Comparative efficacy of S2-alar-iliac versus iliac screw techniques in treating adult spinal deformity: a meta-analysis of postoperative outcomes and complications

Article information

Asian Spine J. 2025;19(5):847-864

Publication date (electronic) : 2025 September 1

doi : https://doi.org/10.31616/asj.2024.0506

Amit Saraf¹, Sanjeev Kumar Jain², Sonika Sharma²

¹Department of Orthopaedics, Teerthanker Mahaveer Medical College & Research Centre, Teerthanker Mahaveer University, Moradabad, India

²Department of Anatomy, Teerthanker Mahaveer Medical College & Research Centre, Teerthanker Mahaveer University, Moradabad, India

Corresponding Author: Sonika Sharma, Department of Anatomy, Teerthanker Mahaveer Medical College & Research Centre, Moradabad–244001, Uttar Pradesh, India, Tel: +91-7055334131, E-mail: soniyasharma.mbd@gmail.com

Received 2024 December 3; Revised 2025 March 26; Accepted 2025 April 6.

Abstract

GRAPHICAL ABSTRACT

Introduction

Adult spinal deformity (ASD) is characterized by abnormal curvature of the spine, leading to significant pain, disability, and diminished quality of life [1]. The primary objectives of ASD surgery are to correct spinal alignment, alleviate pain, and improve functional outcomes, typically achieved through extensive spinal fusion procedures spanning multiple levels (two or more) [2].

Various techniques have been developed to achieve effective lumbosacral fixation [3]. Since its introduction in the late 1980s, the iliac screw (IS) technique has been widely adopted for pelvic fixation, offering a reliable means of stabilization [4]. By engaging the dense cortical bone of the ilium, the IS provides robust anchorage, thereby enhancing construct stability and optimizing load distribution [5]. However, the IS technique is associated with complications such as screw prominence, wound infection, and mechanical failure, prompting the exploration of alternative methods [6].

A more recent technique, the S2-alar-iliac (S2AI) screw technique, aims to mitigate some of the disadvantages of IS fixation [7]. S2AI screws are placed by passing through the sacral ala and ilium, providing a more caudal fixation while preserving the sacroiliac joint (SIJ) [8]. Compared to conventional instrumentation, this technique offers several theoretical advantages, including a lower profile instrument, reduced risk of screw prominence, and fewer wound complications [9].

Despite these advancements, ongoing debate persists among spine surgeons regarding the comparative clinical outcomes of S2AI versus IS techniques [10]. The S2AI technique’s caudal screw trajectory and potential for lower profile instrumentation have garnered significant attention, with proponents citing reduced hardware prominence and decreased soft tissue irritation as potential benefits [11]. However, notable concerns remain, including the steep learning curve associated with S2AI insertion and the risk of sacral ala fracture [12].

The IS technique’s long track record and well-documented biomechanical advantages continue to make it a mainstay in lumbosacral fixation [13]. By direct engagement of the ilium, the IS technique provides a strong and robust anchorage, rendering it an appropriate procedure for long-segment fusion [13,14]. Nevertheless, the drawbacks of IS, including increased rates of wound complications and the need for subsequent hardware removal due to screw prominence, represent significant limitations [15].

The clinical significance of lumbosacral fixation in ASD surgery necessitates a systematic comparison of the S2AI and IS techniques. This meta-analysis aimed to synthesize the available evidence and conduct a comprehensive analysis of clinical outcomes of these two fixation methods.

Methodology

Quality assessment

The quality of the included studies was assessed using the National Heart, Lung, and Blood Institute checklist (Table 1) [16].

Table 1

The quality assessment of the included studies

Results

Study overview

The literature search results are presented in the PRISMA flow diagram (Supplement 1). Sixteen studies were eligible for inclusion in the study [11,15,19–32]. We analyzed 2,316 patients who underwent lumbosacral fixation surgery for various indications. Of these, 1,271 patients underwent fixation utilizing S2 alar-IS cohort. The mean age was 64.6 years in the S2AI cohort and 64.3 years in the IS cohort. The mean body mass index (BMI) was 28.2 kg/m² in the S2AI cohort and 28.62 kg/m² in the IS cohort. The mean number of operated levels was 7.28 in the S2AI cohort and 7.69 in the IS cohort. The demographic characteristics of the included participants and the baseline comorbidities are summarized in Tables 2 and 3.

