Anterior Spinal Column Reconstruction: Anterior, Lateral, and Oblique Approaches to the Spine

Scott J.B. Nimmons, MD

Andrew E. Park, MD

Dr. Park or an immediate family member has received royalties from Zimmer Biomet Virage posterior cervical system and serves as a paid consultant to or is an employee of Titan Spine, New Era Orthopaedics. Neither Dr. Nimmons nor any immediate family member has received anything of value from or has stock or stock options held in a commercial company or institution related directly or indirectly to the subject of this chapter.

INTRODUCTION

Spinal arthrodesis procedures have been performed for approximately 100 years. During that time many different devices, techniques, and surgical approaches have been used to successfully perform such operations. Even in the setting of historically favorable radiographic and patient-reported outcomes, spinal surgeons seek techniques that may allow higher fusion rates and superior deformity correction and minimize the morbidity of the surgical procedures.

Compared with posterior techniques, anterior and lateral interbody approaches allow for direct stabilization of the anterior column without intraoperative manipulation of the spinal cord or nerve roots. In this way, the risk of postoperative adhesions or iatrogenic neurologic injury is minimized. These surgeries also allow surgeons to decompress nerve roots indirectly by restoring decreased intervertebral body height, thereby opening stenotic neuroforamina. Additionally, anterior and lateral techniques allow the placement of larger interbody devices, which results in greater contact area between the implant and vertebral end plate. Early biomechanical studies suggest this may lead to decreased subsidence. A larger cage also allows for an increased volume of bone graft to be placed, potentially improving fusion rates while also decreasing the likelihood of pseudarthrosis. Within the expanding field of interbody techniques, the focus of this chapter will be on anterior and lateral lumbar interbody fusion techniques.

ANTERIOR LUMBAR INTERBODY FUSION

The anterior lumbar interbody technique for fusion of the lower lumbar spine is being performed with increasing frequency. As surgeons become more familiar and more comfortable with this approach, more clinical scenarios traditionally approached via a posterior surgical technique may be handled with an anterior procedure. Lumbar levels from L2 to the sacrum can be accessed via a single retroperitoneal approach in most instances. The anterior lumbar approach presents significant advantages in long deformity constructs, which extend down to the sacrum or pelvis. The caudal level of long spine reconstructions is more likely to develop a pseudarthrosis. This is particularly true of the L5-S1 level. One significant advantage of the anterior technique is its high fusion rate compared with posterolateral intertransverse fusion. This is particularly true for the L5-S1 level.¹^,² In addition, the correction of coronal plane deformity and the graft surface area is substantially greater through an anterior interbody technique.

PATIENT SELECTION

Indications

The anterior lumbar approach for spinal fusion is most often performed at L4-L5 and L5-S1. Most commonly, a single-level fusion is done through a retroperitoneal approach. Alternative approaches include transabdominal and laparoscopic; however, both of those approaches are associated with a higher frequency of postoperative complications. Most notable among the disadvantages are prolonged postoperative ileus, a higher incidence of bowel injury, and a higher incidence of retrograde ejaculation in male patients. The indication most commonly leading to surgery at a single level in the lower lumbar spine is lumbar disk degeneration with low back pain. Other conditions for which an anterior approach may be considered include diskitis/osteomyelitis, nonunion of a posterior fusion procedure, spinal deformity surgery, recurrent disk herniation, total disk replacement/revision, fractures, and tumor surgery.

Contraindications

The primary contraindication to an anterior lumbar surgical approach is in a revision setting, in particular at L4-L5. The interspace at L5-S1 may be approached from the opposite side from the index approach in most cases without a significantly increased risk of vascular injury.
A direct lateral approach to the interspaces above L5-S1 may be a safer alternative to revision anterior surgery. Prior to consideration of a revision anterior lumbar exposure, alternative techniques to address the spinal pathology should be considered. Those approaches may include a direct lateral approach or a posterior approach to avoid the vascular risks associated with revision anterior retroperitoneal exposure. Morbid obesity may be considered a relative contraindication to anterior lumbar surgery.

