Single-position lateral anterior lumbar interbody fusion: anatomic considerations, workflow optimization, and technical nuances

Abstract

In recent years, the single-position combined anterior-posterior approach has emerged as an increasingly utilized technique in lumbar fusion surgery. The approach combining posterior pedicle screw fixation with anterior lumbar interbody fusion (ALIF) performed in the lateral decubitus position is referred to as the lateral ALIF. Compared to traditional approaches that involve flipping the patient mid-surgery or staging the surgery at multiple time points, single-position lateral ALIF has been associated with shorter operative times, reduced estimated blood loss (EBL), shorter hospital length of stay, and lower rates of postoperative ileus, while maintaining comparable rates of fusion, complications, and reoperation. The lateral position also facilitates access to the retroperitoneal space through gravitational displacement of the abdominal contents and can permit simultaneous anterior and posterior surgical exposure. However, safe and effective execution of this approach requires familiarity with the unique anatomic, vascular, and workflow considerations associated with lateral positioning. The purpose of this review is to describe the technical details of single-position lateral ALIF surgery, focusing on surgical anatomy, indications and patient selection, surgical technique, workflow optimization, integration of navigation technologies, and perioperative, radiographic, and clinical outcomes. Preoperative assessment of spinopelvic alignment, vascular anatomy, psoas morphology, and prior abdominal surgery is essential. Intraoperatively, coordinated positioning, simultaneous anterior and posterior exposure, and integration of fluoroscopy, navigation, or robotic assistance can facilitate efficient and accurate placement of instrumentation. Current evidence suggests that single-position lateral ALIF provides comparable radiographic and clinical outcomes to traditional dual-position approaches; however, existing studies are predominantly retrospective and heterogeneous, and long-term clinical outcomes remain incompletely characterized. This review provides a practical framework for surgeons seeking to incorporate single-position lateral ALIF into their practice.

Introduction

The combined anterior and posterior technique is a powerful tool in the spine surgeon’s approach to lumbar fusion. Anterior lumbar interbody fusion (ALIF) with posterior pedicle screw fixation allows for effective correction of lumbar lordosis (LL) and provides indirect decompression of neural foramina given the large cage footprint. Compared to posterolateral approaches, such as transforaminal lumbar interbody fusion (TLIF) with posterior fixation, ALIF with posterior fixation allows for greater improvement in segmental lordosis, greater improvement in disc height, and improved quality of life and pain at 1 year postoperatively (1), with comparable or better fusion rates (2,3). Combined anterior-posterior approaches, however, have higher costs and longer operative times compared to posterolateral approaches (4,5), largely because, traditionally, they require repositioning the patient from supine to prone during the case or performing the anterior-posterior components in 2 separate stages.

In recent years, single-position anterior-posterior techniques in the lateral decubitus position have been developed, obviating the need for flipping or multi-stage surgeries. The single-position approach, however, may be unfamiliar to many spine surgeons given its recent development, technical demands, and operative nuances. A comprehensive understanding of this approach requires integration of patient selection and anatomic considerations with surgical technique, workflow optimization, navigation technology, and the available outcomes literature.

The purpose of this review is to describe the technical details of single-position lateral ALIF surgery, with a focus on pertinent surgical anatomy, indications and patient selection criteria, surgical technique, workflow optimization and technical nuances, practical integration of navigation technology, and clinical and radiographic outcomes.

Anatomic and corridor considerations, indications, and preoperative planning

The ALIF approach is a powerful technique for interbody fusion and anterior column reconstruction. It uses an anterolateral surgical corridor to achieve a wide discectomy and place an interbody spacer with a large footprint and lordotic profile. These spacers allow for indirect decompression through disc height restoration and reduction of spondylolisthesis, restoration of LL, and greater arthrodesis.

