CHAPTER SYNOPSIS:
Axial low back pain is a prevalent cause of impairment with significant socioeconomic consequences. Degenerative disc disease is a common cause of axial back pain. Conservative measures should be the mainstay of treatment in discogenic back pain. Although a great deal of debate still exists regarding the indications and role of surgery in the management of lumbar degenerative disease, in selected cases, lumbar arthrodesis may be a viable option after all other conservative interventions have been exhausted. Although the superiority of one surgical technique is still not clearly established, interbody fusion and posterolateral fusion appear capable of yielding acceptable outcomes in selected patients with lumbar disc disease.
IMPORTANT POINTS:
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Conservative measures including pharmacotherapy and physical therapy should be the mainstay for treatment of axial back pain for lumbar disc disease.
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Surgical management should be reserved as the final option for discogenic back pain because the indications and the role of surgery in disc degeneration are still not firmly established.
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In selected patients, lumbar arthrodesis may be a viable option in the surgical management of lumbar disc disease.
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The use of instrumentation can improve fusion rates, but its routine use should be avoided and made on an individualized basis.
CLINICAL/SURGICAL PEARLS:
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Careful patient positioning and ensuring adequacy of fluoroscopic imaging before beginning the procedure can save intraoperative time and avoid complications such as ophthalmic injury and intraoperative epidural bleeding.
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The pedicle is the key anatomic landmark to safely identify because it allows a spine surgeon to safely find the lateral edge of the nerve root medially and the intervertebral disc superiorly.
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The transforaminal lumbar interbody fusion (TLIF) construct should be compressed at the end of the procedure to establish an optimum graft-bone interface and to re-establish lumbar lordosis.
CLINICAL/SURGICAL PITFALLS:
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If instrumentation will be performed, positioning the patient in lordosis can help avoid “flat back” syndrome.
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During preparation of end plates in TLIF, excessive removal of the bony portions of the end plates should be avoided to reduce the risk for graft subsidence.
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The anterior longitudinal ligament should be preserved in TLIF to reduce the risk for potential vascular injuries to vessels anterior to the vertebral body.
SCOPE OF THE PROBLEM
Low back pain affects approximately 70% to 85% of individuals at some time during their lifetime. Impairment of the spine and the back ranks as one of the most common causes of physical limitation in individuals younger than 50 years. The cost to society from loss of work, compensation, and treatment is astounding.
Back pain can occur with or without radiculopathy. Pure axial back pain is defined as low back pain without radiculopathy. The source of discomfort from axial low back pain can be multifactorial in nature and sometimes difficult to clearly identify. The most common causes of axial pain include degenerative disc disease, facet arthrosis, sacroiliac joint arthrosis, and musculoligamentous injuries.
For the purpose of this chapter, we focus on degenerative disc disease as the source of axial back pain. Although controversial, the subsequent discussion focuses on potential surgical management options for discogenic axial back pain. Specifically, we review the causative factors, operative indications, surface and radiologic anatomy, surgical techniques, and postoperative care for axial back pain resulting from lumbar degenerative disc disease. Lumbar back pain with radiculopathy resulting from disc herniation is specifically addressed in other sections of this textbook.
CAUSES OF DISCOGENIC LOW BACK PAIN
The relation between disc degeneration and low back pain is not well understood and is likely a result of several concomitant factors. A vertebral segment is composed of three joints : the intervertebral disc and the two facet joints. The intervertebral disc consists of a central nucleus pulposus and an outer fibrocartilaginous annulus fibrosus. As the disc degenerates, its cellular composition is altered, which leads to a changes in biomechanical properties. Radiographically, this is seen as lost of hydration followed by the loss of disc height. As the intervertebral disc degenerates, the associated loss of disc height can alter the mechanic of and increase stress across the two facet joints. The increase in stress leads to increased ligamentous and capsular laxity, which results in progressive mechanical overload of the pathologic disc and facets. This may then result in pathologic segmental instability, motion, arthritis, and pain. Although still somewhat controversial, facet arthrosis has also been suggested as a possible source of back pain. Nociceptive nerve fiber innervation of facet joint capsule and pericapsular tissue has been identified, which would seem to implicate facet arthritis as a potential pain generator. However, the overall clinical picture of facet arthritis is variable. Facet joint injections as a diagnostic and therapeutic modality have not always been effective. This has been shown in randomized controlled trials, which have not demonstrated a significant difference between efficacy of placebo and that of steroids and local anesthetics during injections that target the facet joint.
In addition to the change in structure, the neovascularization of a degenerating disc has also been proposed as an additional mechanism that contributes to discogenic back pain. Normally, the nucleus pulposus and inner annular zone of a healthy intervertebral disc are usually devoid of nerves. With degeneration, ingrowth of nerve fibers and blood vessels may occur into the inner annulus fibrosus and nucleus pulposus. This pathologic neurovascular proliferation into the disc combined with release of local chemical mediators that sensitizes the nerve endings may contribute to the cause of low back pain in lumbar disc degeneration.
