ANTERIOR LUMBAR INTERBODY FUSION (ALIF): EPIDEMIOLOGICAL AND RADIOLOGICAL PROFILE

ABSTRACT Objective: Evaluate the epidemiological and radiographic data of patients submitted to the Anterior Lumbar Interbody Fusion (ALIF) technique and the possible complications related to this procedure. Methods: A longitudinal and retrospective study was carried out to analyze electronic medical records and image files of patients who underwent spinal surgery using the ALIF technique between February 2019 and January 2021. Epidemiological data such as age, gender, and level of surgery were analyzed. Radiographic evaluations of lumbar lordosis from L1 to S1 were performed using the COBB technique and the anterior and posterior height of the disc space. The presence of intraoperative and postoperative complications in the patients was analyzed. Results: Initially, 70 patients were analyzed. The most prevalent operated level was L5-S1. The length of stay of the patients varied between 36 and 72 hours. Intraoperative bleeding ranged from 20mL to 400mL. Three patients had significant venous lesions. Differences between anterior and posterior lordosis and height measurements were significant (p < 0.001). Lordosis had a mean increase of 10.3°, anterior height had a mean increase of 7.9mm, and posterior height of 4.0mm. Six cases of intra and postoperative complications were observed. Conclusion: The patients showed improvement in the radiological parameters of the anterior and posterior height of the vertebral discs, with a significant increase in lumbar lordosis. Complication rates were 9.8%, and we had a short hospital stay. Level of Evidence II; Retrospective Longitudinal Study.


INTRODUCTION
The demand for medical treatment related to degenerative diseases of the spine has grown in recent years, mainly due to increased life expectancy.The main cause of low back pain is intervertebral disc degeneration (IVDD), leading to foraminal and spinal canal stenosis. 1It is currently estimated that 53% of the economically active Brazilian population will suffer from low back pain at some point in their lives, and 33% will have associated sciatica, affecting their physical, functional, and emotional capacity. 2 Conservative treatment is the gold standard for DDD; however, in cases where this is ineffective, lumbar fusion plays an important role in treating low back pain and sciatica, especially when associated with vertebral instability. 1,3In this context, a technique that has become common among spine surgeons is anterior lumbar arthrodesis (ALIF).Some current studies demonstrate that ALIF is an effective treatment for DDD with or without radiculopathy, including pathologies with instability such as spondylolisthesis, 4 with significant improvement in clinical-functional scores. 5ompared to other surgical approaches, the ALIF technique allows superior restoration of normal anatomy, including foraminal area, anterior disc height, lumbar lordosis, and sagittal balance. 6,7Unlike posterior approaches, which involve extensive muscle dissection, the ALIF technique does not interfere with any spinal muscles and does not include muscle detachments. 5,8Some studies have shown advantages of this technique over traditional approaches, including shorter surgical and hospital stays, less postoperative pain, and low risk of complications in general. 9However, the anterior approach to the spine has some risks of specific complications: vascular injuries (arterial and venous), visceral injuries, and [10][11][12] sexual and sympathetic plexus dysfunction.The joint approach with an access surgeon, commonly a general or vascular surgeon, has become routine in major referral centers for spine surgery.This teamwork provides greater safety to the procedure, justifying the low complication rates. 9iven the increasing use of this technique, we designed a study aiming to evaluate the epidemiologic and radiographic data of patients undergoing the ALIF technique and assess the possible complications related to this procedure.

