Lumbar spinal stenosis: an update on the epidemiology, diagnosis and treatment

Introduction

Lumbar spinal stenosis (LSS) is a common spinal disorder in the older population, and a clinical syndrome consisting of pain in the buttock or lower extremity, with or without low back pain and corresponding imaging findings of narrowing of spaces around neural and vascular elements in the lumbar spine (1-3). The narrowing factors could be the intervertebral disc herniation, hypertrophy of ligamentum flavum, hypertrophy of facet joint, spondylolisthesis, osteophyte and ectopic fat tissue (Figures 1,2).

Figure 1 The lumbar spinal stenosis could be caused by intervertebral disc herniation, hypertrophy of ligamentum flavum and hypertrophy of facet joint.

Figure 2 The spondylolisthesis patient with upper vertebra slip forward over the lower one may cause narrowing of the lumbar spinal canal.

Epidemiology

The exact prevalence of LSS is still unknown. It is estimated that more than 200,000 adults are affected by LSS in the United States (2), and will rise to 64 million elderly adults by the year 2025 (4). The Framingham Study (5) found that congenital relative LSS was 4.7% and absolute LSS was 2.6%, acquired relative and absolute LSS was 22.5% and 7.3%, respectively, for 60–69 years old population, the relative and absolute LSS was 47.2% and 19.4%, respectively. A population-based study in Japan (6) found that the LSS incidence was increased by age, about 1.7–2.2% in 40–49 years old population, and 10.3%–11.2% in 70–79 years old population. Another study reported the incidence of symptomatic LSS is about 10% (7). The LSS is the most common reason for >65 years old patients to undergo the spinal surgery (8). During 2002 to 2007, the rate of lumbar stenosis surgery per 100,000 Medicare beneficiaries is about 135.5–137.5 persons, the mean hospital charges for decompression alone is about $23,724 and combined with fusion is $80,888, and in 2009, the hospital bill for LSS for Medicare beneficiaries was $1.65 billion (9), which is a significant socioeconomic burden.

History and symptoms

Neurogenic claudication is the most common symptom for LSS patients. The patients complain of pain or discomfort that radiates to the buttock, thigh and lower leg after walking for a certain distance (10,11), therefore leading to functional disability and decreased walking capacity (12,13). For some dynamic components in LSS patients, the pain symptom often is relieved at the position of sitting down or lumbar flexion (using a shopping cart or bicycle), and exacerbated at the position of lumbar extension, which will reduce the area of lumbar spinal canal (14-17). Patients with lumbar stenosis with spondylolisthesis often have low back pain (18,19), and other symptoms include leg numbness, imbalance and lower extremity weakness (12,20).

Physical examination

Physical examination includes the assessment of gait (normal or wide-based gait), modified Romberg maneuver (the patients’ feet are kept together and eyes closed for about 10 seconds and observed for imbalance), no pain with flexion, strength of knee flexors and extensors, ankle dorsiflexors and plantar flexors, pinprick sensation and achilles reflex. The specificity of wide-based gait, abnormal Romberg result is more than 90%, but the sensitivity is less than 50%, the sign of “No pain with flexion” has a sensitivity of 79%, only 44% for specificity (16). None of the above physical examination has higher percentage in both sensitivity and specificity.

Radiographic images

Plain radiography

Spondylolisthesis can be observed from plain radiographic images, but not all spondylolisthesis will lead to LSS. Some other signs of LSS include narrowing height of intervertebral foramina and space of intervertebral disc, small interlaminar window, hypertrophy of facet joint, short pedicles, thick lamina, and deep posterior concavity of vertebral bodies (21). The plain radiographic image is only helpful for some obvious stenosis or spondylolisthesis.

CT and MRI

MRI is commonly used to confirm the LSS. The MRI, which has excellence in observation for soft tissue, is recommended to diagnose LSS by many authors (22-24). CT will be used for some patients with suspected ossification, or if MRI is contraindicated, or unavailable.