Diagnosis

For the purposes of this chapter, degenerative disk disease will be the focus. This diagnosis is most commonly encountered at L4-L5 and L5-S1. Multilevel disease is also commonly seen in the lower lumbar spine. The patient will typically present with a long-standing history of low back pain, usually with occasional exacerbations over a period of many years. After the failure of nonsurgical treatment, including physical therapy, activity modification, and nonsteroidal anti-inflammatory medications, surgical treatment may be an appropriate consideration.

PREOPERATIVE IMAGING

Plain radiographs typically demonstrate height loss on the lateral view (Figure 1). Although instability on flexion-extension views may be coexistent with the degenerative disk, this is relatively uncommon.

The surgeon must beware of spondylolysis affecting the involved motion segment because this may impact the need for additional fixation in the surgical decision making. A vacuum disk sign may also be seen on either standing, recumbent, or flexion-extension radiographs.³^,⁴ MRI changes may include loss of disk space height, loss of signal intensity in the nucleus pulposus of the intervertebral disk on T2-weighted images, posterior disk bulge on axial imaging, and possibly Modic end plate changes affecting the inferior end plate of the superior vertebrae and the superior end plate of the inferior vertebrae (Figure 2). Nerve root compression may also be seen on axial imaging affecting the central canal, the subarticular recess, or the far lateral zone of the neural foramen.⁵ Other diagnostic maneuvers may include diskography and postdiskography imaging. This area continues to be the subject of considerable debate regarding its utility and relevance to surgical decision making. Diskography also introduces variability in techniques and in interpretation of the results. Even the inclusion of a control level is debated based on the theoretical potential for creating accelerated disk degeneration at the control level.

FIGURE 1 Lateral radiograph shows a loss of disk space height at L5-S1.

FIGURE 2 Sagittal T2-weighted MRI demonstrates typical changes associated with a symptomatic lumbar degenerative disk.

PROCEDURE

Room Setup/Patient Positioning

The surgical procedure should be performed on an operating table that allows for intraoperative fluoroscopic imaging (Figure 3). I prefer either a flat Jackson OSI table (Figure 4) or a Jackson Axis OSI table (Figure 5; Mizuho OSI). The Axis table allows for flexion or extension of the table to create more or less lumbar lordosis
during the procedure (Figure 6). This may be of potential benefit in deformity cases or in a severely collapsed disk space. Another alternative would be the use of an inflatable arterial line cuff under the lower lumbar spine as a bolster to increase lumbar lordosis during the procedure. If this option is selected, access to the cuff’s inflation should be checked before beginning the procedure. Patient positioning on the operating room table should be done with great care and precision to ensure that there is no rotation of the pelvis or torso and that the patient is appropriately padded. The arms may be placed to the side or over the chest (Figures 4, 5, 6). Placing the arms over the chest allows the C-arm to stay in the surgical field in the lateral position for periodic imaging without the need for multiple drapes. This will improve the sterile technique by reducing the number of sterile drapes over the C-arm while switching from the AP to lateral imaging planes.

FIGURE 3 True lateral fluoroscopic image demonstrates disk collapse at L5-S1.

FIGURE 4 Photograph depicts a flat Jackson OSI table. The patient’s arms are folded over the chest to allow intraoperative fluoroscopy in the lateral plane.

Special Instruments/Equipment/Implants

The surgical approach may be done with either a self-retaining retractor system or handheld retractors. Surgeon preference (usually dictated by the exposing surgeon) determines which retractor system is used. The Bookwalter self-retaining retractor system (DePuy) or Balfour retractors (V. Mueller) are commonly used at my institution. Handheld vein retractors for management of the inferior vena cava and the abdominal aorta or the iliac vessels are critical to performing this procedure. The retractors shown in Figure 7 are the type that I prefer. This retractor is available in 6-in and 8-in sizes. Intradiskal distractors are also quite helpful to distract the disk space open during disk removal. Typically, distractors of various sizes from 7 to 15 mm in 1-mm increments are used to maintain distraction of the disk space while working to remove the disk material. My preferred method is to alternate the disk space distractors from right to left while working the opposite side. This allows sequential dilation of the disk space while facilitating visualization of the side opposite the disk distractor.

Surgical Technique

Once the patient is positioned, images may be obtained with the C-arm to confirm that there is no significant rotation of the targeted disk space. This also may be helpful in localization of the surgical incision (Figure 8). Direct access to the disk space in the plane of the disk space is required for the insertion of most anterior lumbar interbody devices.