Indications

The lateral ALIF is a single position modification of the traditional supine ALIF that allows concurrent access to the anterior, lateral, and posterior spinal elements without the need for repositioning for posterior column fusion (6-8). The lateral ALIF allows for anterior access to the L4–5 and L5–S1 disc spaces and can be combined with lateral access to additional spinal segments (L1–2, L2–3, L3–4, and/or L4–5). In this way, it preserves the strengths of the traditional ALIF, namely lower lumbar access, large-footprint interbody graft, improved arthrodesis, and restoration of sagittal alignment, with the added advantages of a single-position workflow.

Published series suggest that lateral ALIF maintains radiographic and alignment outcomes that are comparable to traditional supine ALIF (9), and similar safety profiles regarding vascular, abdominal, and neurological complications (3,7). In a multicenter retrospective comparative radiographic study, lateral and supine L5–S1 ALIF achieved similar improvements in disc height and slip reduction, with significantly greater improvement in segmental lordosis among patients treated with the lateral ALIF only at L5–S1 (9). By avoiding the ‘flip’, the lateral ALIF also enhances operative efficiency by reducing operative time, anesthetic load, blood loss, fluoroscopy, hospital length of stay, postoperative ileus, and minimizes risks associated with prone repositioning (7,10).

The indications for single position circumferential lumbar fusion include degenerative disc disease, spinal instability, spinal deformity, foraminal and mild central canal stenosis, low grade spondylolisthesis, adjacent segment disease, and pseudarthrosis (7,8). The lateral ALIF is used to treat lumbar disease requiring anterior and posterior column fusion at the L4–L5 and/or L5–S1 levels. Although this technique primarily targets one- or two-level disease, it can be incorporated into multilevel constructs from L1 to S1, when combined with lateral transpsoas or anterior-to-psoas [lateral lumbar interbody fusion (LLIF)] approaches (3,7).

The lateral ALIF has important limitations. It is less suitable for cases where significant posterior-based decompression is required, when revision posterior instrumentation is anticipated, or when indirect decompression is not sufficient. In a multicenter study of 178 consecutive patients undergoing lateral single-position surgery (SPS) from L4 to S1, Thomas et al. (11) reported a low overall failure rate (1.7%) of indirect decompression requiring reoperation. These findings support its use in appropriately selected patients, while cautioning its use in patients at higher risk of failure, including those with multilevel disease, severe central canal stenosis, facet cysts, severe facet arthropathy or ankylosis, free herniated disc fragments, and rigid deformities. In addition, complicated vascular anatomy or severe retroperitoneal scarring may narrow the working corridor and reduce the margin for safe vessel mobilization; in these cases, a supine ALIF or posterior-only approach may be preferable.

Patient selection and preoperative planning

Achieving optimal outcomes and minimizing intraoperative complications in lateral ALIF surgery requires meticulous patient selection and preoperative planning. Buckland et al. (8) proposed a practical framework for lateral decubitus SPS based on a preoperative assessment of patient history, physical findings, and detailed imaging review.

A careful history and physical examination establish operative indications and identify risk factors for complicated exposure. Prior abdominal operations, including vascular or endovascular procedures, gastrointestinal surgery, and genitourinary surgery, may result in retroperitoneal scarring that increases the difficulty of vascular mobilization. Likewise, a history of malignancy with radiation therapy to the abdomen or pelvis predisposes to intra-abdominal fibrosis and adhesions (8,12). Prior active or chronic discitis or posterior interbody fusion, particularly with bone morphogenic protein (BMP), may cause peridiscal inflammation and scarring. Young male patients should also be counseled on the ~2% risk of retrograde ejaculation due to injury to the superior hypogastric plexus during anterior exposure at L5–S1, which may impact fertility (13,14).

Obesity

Lumbar interbody fusion surgery is associated with higher complication rates in obese patients compared to non-obese patients, with up to a 2.5-fold increase in wound and major medical complications (15). Obesity presents several technical challenges, including limited disc space exposure, more difficult vessel mobilization, suboptimal visualization and illumination, and the need for specialized retractors and longer instruments for adequate dissection and disc preparation. Despite these challenges, the lateral ALIF offers distinct advantages in this population. In the lateral decubitus position, gravity facilitates anterior and inferior displacement of the abdominal contents, peritoneum, and iliac vessels away from the spine, thereby improving access to the retroperitoneal space (16,17). This gravitational effect can enhance visualization and retroperitoneal exposure compared to traditional supine ALIF (8,16,18). Clinical data support the feasibility of this approach in obese patients. Malham et al. (19) reported their experience using a lateral, mini-open, muscle-splitting approach for L5–S1 ALIF in patients with body mass index (BMI) >30 kg/m², demonstrating satisfactory clinical outcomes, acceptable complication rates, and radiographic fusion rates approaching 87% at 35 months.