OPERATIVE INDICATIONS
As with any medical condition, the diagnosis of degenerative disc disease and discogenic back pain is established after performing a careful history, physical examination, and the appropriate confirmatory studies. For axial pain resulting from disc degeneration, nonsurgical options should be exhausted before operative treatment is considered. Most individuals with axial pain resulting from chronic disc degeneration can be treated effectively with nonoperative treatment. The general natural history with lumbar disc disease is resolution of the pain over time. Therefore, every effort to maximize conservative measures should be performed before a spine surgeon and a patient enters into a discussion regarding surgical treatment.
Although most patients improve with conservative measures, surgical intervention may have a role in selected patient with chronic low back pain. In a multicenter, randomized, controlled trial, Fritzell et al. and the Swedish Lumbar Spine Study Group attempted to establish the role of surgical lumbar fusion for patients with chronic low back pain. The study randomized 294 patients with chronic low back pain with radiographic evidence of disc degeneration at L4-L5 and L5-S1 into either a surgical or conservative treatment arm, which consisted of physical therapy, education, and various treatments aimed at pain relief. At minimum 2-year follow-up, all primary outcome measures within the study favored the surgical group including pain reduction, reduction in disability, patient satisfaction, and return to work. Unfortunately, this study did not report on the intermediate- and long-term results of the various interventions.
Although surgical indications may vary, the general indications for lumbar fusion for axial back pain stemming from degenerative disc disease include patients with the following characteristics: (1) unremitting pain and impairment for more than 1 year, (2) failure to respond to aggressive physical therapy and conditioning for 3 to 4 months, (3) magnetic resonance imaging findings consistent with advanced degenerative disc disease, and (4) a negative psychiatric evaluation and no evidence of secondary gain. Concordant pain on provocative discography may be a helpful tool. Despite meeting all the general indications, a thorough discussion regarding expectations and outcome should still occur between a spine surgeon and the patient before a decision is made to proceed with surgical management of lumbar discogenic back pain.
SURGICAL OPTIONS FOR LUMBAR DEGENERATIVE DISC DISEASE
Despite the abundance of literature regarding the topic, the ideal surgical management for degenerative disc disease has not been fully established and remains controversial. Because the pain is thought to be related to mechanical deterioration of the disc that results in pathologic motion between the vertebral segments, the overriding treatment principle remains obtaining a stable lumbar arthrodesis of the diseased segment. Fusion of the painful unstable lumbar segments would theoretically halt the progression of the pathologic motion and pain. The current debate includes whether to perform an anterior, posterior, or combined circumferential procedure. Clear guidance regarding whether to remove the diseased disc in question remains in debate as well. Although the literature contains many comparative studies that analyze the various techniques, a clear consensus has not been reached for surgical treatment of axial back pain from degenerative disc disease.
Common techniques noted in the literature for discogenic back pain include anterior lumbar interbody fusion (ALIF), posterior lumbar interbody fusion (PLIF), posterolateral lumbar arthrodesis with or without instrumentation, and combined anterior-posterior (circumferential) fusion. As improvements are made in our understanding of the surgical anatomy and instrumentation, minimally invasive procedures that decrease the morbidity associated with existing methods are developed. One such technique that utilizes those advances is the transforaminal lumbar interbody fusion (TLIF). Furthermore, as our understanding of the pathophysiology and natural history of degenerative disc disease increases combined with improved surgical techniques, advances in spinal implants, and increased knowledge of the role of biologics, alternative surgical options such as disc regeneration or disc replacement may become a more viable and attractive option.
Historical Perspective
Spinal fusions were first reported in 1911 for treatment of tuberculosis as a means of preventing the progressive deformity related to Pott disease. In that same year, Hibbs reported on his experience using spinal fusions for treatment of the same disease. Hibbs later expanded the use of spine fusion to the treatment of deformities associated with scoliosis in 1924. Spine fusion would later be adapted for the treatment of other forms of spinal deformities and disease such as kyphotic deformities, fractures, spondylolisthesis, and intervertebral disc disease.
Since the initial case reports, the technique of posterolateral spine fusions has been modified and refined. The understanding involving bone fusion biology and instrumentation has also improved drastically. Basics to having a successful bone fusion are: (1) graft material with adequate osteogenic, osteoconductive, and osteoinductive properties; (2) adequate local vascularity for bone formation; and (3) an environment conducive to bone formation. Although the gold standard for bone graft remains the iliac crest graft, there is an increasing interest in the development of synthetic bone substitutes.
