Degenerative lumbar spinal stenosis is one of the common spinal disorders that afflict the elderly, and as patients age, their symptoms often fail to respond to conservative treatment and require surgical intervention.
I. Lumbar spinal stenosis: what are we dealing with?
There are many definitions of lumbar spinal stenosis in the literature. The main definitions are: anatomical, imaging or clinical. This article adopts the North American Spine Society Spinal Stenosis Group’s definition of degenerative lumbar spinal stenosis, which focuses on symptomatic degenerative lumbar spinal stenosis for which there is evidence to support the need for surgical treatment. It is defined as a clinical syndrome of lumbosacral or lower extremity pain, with or without back pain, due to reduced mobility of the lumbar spinal nerves, blood vessels, and other tissues. Usually, anterior flexion, sitting or lying down can relieve the symptoms. However, if daily exercise or a certain position induces severe radicular symptoms or neurologic claudication, surgical intervention is required.
Although back pain is a common concomitant symptom in patients with degenerative lumbar spinal stenosis, it is progressive radicular symptoms or neurogenic claudication that determines the need for surgical treatment. The incidence of spinal stenosis in the elderly population is not fully known, but a survey conducted by the Center for Health and Quality of Life Research in the United States showed that 14% of patients who sought care from a spine specialist for lower back pain had severe bony spinal stenosis that required surgical treatment.
In patients with degenerative lumbar spinal stenosis, the decision to intervene surgically is based on a combination of the patient’s clinical symptoms combined with the imaging presentation. In other words, no matter how severe a patient’s lumbar spinal canal or nerve root canal stenosis may appear on imaging, surgical intervention is not considered first as long as the patient has no clinical symptoms or has mild symptoms. Similarly, if a patient’s clinical symptoms are not supported by strong imaging evidence, surgical intervention is likewise not considered first, regardless of how severe the symptoms are. In addition, surgical intervention should only be considered if conservative treatment is not sufficiently effective in relieving the patient’s clinical symptoms.
For patients whose clinical symptoms and imaging manifestations are consistent and for whom conservative treatment is ineffective, the surgical approach that is most effective in relieving the patient’s symptoms should be selected primarily on the basis of the highest level of evidence provided by evidence-based medicine. For example, a patient with simple central spinal stenosis without vertebral slippage resulting in lower extremity pain can be effectively treated with decompression surgery alone. In contrast, for those patients with extensive central and paracentral spinal stenosis and deformity, also with back pain as the main symptom, a different modality of lumbar fusion surgery needs to be considered.
Second, if fusion is not performed, how should it be treated?
1.Simple decompression
Usually, the more severe the nerve root symptoms or neurogenic claudication symptoms are, the more effective surgical decompression is compared to conservative treatment. In patients with moderate lumbar spinal stenosis symptoms, there is a lack of strong evidence that surgical treatment is superior to conservative treatment (level C evidence). In patients with more severe symptoms, there is direct evidence (level B evidence) that surgical decompression alone is 80% more effective than conservative treatment and lasts up to 10 years postoperatively. The results of the 4-year clinical trial of the Prognostic Follow-up Study of Patients with Lumbar Spinal Stenosis (SPORT), recently published by Weinstein et al, provide the highest level of evidence to support the continued efficacy of surgical treatment over conservative treatment. Its a randomized, controlled, double-blind trial that included 411 patients with surgically treated degenerative lumbar spinal stenosis, 88% of whom underwent only simple decompression surgery without lumbar fusion, and they illustrate the advantages of surgical versus non-surgical treatment in terms of relief of physical pain, restoration of physical function, and improvement in the Oswestry Disability Index.
Limited decompression should be considered in certain patients who are clinically rare and have unilateral or bilateral lower extremity nerve root symptoms due to imaging showing simple lateral saphenous fossa stenosis. Laminar decompression or minimally invasive surgery can be performed. Minimally invasive techniques are used as a reasonable intervention for the treatment of such patients. This is mainly because of the selection bias that occurs in the treatment of young patients with lumbar disc herniation. However, the research evidence supporting minimally invasive surgery as an alternative to open decompression surgery is currently limited. A large series of studies conducted by the Cleveland Clinic has shown that minimally invasive surgery can reduce the use of anesthetics and shorten the length of stay compared to traditional open decompression surgery. Most importantly, the clinical outcomes are comparable. The incidence of reoperation and complications is also relatively low. The incidence of both secondary surgery and complications was low in this investigation. A purely comparative retrospective analysis by Rahman et al. found that the prognosis was similar for minimally invasive surgery and conventional open decompression, but that the former reduced operative time, decreased bleeding and facilitated early mobility.