Spinopelvic parameters, bony and soft tissue anatomy

A comprehensive imaging review is essential to evaluate spinopelvic alignment, bony and soft tissue anatomy, transitional lumbosacral anatomy, and vascular variations. Standing anteroposterior and lateral lumbar radiographs are used to assess pelvic incidence (PI) and sacral slope (SS). Patients with high PI (>70°) and SS (>45°), or high-grade isthmic spondylolisthesis at L5–S1, present technical challenges for both supine and lateral ALIF. These parameters reflect a more vertically oriented sacral endplate, requiring a steep working trajectory for discectomy and graft insertion that is obstructed by the pubic symphysis (7,10). Similarly, a high-riding or anteriorly positioned iliac crest, extending >50% of the L4 vertebral body, can limit access to the disc space, particularly at L4–5, and may favor a supine ALIF or posterior approach alternative.

Bodon et al. (20) emphasized the applied anatomy and technique for lateral ALIF should be considered distinct from its supine counterpart, as it must account for the patient positioning, differences in incision planning, and the effective 90° rotation of the spine and retroperitoneal contents. Preoperative computed tomography (CT) is valuable for assessing bony anatomy, endplate morphology, osteophytes, and disc space dimensions. Magnetic resonance imaging (MRI) provides important information regarding spinal canal and foraminal stenosis, psoas muscle morphology, and vascular relationships. The dimensions of the disc space (anterior, posterior disc heights) and the endplates are measured preoperatively to guide implant selection (8,20).

Anatomic factors such as large anterior or anterolateral osteophytes, disc space collapse, and spondylolisthesis increase the risk of vascular injury during exposure and increase the technical difficulty of disc and endplate preparation, and graft insertion. In addition, conditions such as osteoporosis, severe canal stenosis, high-grade spondylolisthesis, or severe facet arthropathy, and foraminal osteophytes may limit the efficacy of indirect decompression and adversely affect fusion outcomes (8,11).

Vascular anatomy

A detailed understanding of vascular anatomy at each target level is essential for safe exposure. MRI or contrast-enhanced CT should be used to identify the aortic bifurcation, confluence of the iliac veins into the inferior vena cava, and the relationship of the common iliac vessels to the L4–5 and L5–S1 disc spaces (8,20,21). A thin fat pad between the iliac vessels and disc space suggests a favorable anatomic plane to mobilize the vessels, whereas medialized vessels or a thin, tethered left iliac vein predict increased mobilization demands and a more constrained exposure.

At L5–S1, lateral ALIF is typically performed through a left-sided approach (i.e., left side up in right lateral decubitus), between the bifurcated common iliac vessels. Lateralized vessels offer a wider operative window and less mobilization demands, whereas medialized vessels increase technical complexity. At the L4–5 disc, the anatomy differs: the common iliac veins are more midline as they converge, and the operative corridor for a lateral ALIF approximates that of the ‘anterior-to-psoas’ approach. In the right lateral decubitus position, gravitational displacement of the vessels inferiorly (toward the right) can create a working corridor between the left psoas muscle and the iliac veins, rather than directly between the veins themselves. In this setting, lateral ALIF or anterior-to-psoas approaches may provide safer access than transpsoas techniques, particularly in patients with midline or right-sided vessels and an anteriorly positioned psoas muscle (8).