In the 1930s, Capener provided the first description of lumbar interbody fusion, which was an anterior approach described for the treatment of spondylolisthesis in the lumbar spine. Later, Cloward described a technique for performing a lumbar interbody fusion through a posterior laminectomy, which became the first description of the PLIF. The original procedure preserved the facet joint, and hence required a significant amount of nerve root retraction to obtain adequate exposure to the intervertebral disc. As a result, this limited the procedure to levels below L3 because of the unacceptable risk the retraction would pose to the conus medullaris and cauda equina above that level. In 1998, Harms and Jeszensky described and popularized a posterior approach that accessed the intervertebral disc space via a path through the far lateral portion of the intervertebral foramen, which became known as the TLIF. This approach minimized the morbidity associated with PLIF and allowed interbody fusions to be performed above L3 from a posterior approach.
Advantages of a Posterior Surgical Approach to the Spine
A complete posterior approach to treatment of axial back pain is appealing to most spine surgeons because the anatomy of the posterior approach is more familiar, and hence technically easier. The surgery can be done by one surgeon. An anterior approach to the lumbar spine, in contrast, oftentimes requires the assistance of a general or vascular surgeon because most spine surgeons are not comfortable with the territory to perform the approach independently. The anterior approach also places several key structures such as the great vessels, presacral plexus, and the sympathetic chain at risk. In addition, proponents of a complete posterior approach would also argue one can address all three columns of the spine from the back. A posterior approach would allow access to the vertebral body for an interbody fusion, as well as directly visualize, decompress, and instrument the posterior elements.
Interbody Fusion versus Posterolateral Fusion Techniques
Because the pathologic structure in question in discogenic back pain is located anteriorly, proponents of an anterior approach believe that a posterolateral fusion alone may be insufficient to address the pathology at the level of the intervertebral disc. Several authors believe that once the annulus is identified as the pain generator, the pathologic disc should be addressed and eliminated. Many believe this is best accomplished through an anterior approach, which allows the entire intervertebral disc space to be visualized and decompressed. In addition to removing the pain generator, an interbody fusion may better allow for restoration of disc height and indirect decompression of the neuroforamen. Another argument cited by proponents of an anterior stabilization procedure is the theoretical biomechanical advantage of an anterior fusion. Because the biomechanical stiffness of the arthrodesis is greatest if it is closer to the center of the motion segment, many hypothesize that interbody fusions would have the greatest rigidity, whereas the posterior and posterolateral fusion would have the least.
Proponents of the posterolateral fusion, however, would argue that a posterior fusion alone is sufficient to provide relief of the axial pain symptoms in the majority of patients. In addition to the morbidity related with exposing the diseased disc, interbody fusions are also associated with complications regarding the graft such as partial collapse, migration, and even extrusion. Hence, for some authors, the associated morbidity with an interbody fusion procedure may outweigh the proposed benefit. Although still debated, reported available comparison studies evaluating fusion rates and outcome in patients undergoing interbody fusion versus posterolateral fusion with or without instrumentation alone appear to favor an isolated posterolateral fusion alone.
In a prospective, multicenter, randomized study from Fritzell et al. and the Swedish Lumbar Spine Study Group, simple posterolateral fusions yielded similar results in terms of pain relief and decrease in disability when compared with the anterior and posterior interbody fusion group at 2-year follow-up. In addition to similar patient outcomes, fusion rates between an anterior and posterior interbody fusion procedure and posterolateral fusion were also similar. The authors therefore conclude that the risks associated with interbody fusion versus a posterolateral alone technique may not be necessary. Similarly, Lidar et al. retrospectively evaluated 100 patients who underwent either PLIF or noninstrumented posterolateral fusion. The authors found that although PLIF was able to maintain disc height better than the posterolateral fusion group, the clinical and functional outcomes between the two groups were similar at approximately 2-year follow-up. In the authors’ opinion, they believe that performing the least demanding procedure, which was the posterolateral fusion without instrumentation, may be the most prudent.
Instrumented versus Noninstrumented Posterolateral Fusion
The decision whether to instrument in posterolateral lumbar fusions for lumbar degenerative disc disease remains an area of controversy. Methods of fixation are numerous, which include wires, hooks, and pedicle-screw–based segmental fixation. The current construct of choice is segmental fixation using pedicle screws. Pedicle screws allow for the ability to control all three columns of the spine through a posterior approach, the ability to limit the fusion to the involved motion segments, and the ability to instrument despite the lack of posterior elements, and it avoids placing fixation in the spinal canal.
The obvious advantage of pedicle instrumentation is the immediate stability it provides to the involved spinal segment, which theoretically may increase the fusion rates. This hypothesis has been confirmed in multiple studies in which addition of pedicle instrumentation reduced the rate of pseudoarthrosis when compared with posterolateral fusion without instrumentation. Lorenz et al. prospectively studied a group of 68 patients they treated with posterolateral lumbar fusion. Twenty-nine patients were treated with pedicle screw fixation and 39 patients were treated without pedicle screw fixation. The patients treated with pedicle screw fixation had improved fusion success rates (100% vs. 58%) compared with patients treated without instrumentation as demonstrated on dynamic radiographs. Patients treated with instrumentation also had better back pain relief and greater return-to-work rates than patients treated without instrumentation (72% vs. 31%).
