Introduction
Lumbar spine disorders and the disabling pain associated with these conditions are associated with significant healthcare resource use and costs in the United States. Of these patients, an estimated 3% with back pain will require surgical intervention. Spine surgery in this patient population continues to be more prevalent, accelerated by the increasing number of aging patients. These patients are afflicted by a range of degenerative pathology for failed back surgery syndrome (adjacent segment disease [ASD], pseudarthrosis, and same-level recurrent stenosis) resulting in the need for revision surgery.
Revision surgery has its own intrinsic technical challenges and is exponentially more challenging in our aging population. Surgery can be confounded by patients with a long duration of symptoms and significant underlying medical comorbidities. Conditions such as diabetes or smoking have implications on bone biology and recovery. The indications for revision surgery may necessitate a range of interventions from a revision decompression to an extensive deformity correction. The reoperation rates for lumbar canal stenoses as a result of inadequate decompression or instability range from 7% to 12%, depending on the initial index surgery. The majority of published studies have been retrospective case series with varying definitions of successful outcome. Some are published reports of provider-defined outcomes rather than validated patient-reported outcome metrics. Hence effectiveness and long-term outcomes in elderly patients undergoing revision lumbar surgery remain unknown.
Indications for revision lumbar decompression can include ASD (owing to prior lumbar fusion) with disc degeneration, spondylolisthesis, or adjacent segment stenosis. These patients can present with recurrent mechanical low back and radicular pain localizing to the adjacent segment. Moreover, same-level recurrent stenosis from a prior lumbar laminectomy with persistent symptoms of claudication may occur. In addition, patients can develop coronal and sagittal deformities in the setting of prior surgery. Development of these deformities may be accelerated with conditions such as osteoporosis and osteomyelitis. Therefore it is important to apply the principles of diagnosis and pathophysiology in determining the optimal treatment needed as well as the appropriate surgical technique that is indicated.
Diagnosis and Indications for Surgery
Degenerative lumbar conditions can present clinically with pain, neurological compromise, spinal deformity, or a combination of all three. The etiology may stem from the previous surgical level, the adjacent level, or from a global combination of sagittal/coronal imbalance. Eliciting an accurate account of the location, timing, and inciting events for the chief complaint is important, to better understand the etiology and natural history of the disease process. The physical examination is a critical part of the assessment and should include a complete assessment of motor function, sensation, and reflexes. Evaluating for long tract signs may exclude upper motor neuron pathologies. Examination of the patient’s overall posture is necessary to evaluate spinal alignment in both the coronal and sagittal planes. Compensatory findings such as hip flexion contractures could be identified in the setting of suspected spinal deformity. Diagnostic imaging may include upright and bending films, computed tomography (CT) imaging, magnetic resonance imaging (MRI), or technetium bone scans to identify areas of increased bone turnover. These concordant findings may help support indications for surgical treatment of pseudarthrosis, fracture, ASD, instability, deformity, infection, and even device irritation.
Outcome Measures
Outcome metrics that measure pain, disability, and quality of life in the preoperative and postoperative period help determine the success of treatments. Examples of such measures include the visual analog scale for low back pain (BPVAS) and leg pain (LPVAS), Oswestry Disability Index (ODI), Zung self-rating depression scale, and Zurich Claudication Questionnaire. These measures can be used during patient visits, as mailed questionnaires, or even with phone interviews by an independent investigator not involved with clinical care (to avoid bias). Two important endpoints are time to narcotic independence and time to return to baseline level of activity. Improved pain and functional outcomes in the perioperative period are not only important for overall patient care, but also for managing healthcare costs and assessing the utility of a revision operation. Studies reporting successful clinical outcomes and functional improvement rates after revision spine surgery vary widely. Nevertheless, in the healthcare environment of value-based care, the effectiveness of revision decompression for symptomatic lumbar pseudarthrosis, ASD, or same-level recurrent stenosis remains poorly quantified but is overall positive. For example, Schlegel evaluated 37 patients who underwent either decompression alone or decompression and extension of fusion for symptomatic ASD, and observed significant improvement in visual analog pain scores in 70% of their patients who underwent extension of their fusion construct after decompression.
