Abstract

BackgroundAdult spinal deformity (ASD) surgeries often face complications, such as pseudoarthrosis and rod fractures (RFs), particularly at the lumbosacral junction. While transforaminal lumbosacral interbody fusion (TLIF) at L5-S1 is thought to improve outcomes, its efficacy in major ASD surgeries remains unclear. This study aims to compare clinical and radiological outcomes and implant complications in patients undergoing spinopelvic fixation with or without L5-S1 TLIF.

MethodsA retrospective cohort study was conducted, including 157 ASD patients who underwent high-grade osteotomies and spinopelvic fixation from 2021 to 2024. Patients were divided into two groups: those with L5-S1 TLIF (C group, n = 71) and those without (NC group, n = 86). Outcomes included rod fracture (RF) rate, sagittal alignment, and patient-reported measures such as the Visual Analog Scale (VAS), Oswestry disability index (ODI), and 36-Item Short Form Survey (SF-36), assessed at baseline, 1, 6, and 12 months postoperatively.

ResultsRFs were significantly lower in the C group (4% vs. 13%, P = 0.03). Improved postoperative sagittal vertical axis and pelvic tilt were noted in the C group (P P

ConclusionThe use of L5-S1 TLIF reduces RF rates, improves sagittal alignment, and clinical outcomes in ASD surgery. Incorporating TLIF at L5-S1 may optimize outcomes without increasing perioperative risks.

Keywords: Cage, Interbody fusion, Nonunion, Pseudoarthrosis, Rod fracture, Sagittal

INTRODUCTION

A significant portion of the financial burden of adult spine deformity surgery comes from its complications. Of these complications, the incidence of rod fractures (RFs) in the lower lumbar spine, particularly at the LS junction (L4–S1), is considerable among adult spinal deformity (ASD) patients.[ 3 , 6 ] Incorporating sacro-pelvic fixation techniques with iliac screws and S2 alar iliac (S2AI) screws has been demonstrated to safeguard the S1 screws and enhance fusion rates in lengthy constructs.[ 3 ] Previous studies have shown that anterior approach minimally invasive L5/S1 interbody fusion in ASD patients improves clinical outcomes and reduces the implant failure rate.[ 7 ] In this study, we compared patients with ASD who underwent spinopelvic fixation and high-grade lumbar spinal osteotomies, with or without L5/S1 TLIF.

MATERIALS AND METHODS

Study setting and data source

Following Institutional Review Board approval, we retrospectively analyzed ASD patients who underwent high-grade lumbar osteotomy with spinopelvic fusion with or without accompanying L5-S1 transforaminal lumbosacral interbody fusion (TLIF), performed by the senior author (MR) between 2021 and 2024. Demographic, clinical, and surgical data were obtained from the medical records/operative database (i.e., The Yas Spine Center of Excellence Registry Group [YAS-SCORG]).

Study design, grouping, and data extraction method

This retrospective study utilized the YAS-SCORG registry database for analyzing 538 Adult Deformity patients undergoing spinopelvic fusion and lumbar osteotomy in 2021 and 2024 [ Figure 1 ]. Using multiple inclusion and exclusion criteria [ Table 1 ], we identified 157 patients; 86 had bilateral S2AI without a cage (the No Cage [NC] group or NC Group) versus 71 receiving bilateral S2AI plus L5-S1 interbody cages (the Cage group or C group). Patients in both groups averaged 60.5 years of age, and there were no significant differences between groups regarding baseline demographics, radiographic parameters [ Table 2 and Figure 1 ].

Figure 1:

Study design and data collection of the study.

Table 1:

Inclusion and exclusion criteria for the study.

Table 2:

Baseline characteristics of patients included in the study.

Surgical procedures

All surgeries were performed by the same surgeon and involved Grade 3 or 4 osteotomies in the lumbar spine. The four-rod technique (satellite rod) was used at the osteotomy level.[ 4 ] Two 6.2 mm diameter chromium-cobalt rods were attached to the upper instrumented vertebra and bilateral S2AI screws, spanning the vertebrae except those directly adjacent to the osteotomy. No interbody cage was used in the NC group of patients treated from 2021 to 2023 [ Figure 2 ]. In contrast, the cage (C) group from 2023 to 2024 underwent an L5-S1 discectomy, during which an autologous bone-filled polyether ether ketone (PEEK) interbody cage was placed through open TLIF [ Figure 2 ]. The cage size was determined intraoperatively after clearing the disc space, and the largest fitting cage was positioned with intraoperative imaging confirmation. If the surgery lasted over 6–8 h or blood loss exceeded 2000 cc, a temporary rod was placed on both sides, and the procedure was paused after consulting the anesthesiologist. The second stage, involving osteotomy completion and final rod fixation, was delayed by 4–6 days.

Figure 2:

Schematic illustration shows the surgical procedure. (a) Demonstrates the Cage Group (there is a rectangular L5-S1 cage and satellite rod between the L3 and L5), (b) Demonstrates the no-cage group (there is no cage in L5-S1 space, there is a satellite rod between L3 and L5).

Statistical analyses

Statistical analyses were conducted using IBM Statistical Package for the Social Sciences version 26.0. The Kolmogorov–Smirnov test assessed normal distribution, and continuous variables were reported as means (standard deviation). Parametric tests, including Chi-square and independent sample t-tests, compared outcomes between groups. A two-sided P < 0.05 was deemed significant, with results visually represented using GraphPad Prism.

