Anterior Lumbar Interbody Fusion

Manish K. Kasliwal, Carter S. Gerard, Lee A. Tan, and Richard G. Fessler

Abstract

Anterior lumbar interbody fusion (ALIF) is a well-known surgical technique utilized by many spine surgeons to treat various degenerative lumbar pathologies. This chapter describes the indications, contraindications, preoperative evaluation, surgical techniques, and complications associated with ALIF in detail. A discussion regarding surgical nuances is provided along with clinical pearls and a review of pertinent literature. Proper patient selection remains the key to achieve successful clinical outcome.

Keywords: anterior lumbar interbody fusion, degenerative disc disease, lumbar spine

36.1 Introduction

Spinal fusions are often performed to treat various lumbosacral pathologies including degenerative conditions, tumor, trauma, infection, and spinal deformity. There has been a steady rise in the number of lumbar fusions performed in the United States between 1992 and 2003 in patients older than 65 years.¹ This is not surprising given that low back pain (LBP) is the most common health problem in men and women between the ages of 20 and 50 years in the United States with approximately 13 million visits to physicians and is associated with significant loss in productivity.²

There has been an evolution of surgical treatment for lumbar degenerative disease over the last several decades, and various interbody fusion techniques had grown increasingly more popular as an alternative or supplement to the traditional posterolateral fusion (PLF).³ The common theme for various interbody fusion techniques is placement of the bone graft or a cage in the disc space. Since the anterior and middle spinal columns support 80% of the axial load, the interbody fusion techniques are biomechanically superior and can result in higher fusion rates with improved patient outcomes compared with PLF techniques.³ In addition, the restoration of intervertebral height and segmental lordosis is possible with interbody fusion devices, which is correlated with favorable clinical outcomes.⁴ However, there is not yet conclusive evidence regarding the superiority in terms of clinical and radiographic outcomes with various interbody fusion techniques.⁴^,⁵

Surgical treatment of disabling back pain with spinal fusion has been shown to be superior to conservative treatment in a landmark prospectively randomized study, conducted by a Swedish lumbar spine study group.⁶ A variety of techniques are available for the application of interbody grafts—anterior lumbar interbody fusion (ALIF), transforaminal lumbar interbody fusion (TLIF), and extreme lateral interbody fusion (XLIF)—and each technique has its advantages and disadvantages. Currently, there is no randomized study demonstrating the superiority of one fusion technique over another for surgical management of back pain.⁶ The choice of a specific fusion technique depends on multiple factors including age, gender, medical morbidities, the specific pathology, presence of scar tissue from previous surgery, the surgeon’s preference, and anatomic considerations.⁵

The first attempted anterior approach to the lumbar spine was performed by Muller in 1906, where he used a transperitoneal approach to debride tuberculosis of the lumbar spine.⁷ Previously, most anterior lumbar approaches were performed through extensive transperitoneal exposures. In 1944, Iwahara et al⁸ performed an interbody fusion using a retroperitoneal approach to treat lumbar degenerative disease, which was then further described by Southwick and Robinson in 1957.⁹ Technical challenges and device limitations initially restricted the application of interbody procedures until the advent of newer interbody fixation devices, which significantly increased the technical ease and efficacy.¹⁰

The modern concept of interbody fixation was introduced by Wagner and coworkers following the implantation of a bonefilled cage in horses with Wobbler’s syndrome.¹¹ The intervertebral disc space was distracted by placement of an oversized, perforated, stainless-steel cylinder (the Bagby basket) filled with autogenous bone graft, ultimately yielding a reported fusion rate close to 88%.¹² Subsequent material evolution and physical modifications of the Bagby basket led to the production of the Bagby and Kuslich (BAK) implant.¹³ There was a tremendous increase in the number of graft options available over the last few years including the autologous iliac crest graft, structural allograft, bone chips within metallic cages, titanium mesh cages, carbon fiber cages, and polyetheretherketone (PEEK) cages.¹⁰^,¹⁴^,¹⁵^,¹⁶ Even though anterior interbody fusion technique has been traditionally considered a predominant technique to treat discogenic back pain, there has been an increasing enthusiasm and resurgence in the applications of ALIF technique to restore segmental lordosis, secondary to improved understanding of spinal alignment and the possibility of achieving increased fusion, especially at the L4/L5 and L5/S1 with ALIF for long thoracolumbar constructs.¹⁷^,¹⁸

The anterior approach provides direct access to the ventral surface of the vertebral bodies and disc spaces. It also provides a direct and more complete view of the anterior surface of the lumbar spine from L3 to S1.¹⁹^,²⁰^,²¹ Various advantages of ALIF are listed in the following text box.

Advantages of ALIF

• Efficient and direct access for reconstruction of the anterior spinal column.

