Axial back pain is a common problem encountered clinically, frequently related to degeneration of lumbar segments. This chapter summarizes anterior, posterior, and combined approaches for fusion. The risks and benefits of these approaches are discussed. Although surgical technique used to achieve fusion is usually one of surgeon preference, the principles discussed can aid the clinician in choosing an appropriate technique for each patient. The purpose of this chapter is to review the available surgical options to treat axial low back pain that is degenerative in nature.
Anterior and lateral techniques allow sparing of posterior soft tissue, yet offer fewer decompressive options.
Posterior techniques allow for maximal decompression, interbody and posterior fusion, yet lead to more destruction of posterior soft tissues.
Anterior and posterior approaches allow maximal fusion rates but pose greatest risk to patients secondary to assuming risk of both approaches.
Maximal removal of disc and insertion of bone graft into interbody space, and restoration of lordosis to an interspace through distraction can be accomplished with an anterior or lateral approach.
Decompression of neural structures is more complete and fusion is possible through posterior approach.
Combined approaches allow advantages of both the anterior and posterior approaches to be accomplished.
Anterior and lateral approaches allow less decompression to be accomplished.
Anterior and lateral approaches pose greater risk to vascular structures, ureters, and bowel.
Posterior approaches lead to greater destruction of posterior soft tissues.
Posterior approaches limit the distraction and amount of interbody grafting that can be accomplished.
Combined approaches increase surgical risks by exposing patients to risks of two procedures and increasing surgical time.
Axial back pain is a vexing problem that plagues many patients and can be refractory to both surgical and nonsurgical treatment alike. Anatomically, the lumbar spine is a complex organ with many potential pain generators including the intervertebral disc, facet joints, muscles, tendons, and ligaments. Other potential sources of pain include mechanical spinal instability, spondylolysis, osteoporotic fractures, tumor, and infections. As a result, successful identification of the pain generator requires a full understanding of the various causative factors, a thorough history, complete examination, and careful correlation with imaging and provocative studies as indicated.
Once an evaluation is completed and conservative measures attempted, and the surgeon has determined that a patient is a reasonable candidate for surgical intervention, the process of surgical technique selection begins. Controversy continues to exist concerning the role of surgery in the treatment of patients with axial back pain. Fritzell et al. have demonstrated in a randomized study, however, that surgical intervention can offer significant pain relief in patients with back pain who do not respond positively to conservative measures when compared with continued conservative measures alone. This study was limited to back pain presumed to originate from degenerative disease of the lumbar spine.
Strong opinions as to the ideal technique in different patients vary widely in the surgical community. Few data exist to support one technique versus another in most cases. Indeed, Fritzell et al. have demonstrated in a randomized study that surgical technique had little effect on ultimate clinical outcome. Therefore, the purpose of this chapter is to review the various surgical techniques available and discuss some of the potential advantages or disadvantages of these techniques, rather than make direct comparisons of these techniques to one another. Furthermore, it is important to note that, although patient selection, diagnostic testing, and selection of surgical technique are no less controversial than the role of surgery, they remain outside the primary scope of this chapter.
ANTERIOR APPROACH: THEORETICAL ADVANTAGES AND DISADVANTAGES
Anterior approaches to the lumbar spine for axial back pain have become increasingly popular in the last decade as the approach has become more familiar and instrumentation has advanced. Several potential advantages have been reported in the literature with the use of the anterior approach.
By definition, the anterior approach, either from a direct anterior or a lateral approach to the vertebral body and intervertebral disc, avoids injury to the posterior structures of the spine. The musculature, tendons, ligaments, and neural innervation of the musculature located posteriorly in the lumbar spine are spared direct surgical trauma. As a result, anterior approaches reduce the risk for injuring structures that contribute to the potential causes of low back pain.
