Anterior Lumbar Fusion

Introduction

In 1969 and 1971, Coventry and Stauffer provided the first descriptions of anterior fusion for the treatment of failed posterior spine surgery, reporting overall good results. Since then, anterior lumbar interbody fusion (ALIF) has been used to treat a variety of pathologies, but controversy remains about the merits of ALIF compared with other approaches for interbody fusions, such as posterior (PLIF), transforaminal (TLIF), and lateral (LLIF) approaches, with the last gaining popularity more recently as minimally invasive surgical (MIS) techniques are developed and refined. Indications for ALIF in both the primary and revision setting are not clearly identified in the literature, and its use is often dictated by a combination of surgeon preference and familiarity with the approach and the pathology being addressed. The number of revision spinal surgeries are expected to increase significantly in the future, and there are situations where an ALIF may be of great benefit to the operating surgeon.

The success of revision posterior lumbar surgeries varies widely in the literature, with reports ranging from 25% to 92%. Altered anatomy, scarring of the soft tissue and neural elements, and repeated insult to the supportive spinal musculature may predispose to unintended injuries to the neural structures and deleteriously impact functional outcomes. As such, there are certain advantages to avoiding a revision posterior approach if the goals of surgery can be adequately accomplished from a different approach. An anterior approach can (1) mitigate the risk of neural injury by avoiding the epidural scarring posteriorly; (2) allow for near-complete excision of disc tissue, including the posterior annulus, thereby decreasing the chances of recurrent herniation and maximizing the surface area for fusion mass; (3) permit complete excision of the anterior longitudinal ligament (ALL), anterior and posterior annulus, and release of the posterior longitudinal ligament (PLL), which can help maintain or restore sagittal balance and spinopelvic alignment parameters; and (4) facilitate large lordotic structural bone graft or cage implantation that widely distributes contact forces across the end-plates, minimizing the risk of subsidence and maximizing contact area for fusion.

There is a relative dearth of published research on ALIF for revision surgery. The studies that exist report on heterogeneous patient populations with small numbers, making it difficult to draw definitive conclusions. Some of the most common reasons to consider ALIF in a revision lumbar surgery include symptomatic segmental pseudarthrosis, sagittal imbalance, patients with mechanically induced back or leg pain secondary to abnormal segmental motion (i.e., spondylolisthesis/instability, degenerative disc disease, adjacent segment disease), and recurrent disc herniations. These topics will be discussed systematically in the following sections, with particular emphasis on the pertinent available literature and case illustrations to emphasize important points and the author’s preferences for treatment.

Anterior Lumbar Interbody Fusion for Lumbar Pseudarthrosis

Pseudarthrosis represents the failure of fusion following a prior attempted spine fusion surgery. The subtypes and classification of lumbar pseudarthrosis have been defined by Heggeness and Esses, the most common of which is the transverse type. The diagnosis of a lumbar pseudarthrosis, as well as the indications for revision surgery, are controversial. Despite this, certain patients with recalcitrant symptoms who fail prolonged nonoperative management are deemed surgical candidates.

The goals of revision surgery for lumbar pseudarthrosis include improving both the biomechanical and biological setting to maximize the potential of the fusion environment. ALIF has been established as a revision surgery option when other approaches have failed to produce a solid fusion. ALIF provides the theoretical advantages of a large surface area in the anterior column for fusion, with excellent end-plate vascularity and anterior column compression loading of grafts.