Importantly, the operative corridor to the lower lumbar disc spaces is dynamic and changes significantly with patient positioning. A supine MRI may overestimate the available window to the L5–S1 disc. In a prospective study of 20 consecutive patients who underwent MRI in both supine and right lateral decubitus positions, Choi et al. (17) demonstrated a mean reduction in the anterior L5–S1 disc space by 5.2 mm, from 27 mm in the supine position to 22 mm in the lateral decubitus, as the left common iliac vein shifted closer into the operative field. Gandhi et al. (16) similarly showed on positional MRI that the psoas muscle, and therefore lumbar plexus, and vasculature shift significantly with changes in positioning. In the left lateral decubitus position with the hips flexed, the ipsilateral psoas muscle migrates anteriorly, the inferior vena cava falls medially, and the aorta shifts laterally. These anterior shifts of the psoas muscle and iliac vessels may reduce the effective working corridor at both L4–5 and L5–S1 and must be anticipated during preoperative planning.

Psoas anatomy

Psoas muscle morphology is particularly relevant for anterior and lateral approaches to the lower lumbar spine, as the psoas and iliac vessels together define the operative corridor. The lumbar plexus resides within the posterior third of the psoas muscle proximally, but migrates anteriorly at more caudal levels (22). On MRI, the plexus may be visualized as a fat streak within the muscle (23,24). An anteriorly positioned psoas, the so-called ‘Mickey Mouse’ sign, indicates a more anteriorly located lumbar plexus and an increased risk of neural injury during transpsoas or ‘anterior-to-psoas’ LLIF approaches (8,22,24). In such cases, ALIF may be favored for anterior column reconstruction.

Lateral positioning itself may further influence these anatomic relationships. Gandhi et al. (16) demonstrated that the greatest positional changes in the psoas occur at the proximal and distal poles, near T12–L1 and L4–S1. Buckland et al. (8) similarly noted that in the flexed lateral decubitus position, the psoas becomes more anteriorly displaced compared to the supine extended position, which may reduce the corridor between the inferior vena cava and the left psoas at L4–5. Thus, in selected cases with an anteriorly positioned psoas, a supine ALIF may provide a more favorable and safer working corridor than any lateral approach.

The lateral ALIF offers the advantages of anterior column reconstruction and large footprint interbody devices, with the efficiency of a single-position workflow. However, safe and effective execution requires a detailed, level-specific understanding of vascular and vertebral anatomy, psoas morphology, spinopelvic alignment, and the dynamic positional changes that occur in the lateral decubitus position. A structured approach to preoperative evaluation that integrates clinical assessment with detailed imaging review can optimize patient selection, reduce complications, and improve outcomes.

Surgical technique and single-position workflow

The general order of operations is as follows: patient positioning, navigation setup (if applicable), simultaneous anterior and posterior exposure, pedicle screw placement, ALIF, rod placement, and closure.

The patient is positioned in a lateral decubitus position on a well-padded flat-top table (Figure 1A,1B). Importantly, the patient’s back should be placed as close to the edge of the table as possible for feasibility of pedicle screw placement on the down side (Figure 1A). This is particularly important if robot-guided pedicle screw placement is used, since the robot arm may collide with the table if the patient is not sufficiently close to the table edge. An axillary roll is placed under the dependent axilla to prevent brachial plexus and axillary vessel injury. The dependent arm can be placed in an extended position, while the non-dependent arm can be placed on the patient’s chest. Alternatively, the arms can be positioned in a ‘preacher position’ with sufficient pillows or cushioning between the arms. The patient’s hips and knees are slightly flexed, and pillows are placed between the legs to prevent pressure injury. The patient is secured in this position by taping the hips and chest to the operating table.

Figure 1.

Patient positioning and surgical workflow. (A,B) The patient is positioned on a flat-top table with hips, chest, and arms taped securely. Importantly, the patient’s back is positioned as close to the table edge as possible for ease of pedicle screw placement. (C) Navigation reference arrays can be placed into the iliac crest. (D) Exposure of the anterior and posterior spine can proceed simultaneously, typically alongside a vascular access surgeon. (E) The common iliac arteries and veins are retracted to expose the disc space of interest. (F) After disc space preparation, trial interbodies are malleted into the disc space under fluoroscopic guidance to determine the optimal interbody size. (G) The final interbody is malleted into position and fixed to the adjacent vertebral bodies with screws.