• The ability to avoid paraspinal muscle trauma and denervation, and posterior tension band compromise (in stand-alone ALIF or ALIF with minimally invasive posterior fixation), resulting in significantly decreased postoperative pain and subsequently decreased length of postoperative hospital stay.²²

• The ability to undertake indirect decompression of the intervertebral foramen.

• Avoidance of dural or posterior neural structure manipulation.

• Improves sagittal balance.

The increasing familiarity with the posterior instrumentation and the utilization of posterior osteotomy techniques and TLIFs have led to a greater number of surgeries being performed with all posterior approaches for adult spinal deformity. However, ALIF at L4/L5 and L5/S1 can be very useful in patients who have had previous radiation, large posterior bony resection with laminectomy and destabilization, or significant osteoporosis.¹⁸ One recent study compared ALIF with TLIF, and showed an increased ability of ALIF to improve foraminal height, local disc angle, and lumbar lordosis.²³ Other studies have demonstrated decreased rate of adjacent segment degeneration with ALIF compared to posterior lumbar interbody fusion (PLIF).

Nevertheless, ALIF has certain disadvantages including possible need for an access surgeon, potential for increased risk of deep vein thrombosis (DVT), increased risk for vascular injury secondary to vessel retraction, and retrograde ejaculation (RE) associated with hypogastric plexus injury.³^,⁷^,²⁴^,²⁵^,²⁶^,²⁷^,²⁸ In addition, in cases requiring subsequent posterior instrumentation and fusion, ALIF is associated with increased operating time and blood loss, as well as prolonged recovery time. There is also a potential risk of muscular atony of the abdominal wall and abdominal hernias.

36.2 Indications

Traditionally, ALIF has been performed most commonly for patients with discogenic back pain. Lumbar disc degeneration encompasses a dynamic process with overlapping findings at individual and adjacent levels; although the exact role of degenerative disc disease (DDD) is controversial in patients with back pain, disc degeneration has been shown to be a pain generator.²⁹^,³⁰ Determining the ideal candidate for surgical management of DDD can be more challenging than performing the procedure itself because of the unclear relationship between patient symptoms, diagnostic studies, and surgical outcomes. Due to the lack of a “gold standard” test, attempts to identify the source of a patient’s LBP in the absence of neurological deficit can be frustrating for both the patient and the treating physician. Hence, before embarking on surgical intervention in patients with LBP, a trial of conservative management, including oral medication, lifestyle modification, and active rehabilitation, is imperative. Nevertheless, ALIF has been shown to result in significant improvement in a subgroup of patients with discogenic back pain.⁶ The ideal candidate for ALIF has chronic, disabling back pain of discogenic origin for one or two levels with loss of height, stability, and mobility of the diseased segment or neurological deficit.¹³^,¹⁷^,²¹^,³¹ Though often considered to be a procedure performed for discogenic LBP, ALIF is a versatile technique with much wider application and can be performed for various other indications.

Indications for ALIF

• Lumbar degenerative disc disease.

• Anterior column support in long fusion constructs.

• Restoring lumbar lordosis.

• Pseudarthrosis following posterior lumbar fusion.

• Lumbar fusions at high risk for nonunion.

• Tumor and trauma.

• Spondylolisthesis (usually grade I or II).

• Intervertebral foraminal stenosis secondary to loss of disc height, in conjunction with the need for interbody fusion.

In our experience, ALIF is the best at achieving L5–S1 interbody arthrodesis. At L5–S1, unlike the L4–L5 interspace, excessive retraction of the iliac vessels is typically unnecessary. The ideal patients for mini-ALIF are those with DDD limited to L5–S1 or those patients with DDD in combination with low-grade L5–S1 spondylolisthesis. Similarly, anterior lumbar fusions should be avoided in young men or in men who wish to have children because of the risk of RE.³² We also avoid ALIF in patients with a history of extensive abdominal surgery, in which tissue scarring in the retroperitoneal space can make the exposure difficult with potential for increased complications.²⁶^,³³

36.3 Contraindications

Relative contraindications for ALIF include advanced atherosclerosis of the major vessels and morbid obesity.³^,¹³^,²⁶^,²⁸^,³⁴^,³⁵ Some consideration should be given to patients who have previously undergone abdominal surgery or have inflammatory diseases because these conditions create significant scarring that may increase the risk of approach-related complications.³³ A transperitoneal approach may be performed as an alternative in these patients. Other relative contraindications for lumbar interbody fusion in general may include multilevel (three levels) disc disease (in patients without lumbar spinal deformities).³ Male patients may have a 2 to 5% risk for RE with the anterior lumbar approach.³⁴

36.4 Preoperative Planning

The preoperative evaluation of patients who will undergo ALIF for LBP first requires careful selection of those patients likely to have a successful outcome after an anterior fusion. Studies have shown the following to be associated with a good outcome after ALIF in patients with discogenic LBP⁶^,¹³^,¹⁷^,³⁶^,³⁷:

• Axial back pain aggravated by spinal loading and fusion.