FIGURE 5 Photograph shows a Jackson Axis OSI table in the flat position.

Anterior spinal exposures may be done through relatively small incisions and should be quick and relatively bloodless procedures. Experienced surgeons should be able to perform a one- or two-level exposure safely in 10 to 15 minutes. The spine is approached through a midline vertical fascial incision, even if the skin is cut transversely. The literature describes other approaches, including oblique and paramedian fascial incisions. It is my opinion that these are more difficult because the spine is a midline structure, and general and vascular surgeons are most familiar with the midline fascial incision. Once the disk space is exposed, both AP and lateral images should be obtained to confirm the surgical level and establish the midline of the disk space. The midline should be marked on the disk space (Figure 9) or on the vertebral body to be used later as an internal reference point for placing the implant in a central location within the disk space. Many different interbody devices exist that may accomplish the objective of reconstructing the interspace and achieving a solid fusion. Some devices have integrated fixation designed into the implant. Others may be used alone or in conjunction with supplemental fixation. One type of cage used is shown in Figure 10.

FIGURE 6 Note the increased lordosis at L5-S1 as seen on a lateral fluoroscopic image (A) with extension of the operating table using the extension function of the Axis table (B).

FIGURE 7 Photographs of the instruments used for anterior lumbar interbody fusion. A, Handheld vascular retractors of various lengths. B, Note the gentle curve at the tip of the vein retractor to assist with retraction and visualization.

COMPLICATIONS

Exposure-related complications include injury to vascular structures, bowel injuries, or retrograde ejaculation. Additional complications may include thrombophlebitis, pulmonary embolism, incisional hernia, and prolonged ileus. Management of the vascular structures is the most critical component of the surgical exposure. The assistance of a general or vascular surgeon who is familiar with the type of exposure and visualization needed to safely perform the diskectomy and reconstruction may be helpful. The L5-S1 interspace is generally easier and safer to expose than the L4-L5 level. At L5-S1, it may be preferable to do the exposure from the right side through a retroperitoneal plane. This allows L4-L5 to be exposed in a subsequent procedure from the left side. To expose L4-L5 or multiple levels, generally a left-sided approach is preferred to ligate the iliolumbar vein, which is typically a left-sided structure.

FIGURE 8 Illustration shows localization of the incision. A, The view should be parallel to the disk space of the surgical level. The retroperitoneal plane may be approached from either the right or the left side and allows full exposure of the disks while retracting the great vessels. B, Illustration shows a left-sided approach. The retractors should not be depressed too firmly, or compression of the neurologic structures within the psoas muscle could result in a neurologic deficit following the surgery.

Some authors have suggested that a right-sided retroperitoneal approach may be done for any level from L2 through the sacrum.⁶ They have also proposed that the incidence of retrograde ejaculation is less frequent through a right-sided approach because the dissection of the left side superior hypogastric plexus is a sensitive structure. Bowel injuries are very uncommon with a retroperitoneal approach. It is more common when doing the exposure transperitoneally. Bowel injuries are most frequent through a laparoscopic approach, especially
when combined with a threaded interbody device, because visualization may be impaired.⁷ The incidence of retrograde ejaculation has recently been the subject of considerable debate. The historical literature supports that the incidence is primarily exposure related. The highest frequencies are seen in laparoscopic and transperitoneal approaches (10% to 15%) and least often seen in retroperitoneal exposures (1.5%).⁸^,⁹ The routine use of monopolar electrocautery also appears to increase the incidence of this complication compared with bipolar electrocautery. The impact of bone morphogenetic protein-2 (BMP-2; Infuse, Medtronic) on the incidence of retrograde ejaculation is uncertain. Recent reports have implicated that Infuse may be associated with an increased incidence of this complication.¹⁰^,¹¹ However, the precise mechanism of this relationship is not understood at this time. Considerations include the possibility that Infuse may have some unintended reaction with the autonomic nervous system in the vicinity of the anterior lumbar spine. Deep vein thrombosis and pulmonary embolism are unfortunate complications seen with anterior exposures. The incidence of deep vein thrombosis has been reported in the range of 3% to 5%. Pulmonary embolism occurs in less than 1% to 2% of patients.¹²^,¹³^,¹⁴

FIGURE 9 Intraoperative photograph shows the marking of the midline of the disk space. This is important for providing a reference point when placing the final implant.