The current literature supports the concept of ALIF for failed lumbar fusion, particularly via prior posterior approaches, although the number of studies and indicated cases examining ALIF as pseudarthrosis salvage is low, making it difficult to draw conclusions. Certain studies demonstrate excellent fusion results after ALIF for posterior pseudarthrosis. Mobbs et al. analyzed 20 patients with posterior pseudarthrosis treated with salvage ALIF and showed a 95% fusion rate with significant improvements in pain and physical function. Lee et al. reported on seven patients with lumbar pseudarthrosis who were treated with ALIF and percutaneous screw fixation. Seventy-one percent of the patients in their study had improvement in their Oswestry Disability Index (ODI), and 86% and 57% of patients had improvement in their visual analog score (VAS) for back pain and leg pain, respectively. Yun et al. similarly showed 100% fusion rate and excellent clinical results in a series of 10 patients treated with ALIF for pseudarthrosis following posterior fusion with either TLIF or PLIF. One study demonstrated an 81% fusion rate after pseudarthrosis following TLIF, which was improved to 88% when posterior screws were added to the salvage ALIF operation.

Conversely, other studies have demonstrated poor results after performing ALIF in this revision setting for pseudarthrosis. Owens et al. demonstrated that only 17% of patients that underwent ALIF for pseudarthrosis achieved the minimum clinically important difference (MCID) for ODI, with overall poor to modest improvement in ODI. However, these poor results were similar for all 60 patients in this series regardless of revision technique, including posterior spinal fusion, PLIF, anterior-posterior combined fusion, or standalone ALIF. Other studies have shown fusion rates as low as 33% following revision ALIF with similarly poor physical function postoperatively. Albert et al. recommends that revision surgery for lumbar pseudarthrosis should ideally be a combined anterior and posterior revision fusion, backed by their case series and literature review for lumbar pseudarthrosis management, citing poorer result for standalone ALIF as a pseudarthrosis salvage operation.

ALIF has also been shown to have the added benefit of appropriately restoring alignment (namely pelvic incidence-lumbar lordosis mismatch, T1 pelvic angle, lumbar lordosis, and sagittal alignment) in the particular setting of revision surgery for lumbar pseudarthrosis. Additionally, biomechanical studies have demonstrated that using ALIF as a revision for pseudarthrosis following posterior spinal fusion with TLIF achieves appropriate biomechanical stability and range of motion without sacrificing biomechanical stability. Buttermann et al. demonstrated that the use of allograft is equally effective as autograft with respect to fusion rates, function, and pain when performing ALIF for pseudarthrosis.

In summary, despite the conceptual advantages of ALIF as a revision option for lumbar pseudarthrosis, the results in the literature are limited and divided in their conclusion. This may be a reflection of the particular challenge of studying pseudarthrosis management.

Case Illustration: Pseudarthrosis

This patient was a 59-year-old female with a history of thoracolumbar scoliosis and lumbar spinal stenosis, for which she underwent an L3–S1 laminectomy, T3–S1 posterior spinal fusion, and L4–L5 and L5–S1 TLIFs for spinal deformity correction. She presented with worsening back and leg pain at the lumbosacral junction, and was found to have an L5–S1 pseudarthrosis with broken rods at the L5–S1 pseudarthrosis site. She underwent L5–S1 ALIF for pseudarthrosis repair with removal of the TLIF cage through the anterior approach and revision posterior spinal fusion and instrumentation. She went on to solid fusion at the nonunion site ( Fig. 12.1A–E ).

Anterior Lumbar Interbody Fusion for Correction of Sagittal Deformity

Interbody fusions can help improve fusion efficacy and provide anterior column support, but each technique’s ability to correct sagittal deformity varies and is the subject of debate. It is well established in the literature that sagittal malalignment deleteriously affects patient functional outcomes and health-related quality of life (HRQL). There is a strong correlation between sagittal vertical axis (SVA), pelvic tilt (PT), and pelvic incidence-lumbar lordosis (PI-LL) mismatch and HRQL, emphasizing the need for preoperative evaluation and intraoperative correction of these parameters. There is recent focus on the LL distribution with the low LL (L4–sacrum) being a critical measure itself. Although there is conflicting evidence in the literature with respect to the amount of deformity correction possible with each technique, there is general agreement that MIS techniques are not appropriate for the correction of more severe deformities.