Adjacent Segment Stenosis
Adjacent segment stenosis is one of the main pathophysiological mechanisms leading to revision surgery. By definition, adjacent segment degeneration (ASDeg) refers to radiographic stenosis in the intervertebral discs adjacent to the surgically treated level, regardless of the presence of symptoms. ASD, however, is the presence of symptoms such as pain or numbness caused by instability or nerve compression as a result of ASDeg. In a meta-analysis of 94 articles, the incidence of ASDeg and ASD following lumbar surgery ranged from 21% to 31% and 6.4% to 10.7%, respectively. The data show that approximately 25% to 33% of ASDeg progresses to symptomatic ASD.
A number of factors, including natural history, biomechanics, and predisposing risk factors, are likely responsible for ASDeg. Patient age at the time of index surgery has a significant influence on the incidence of failed back surgery syndrome. There is an increased incidence of ASD, recurrent stenosis, and pseudoarthrosis in patients over the age of 50 years. Cheh et al. reported that 36% of patients over the age of 50 years developed ASD compared with only 17% of patients younger than 50 years. The degree of disc degeneration is also significantly correlated with aging in all levels of the spine, including in healthy volunteers. As a result, the observed association may presumably be secondary to the confounding effects of aging, such as a higher prevalence of osteoporosis and spondylosis with biochemical alterations, in addition to comorbidities related to fusion and instrumentation. Biomechanically, fusion of a motion segment creates a larger lever arm and nonphysiological center of motion that can lead to increased stress on the adjacent cephalad levels. Using a three-dimensional finite element model, it was shown that fusion at L4–L5 increased stress during flexion and extension movements on the L3–L4 vertebral end-plates and intervertebral discs. Similarly, cadaveric models also demonstrated increased intradiscal pressure on the adjacent proximal level to the instrumented level. Cunningham et al. showed a 45% increase in L2–L3 intradiscal pressure on flexion extension stress in an L3–L4 fixation model. Therefore, the use of instrumentation in the primary surgery appears to be a risk factor for the development of ASD. Two published series involving noninstrumented fusion reported longer intervals between the index and revision surgery. Schlegel et al. and Lee reported intervals of 8.5 and 13.1 years, respectively, before the development of symptomatic ASD. Kumar et al. found that patients with noninstrumented fusion remained symptom-free for 13.1 years before the onset of symptomatic ASD compared with only 5.2 years after a circumferential fusion was performed. This could be related to surgical techniques for dissection with compromise of integral structures such as the capsular ligament of the facet joint. Instrumentation has the potential for violation of the facet joint with placement into the superior articular facet. This can result in alteration of the facet load-bearing capability, as well as potentiated loads and forces at adjacent levels.
Other risk factors that have been shown to lead to ASDeg include high body mass index (BMI), preexisting ASDeg, laminectomy at the adjacent level of fusion, excessive distraction of the fusion level, spinopelvic mismatch, and osteoporosis. With regard to physical attributes, there is an increased risk of developing ASD in patients older than 60 years or with a BMI of greater than 25. Preexisting adjacent segment narrowing greater than 47% or degeneration of intervertebral disc and facet joint can also predispose to ASDeg. Laminectomy at the adjacent level of fusion or excessive distraction of the fusion level by interbody cage can increase the risk of ASD. The loss of lordosis following fusion or the presence of a multilevel construct with a longer lever arm can place more stress at the adjacent level. Floating fusion with the lower-end vertebra at L5 and high pelvic tilt are also potential risk factors for ASDeg.
Several strategies to reduce the risk of ASDeg have been proposed. Studies have indicated that preservation of the posterior elements at the fusion site is a key factor in reducing the risk of ASDeg. For example, patients with total laminectomy as opposed to less extensive hemilaminectomy or fenestration following fusion are more likely to develop ASDeg. In addition, the use of a low-profile interbody cage to minimize disc distraction can also reduce the risk of adjacent-level disease. Lastly, some animal studies have shown that the use of bisphosphonates or parathyroid hormone can significantly improve bone mass and improve vertebrae microstructures to reduce the risk of adjacent-level degeneration.
Revision Lumbar Laminectomy
Following a trial of conservative therapy, surgical options for ASD can include decompression alone or decompression with extension of the fusion construct. As a result, it is important to subdivide ASD into stenosis with or without instability to determine whether an extension of fusion is necessary. Given these criteria, a treatment-based classification of ASDeg has been proposed: (1) ASDeg without stenosis or instability, (2) ASDeg with stenosis alone and no instability, (3) ASDeg with instability alone and no stenosis, and (4) ASDeg with both stenosis and instability ( Fig. 7.1 ). Surgical strategies can include surgical decompression and extension of the posterolateral fusion, posterior lumbar interbody fusion with instrumentation, or minimally invasive interbody fusion.