In comparison with currently described posterior approaches, anterior approaches allow for increased exposure and access to bony surface area between vertebral bodies. Because virtually the entire end plate of the vertebral bodies can be exposed, this maximizes the surface area available for potential fusion. Biomechanically, anterior grafts within the interbody space are placed under direct compression, as opposed to posterior and posterolateral grafts, which are applied under tension in an onlay fashion and therefore may increase fusion rates. Furthermore, in many cases, the ability to restore normal intervertebral body height may be maximized because of fewer structures inhibiting access and the ability to place a larger interbody graft than in the posterior approaches
Several potential disadvantages exist as well, and most are approach-specific–related complications. The bowel, ureters, and neurovascular structures are all at risk for injury during the anterior approach. Other complications, such as deep venous thrombosis (DVT) and postoperative ileus, can occur with other surgical approaches as well but may be greater during anterior approaches.
Direct ureter and bowel injuries are less common but are still possible. After surgery, bowel problems can occur as a result of incisional or internal hernias, or as the result of adhesions. Furthermore, a postoperative ileus can be common after all spinal surgeries but may be greater after an anterior approach in both transperitoneal and retroperitoneal lumbar approaches because of mobilization of the peritoneal cavity.
Vessel injury occurs at varying rates in the literature but occurs in about 2% to 4% of patients. Vessel injury can lead to a large and potentially life-threatening hemorrhage. This can occur as a direct injury to the great vessels during the surgical exposure or to their branches during mobilization of the great vessels. Because the segmental vessels run horizontally in the midvertebral body, they are not at great risk during exposure of the intervertebral disc, but they should be identified and ligated during exposure of the vertebral bodies. In particular, during exposure of the L5 body, care should be taken to identify and control the iliolumbar vein, which if inadvertently cut or avulsed, can result in rapid, massive bleeding that can be life-threatening and difficult to control. The middle sacral artery is at risk when exposing the L5-S1 intervertebral disc space.
Neurologically, several structures are at risk and include the autonomic nervous system and lumbosacral plexus. Injury to the autonomic nervous system, in particular, the sympathetic chain can lead to complications such as differing vascular tone in the legs and, therefore, temperature differences between the legs. Although this will result in a warmer leg on the side of the sympathetic injury, the more typical patient complaint is a cooler contralateral lower extremity. Although this is usually self-limiting, and typically normalizes approximately a year after surgery, preoperative patient and staff education and perioperative recognition can help alleviate worries and unnecessary additional studies.
Injury to the superior hypogastric plexus can result in retrograde ejaculation in male patients and sexual dysfunction in both male and female patients. Retrograde ejaculation in male patients is the most common complication, occurring in 0.5% to 2% of male patients, resolving in 25% to 33% of these patients by the second year after surgery. Because the superior hypogastric plexus lies anteriorly to the L5-S1 disc space, it is at particular risk during exposure of this level. The use of blunt dissection and limiting use of Bovie to bipolar electrocautery can help reduce this complication.
The lumbosacral plexus or psoas muscle can be injured, leading to lower extremity weakness or numbness, particularly with the lateral transpsoas approach. Anatomic dissections have demonstrated that, in most patients, the lumbosacral plexus lies predominantly in the posterior half of the psoas and may be at greater risk for injury during dissection of the posterior aspect, in comparison with the anterior aspect, of the psoas. As a result, the use of neuromonitoring is recommended if a transpsoas approach is being used. Injury to the genitofemoral or ilioinguinal nerve has also been reported.
Because of direct manipulation and compression of the inferior vena cava (IVC) and common iliac vein, the rate of DVT may be increased over posterior approaches, and occurs in 1% to 11% of patients. Arterial thrombosis is also possible, though less common, and can be limb-threatening.