Although there is no gold standard quantitative criteria in MRI to diagnose the LSS, currently, several parameters are used clinically, the most common ones for central LSS are anteroposterior canal diameter, cross sectional area; for lateral LSS, the most common ones are the height and depth of the lateral recess and the lateral recess angle; for foraminal stenosis, they are foraminal diameter and height, hypertrophic facet joint degeneration and foraminal nerve root impingement (25,26). It is reported that anteroposterior canal diameter <10–15 mm, the cross sectional area <75–145 mm² as the cut-off values to definition of central stenosis (27-37) (Figure 3), the details of them are shown in Table 1. It is reported that the height/depth of lateral recess ≤2–5 mm, and angle of lateral recess <30° to define the lateral stenosis (38-40) (Figure 4), the details of them are showed on Table 2.

Figure 3 Left: the measure method of anteroposterior canal diameter of spinal canal (red arrow); right: the measure method of cross sectional area of spinal canal (the red hatched area).

Figure 4 The measure method of height/depth of lateral recess: the distance between the anterior portion of the superior articular facet and the posterior border of the spinal canal at the level of the superior margin of the corresponding pedicle (red arrow); the angel of lateral recess is the angle between the lines parallel to the floor and the roof of the lateral recess (yellow angle).

In a large-scale MRI study (41) with standardized measurements to determine the clinical MRI criteria for developmental LSS, the results suggest the developmental LSS can be defined if the anteroposterior canal diameter was at L1 <20 mm, L2 <19 mm, L3 <19 mm, L4 <17 mm, L5 <16 mm, and at S1 <16 mm.

Another radiographic sign—“sedimentation sign”—the lack of sedimentation of the nerve roots to the dorsal part of the dural sac (positive sedimentation sign) in MRI is recognized as a reliable sign to diagnose LSS (42-45). A recent meta-analysis (46) including seven studies found that the sensitivity of sedimentation sign is 0.80 (95% CI: 0.77–0.83) and the specificity is 0.96 (95% CI: 0.94–0.98). In patients with severe morphological LSS, the sedimentation sign had even higher sensitivity of 0.899 (95% CI: 0.87–0.92) and specificity of 0.99 (95% CI: 0.98–1.00). It was also reported that patient with positive sedimentation sign may had greater surgical treatment effect and as an informed treatment choice regarding surgery for LSS (47,48), the reversibility of a pre-operative positive sedimentation sign after surgery was associated with an improved clinical outcome, however, the persisting post-operative positive sedimentation sign could be the result of incomplete decompression or surgical complications (49).

Myelography

It has been found that myelography had a slightly higher accuracy in diagnosing LSS than CT (33), Bell et al. reported that the accuracy of myelography was 93% vs. 89% by CT (50). MRI and myelography may have similar accuracy in diagnosing lumbar canal stenosis (51), in study of Bischoff et al. (52), they found that myelography was the most specific diagnostic method (with specific 88.9%) when compared to the myelo-CT and MRI in diagnosis of lumbar canal stenosis. However, because of the drawbacks of invasiveness and relative side effects of myelography, it is not commonly used in clinical practice.

Additional investigations

The electromyography is not routinely used in clinic, however, for some special clinical conditions where the radiographic images cannot explain the symptoms of patients, or unilateral symptoms with bilateral pathology (53), or if there is a need to differentiate between LSS and peripheral neuropathy (54), electromyography may be helpful. Caution needs to be taken if there is co-existing LSS and peripheral neuropathy. A quantitative electromyographic technique—paraspinal mapping—may be useful in diagnosis of LSS, and reflects physiology of nerve roots better than the limb electromyography (55). Selective lumbar nerve root block can be used to identify the responsible level for some patients with multiple anatomic LSS, and may reduce the levels of operation (56,57).

Some other techniques of magnetic stimulation caudal motor conduction time (58), dermatomal somatosensory-evoked potentials (59,60) are rarely used, and their accuracy remains uncertain.