Table 2

The characteristics of the involved studies and patients

Table 3

The baseline comorbidities of the included patients

Analysis of outcomes

Operation time (minutes)

The analysis of operation time for 421 cases revealed no significant difference between the S2AI and IS cohorts (MD, −31.23; 95% CI, −87.97 to 25.50; p=0.28). However, the pooled data exhibited heterogeneity (I²=76%, p=0.008). To address this heterogeneity, subgroup analysis and sensitivity analysis were performed. The first subgroup, comprising cases with a follow-up period of less than 2 years, showed no significant difference between the two groups (MD, −50.76; 95% CI, −138.67 to 37.15; p=0.26), with moderate heterogeneity (I²=61%, p=0.08). Exclusion of the Ishida 2017 study resolved the heterogeneity in this subgroup (MD, −85.60; 95% CI, −118.91 to −52.30; p=0.001), with no remaining heterogeneity (I²=0%, p=0.84) (Fig. 1B). Similar results were observed in the second subgroup, where the follow-up period exceeded 2 years (MD, −9.47; 95% CI, −73.70 to 54.75; p=0.77), with moderate heterogeneity (I²=64%, p=0.06) (Fig. 1A). Exclusion of the Elder 2016 study resolved the heterogeneity in this subgroup (MD, 10.86; 95% CI, −39.24 to 60.95; p=0.67) (I²=51%, p=0.15) (Fig. 1B).

Fig. 1

(A, B) Forest plot illustrates the results of the analysis of operation time. S2AI, sacral 2 alar-iliac screw; IS, iliac screw; SD, standard deviation; IV, inverse variance; CI, confidence interval; df, degree of freedom.

Estimated blood loss (mL)

Seven studies had reported data on estimated blood loss (n=486). The analysis revealed that the S2AI cohort had significantly lower blood loss compared to the IS cohort (MD, −140.70; 95% CI, −241.21 to −40.18; p=0.006). There was no significant heterogeneity among the included studies in this respect (I²=31%, p=0.19) (Fig. 2).

Fig. 2

Forest plot shows the results of the analysis of blood loss. S2AI, sacral 2 alar-iliac screw; IS, iliac screw; SD, standard deviation; IV, inverse variance; CI, confidence interval; df, degree of freedom.

Length of hospital stay (days)

Five studies (n=381) had reported data on the length of hospital stay. The postoperative length of hospital stay in the IS cohort was significantly longer than that in the S2AI cohort (MD, −1.50; 95% CI, −2.70 to −0.30; p=0.01). There was no significant heterogeneity among the included studies in this respect (I²=0%, p=0.94) (Fig. 3).

Fig. 3

Forest plot demonstrates the results of the analysis of hospital stay. S2AI, sacral 2 alar-iliac screw; IS, iliac screw; SD, standard deviation; IV, inverse variance; CI, confidence interval; df, degree of freedom.

Ambulatory status score

Four studies had reported the ambulatory status score. The ambulatory status score was significantly lower in the IS cohort than the S2AI cohort (MD, 0.22; 95% CI, 0.07 to 0.37; p=0.004), with no significant heterogeneity among the included studies (I²=0%, p=0.41) (Fig. 4).

Fig. 4

Forest plot demonstrates the results of the analysis of the ambulatory status score. S2AI, sacral 2 alar-iliac screw; IS, iliac screw; SD, standard deviation; IV, inverse variance; CI, confidence interval; df, degree of freedom.

Screw prominence

Five studies had reported the incidence of screw prominence. The S2AI cohort showed a significantly lower incidence of screw prominence than the IS cohort (OR, 0.08; 95% CI, 0.02 to 0.26; p=0.001). There was no significant heterogeneity among the studies in this respect (I²=0%, p=0.5) (Fig. 5).

Fig. 5

Forest plot demonstrates the results of the analysis of screw prominence incidence. S2AI, sacral 2 alar-iliac screw; IS, iliac screw; M-H, Mantel-Haenszel; CI, confidence interval; df, degree of freedom.