POSTERIOR APPROACH: THEORETICAL ADVANTAGES AND DISADVANTAGES
Posterior approaches to the lumbar spine have enjoyed a significant increase in the number of implants and techniques available during the last decade as well. These provide many advantages over anterior approaches. The greatest advantage is the familiarity of the posterior approach to the spine surgeon, and ability to access both the anterior and posterior column of the spine through a single surgical exposure. Although full access to the vertebral body and intervertebral disc can be limited from a posterior approach, in most cases, sufficient exposure can be achieved to perform the necessary procedures (discectomy, interbody fusion, partial, and in selected cases, complete corpectomies).
Therefore, by avoiding the anterior approach, surgical injury to the ureter, vessels, and bowel are less common. Notably, injury to these structures can occur from a posterior approach and have been reported. This typically occurs when spinal instruments and implants are inadvertently placed beyond the confines of the intervertebral disc and vertebral body resulting in direct vessel injury, bowel perforation, or both. Similarly, the risk for ileus, autonomic injuries, and DVTs may also be less common because of the ability to avoid manipulation and retraction of these structures during the posterior approach.
Lastly, as techniques and implants continue to improve, the ability to reconstruct both the anterior column support and posterior tension band through a single incision is an appealing advantage. More specifically, interbody fusions either as a posterior lumbar interbody fusion or transforaminal lumbar interbody fusion can potentially achieve biomechanical fixation similar to what is seen during a combined anterior-posterior approach, but through a single approach and stage of the operation. Furthermore, it is believed that exposure of the entire facet complex, part of most posterior approaches, essentially denervates the facet joint, thus potentially removing or reducing pain from a potential pain generator in the commonly degenerative facet joint.
Disadvantages of the posterior approach include direct trauma to the musculature during exposure, with detachment of the muscles from their insertion points to the posterior vertebrae. This can lead to muscle atrophy, and potentially produce pain and decrease the overall strength of the lumbar spine; it has been termed fusion disease.
During instrumentation, if used, neural structures are at risk for injury, particularly when interbody fixation or fusion is performed (0.5–4% of patients). Dural violations are also more common and can occur with or without the use of instrumentation.
In regard to fusions, posterior and posterolateral fusions are under shear and tension; therefore, they are at risk for bony resorption and development of fibrous unions when compared with anterior fusions that are placed under compression. In cases where a posterior decompression (laminectomy) has been performed, the bony anatomy available (facet and intertransverse process fusions) is more limited in surface area. Furthermore, when compared with anterior interbody fusions, posterior interbody fusions provide less complete end-plate and surface area preparation, which is due, in part, to the neural structures limiting access to the interbody space.
In the event of vascular injury, no immediate access exists to these structures to tamponade and achieve control for repair of the structures, and this injury can lead to life-threatening hemorrhage. Lastly, deep wound infections that affect instrumentation or grafting are generally more common than in anterior approaches.
Combining an anterior approach with a posterior approach allows for maximal fixation and grafting to be accomplished, and can therefore maximize fusion rates. However, the risks of both procedures are also combined, as well as significantly increasing operative time, blood loss, infection rates, soft tissue damage, and recovery times.
Direct Anterior Approaches
Several procedures can be performed through a direct anterior approach for the management of degenerative lumbar disease. This section briefly reviews the two most common procedures: anterior lumbar interbody fusion (ALIF) and anterior intervertebral disc replacement.
Anterior Lumbar Interbody Fusion
ALIFs have been well described. Numerous variations exist on the general theme of accomplishing access to the intervertebral disc space from a direct anterior approach, which can be performed either transperitoneally or retroperitoneally. Laparoscopic transperitoneal approaches have also been described; however, significant risk for vessel injury and difficulty controlling vessel bleeding if injury occurs have been reported.
Anatomy of this region is shown in Figure 21-1 . Generally, a left retroperitoneal approach is used. This approach allows easier retraction of bowel, vessels, and ureters, whereas avoiding the morbidity of direct trauma to the bowel (prolonged ileus, bowel adhesion formation, among other complications). Figure 21-2 demonstrates the standard plane of dissection for a left anterior retroperitoneal approach.