Anterior Lumbar Interbody Fusion

Anterior lumbar interbody fusion (ALIF) is a procedure that has become an important tool in the armamentarium of the modern spine surgeon. Over the last two decades, great advancements have been made in understanding the generators of low back pain and in mini-open and minimally invasive techniques to access the lumbar spine. Technological advances in interbody implant design and the availability of biological bone growth factors have enhanced our ability to treat common lumbar spine disorders, as well as more complex spinal deformity. This chapter reviews the indications for ALIF and important considerations in patient selection and counseling, with emphasis on techniques for minimizing complications during the surgical approach. Special attention is given to implant options and considerations when using biologic products such as bone morphogenetic protein (BMP-2). The ALIF procedure can be used both as an adjunct to extensive deformity operations, as well as the primary technique in treating patients with short-segment degenerative disease. This chapter focuses on the application of ALIF for short-segment pathologies.

50.2 Patient Selection

There are specific clinical scenarios in which anterior approach to the lumbar spine and fusion of a disk space may present an advantage over other (posterior) techniques. Indications for the anterior approach include one- or two-level degenerative disk disease, low-grade spondylolisthesis, septic diskitis, aseptic spondyloarthropathy, posterior pseudarthrosis from previous posterolateral arthrodesis, and even pseudoarthrosis from previous posterior lateral or transforaminal (PLIF or TLIF) or even lateral interbody fusion.

When an aggressive approach is deemed necessary, such as in the setting of a highly mobile spondylolisthesis or difficult pseudoarthrosis, the ALIF may be used in combination with a posterior instrumentation and arthrodesis procedure (so-called 360, front–back, or circumferential technique). Pedicle screws (open or percutaneous), translaminar facet screws, and cortical bone screws are posterior instrumentation options.

A thorough preoperative history should screen for prior abdominal or pelvic surgeries, as well as previous sexual or urinary dysfunction (particularly in male patients). Such issues can be relative contraindications and should be discussed with your access surgeon. Preoperative urological consultation may be considered in patients with a history of urological issues. Male patients should be counseled about the risk of retrograde ejaculation.

Patients should have plain radiographs (including dynamic flexion and extension views) and magnetic resonance imaging (MRI) studies confirming disk degeneration at one or two levels without significant central canal stenosis or other masses within the spinal canal (e.g., large herniated disk or synovial cysts) and without mobile instability. Consideration should be given to obtaining standing 36-inch films to enable calculation of spinopelvic parameters (specifically, lumbar lordosis and pelvic incidence), as well as the overall evaluation of global sagittal balance in the appropriate patient.

50.3 Preoperative Preparation

The procedure is performed with the patient under general anesthesia with endotracheal intubation. A nasogastric tube may be placed in the stomach, although this is not mandatory. Perioperative antibiotics are always administered per surgical care improvement protocol guidelines. We recommend administering a single dose of intravenous heparin (~ 5,000 units) to help prevent pelvic deep vein (iliac vein or vena cava) thrombosis. This can be safely administered before the incision is made and has not been shown to increase the risk of bleeding during or after the operation. ¹

50.4 Operative Procedure

50.4.1 Surgical Technique at L5–S1

The patient is placed in the supine position in Trendelenburg. A regular operating table can be used if the orientation is reversed. We find it useful to use a flat Jackson table, which is radiolucent and allows easy access for the fluoroscope. A pad should be placed under the patient’s buttocks and lower lumbar region to create a lordotic angle that approximates or slightly exceeds (hyperextension) the sagittal balance in the standing position ( ▶ Fig. 50.1). The arms are placed on arm boards at 90 degrees to the trunk. The surgeon may choose to operate between the legs of the patient or, conversely, to stand at either side of the patient (with legs apposed). The suprapubic area is prepared with antiseptic solution. Sterile drapes are placed from above the umbilicus and as far laterally as desired (e.g., if iliac crest autograft is to be harvested).

Fig. 50.1 Supine position with pad to create lumbar lordosis (just before being placed in Trendelenburg).

50.4.2 Retroperitoneal Approach

A left paramedian vertical incision is marked below the umbilicus with fluoroscopic guidance. The incision is carried through the subcutaneous tissues using electrocautery to expose the anterior rectus sheath. The sheath is divided longitudinally in the direction of its fibers, with preservation of a tissue cuff to permit tight closure. The rectus muscle is retracted medially and the posterior rectus sheath or transversalis fascia divided as needed. The ureters are identified and protected. Great care is also taken to prevent damage to the iliohypogastric and ilioinguinal nerves between the layers of the internal and transverse abdominal muscles.

The peritoneum and its contents are retracted medially by blunt dissection to expose the iliopsoas muscles and the anterior longitudinal ligament. Even small rents in the peritoneum are immediately repaired to reduce the possibility of herniation. A circular frame is attached to the operating table, and the abdominal contents gently retracted behind padded blades. The left common iliac artery and vein are traced to their bifurcations and the iliolumbar vein (for L4–5), middle sacral vessels (for L5–S1), and segmental vessels (for proximal exposure) are ligated and divided as necessary. The great vessels, including the aorta, inferior vena cava, and iliac, are mobilized to the right with hand-held retractors. Pressure on the vessels is ideally released at least hourly.

50.4.3 Transperitoneal Approach

A vertical midline incision is made centered over L5–S1 ( ▶ Fig. 50.2). The sacral promontory is often palpable after the induction of general anesthesia and administration of muscle relaxation before incision. Lateral fluoroscopy can also be used at this time to confirm orientation of the L5–S1 disk space. This location is usually centered over the lower and middle third of the distance between the umbilicus and the symphysis pubis. After skin incision, monopolar cautery or sharp dissection is used to approach the peritoneum via the linea alba in the midline ( ▶ Fig. 50.3). The peritoneum is opened exposing the abdominal viscera ( ▶ Fig. 50.4). A self-retaining retractor is placed. The ileum and its mesentery are displaced toward the right upper quadrant with moist laparotomy sponges. The sigmoid colon is retracted to the left and secured with moist laparotomy sponges. A table-mounted tractor is placed just superior to the promontory in the midline retracting the transverse colon cephalad ( ▶ Fig. 50.5). Renal vein retractors are readied bilaterally.