Diagnosis and differential diagnosis

No gold standard diagnostic criterion is widely accepted among physicians (22,61). Therefore, to diagnose LSS, we need comprehensive consideration of the history, physical examination, and radiographic images. Most often information including age, neurogenic claudication, the radiating buttock or leg pain which is exacerbated when lumbar extension and relieved at seat or lumbar flexion, wide based gait, and the anatomic narrow observed at radiographic images, sometimes even the results of electromyography and nerve root block is used.

Common conditions that need to be included in the differential diagnoses include vascular claudication, peripheral neuropathy, hip osteoarthritis and trochanteric bursitis. The symptomatic presentation of a shopping cart sign, symptoms located above the knees, triggered with standing alone and relieved with sitting had a strong correlation with neurogenic claudication, while symptoms in calf and relieved with standing alone is related to vascular claudication (62), and peripheral neuropathy patients may have history of diabetes mellitus (63). Electromyography may help the differential diagnosis (64,65). Hip osteoarthritis and trochanteric bursitis are also common in elderly patients, selective anesthetic and corticosteroid injection at hip joint or trochanteric bursa may help the differential diagnosis. Nonetheless, the above diseases may co-exist with LSS, making it complicated to differentiate occasionally.

Classification

Many different classifications have been reported, but there is a lack of an accepted classification system. One of the most common classification systems was described by Arnoldi et al. (66), which categorized the LSS into congenital LSS and acquired LSS. Congenital LSS includes idiopathic and achondroplastic LSS, and acquired LSS including degenerative, combined, spondylolisthesis, iatrogenic, post-traumatic and miscellaneous. The details of the Arnoldi classification are summarized in Figure 5.

Figure 5 The Arnoldi classification of lumbar spinal stenosis.

Treatment

Non-operative

Many non-operative options can be selected for LSS patients, including lifestyle modifications, drugs, physiotherapy, multidisciplinary rehabilitation, epidural injections and some complementary medicine. There is still a lack of high quality randomized controlled trials to prove the efficacy of non-operative methods (67,68). Lifestyle changes such as weight loss, quit smoking may decrease the incidence of low back pain (69), improve walking capacity and quality of life (70). The prescriptions of over-the-counter (OTC) drugs include gabapentin, vitamin B1 and prostaglandins, non-steroidal anti-inflammatory drugs (NSAIDs) may provide some symptomatic relief. Recent systematic reviews found (71,72) that oral NSAIDs are more effective than placebo and acetaminophen for persistent low back pain, intramuscular NSAIDs have similar outcomes as combined manipulation and soft tissue therapy. No evidence suggests that calcitonin administration has benefit in pain relief or walking distance improvement for patients with LSS (73,74). Opioid may be prescribed for some severe pain patients, however, long-term opioid use had higher risk, operative option may better for them (75).

Physiotherapy including many different kinds of treatments, such as massage or manipulation, exercises (strengthening exercises and flexibility exercises), balance training, wear braces or corset), pain management by heat, ice, electrical stimulation, some lifestyle modification and complementary medicine (acupuncture) also could be included in physiotherapy category (76). The exercises may have short-term benefit for leg pain and function compared with no treatment, but the quality of evidence is low (68). Currently, there is no evidence to show that one kind of treatment is superior to the others (77).

Epidural injections may include local anesthetic injection with or without steroids. The epidural injections may result in some improvement in radicular pain in short term (78-80), improvement in pain and functional parameters seen similar between epidural injections and physical therapy (29). Researchers also found that epidural injection of combinations of anesthetic and steroids has no beneficial effect compared with epidural anesthetic alone injection (28,81). Moreover, epidural injection does not have any impact on average impairment of function, risk of need for surgery, or provide long-term pain relief (78-80).

Operative

Surgical intervention is recommended if the symptoms are persistent. There are several kinds of operative techniques, including decompression alone, interspinous spacers, and spinal arthrodesis.