If navigation is used, the reference arrays can be placed into the non-dependent iliac crest (Figure 1C); a three-dimensional (3D) CT scan is subsequently acquired for navigation. Exposure of the anterior and posterior spine can proceed simultaneously (Figure 1D). We partner with a vascular surgeon to provide anterior access. Anteriorly, the skin, subcutaneous adipose tissue, external oblique aponeurosis, and internal oblique muscle are separated to reveal the retroperitoneal space. The common iliac arteries and veins are mobilized away from the operative field with self-retaining retractors to expose the disc space of interest (Figure 1E). Posteriorly, the skin, subcutaneous tissue, and thoracolumbar fascia are incised to access the posterior lumbar vertebrae. In our practice, CT-guided or robot-guided intraoperative navigation is used to place lumbar pedicle screws along paramedian incisions. The pedicle screws are then placed under CT or robot guidance, starting with the dependent pedicle screws to avoid blood rundown from the non-dependent pedicle screw placement. After the screws are placed, another 3D CT scan is performed to confirm satisfactory placement of the screws.

Attention is then moved to the ALIF portion of the case. After the correct level is confirmed by fluoroscopy or navigation, a box annulotomy is made in the anterior longitudinal ligament and intervertebral disc. The disc contents are removed with pituitary forceps, curettes, and Cobb retractors. Fluoroscopy can be used to confirm the depth of the discectomy. A series of trial interbodies is malleted into the disc space under fluoroscopic guidance to determine the ideal interbody size and angle (Figure 1F). The final interbody is then malleted into the disc space under fluoroscopic guidance (Figure 1G). Some implants have pre-drilled holes to allow additional screws to be placed into the adjacent vertebral bodies anteriorly.

After anterior interbody placement, the transverse processes of the posteriorly fixed vertebral bodies can be decorticated with a navigated drill. Rods are placed to link the pedicle screws, and bone graft can be placed lateral to the rods to promote posterior bony fusion. The incisions are then closed in the usual standard fashion.

All procedures performed in this study were in accordance with the ethical standards of the institutional and/or national research committee(s) and with the Declaration of Helsinki and its subsequent amendments. Written informed consent was obtained from the patient for the publication of this review article and accompanying images. A copy of the written consent is available for review by the editorial office of this journal.

Perioperative and workflow outcomes

Compared with traditional flip-based circumferential fusion workflows, single-position lateral ALIF has demonstrated perioperative advantages, including shorter operative time, lower estimated blood loss (EBL), and improved overall efficiency (3,10,18).

Surgical efficiency is greatly enhanced by the single position nature of the lateral ALIF as it allows multiple surgeons to work in tandem on both the anterior and posterior portions of the procedure. The surgical team can not only perform critical portions of the case in an orchestrated and effective fashion, but also undertake opening and closing the incisions simultaneously. By working in parallel rather than in series, operative times have been shown to be significantly reduced. A multi-institutional analysis of 442 ALIF patients (352 lateral, 90 “flip”) demonstrated that operative times were dramatically decreased at 98 minutes for the lateral group and 297 minutes for the “flip” group (P<0.001) (18). In this same analysis, EBL and ileus rates were significantly reduced as well (P<0.001), and it was hypothesized that this was due to decreased time under anesthesia (18). They also demonstrated lower rates of radiation exposure for the patient and operating room staff. Decreasing operative times is also important to spinal fusion in regard to infection, as increased operative times have been found to be associated with higher infection rate (25,26). These findings have been reproducible across studies, and were further demonstrated in a meta-analysis by Guiroy et al. (27) analyzing the literature comparing single position versus dual position lateral ALIF and true LLIF. They identified 4 studies which met the inclusion criteria, and reported significant decreases in operative time with similar complication profile across the groups (10,27-30). This demonstrates that the ability to operate in single position surgical set-up can provide excellent workflow benefits irrespective of interbody fusion type.