Failure to restore spinopelvic parameters at the index operation will predispose the patient to suboptimal outcomes and may, ultimately, necessitate revision surgery to address the malalignment. National trends suggest that such cases are likely to become increasingly common in the future and present a significant challenge to the spine surgeon. Conventional surgical options consist of posterior-only approaches that rely on Smith-Peterson, pedicle-subtraction, or more aggressive three-column osteotomies to achieve sagittal correction. Complication rates at the time of the index procedure are reported as high as 58% in the literature, a figure that is almost certainly higher in a revision surgery. A posterior-anterior-posterior procedure, known colloquially as a “540” fusion, is another revision option, but has become less commonly used since the description of and familiarization with three-column osteotomies. This more traditional method first requires removal of the previously placed posterior instrumentation with or without posterior releases or osteotomies, followed by ALIF to improve sagittal deformity, and concluding with the reinsertion of posterior instrumentation to maintain the alignment.

In primary lumbar fusions and in the absence of spondylolisthesis, research has demonstrated that contemporary hyperlordotic ALIF cages impart nearly the same amount of segmental lordosis (SL) as that built into the cage and reliably restores LL from the anterior approach. Hyperlordotic ALIF cages have also created new opportunities for deformity correction in revision surgery, but this particular area of research is in its nascency. In a preliminary feasibility study, Kadam et al. examined whether release of the ALL and implantation of hyperlordotic cages would allow adequate sagittal deformity correction in the presence of previously placed posterior instrumentation and/or fusion mass. Their surgical techniques emphasized extensive exposure to facilitate wide discectomies and complete release of the ALL, releasing the PLL except in cases of previously placed TLIF or PLIF cages, gradual distraction of the interbody space with large footprint end-plate distractors and concurrent “jackknifing” of the operating room table to increase lordosis, and implantation of 12-degree, 20-degree, or 30-degree hyperlordotic ALIF cages secured with screws to prevent cage extrusion. After completion of the ALIF(s), the second stage was performed to revise the posterior instrumentation and further correct any residual deformity. A total of 20 patients were included in the radiographic analysis, which demonstrated statistically significant improvement in all spinopelvic parameters. The average amount of absolute SL obtained was found to be 13.1 degrees, 19 degrees, and 22.4 degrees with 12-degree, 20-degree, and 30-degree cages, respectively, leading the authors to conclude that all the hyperlordotic cages used effectively overpowered the posterior instrumentation and allowed for sagittal deformity correction. Additionally, there were no differences in the amount of correction achieved at levels with pseudarthrosis and those with solid fusion.

The presence of previously placed interbody devices with suspected fusion mass does not preclude retrieval and reinsertion of another interbody device. In fact, an anterior approach is ideal for this situation and has demonstrated safety and excellent sagittal correction. Janjua et al. reported on six patients who previously underwent TLIF and posterior instrumentation who required revision surgery for sagittal imbalance and symptomatic pseudarthrosis. In addition to describing their technique for implant retrieval and reinsertion of a hyperlordotic cage, with specific attention paid to preserving the integrity of the end-plates, the authors reported significant improvement is spinopelvic alignment parameters. All patients underwent revision posterior instrumentation after the anterior approach, with 66% requiring Ponte osteotomies for further sagittal correction and none requiring three-column osteotomies. Kadam et al. safely removed nine TLIF devices with subsequent reinsertion of hyperlordotic cages and resultant correction of sagittal imbalance. These studies demonstrate that both removal of previously placed interbody devices and reimplantation of a lordotic or hyperlordotic cage at the index level are important for restoring appropriate sagittal balance and mitigating the risk for pseudarthrosis.

In conclusion, patients requiring revision lumbar spine surgery for correction of sagittal imbalance present significant challenges for the treating spine surgeon. ALIF offers some distinct advantages over other techniques in its ability to correct deformity, especially with modern hyperlordotic cages and when placed at the L4–L5 and L5–S1 levels.