Decompression

The aim of the decompression is to decompress the spinal canal and foramina, remove the pressure factors and release the nerve roots. The decompression approaches include conventional laminectomy, bilateral laminotomy, unilateral laminotomy with contralateral recess decompressed by transmedia way (Figure 6), partial facetectomy and split-spinous process laminotomy/laminoplasty (82-86). Decompression can significantly relieve the symptoms of claudication and radicular leg pain, improve the physical function for LSS patients (87,88). A prospective 10-year study comparing surgical decompression with conservative treatment found excellent or fair results in half of conservative patients and in four-fifths of surgical decompression patients after a period of 4 years, and the treatment result for the patients randomized for surgical treatment was considerably better than for the patients randomized for conservative treatment (89).

Figure 6 A L3–4 lumbar stenosis female patient with both sides leg claudication, hypertrophy of ligamentum flavum of both sides were observed from the MRI (A), the unilateral laminotomy with contralateral recess decompressed by transmedia way (B) was performed on her, the symptom was relieved after surgery.

One randomized controlled study (RCT) (90) included a total of 94 patients with 50 operative and 44 nonoperative patients found both operative and nonoperative managements showed improvement of pain and Oswestry Disability Index (ODI), but the mean difference in favor of operation was 11.3 in disability (95% CI: 4.3–18.4), 1.7 in leg pain (95% CI: 0.4–3.0), and 2.3 (95% CI: 1.1–3.6) in back pain at one year follow up and 7.8 in disability (95% CI: 0.8–14.9) 1.5 in leg pain (95% CI: 0.3–2.8), and 2.1 in back pain (95% CI: 1.0–3.3) at two year follow up. Walking ability, either reported or measured, did not differ between the two different treatments. Another clinical trial included 289 randomized assigned patients and 365 non-randomized assigned patients showed a significant treatment effect favoring surgery on the SF-36 scale for bodily pain and no significant difference in ODI in randomized assigned patients. When combining the randomized and non-randomized assigned patients, the ones who underwent surgery showed more significantly improvement in pain scores and ODI than non-operative ones (87).

A Cochrane systematic review found that: compared to the conventional laminectomy, the bilateral laminotomy may be better in perceived recovery, the unilateral laminotomy for bilateral decompression and bilateral laminotomy may have lower incidence of iatrogenic instability, and the bilateral laminotomy and split-spinous process laminotomy may have less severity of postoperative low back pain (84).

Interspinous spacer

For the theory of dynamic component in LSS patients, and the pain relieved at the position of sitting down or lumbar flexion, exacerbated at lumbar extension (14-16), many interspinous spacers (such as X-stop, coflex, DIAM, and Aperius devices) were designed and used in clinic (91-93). Biomechanical study (94) showed the interspinous spacer significantly increased the canal area by 18%, subarticular diameter by 50%, canal diameter by 10%, the foraminal area by 25%, and the foraminal width by 41% in extension. Therefore, interspinous spacer is an alternative choice for LSS nowadays (95), it can be inserted percutaneously alone without decompression or combined with open or microsurgical decompression. The percutaneous stand-alone spacer implantation has advantages of being minimally invasive (96,97), however, may have high risk of un-satisfactory back pain, leg pain, quality of life and failure of implantation (98). The combined use of interspinous spacer with decompression patients had similar results in pain and functional outcomes to the decompression alone (99,100). The meta-analysis (101) found that patients treated by interspinous spacers had high cost and high reoperation rate, and did not confer significantly more benefit to patients than decompression alone, therefore, there is no good evidence to support its use for LSS patients.

Lumbar fusion

To treat the LSS by decompression alone or decompression with fusion is an old and persistent controversy (102-106). Many kinds of lumbar fusion techniques via different approaches have been described, including posterior/posterolateral lumbar fusion, posterior lumbar interbody fusion, transforaminal lumbar interbody fusion (TLIF) and oblique lumbar interbody fusion (OLIF) (107-109) (Figure 7), and the rate of decompression plus fusion for lumbar stenosis was increased while the decompression alone was decreased (110,111).

Figure 7 A L4–5 spondylolisthesis (A, MRI; B, plain radiography) male patient with both low back pain and claudication, laminectomy and posterior lumbar interbody fusion was performed on him; (C,D) the slip was reduced and symptoms were disappeared after surgery.