Wound infection

Eight studies had reported the incidence of postoperative wound infection. The incidence of wound infection in the S2AI cohort was significantly lower than that in the IS cohort (OR, 0.24; 95% CI, 0.13 to 0.46; p=0.0001). There was significant heterogeneity among the included studies in this respect (I²=70%, p=0.002). The heterogeneity was addressed by performing subgroup analysis and sensitivity analysis. In the first subgroup, involving cases with a follow-up period of less than 2 years, the incidence of wound infection after using the S2AI screw was significantly lower compared to the IS (OR, 0.33; 95% CI, 0.14 to 0.79; p=0.01) (I²=75%, p=0.08). Exclusion of the Mazur 2015 study from this subgroup resolved the heterogeneity (OR, 0.10; 95% CI, 0.03 to 0.36; p=0.005) (I²=0%, p=0.79) (Fig. 6B). Similar results were observed in the second subgroup involving a follow-up period exceeding 2 years (OR, 0.17; 95% CI, 0.06 to 0.46; p=0.006) (I²=75%, p=0.08) (Fig. 6A). Exclusion of the Luo 2021 study from this subgroup resolved the heterogeneity (OR, 0.05; 95% CI, 0.01 to 0.21; p=0.001) (I²=0%, p=0.39) (Fig. 6B).

Fig. 6

(A, B) Forest plot demonstrates the results of the analysis of wound infection incidence. S2AI, sacral 2 alar-iliac screw; IS, iliac screw; M-H, Mantel-Haenszel; CI, confidence interval; df, degree of freedom. (Continued on next page.)

Wound dehiscence

Six included studies had reported the incidence of postoperative wound dehiscence. The incidence of wound dehiscence in the S2AI cohort was significantly lower than that in the IS cohort (OR, 0.14; 95% CI, 0.06 to 0.34; p=0.0001). There was no significant heterogeneity among the included studies in this respect (I²=42%, p=0.12) (Fig. 7).

Fig. 7

Forest plot demonstrates the results of the analysis of wound dehiscence incidence. S2AI, sacral 2 alar-iliac screw; IS, iliac screw; M-H, Mantel-Haenszel; CI, confidence interval; df, degree of freedom.

Revision surgery

Eight studies (n=1,341) had reported the incidence of revision surgery. Pooled analysis revealed a significantly lower incidence of revision surgeries in the S2AI cohort compared to the IS cohort (OR, 0.32; 95% CI, 0.21 to 0.48; p=0.0001). There was no significant heterogeneity among the included studies in this respect (I²=29%, p=0.19) (Fig. 8).

Fig. 8

Forest plot demonstrates the results of the analysis of revision surgery incidence. S2AI, sacral 2 alar-iliac screw; IS, iliac screw; M-H, Mantel-Haenszel; CI, confidence interval; df, degree of freedom.

Sagittal vertical axis (mm)

Four studies (n=329) had reported SVA. Pooled analysis revealed no significant difference between the two cohorts in this respect (MD, 1.49; 95% CI, −0.97 to 3.94; p=0.23), with no significant heterogeneity (I²=9%, p=0.35) (Fig. 9).

Fig. 9

Forest plot illustrates the results of the analysis of sagittal vertical axis outcome. S2AI, sacral 2 alar-iliac screw; IS, iliac screw; SD, standard deviation; IV, inverse variance; CI, confidence interval; df, degree of freedom.

VAS score for pain

The analysis of 449 patients from six studies revealed similar VAS scores in the S2AI and IS cohorts, with no significant difference (MD, 0.01; 95% CI, −0.31 to 0.33; p=0.94). There was no significant heterogeneity among the included studies in this respect (I²=45%, p=0.11) (Fig. 10).

Fig. 10

Forest plot illustrates the results of the analysis of the Visual Analog Scale score outcome. S2AI, sacral 2 alar-iliac screw; IS, iliac screw; SD, standard deviation; IV, inverse variance; CI, confidence interval; df, degree of freedom.

Postoperative ODI (%)

There was no significant difference between S2AI and IS cohorts regarding the postoperative ODI (MD, 0.14; 95% CI, −1.20 to 1.47; p=0.84). There was no significant heterogeneity among the included studies (I²=49%, p=0.12) (Fig. 11).

Fig. 11

Forest plot illustrates the results of the analysis of the postoperative Oswestry Disability Index. S2AI, sacral 2 alar-iliac screw; IS, iliac screw; SD, standard deviation; IV, inverse variance; CI, confidence interval; df, degree of freedom.

Implant failure

The analysis of 1,263 patients from 12 studies revealed no significant difference between the S2AI and IS cohorts regarding the incidence of implant failure (OR, 0.74; 95% CI, 0.45 to 1.22; p=0.23). To resolve the heterogeneity (I²=49%, p=0.03), subgroup analysis was performed based on the duration of follow-up. In the first subgroup, involving cases with a follow-up period of less than 2 years, there was no significant difference between the two cohorts (OR, 0.58; 95% CI, 0.31 to 1.07; p=0.08) (I²=39%, p=0.12). Similar results were obtained in the second group, where the follow-up period exceeded 2 years (OR, 1.11; 95% CI, 0.52 to 2.38; p=0.79) (I²=44%, p=0.15) (Fig. 12).