RESULTS

Surgical data assessment

Table 3 shows that a greater percentage of patients in the C group underwent single-stage surgeries compared to the NC group (C: 73% vs. NC: 47%; P = 0.03). In addition, the interval between stages for two-stage surgeries was longer in the C group (C: 5.5 ± 1.1 days vs. NC: 4.1 ± 1.6 days; P < 0.01).

Table 3:

Surgical data of patients who underwent grade 3 or 4 osteotomy.

Postoperative complication profile

The complication profiles of both groups showed no significant differences in reoperation, proximal junctional kyphosis, incidental durotomy, surgical site infection, sepsis, or deep vein thrombosis. However, the C group had a significantly lower RF rate of 4% compared to the NC group’s 13%, with an odds ratio of 0.27 [ Table 4 ].

Table 4:

Complication profile of patients who underwent grade 3 or 4 lumbar osteotomies with or without L5-S1 cage.

Radiological outcome

Table 5 shows no significant differences in baseline preoperative radiological parameters between the two groups. Postoperatively, lumbar lordosis and thoracic kyphosis were similar, but the pelvic tilt was significantly lower in the C group (C: 12.9 ± 5.6 vs. NC: 17.7 ± 5.0). The final sagittal vertical axis was also lower in the C group (C: 44.1 ± 18.4 vs. NC: 59.3 ± 13.3).

Table 5:

Radiological outcomes of patients who underwent grade 3 or 4 osteotomies with or without L5-S1 cage insertion.

Clinical outcomes

Table 6 and Figure 3 show the patient-reported outcomes of the study. The Visual Analog Scale (VAS) scores were similar at baseline and 1 month postsurgery but significantly lower in the C group at the 6-month and 12-month follow-ups. The Oswestry Disability Index (ODI) and SF-36 demonstrated similar trends, with no significant differences initially but improved scores in the C group at later follow-ups.

Table 6:

Comparison of outcome measurements between the groups.

Figure 3:

Diagram illustrating the patient-reported outcome measures of cage and no-cage groups. (VAS: Visual Analog Scale, ODI: Oswestry disability index, Quality of life [SF-36]).

DISCUSSION

Table 7 summarizes the characteristics and results of the study and we will discuss our findings in the following part. Table 8 summarizes the studies included in discussion with results and design.

Table 7:

Comprehensive summary of clinical and radiological outcomes, highlighting the effects of L5-S1 TLIF on rod fracture rates, sagittal alignment, and patient-reported measures.

Table 8:

Summary of references with study design and results.

RF is reduced by L5-S1 interbody fusion

The rate of RF after ASD, based on the surgical approach and constructs used in different studies, varies widely in reports, ranging from 15% to 40%.[ 2 , 6 , 9 ] We found a reduced RF rate of 9.5% in our study. This may be attributed to (1) using cobalt-chromium rods that exhibit superior strength/fatigue resistance and reduced susceptibility to fracture versus Ti rods, (2) using satellite rods around the osteotomy level [ Figure 4 ],[ 10 ], (3) improved anterior column supports and better load sharing,[ 5 ] (4) decreased L5-S1 pseudoarthrosis by providing a circumferential fusion,[ 8 ] and (5) better spinopelvic alignment: Sardi et al.[ 9 ] have demonstrated a correlation between postoperative PT and the risk of RF.

Figure 4:

The rod fracture rate in the cage group is significantly lower than in the no-cage group.

Impact of the L5-S1 interbody cage on sagittal alignment parameters

We demonstrated that L5-S1 IF led to improved spinopelvic alignment in our study, in which we showed more significant improvement in PT and a more corrected postoperative SVA. However, Cho et al.[ 1 ] found no such significant difference in sagittal alignment correction when using different lordotic cages at L5-S1.

Clinical and patient-reported outcome measures

In Figure 3 , the results show no significant difference in patient-reported outcomes (PROs) between the baseline and the 1^st month of follow-up. However, at the 6 and 12-month follow-ups, patients with L5-S1 cage had significantly better outcomes (lower ODI, lower VAS, higher SF-36). This is likely due to L5S1 TLIF restoration of intervertebral space providing indirect decompression and decreased RF rate.[ 6 ]

Limitations

Our study’s retrospective design poses limitations. Open TLIF complications include nonunion, cage subsidence, and exiting nerve root injury, but we did not record this data. We also did not collect information on RFs’ unilateral or bilateral nature, their locations, or the need for reoperation due to these fractures.

CONCLUSION

In adult deformity surgery patients with high-grade lumbar osteotomy and long segment constructs with spinopelvic fusion, using interbody fusion in L5-S1 by open TLIF with rectangular PEEK cage reduces the RF rate, improves sagittal alignment results, and enhances PROs in terms of VAS, ODI, and SF-36.

Data and material availability

The article includes all the data regarding the presented case.

Ethical approval

The research/study was approved by the Institutional Review Board at Imam Khomeini Hospital Complex, number IR.TUMS.IKHC.REC.1403.046, dated 2024.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent.

Financial support and sponsorship

Publication of this article was made possible by the James I. and Carolyn R. Ausman Educational Foundation.

Conflicts of interest

There are no conflicts of interest.

Use of artificial intelligence (AI)-assisted technology for manuscript preparation

The authors confirm that there was no use of artificial intelligence (AI)-assisted technology for assisting in the writing or editing of the manuscript and no images were manipulated using AI.

Disclaimer

The views and opinions expressed in this article are those of the authors and do not necessarily reflect the official policy or position of the Journal or its management. The information contained in this article should not be considered to be medical advice; patients should consult their own physicians for advice as to their specific medical needs.

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