Similar to single-level posterolateral fusions, use of instrumentation for multilevel fusions have also reduced pseudoarthrosis rates. In a prospective multicenter trial, Wood et al. examined the use of instrumentation in one- to four-level fusion in lumbar degenerative disc disease, with most patients having two-level fusion or greater. When compared with historic controls, the authors conclude that the patients who had noninstrumented fusion were 24 times more likely to experience development of a pseudoarthrosis when compared with patients with instrumented fusion. In addition to increasing fusion rates, instrumentation also has been suggested to improve the postoperative course in patients who underwent posterolateral fusions. The advantage of instrumentation includes decreased rehabilitation time, obviating the need for postoperative bracing and reducing postoperative analgesic requirements.
Although several studies have demonstrated the advantage of pedicle screw fixation in lumbar posterolateral fusion, as in all cases, these findings should be individualized to the patient’s disease and to the spine surgeon’s experience and preference. Instrumentation does present a new set of potential morbidity when compared with in situ (onlay) posterolateral fusion. One study reported overall complication rate associated with pedicle instrumentation at approximately 5%. Hence, the authors currently recommend pedicle instrumentation to be performed only by surgeons who are knowledgeable and comfortable with this technique. Although pedicle instrumentation should be performed judiciously, the authors believe that use of instrumentation should be strongly considered in cases in which patient risk factors for pseudoarthrosis are present, such as smoking, diabetes, revision surgery for failed back treatment, or pseudoarthrosis.
Posterior Lumbar Interbody Fusion versus Transforaminal Lumbar Interbody Fusion
An alternative to an anterior approach for interbody fusion is a posterior approach. A posterior approach avoids the aforementioned risks and morbidities associated with manipulating the abdominal structures. Unfortunately, because of the amount of retraction on the neural elements to gain access to the intervertebral discs, PLIF frequently cannot be safely performed above L3. In an effort to minimize the morbidity with PLIF while maintaining the advantages of a posterior interbody fusion procedure, Harms and Jeszensky described the TLIF technique. When compared with the standard bilateral PLIF procedure, TLIF offers the following advantages: (1) theoretical smaller risk for adjacent segment instability and a larger surface area for fusion purposes because one facet and posterior lamina are preserved; (2) elimination of contralateral scar formation; (3) less dural retraction for visualization of the disc space; and (4) access to disc levels above the level of L3.
The reported early results with TLIF have been favorable. Hackenberg et al. report their experience with TLIF on 52 patients with minimum of 3-year follow-up. They found significant improvement in pain relief and Oswestry Disability Index scores at the latest patient follow-up. The overall fusion rate achieved within that study was also comparable with other reported interbody techniques such as ALIF and PLIF. In addition to similar fusion rates, TLIF also appears to decrease the morbidity associated with PLIF. Humphreys et al. compared 34 PLIF procedures with 40 TLIF procedures with respect to blood loss, operative time, and complications. Although similar fusion rates and no differences in outcomes were noted for single-level fusions, significantly less blood loss was noted with TLIF in two-level procedures. More importantly, PLIFs were associated with multiple complications, whereas none was reported with the TLIF procedure. The combination of minimizing the morbidity while maintaining the ability to perform a posterior “360”-degree procedure make TLIF an important procedure of which every spine surgeon should be aware.
Minimally Invasive Surgery: Pedicle Instrumentation and Transforaminal Lumbar Interbody Fusion
An emerging area of treatment that is becoming an alterative to traditional open fusion procedures is minimally invasive techniques for lumbar arthrodesis. Compared with the open approach, these minimally invasive techniques, which involve the use of a tubular retraction system inserted through muscle fascicles, minimizes the incision, tissue disruption, and muscle stripping associated with accessing the spine. Several retractor systems exist, and although not inclusive, include the MAXCESS system (NuVasive, San Diego, CA), Pipeline system (DePuy, Johnson and Johnson, Raynham, MA), and the METRx dilator system (Medtronic Sofamor, Danek, Memphis, Tenn.) ( Fig. 19-1 ).
Related posts:
Rheumatoid Arthritis of the Cervical Spine
Instrumentation of the Lumbar Spine for Degenerative Disorders
Posterior Lumbar Interbody Fusion for Degenerative Disorders of the Spine
Failure of Cervical Spine Instrumentation
Failure of Lumbar Spine Instrumentation
Facet Joint Replacement for the Treatment of Degenerative Disorders of the Spine
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