MATERIALS AND METHODS
This is a longitudinal, retrospective study conducted in a tertiary hospital, a reference in spinal surgery.After approval by the Research Ethics Committee (CAAE: 58184222.2.0000.5225), a search was performed of the electronic medical records and image files of patients undergoing spinal surgery using the ALIF technique, with Cages of 10, 12, and 15 degrees of lordosis and blocked with transcage screws (Nuvasive®), between February 2019 and January 2021.
The procedures were performed by six spine surgeons, members of the Brazilian Spine Society, experienced in the technique, and three access surgeons.The orthopedic and access surgeons were not the same in all surgeries.
Patients aged 18-100 years with degenerative spinal diseases and who underwent surgical treatment using the ALIF technique were included in the study.When there were signs of instability, as in spondylolisthesis, only low-grade (grade 1 or 2) were included.Only cases operated alone, i.e., without subsequent supplementation with pedicle screws, were selected.(Figure 1) Exclusion criteria were high-grade spondylolisthesis, age over 100 years or under 18 years, patients undergoing ALIF technique with posterior supplementation, patients diagnosed with primary or metastatic neoplasms, infection in previous spinal surgeries, those who did not agree to participate in this study and those with incomplete medical records.
Epidemiological data such as age, sex, and level of surgery (one or more levels) were analyzed.Radiographic assessments of the lumbar lordosis from L1 to S1 were performed using the COBB technique (Figure 2) and the anterior and posterior height of the disc space.All these measurements were compared with radiographic values measured preoperatively and on postoperative day 1.
The presence of intraoperative and postoperative complications such as bleeding (venous and arterial lesions), visceral lesion, paralytic ileus, surgical site infection, suture dehiscence, retrograde ejaculation/dry vagina, implant migration, implant breakage, and associated fractures were assessed through chart review.Intraoperative bleeding volume and length of stay were quantified.All these patients were followed up on an outpatient basis for at least 12 months postoperatively.
Quantitative variables were represented by mean and standard deviation, while absolute and relative frequencies represented qualitative variables.Comparisons of lordosis and anterior and posterior height values between pre-and postoperative times were made using Student's t-test for paired samples.Pearson's correlation coefficient calculated correlations between measures.All analyses were performed in R statistical computing software using the 5% significance level.

RESULTS
A total of 70 patients treated surgically with the ALIF stand-alone technique (Figure 3) from February 2019 to January 2021 were initially analyzed.Still, nine did not present complete medical records and were excluded, totaling 61 patients in this study.The mean age of the patients was 51.8 years (31-84 years), with 35 women and 26 men (Table 1).The most prevalent operated level was L5S1 (85.25%).(Table 1) The length of stay of patients ranged from 36 to 72 hours, and those who presented intraoperative vascular complications stayed longer (72 hours).Intraoperative bleeding ranged from 20mL to 400mL, averaging 53mL per patient.Three patients had significant venous lesions, all in the left iliac vein at the L4-L5 level, with intraoperative bleeding controlled with compression of the vessel and using sterile absorbable gelatin hemostatic sponge.These patients had the highest recorded bleeding, 400ml, 340ml, and 240ml, respectively.No patient presented hemodynamic instability in the transoperative period and did not need a blood transfusion.
The differences between pre-and postoperative measurements of anterior and posterior lordosis and height were all significant (p < 0.001) (Table 2).The lordosis had a mean increase of 10.3°, the anterior height had a mean increase of 7.9mm, and the posterior height of 4.0mm (Table 2).Patients with higher preoperative lordosis measurements had higher postoperative anterior and posterior disc height measurements.(Table 2) The correlations of postoperative lordosis with postoperative anterior and posterior intervertebral disc height and lordosis variation with pre-and postoperative anterior and posterior height variation were not significant (Table 3).This means that individuals who showed greater variation in lordosis in the pre-and postoperative comparison did not necessarily show a greater increase in anterior and posterior height postoperatively.
In addition to the three vascular complications, we had 01 case of retrograde ejaculation -without resolution during the follow-up period, 01 urinary retention -which showed improvement on the 2nd day of hospitalization, 01 superficial infection of the surgical site -treated with oral antibiotics and without clinical repercussion (Table 1).No patient had postoperative complications with serious clinical repercussions.No patient died.