Fig. 12

Forest plot illustrates the results of the analysis of implant failure. S2AI, sacral 2 alar-iliac screw; IS, iliac screw; M-H, Mantel-Haenszel; CI, confidence interval; df, degree of freedom.

Publication bias

The funnel plot revealed moderate asymmetry, indicating an uneven distribution of studies around the vertical line (OR, 1), particularly for those with longer follow-up periods. This asymmetry may suggest potential publication bias, but other factors, such as heterogeneity, small-study effects, or methodological differences, could also contribute to the observed pattern. Notably, smaller studies (higher standard error) appeared more scattered, while larger studies clustered near the overall effect size. Due to the limited number of studies (fewer than 10), formal tests for publication bias lacked sufficient power, and the interpretation of this plot should be approached with caution. Therefore, while publication bias cannot be ruled out, the observed asymmetry is likely multifactorial (Supplement 2).

Pelvic tilt

There was no significant difference between the two cohorts regarding the incidence of pelvic tilt (MD, −0.44; 95% CI, −2.33 to 1.45; p=0.65). No significant heterogeneity was observed among the included studies in this respect (I²=0%, p=0.69) (Fig. 13).

Fig. 13

Forest plot illustrates the results of the analysis of pelvic tilt. S2AI, sacral 2 alar-iliac screw; IS, iliac screw; SD, standard deviation; IV, inverse variance; CI, confidence interval; df, degree of freedom.

Sacral slope

Both cohorts showed similar results regarding the incidence of sacral slope, with no significant difference (MD, −0.82; 95% CI, −2.98 to 1.34; p=0.46). There was no significant heterogeneity among the included studies in this respect (I²=37%, p=0.19) (Fig. 14).

Fig. 14

Forest plot illustrates the results of the analysis of the sacral slope. S2AI, sacral 2 alar-iliac screw; IS, iliac screw; SD, standard deviation; IV, inverse variance; CI, confidence interval; df, degree of freedom.

Lumbar lordosis

The incidence of lumbar lordosis was comparable in the two cohorts (MD, −0.19; 95% CI, −2.96 to 2.58; p=0.89), with no significant heterogeneity among the included studies (I²=0%, p=0.46) (Fig. 15).

Fig. 15

Forest plot shows the results of the analysis of lumbar lordosis. S2AI, sacral 2 alar-iliac screw; IS, iliac screw; SD, standard deviation; IV, inverse variance; CI, confidence interval; df, degree of freedom.

Pelvic incidence

The pelvic incidence in the S2AI cohort was similar to that in the IS cohort, with no significant differences (MD, −0.38; 95% CI, −3.00 to 2.24; p=0.78). There was no significant heterogeneity among the included studies in this respect (I²=0%, p=0.65) (Fig. 16).

Fig. 16

Forest plot shows the results of the analysis of pelvic incidence. S2AI, sacral 2 alar-iliac screw; IS, iliac screw; SD, standard deviation; IV, inverse variance; CI, confidence interval; df, degree of freedom.

Discussion

Surgical management of ASD is complex, involving various strategies aimed at correcting deformities, alleviating neurological deficits, and improving overall functional outcomes. Non-operative treatment options often have limited effectiveness, especially for patients presenting with clinical deformities, pain, or significant neurological impairments. The primary objectives of ASD surgery are to restore spinal alignment and optimize patient outcomes [33].

Our meta-analysis comparing S2AI screws and IS in spinopelvic fixation for ASD yielded notable results. While operation time was not significantly different between the two cohorts, the S2AI cohort demonstrated a clear advantage in terms of lower estimated blood loss, shorter hospital stays, and improved ambulatory status, with no significant heterogeneity among the included studies. Notably, the S2AI group had a significantly lower incidence of complications, such as screw prominence, wound infection, and wound dehiscence, as well as a reduced need for revision surgeries (OR, 0.32; p=0.0001), further supporting its favorable safety profile. The most important advantage of S2AI screws over iliac screws is that S2AI screws have a more medial and deeper trajectory that reduces soft tissue irritation and prominence on the skin, a common issue with iliac screws. This lower profile decreases postoperative discomfort and hardware-related complications, thus minimizing the need for revision surgeries. Additionally, the IS approach requires a larger skin incision and more extensive soft tissue dissection, increasing the risk of wound dehiscence and surgical site infection (SSI). This less invasive approach is particularly beneficial in patients with complex spinal deformities and/or those requiring long length fixation. However, data also indicates that patients receiving S2AI screws have a greater rate of ambulation (postoperative) owing to improved biomechanical stability and reduced incidence of screw prominence and infection. S2AI screws provide a more direct and stable lumbosacral fixation, thereby reducing mechanical stress at the lumbopelvic junction and facilitating early return to mobility. This improved stability enhances functional outcomes and quality of life compared to IS fixation [8,11]. Conversely, no significant differences were observed between the S2AI and IS cohorts regarding SVA, VAS scores, postoperative ODI, implant failure, pelvic tilt, sacral slope, lumbar lordosis, and pelvic incidence, with no significant heterogeneity among the included studies.