However, research suggests that decompression with fusion has small or even no benefit for most LSS patients (112,113). A recent RCT found the instrumented fusion may reduce the further progression of spondylolisthesis patients. In 2016, Försth et al. (114) published a 5 years RCT to compare the decompression plus fusion with decompression alone for LSS patients with and without spondylolisthesis, and there was no significant difference between them in clinical outcomes. Ghogawal et al. (115) published another RCT and found that for degenerative grade I spondylolisthesis patients, decompression plus fusion had statistically significant more improvement in overall physical health-related quality of life than decompression alone (score change from baseline: 14.1 vs. 7.4, P=0.02) at 4 years follow up. In both of the above two RCTs (114,115), decompression plus fusion had more blood loss, longer operative time and longer hospital stay.

Fusion is a complex operation compared with decompression alone, and therefore can potentially increase the peri-operative complications or mortality, and cost (9). Since there is a lack of evidence for advantages of fusion, this technique should be restricted to those with spinal instability, spinal deformities, or vertebral destruction caused by trauma, tumors and infections, or neuroforamen stenosis with compressed exiting nerves caused by postsurgical disk collapse (102,104).

Minimally invasive trends

Some surgeons use posterior microdecompression technique in treatment of LSS to minimize destruction to tissues with assistance by micro-endoscopy (116). Also, percutaneous endoscopic interlaminar and transforaminal decompression has been designed (117) and used in LSS (118-121).

The techniques of TLIF was also modified as minimally invasive TLIF (MI-TLIF) (122-124) and the meta-analysis found the MI-TLIF have similar clinical outcomes to the traditional TLIF technique with less trauma for LSS with or without grade I–II spondylolisthesis (125-127).

Minimally invasive techniques of lateral lumbar interbody fusion (LLIF) and OLIF (128-130) were also reported as indirect decompression choice for LSS. The efficacy and safety of indirect decompression technique was still controversial. Contrary to the direct decompression techniques, indirect decompression technique may alleviate the symptoms of radiculopathy and neurological claudication by restoration of intervertebral and foraminal heights and correction of spinal alignment (131), and is preferred for LSS patients with degenerative scoliosis by some surgeons (132). However, indirect decompression should be not performed on patients with bony lumbar stenosis, congenital stenosis and/or locked facets (133,134).

With the development of advanced image guidance systems (135), the number of surgeries performed using minimally invasive techniques has increased quickly in last decades, however, minimally invasive techniques also have some limitations, including longer learning curves, risk of some special complications (136,137), specific and limited indications, and heterogeneous clinical outcomes from different surgeons. Therefore, minimally invasive techniques in treatment of lumbar stenosis is still under development, and the safety and efficacy still need more high quality studies to prove.

Summary and key points

• LSS has high prevalence in aged population, and the most common reason for old patients to undergo the spinal surgery.
• No existence of gold standard diagnostic criteria for LSS, the diagnosis of LSS needs comprehensive consideration of the patient’s history, physical examination, radiographic images (CT or MRI), sometimes needs electromyography or nerve root block to aid diagnosis.
• Variety of non-operative options for most primary LSS patients but no evidence show which one is superior to others.
• Patients with persistent symptoms are recommended to undergo operative treatment, decompression alone or plus with fusion is an old and persistent controversy, with more evidence suggesting fusion should be used in limited indications, and interspinous spacer should be cautiously used.
• Minimally invasive technique is a new trend in spine surgery, however, their indications, safety and efficacy still need more high quality studies to prove.

Acknowledgements

Funding: This work was funded by the National Natural Science Foundation of China (81501933), Zhejiang science and technology innovation project (2016R413061), Wenzhou Science and Technology Project (Y20160369). The funders had no role in the design, execution, or writing of the study.

Footnote

Conflicts of Interest: The authors have completed the ICMJE uniform disclosure form (available at http://dx.doi.org/10.21037/amj.2017.04.13). Dr. Wu serves as an unpaid Section Editor of AME Medical Journal. The other authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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