DISCUSSION
Anterior lumbar interbody fusion is becoming increasingly prevalent in the surgical treatment of lumbar DDD. 13 The anterior approach to the spine allows resection of the degenerated disc, distracts and reshapes the disc space, restoring spinal disc height and lumbar lordosis. 3,14LIF is superior to other techniques, such as transforaminal lumbar interbody fusion (TLIF), in its ability to increase foraminal height and lumbar lordosis. 6,15Phan et al., in their meta-analysis study, revealed that ALIF may be a better approach for restoring foraminal height, local disc angle, and lumbar lordosis compared to other techniques. 15As in other studies found in the literature, 1,16 in the present study, an increase in anterior and posterior intervertebral  disc height and lumbar lordosis was observed after ALIF, demonstrating this technique's efficacy for restoring these parameters.
In contrast to posterior or posterolateral approaches, such as posterior lumbar interbody fusion/transforaminal fusion (PLIF/TLIF), ALIF restores disc height, allowing foraminal re-expansion and indirect spinal nerve decompression. 1 No patient in this study had postoperative neurological damage with indirect decompression, corroborating previously published papers in the literature. 1 Nanni FN et al., 17 in their study on radiographic evaluation of patients undergoing ALIF -observed increased segmental lordosis and reduced lumbar lordosis.This author believes that the antalgic kyphotization may have influenced these values in the radiograph caused by pain in the immediate postoperative period (PO), considering that the control radiographs were performed in the early PO. 17 In our study, an increase in lumbar lordosis and the anterior and posterior height of the intervertebral disc was observed after ALIF

CONTRIBUTIONS OF THE AUTHORS:
The manuscript was developed through the individual and significant contributions of each author.FSK contributed towards writing, data collection, literature review, intellectual concept, and research project design.ALS performed surgeries, conducted statistical analysis, provided intellectual input and reviewed the manuscript.ALK realized the surgeries, contributed intellectual input, and reviewed the manuscript.CSP, PGDS, and XSG each performed surgeries, provided reviews, and contributed to the intellectual concept of the manuscript.
was measured in the X-ray of the 1st PO day, showing no impairment in the improvement of these radiological parameters by the clinical status of the patient, a result also corroborated by other authors. 1,16,18istorically, ALIF has been associated with high rates of intraoperative complications due to the use of the transperitoneal route and implant-related adverse events, 19 but this route is now an exception.The evolution of implants and retractors has also contributed to the greater safety of the procedure.Complications related to the ALIF approach are distinct from those of posterior approaches to the lumbar spine and are predominantly related to visceral 9 and vascular injuries. 9,4,13In the present study, 9.8% of complications were observed -a result similar to that found in the literature 1,9,19 -this low rate must be related to the participation of access surgeons, which provides greater safety to the procedure.
The occurrence of vascular lesions in the literature varies from 1% to 40%, depending on the group and type of case treated, with a higher prevalence at the L4-L5 level. 19As in other studies, vascular lesions were the most common complications in this study, 1,13 being observed in only 4.9% of patients (all at the L4-L5 level).These findings are similar to other studies in the literature, 4,9,19,20 proving the low rate of these lesions.Despite the risk of life-threatening complications associated with the anterior abdominal retroperitoneal route, we believe that teamwork between the spine surgeon and the access surgeon has made the procedure safer, where experiences are shared, leading to lower complication rates.
Flouzat-Lachaniette et al. reported urinary symptoms as the most common, 21 which was not observed in the present study.In addition, ejaculatory disorders are a commonly cited complication 4,20 related to hypogastric plexus injury during surgical corridor access. 20One case of retrograde ejaculation was observed in our study, which did not show improvement in symptoms during the follow-up period.This patient was 52 years old with already established offspring.Particular attention should be paid to this risk when indicating the procedure in young adults interested in parenthood.No cases of dry vagina were observed, which may be biased by the omission of these symptoms by the women being assessed by the orthopedic physician.
As found in the literature, in the present study, patients submitted to the ALIF technique remained hospitalized for a short period, 4,9,12,19 and those hospitalized for a longer time presented complications. 9he main limitations of this study are the lack of assessment of clinical outcomes and the follow-up of only 12 months.However, this study begins a line of research in which patients will be followed up, and new results will be presented.
3][24] Thus, we believe that we will move towards expanding ALIF indications, an even greater increase in the procedure's safety with the experience acquired, and the continuous improvement of implants and instruments.

Figure 2 .
Figure 2. Reproducibility of the Cobb method in measuring L1-S1 lordosis Pre and Post-operative ALIF.

Figure 3 .
Figure 3. A: Anterior discectomy for Cage implantation; B: Implanted ALIF cage; anterior ALIF access under preoperative scar from cesarean section and evidence of implant used.

Table 1 .
Demographic and surgical variables.

Table 3 .
Variation in posterior height.