2. Which patients cannot be decompressed alone
In patients with low back pain as the main clinical manifestation and degenerative lumbar spinal stenosis with multiple segments, the effect of single-segment decompression alone is very limited. A search of Pubmed for literature on laminectomy and open decompression surgery for simple low back pain yielded 246 articles, most of which were studied in young patients with predominantly herniated discs and back pain treated with percutaneous surgery, and rarely in young patients with concomitant lumbar spinal stenosis. There is no reliable evidence that decompression alone can achieve better clinical outcomes in patients with predominantly low back pain and degenerative lumbar spinal stenosis.
3.Indirect decompression
Patients with only one or two segments of spinal stenosis and intermittent claudication that is relieved in forward flexion may be treated with one of several interspinous spine spacers (IPS) currently available on the market. Imaging studies in live patients as well as cadaveric specimens have found that for degenerative lumbar spondylolisthesis of at least one degree and the resulting stenosis, the spinal canal space can be increased with appropriate implantation of an ISP device. This works primarily by increasing the lordosis of the implanted segment, reducing the redundancy of the ligamentum flavum and increasing the spinal canal and nerve root canal space. A recently published systematic review summarized the relevant articles and concluded that all devices currently available on the market have good biomechanical effects for the treatment of degenerative lumbar spine degeneration. Two clinical randomized controlled trials were conducted in which the authors compared the clinical effectiveness of a specific ISP with non-surgical treatments. After two years of follow-up, ISP was shown to significantly improve function. However, given the selective bias of this literature, there is no conclusive evidence, so the authors neither recommend nor oppose the use of such devices.
III. Decompression and fusion: how to choose?
There is direct evidence to support lumbar fusion in patients with lumbar spondylolisthesis as well as vertebral instability. In a classic study cited, Herkowitz and Kurz studied 50 patients with degenerative lumbar kyphosis accompanied by back pain and lower extremity pain, and they prospectively compared 25 patients who underwent decompression alone with 25 patients who underwent decompression with non-instrumented fusion. It was a small single-center trial. However, after 3 years of follow-up, the fusion group was found to provide significant pain relief.Mardjetko et al. performed a meta-analysis that meta-summarized the literature on studies of lumbar degenerative scoliosis accompanied by lower extremity pain or neurogenic claudication published from 1970 to 1993. Although only three of these were clinically randomized controlled trials, 25 papers with a total of 889 patients were included. When comparing decompression alone with decompression combined with non-instrumental fusion, the former had a satisfactory outcome of 69% of patients and the latter 90%. Martin et al. performed a systematic review of all studies of decompression alone or decompression with non-instrumented fusion for degenerative lumbar kyphosis from 1966 to 2005. Only comparative observational studies with clinical randomized controlled trials or at least 1-year follow-up could be included. A meta-analysis could not be performed because of the heterogeneity of all studies. The authors screened out eight of these studies, all of which were considered to have flawed study methodology. The results after subgroup analysis demonstrated that decompression combined with fusion was more likely to achieve clinically satisfactory outcomes than fusion alone. Interestingly, the treatment advantage of the decompression and fusion group was reduced in a subgroup analysis of patients without low back pain but with lower extremity pain.
IV. Which patients should not be fused
In patients with degenerative lumbar spinal stenosis without lumbar spinal slippage or instability, there is currently insufficient evidence in the literature to warrant routine spinal fusion.Grob et al. performed a clinically randomized controlled study in a group of patients who presented with spinal stenosis on imaging but without vertebral instability. They were randomized into 3 groups: a decompression group with laminectomy and medial intervertebral facet resection, a canal decompression and fusion at the stenotic segment only group, and a homogeneous decompression and fusion group at all segments. Outcome assessments included the use of anesthetics, loss of daily activity, and objective pain relief. Yone and Sakou conducted a prospective comparative study of 60 patients with symptomatic (low back pain/limp) lumbar spinal stenosis. 33 of the 60 patients met Posner criteria for vertebral instability on x-ray. In total, there were 3 surgical groups: Group 1 (27 patients without instability) received only decompression. Group 2 (19 patients with instability) underwent decompression with fusion. Group 3 (14 patients with instability but not fusion) received decompression only. Assessment was performed using the JOA score. Excellent clinical outcomes were demonstrated in 80% of patients in group 1 (no instability) and in all group 2 (stable and fused). Only 43% of patients in group III (stable but not fused) showed excellent outcomes. Based on the current limited evidence, combined with evidence of a therapeutic effect at 10-year follow-up after decompression alone, it is recommended that interbody fusion is not routinely required for patients with degenerative lumbar spinal stenosis without lumbar spondylolisthesis or vertebral instability.