FIGURE 10 Postoperative lateral (A) and true AP (B) fluoroscopic images show an interbody cage in place. This particular cage is constructed of titanium and comes in four pieces: superior and inferior end plate devices and two lateral struts. The cage is constructed in situ within the disk space for nontraumatic insertion and expansion of the disk space. Proper imaging is essential to ensure appropriate placement of the reconstructive device.

POSTOPERATIVE CARE AND REHABILITATION

Patients may be mobilized either on the day of surgery or the following day with physical therapy. The use of an external brace may be at the discretion of the operating surgeon. Once the patient’s mobility allows, the indwelling Foley catheter may be removed. Following surgery, clear liquids may be started once bowel sounds return. Advancing diet to solid foods is typically allowed with the return of flatus. Most patients with single-level surgery are able to return to a normal diet by postoperative day 1 or 2.

LATERAL LUMBAR INTERBODY FUSION

Lateral lumbar interbody fusion (LLIF) is a minimally invasive spine surgical technique that utilizes laterally based flank incision to access the intervertebral disk by way of the retroperitoneal space.¹⁵^,¹⁶ There are other names for this procedure, such as “transpsoas interbody fusion,” “extreme lateral interbody fusion,” direct lateral interbody fusion, or even “oblique lateral lumbar interbody fusion (OLIF),” but each represents a modification of procedures described by Mayer in 1997, McAfee et al in 1998, Bertagnoli et al in 2003, and Ozgur et al in 2006.¹⁵^,¹⁷ The procedure has generated interest among spine surgeons because of the relative simplicity of the technique and the potential reduction in complications compared with open anterior approaches to the lumbar spine. Along with this enthusiasm, there has been an increase in the number of LLIF procedures performed and a broadening of surgical indications.¹⁸

Despite a general lack of long-term, evidence-based literature supporting this rapid acceptance within the field, there are several perceived advantages of LLIF. Firstly, this approach does not require direct entry or violation of the spinal ligamentous structures, the spinal canal, the neuroforamen, or the retraction of nerve roots, allowing for a more atraumatic approach to the spine, the potential for less blood loss, and a more rapid functional recovery for the patient.¹⁵^,¹⁶ Furthermore, the procedure allows for the placement of a larger interbody cage than those placed during transforaminal lumbar interbody fusion (TLIF) or posterior lumbar interbody fusion (PLIF) techniques. It is thought that the larger interbody cage increases stability, with an associated reduction in rates of device subsidence through the accommodation of a greater volume of graft material. Increased density of graft creates a more favorable biomechanical environment for fusion because of increased cage-end plate contact surface area. Additionally, this technique allows for the indirect decompression of neuroforaminal impingement or lateral recess canal stenosis through restoration of intervertebral height.¹⁵ More specifically, the placement of wider interbody cages with higher profiles than those used with PLIF or TLIF procedures results in the spanning of the lateral extent of the apophyseal ring bilaterally, an area composed of more structurally sound bone.¹⁷ When applying similar criteria to LLIF cases as those applied to anterior interbody fusion procedures, Berjano et al found fusion rates of their cohort to be high, with percentages that fell within previously reported ranges. Based on their classification, 87.1% of operated levels within their cohort were “completely fused,” 10.2% were deemed “stable” or “probably fused,” and only 2.6% of levels had a “pseudarthrosis.”¹⁹

Although its use has expanded dramatically over the past decade, surgeons must balance the procedure’s benefits with its drawbacks. This technique (LLIF) is still unfamiliar to many spine surgeons. As such, the orientation of the regional anatomy may be confusing to those surgeons first attempting the technique. Another drawback is the approach-related morbidity to structures surrounding the spine; with dissection of the psoas muscle, there is often postoperative hip flexion pain and weakness.¹⁵ There are also limited reports of bowel perforation and ureteral injury related to the surgical approach. Aside from iatrogenic injuries, the approach itself can have practical limitations. The L5-S1 level is considered inaccessible and access to the L4-L5 should be limited to those who have advanced experience with LLIF techniques because of risk of injury to the adjacent lumbar plexus.¹⁵

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