deformity, correction of pelvic obliquity, high-grade spondylolisthesis, sacrectomy, sacral fractures, spinopelvic dissociation, and osteoporosis in the setting of lumbosacral fusion.

Currently, several options exist to improve caudal fixation in long constructs. These include iliosacral screws, iliac screws, S2 pedicle screws, sacral alar screws, and S2AI screws. Because of the weak sacral bone stock, alar, S1, and S2 screws alone or in conjunction have had less promising results, with higher rates of failure and pullout [1], [2], [3]. Iliac and iliosacral screws have improved rates of success, with lower rates of pseudarthrosis (5%) and failure; however, these techniques require separate incisions, and use of offset connectors adding to surgical time and morbidity [4], [5], [6]. In addition, Tsuchiya et al. found a 34% rate of iliac screw removal at 5 years after iliac screw pelvic fixation in a series of adult spinal deformity (ASD) patients [6]. Fusion to the pelvis continues to be a challenge in spine surgery. Much of this is due to the challenging anatomy, biomechanics, and morbidity related to invasive procedures.

Recently, the S2 alar iliac (S2AI) screw has shown promising results for fusion, with low complications rates. S2AI is a low-profile, in-line technique that provides durable distal fixation [7]. Specifically, it is a modified-trajectory S2 alar screw placed across the sacroiliac (SI) joint into the ilium (Fig. 1A–C) [8]. Because the S2AI screw is placed in line with more cephalad instrumentation, there is generally no need for offset connectors. Additionally, the screws can be placed either open or percutaneously (Fig. 2A and B) [9]. The use of S2AI has been present for several years, with groups starting to publish promising results [10], [11], [12], [13]. Strike et al. in a prospective review found very low rates of instrumentation complications at 5 years after S2AI screw placement and extremely high fusion rates (98%) from L4 to S1 [13].

Section snippets

Methods IRB approval needs to be added

From 2009 to 2014, all fusions to the sacrum were performed by senior surgeons (WY, JOB) using bilateral S2AI technique as described radiographically by Chang et al. and anatomically evaluated by O'Brien et al. [7], [8]. Cases were retrospectively reviewed in patients who had placement of bilateral S2AI screws with at least a two-year follow-up extending over four disc levels: for example, L2–S1 was considered four levels. This was considered a “long segment” construct in accordance with

Results

The mean age at the time of surgery was 63.6 ± 9.2 (range 34–81), 79% of patients were women (68), and 21% were men (18). The average number of levels fused was 8 ± 2.6 (range 4–17) (Table 1). Polyaxial screws were used in all cases, with diameters ranging from 6.5 to 8.5 mm, and average length of 73 mm. There were 29 minor complications in 25 patients (overall rate 34%) (Table 2), with 16 (55%) of these being intraoperative dural tears. The overall rate of dural tears was 18.6%. Eight patients

Discussion

Lumbosacral arthrodesis and maintenance of sagittal balance after long fusion to the sacrum remains a challenge in adult spinal deformity surgery. Multiple studies have shown high pseudarthrosis rates when S1 pedicle screws are used without complete lumbosacral fixation [3], [15], [16], [17]. Complete fixation for long fusions to the sacrum includes iliac fixation as well as interbody support—whether anterior lumbar interbody fusion or transforaminal lumbar interbody fusion [4]. There are

Conclusions

S2AI fixation appears to provide safe, durable fixation with low rates of technique-specific complications. Additionally, S2AI provides stable fixation during revision surgery for previous pseudarthrosis with a high rate of arthrodesis. Major and minor complication rates are similar to other large series on long fusions to the sacrum. Finally, there were very few reported complications specific to S2AI screws and when comparing to other methods of pelvic fixation, there was an extremely low

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    IRB Approval: This study was reviewed and approved by the George Washington University research ethics board.

    Author disclosures: EJS (none); JK (none); RD (none); WY (none); JO'B (personal fees from Globus, NuVasive, Stryker, and Relivent; nonfinancial support from Globus; stocks and private investments in Spinicity, K2 Medical, and ISD, all unrelated to this work).

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