• Radiographic studies consistent with disc degeneration.

• Provocative discography that produces pain only at the affected levels.

• Dynamic studies demonstrating motion/sagittal deformity on sagittal views.

Though provocative discography had been used in the past during preoperative evaluation of patients with LBP for performing lumbar fusion, the current status of its use remains controversial at most. Even though lumbar discography can still be used in the evaluation of a patient presenting with chronic LBP based on level II evidence, treatment decisions should not be based on discography alone in patients with LBP and abnormal imaging studies.⁵^,³⁷ More recently, there are data from both animal and human studies suggesting that diagnostic disc injections may lead to iatrogenic injury to the disc and accelerated disc degeneration.³⁸

A preoperative MRI should be obtained in all patients, especially in those with suspected DDD in the presence of neurological symptoms or deficits. A CT myelogram may need to be performed if MRI cannot be obtained. A standing lateral radiograph of the lumbar spine should be obtained to assess the sacral slope to ensure the L5–S1 disc space can be accessed through the anterior approach. If the sacral slope is too steep (often in cases of L5–S1 spondylolisthesis), access to the disc can be very difficult. The degree of sagittal imbalance should also be assessed on preoperative imaging in patients with deformity to allow appropriate graft selection. Preoperative evaluation by the exposure surgeon is advisable with special attention paid to patients with elevated body mass index (BMI) due to potential for increased vascular complications in this subgroup of patients.²⁶

36.5 Surgical Approach

Various techniques have been described to gain access to the anterior lumbar spine (transperitoneal, laparoscopic, open and mini-open retroperitoneal).²⁵ In 1932, Capener was the first to describe using ALIF in the treatment of spondylolisthesis.³⁹ Harmon⁴⁰ described a left extraperitoneal approach to the lumbar spine with subsequent modification of the basic approach, which over time led to the development of mini-open and laparoscopic approaches aiming toward decreasing postoperative morbidity, reducing hospitalization time, and shortening rehabilitation time.²⁵^,⁴¹ The introduction of laparoscopic techniques represents minimally invasive modification of the ALIF. Developed in the 1990s, laparoscopic ALIF achieved early success with its pioneers.⁴² Laparoscopic ALIF was reported to be less invasive with less blood loss and faster recovery; however, later reports contradicted these findings, noting that there were no identifiable advantages, but with added technical challenge, and increased specific complications such as RE.²⁵^,²⁷^,⁴¹ More recently, mini-open retroperitoneal approach, a modification of conventional retroperitoneal approach, has been found to be superior to laparoscopic approaches and has become the “workhorse” approach, with mini-open transperitoneal and open procedures saved for revision or salvage procedures.³^,²⁰^,²⁵^,⁴¹ Retroperitoneal and transperitoneal corridors allow complete exposure of the ventral surface of the spine and placement of a single large interbody implant that matches the vertebral end plate. Avoidance of the posterior musculature reduces postoperative pain and disability associated with extensive muscle stripping, denervation, and devascularization, often noted as a cause of failed back syndrome.⁶^,²⁰^,²¹^,²⁸^,⁴³ The mini-open retroperitoneal approach is described in detail in this chapter.

36.5.1 Surgical Technique

The patient is positioned supine on a radiolucent operating room table with the arms positioned at the sides in an abducted position on arm rests to allow lateral imaging. Alternatively, they can be positioned across the chest with adequate padding of all bony prominences. A bolster can be placed under the lumbar spine to accentuate lumbar lordosis. Obtaining fluoroscopic images before prepping the patient can be helpful to ensure that all views are obtainable without obstruction from the table or patient’s extremities. A lateral fluoroscopic image is used to localize and mark the level of incision. A radiopaque rod or pin is used to mark the angle of the disc and the corresponding trajectory to the abdominal wall. The incision site can be adjusted to give optimum access to the intended disc space. A transverse or longitudinal incision is made a few centimeters lateral to midline at the corresponding disc level, in line with the angle of the disc space. While a Pfannenstiel incision is more cosmetically appealing and provides good access to the L5–S1 level ( Fig. 36.1), direct midline or paramedian incision may be preferable for multilevel exposures as they can be easily extended distally along the anterolateral portion of the flank toward the abdomen and the lateral border of the rectus abdominis muscle. Attention should be paid to identifying the correct disc level to be addressed in cases in which there is transitional lumbosacral anatomy. Use of electrocautery should be avoided as it may help minimize the risk of iatrogenic injury of the hypogastric plexus and resultant RE; using bipolar cautery or hemostatic agents to achieve hemostasis is recommended.