A previous meta-analysis by Shin et al. [34] in 2023 involving 1,931 patients found that S2AI screws demonstrated significantly better performance in several key aspects compared to IS. They found no significant difference in implant failure rates between IS and S2AI (21.9% vs. 18.9%, respectively), which was similar to our finding (20% vs. 25%, respectively). However, the IS group experienced notably higher rates of revision surgeries (21.0% vs. 8.5%), screw prominence (9.6% vs. 0.0%), and wound complications (31.7% vs. 3.9%) compared to the S2AI group.

Our results are consistent with a previous meta-analysis by De la Garza Ramos et al. [8] comparing IS and S2AI screw fixation in adult patients. Their analysis of five retrospective cohort studies, including 323 adult patients, found that S2AI screw fixation was associated with significantly lower rates of mechanical failure and complications compared to IS fixation. Specifically, the revision surgery rate due to mechanical failure or wound complications was 27.9% in the IS group compared to 14.2% in the S2AI group, reflecting an absolute risk reduction (ARR) of 13.7% (p<0.001). Additionally, the incidence of wound infections was markedly lower in the S2AI group (2.6%) compared to the IS group (25.4%), with an ARR of 22.8% (p<0.001).

A retrospective cohort review of a multicenter database conducted by Eastlack et al. [15] found an overall lumbopelvic fixation failure rate of 23.74%. The study revealed that S2AI screws had a higher likelihood of pelvic fixation (13.4%) and S1 screw (2.9%) loosening compared to IS, with statistically significant (OR, 2.63; p=0.001; OR, 6.05; p=0.022). However, the rates of pelvic screw (2.3%) and rod fracture (14.1%) were similar between the groups, with a trend toward fewer occurrences with S2AI screws (OR, 0.47; p=0.06). The overall revision surgery rate was 22.7%, with 8.5% specifically for iliac fixation, but there were no significant differences between the fixation types (p=0.55 and p=0.365).

A study comparing postoperative complications between S2AI and IS groups found that the S2AI group had significantly lower rates of reoperation (8.8% vs. 48.0%), SSI (1.5% vs. 44.0%), wound dehiscence (1.5% vs. 36.0%), and symptomatic screw prominence (0.0% vs. 12.0%). Both techniques achieved significant pain relief and functional recovery, with no significant between-group differences. Multivariate analysis revealed that S2AI instrumentation was protective against reoperation (OR, 0.08; p<0.001) and SSI (OR, 0.09; p<0.001), while diabetes mellitus and preoperative tumor diagnosis increased the risk of SSI. These findings are consistent with our results, which showed that S2AI was associated with lower incidence of reoperation (6.1% vs. 14.7%), SSI (3.3% vs. 13.2%), wound dehiscence (2.4% vs. 13.4%), and symptomatic screw prominence (0.5% vs. 15.7%) [26].

Another retrospective cohort study comparing S2AI screws and IS for spinal deformity correction found that the S2AI technique was associated with a significantly lower reoperation rate (21.7% vs. 58.8%, p=0.01) and a longer time to reoperation compared to the IS technique [11]. While the incidence of proximal junctional kyphosis (PJK) was similar between the two groups (32.6% vs. 35.3%, p>0.99), the time to reoperation due to PJK trended toward being longer in the S2AI group (p=0.08). The S2AI group also showed a significantly greater change in pelvic incidence compared to the IS group (p=0.001). However, our analysis found similar rates of pelvic incidence in the two groups (MD, −0.38; 95% CI, −3.00 to 2.24; p=0.78), which differed from the study’s findings.

