Case SeriesS2 Alar Iliac Fixation in Long Segment Constructs, a Two- to Five-Year Follow-up
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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Cited by (29)
The posterior superior iliac rim screw as an adjunct to pelvic fixation in complex spinopelvic stabilization
2021, North American Spine Society JournalSacroiliac joint arthropathy in adult spinal deformity patients with long constructs to the pelvis
2021, Clinical Neurology and NeurosurgeryCitation Excerpt :Low back pain, however, can be differentiated from SIJ pain by following a systematic approach to the diagnosis of SIJ pain using specific physical examination tests [thigh thrust, pelvic distraction, pelvic compression, Fortin finger test, Faber/Patrick’s, Yeomen’s, Gaenslen’s] [25] and acute reduction or resolution of pain after selective SIJ injections with local anesthetics [24]; SIJ pain was diagnosed in our patients using these well-established criteria. Some studies reported non-fusion of the SIJ and radiographic evidence of S2AI screw loosening in up to 10 % of patients [34,35]; partial peri-screw lucency and screw dislodgement are reported at 2.2 % in patients instrumented with S2AI screws, and screw fractures occur in 1.9 % [28]. Iliac screw loosening and fractures are higher, reported at 3.5 % and 4.6 %, respectively [36].
Simultaneous Sacroiliac Joint Fusion in Patients with Long Lumbosacral Constructs: Case Report and Operative Technique
2020, World NeurosurgeryCitation Excerpt :Possible explanations include inadequate support at a fixed but nonfused SIJ, which is bearing the load of a long lumbosacral fusion mass. The S2AI screw is supposed to fix the SIJ in place; however, micromovement manifesting as screw loosening may be the cause of SIJ disease in these patients.6 After changing our practice by fusing the SIJ simultaneously during sacropelvic fixation in the context of a long lumbosacral fusion surgery, we observed a significant decline in the incidence of SIJ disease, as well as remission of SIJ pain in patients requiring revision surgeries.
Management of complex pelvic fracture and sacral fracture Denis type 2 using spanning unilateral fixation of L5 to S2AI screw
2020, International Journal of Surgery Case ReportsSacropelvic Fixation: A Comprehensive Review
2019, Spine DeformityCitation Excerpt :The authors' preferred choice is a polyaxial screw with a favored angle and a smooth shank across the sacroiliac joint, with a typical length of 80 to 100 mm and diameter of 8 to 10 mm [13]. In a recent study, Smith et al. [75] reported the 2- to 5-year outcomes and complications of sacropelvic fixation in long constructs using the S2AI technique. Fusion rates at L5–S1 were high for patients with preoperative L5–S1 pseudarthrosis (95% fusion rate) and for those without (95.3% fusion rate).
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).