V. Decompression and fusion: when (and if) internal fixation is needed
Although internal fixation devices are currently being used for almost any type of lumbar fusion, there is now direct evidence that treating symptomatic lumbar degenerative stenosis without internal fixation improves the rate of symptom relief. in a small prospective comparative study, Bridwell et al. found a 2-year follow-up of patients treated with surgery for lumbar degenerative scoliosis. A total of 44 patients were studied, of whom 9 had decompression only, 10 had decompression without instrumented fusion, and 24 had decompression and instrumented fusion. These patients underwent imaging as well as initial functional evaluation. The authors noted that the decompression-only group significantly reduced the incidence of instrumentation-induced pseudarthrosis, slowed the progression of scoliosis, and increased walking distance compared to the other two groups.
Fischgrund et al. studied 76 patients with degenerative scoliosis of the lumbar spine in a prospective randomized controlled clinical trial. These patients underwent decompression and were divided into a fusion-only group and a fusion-with-internal-fixation group after decompression. At two-year follow-up, only 76% of patients in the instrumented fusion group had an excellent final assessment compared with 85% in the non-instrumented fusion group, but 82% of patients in the instrumented fixation group showed stable intervertebral fusion compared with only 45% in the non-instrumented fixation group, as assessed by x-ray. Firm fusion was not associated with a good patient prognosis, so the authors concluded that in single-segment degenerative slippage, although instrumented internal fixation may result in higher fusion rates, clinical results showed no correlation between fusion and improvement in lower back pain and leg pain.
Gibson and Waddell systematically reviewed 31 randomized controlled clinical trials evaluating all surgical treatment modalities for lumbar degeneration and found 8 trials that demonstrated that endofixation, while achieving higher fusion rates, had only a critical no-difference effect on improving patient prognosis. Intra-appliance fixation is associated with additional complications. In the analysis by Mardjetko et al. there was no significant difference in the effect of instrumentation or non-instrumentation on fusion rates, although this study was too heterogeneous. in a systematic review of the literature, Martin et al. found that instrumented fusion significantly improved fusion rates but did not improve clinical outcomes.
In order to suggest that instrumentation is not routinely used for fusion during the treatment of lumbar degenerative stenosis, the investigators noted the lack of sufficient evidence demonstrating a link between the occurrence of pseudarthrosis assessed radiographically and patient prognosis, as well as the lack of evidence that instrumentation use significantly improves outcomes. In addition, they emphasize that complications and the expense associated with instrumentation can pose risks and problems for the procedure. Also more radical surgical approaches, such as combined anterior-posterior fusion (also called 360° fusion) are not helpful in treating degenerative lumbar stenosis per se.
VI. Treatment of complex cases of combined scoliosis and stenosis: evidence is still lacking
Patients with lumbar spinal stenosis are often found to have degenerative scoliosis as well. In these patients, surgical decompression requires not only excellent surgical skills, but also a detailed preoperative plan. Scoliosis can be divided into two groups: patients with no or only slight rotation and patients with significant rotation deformity. The latter are usually patients who have a degenerative process that is inherently idiopathic to scoliosis deformity and thus exhibit a significant loss of pronation. In the former, treatment of spinal stenosis using decompression and limited internal fixation fusion is performed with attention to managing vertebral instability due to scoliosis, lateral subluxation, and medically induced factors. In the latter case, decompression at the stenotic segment, internal fixation combined with fusion (or even osteotomy) is usually used to correct the sagittal instability of the vertebral body. The conclusions summarized in this article do not provide guidance for surgical treatment decisions in these patients. The reader is referred to other articles examining adult lumbar spine deformities for guidance on such issues.