Another study involving 60 patients who underwent lumbosacropelvic fixation found that the use of S2AI screws was associated with a significantly lower incidence of complications compared to IS [29]. The S2AI group exhibited lower rates of reoperation (18.6% vs. 47.4%, p=0.02), SSI (2.3% vs. 29.4%, p=0.006), wound dehiscence (2.3% vs. 29.4%, p=0.006), and postoperative anemia (7.0% vs. 29.4%, p=0.03). The S2AI group also had a lower estimated blood loss (1,846.4 mL vs. 2,721.2 mL, p=0.02) and required fewer red blood cell transfusions (4.7 units vs. 7.2 units, p=0.04). While rates of L5–S1 pseudarthrosis and other cardiorespiratory complications were comparable between the groups, multivariate analysis identified S2AI screws, operative time, and BMI as independent predictors of estimated blood loss. The findings suggest that S2AI screws offer a safer profile for elderly patients, characterized by fewer complications and reduced blood loss, making them a viable alternative to IS in this demographic.

A study compared the outcomes of lumbosacral instrumentation using S2AI and IS screws in 60 patients (mean follow-up: 2.5 years). The results showed that screw loosening (SL) was significantly less common in the S2AI group (16.7%) compared to the S2A (55.0%) and I (27.3%) groups (p=0.03) [30]. Additionally, SIJ pain improvement was notably higher in the S2AI group at both 3 months and maximum follow-up, with 61.1% of patients showing improvement compared to 25.0% in the S2A group and 22.7% in the I group (p=0.02). Despite no significant differences between the groups regarding bone mineral density and the number of operated segments, and more frequent use of cages in the S2A group (p=0.04), the S2AI technique demonstrated greater reduction in caudal SL and SIJ pain. These findings suggest that S2AI screws are a preferable option over S2A and I screws, even for shorter or mid-length lumbar constructs [29].

Arslan et al. [19] found significant postoperative improvements in radiographic parameters, including SVA, sacral slope, pelvic tilt, and lumbar lordosis, for both S2AI and IS techniques. However, no significant differences were observed between the two methods, with p-values ranging from 0.117 to 0.696, which is consistent with our findings (p-values ranged from 0.2 to 0.8). The study also found significant improvement in ODI in all patients, with no significant difference between the S2AI and IS groups (p=0.522), which is also consistent with our results. The overall complication rate was 32.1%, with no significant difference between the S2AI (24.1%) and IS (40.7%) groups.

Yu et al. [24] assessed the feasibility and clinical outcomes of S2AI and IS techniques in lumbopelvic reconstruction for patients with lumbosacral tuberculosis. The retrospective study included 26 patients, with 16 in the S2AI group and 10 in the IS group. The study found significantly shorter operation times in the S2AI group, which differs from our findings of similar operation times between the two groups. However, similar to our study, they found less intraoperative blood loss in the S2AI group compared to the IS group (p<0.05). Both groups showed significant postoperative improvements in erythrocyte sedimentation rate, C-reactive protein levels, ODI, VAS scores, ambulatory status, and quality of life (36-Item Short Form Health Survey scores) (p<0.05), with no significant difference in the degree of remission between them. Additionally, the S2AI group had a significantly lower rate of symptomatic screw prominence (p<0.05) compared to the IS group.

Some limitations of this meta-analysis should be considered while interpreting the results. A key limitation is the significant heterogeneity observed in some outcomes, which may stem from differences in patient populations and surgical techniques across the included studies. However, we were able to address the heterogeneity through subgroup and sensitivity analyses. Another limitation is that many of the included studies were retrospective, which introduces selection bias and limits the ability to establish causal relationships. The reliance on retrospective data may also lead to inconsistencies in the reporting of outcomes, contributing to the observed heterogeneity. Furthermore, the meta-analysis did not adequately address the long-term outcomes of S2AI and IS fixation techniques, including degenerative changes and quality of life, due to the limited follow-up periods in the included studies. Further research with extended follow-up durations is necessary to enable a comprehensive evaluation of the long-term sustainability and complications associated with these techniques.

Conclusions

This meta-analysis compared the S2AI and IS techniques in adult spinal deformity and found that they have similar operation times. However, the S2AI technique demonstrated significant benefits, including reduced blood loss, shorter hospital stays, and lower rates of complications such as screw prominence and wound infections. Additionally, S2AI was associated with improved postoperative ambulatory status. Despite these advantages, both techniques yielded comparable results in terms of overall radiographic parameters and other clinical outcomes. However, the study highlights the need for further prospective research owing to heterogeneity and the retrospective design of the included studies.

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