An important perioperative consideration for performing the lateral ALIF is the availability and comfort of the surgical team with lateral positioning and obtaining anterior access in this position. As evident from the positioning and setup considerations outlined previously, careful patient positioning facilitates reproducible anterior and posterior access in the lateral decubitus position. Vascular and spine surgeons who have experience operating together with standard “flip” ALIF procedures (or spine surgeons who obtain their own access for traditional anterior or lateral interbody procedures) have been able to adapt successfully to lateral positioning with similar complication and clinical success rates, indicating the lateral ALIF operating corridor and workflow is able to be learned through experience and is reproducible across institutions who are performing traditional supine “flip” ALIF (9,18,19,31,32).

A component of single position ALIF surgery that some surgeons may find challenging is posterior instrumentation placement in the lateral position rather than a traditional prone position. Although the surgical workflow described in this review paper uses freehand computer-assisted navigation, the introduction of robotic surgery has been an asset for SPS, especially in the placement of the posterior hardware. Robotic systems designed for pedicle screw placement have been shown to be safe, accurate, and reliable, and can be especially useful for surgeons that may have less experience with posterior hardware insertion in the lateral position (33,34). Augmented reality is also a new tool that is being increasingly utilized in spinal surgery for hardware insertion, and can also be a valuable adjunct to assist surgeons in accurate and reliable screw insertion as they gain increasing experience placing posterior instrumentation in the lateral position (35,36).

Radiographic and clinical outcomes

Several studies have compared the efficacy of lateral ALIF SPS (also called circumferential fusion) to traditional dual-position surgery (DPS) that flips the patient from supine to prone. Compared to DPS, SPS has shorter operative time, less blood loss, a shorter hospital length-of-stay, and lower rates of ileus (18,37). Rates of complications, such as vascular injury, neurologic deficit, wound complications, and deep vein thromboses, are comparable between SPS and DPS. Rates of reoperation, fusion, and interbody subsidence are similar between SPS and DPS, including in series with up to 2-year follow-up (18).

Radiographically, lateral positioning during ALIF has been associated with a greater change in segmental LL and PI-LL mismatch, a finding replicated in other studies (9). Other radiographic parameters, such as disc height gain and degree of spondylolisthesis reduction, are similar between lateral and supine ALIF positioning (9). Robot-guided posterior fixation during SPS ALIF surgery is safe and accurate, with high pedicle screw placement accuracy (~97%) and low revision rates (31).

Single-position lateral ALIF surgery has also been compared to other types of fusion surgery, such as minimally invasive (MIS) TLIF. Compared to MIS TLIF, SPS ALIF has shorter operative time, less blood loss, and shorter hospital length-of-stay (3). SPS ALIF also has a higher rate of bony fusion, less interbody subsidence, and greater changes in segmental LL and PI-LL mismatch compared to MIS TLIF. At 1 year, both SPS ALIF and MIS TLIF have similar rates of back pain, as measured by visual analog scales (3).

Current SPS ALIF comparative efficacy studies are limited by their retrospective, non-randomized nature. Additionally, while studies have thoroughly described the radiographic and perioperative outcomes of SPS ALIF surgery, clinical outcome reporting remains heterogeneous, with variable use of disability indices, pain scales, minimal clinically important difference thresholds, and limited long-term follow-up, warranting further study.

Conclusions

Single-position lateral ALIF has emerged as an increasingly adopted surgical approach in recent years. It has many of the benefits of traditional DPS, such as comparable rates of fusion, with the added benefits of less blood loss, shorter operative time, and shorter hospital length-of-stay (18,37,38). When performed with appropriate patient selection, positioning, and workflow optimization, this approach represents a reliable and efficient strategy for circumferential lumbar fusion. This review synthesizes the available evidence and technical considerations to provide a practical framework for surgeons seeking to incorporate single-position lateral ALIF into their practice.

Supplementary

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Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. All procedures performed in this study were in accordance with the ethical standards of the institutional and/or national research committee(s) and with the Declaration of Helsinki and its subsequent amendments. Written informed consent was obtained from the patient for the publication of this review article and accompanying images. A copy of the written consent is available for review by the editorial office of this journal.