Lumbar Spinal Stenosis

Introduction

• LSS refers to a narrowing of the spinal canal in the lower back, particularly within the lumbar region. This narrowing compresses the spinal cord and nerve roots, leading to pain, weakness, or sensory deficits. It is one of the leading causes of disability in older adults and a primary reason for spinal surgery among individuals older than 65 years.^1,2
• Despite its prevalence, there remains no universally accepted definition or standardized radiologic criteria for LSS. The variability in how and where the narrowing occurs means that LSS can present differently in each patient and is sometimes confused with other spinal or neurologic conditions.¹

Anatomy of the Lumbar Spine

• The human spine consists of two main regions: an anterior portion made up of vertebral bodies and intervertebral (IV) discs, and a posterior portion formed by the vertebral arches, laminae, and processes.²
• The IV discs act as shock absorbers, consisting of a gelatinous center (nucleus pulposus) surrounded by a fibrous ring (annulus fibrosus). The posterior spine protects the spinal cord and provides attachment sites for muscles and ligaments, including the ligamentum flavum, a thick elastic structure that can contribute to stenosis when it thickens or buckles inward. The lateral recess, a small space near the nerve roots, is another key site of compression in LSS.^2,3

Types and Mechanisms of Stenosis

LSS can occur in different anatomical regions:^2,3

• Central canal stenosis: compression of the thecal sac and multiple nerve roots, often producing bilateral symptoms.
• Lateral recess stenosis: compression before the nerve exits the foramen, typically leading to unilateral radicular pain.
• Foraminal or extraforaminal stenosis: nerve root compression inside or beyond the IV foramen.

• The most common level affected is L4-L5. Causes include ligamentum flavum hypertrophy, disk protrusion, facet joint arthropathy, and osteophyte formation.³

Causes and Risk Factors

• LSS may be congenital or acquired, but most cases result from degenerative changes due to aging. Chronic stress on the lumbar spine leads to disk degeneration, osteophyte growth, ligament thickening, and joint hypertrophy, all of which narrow the spinal canal.^1,3
• Other causes include:
  • Degenerative spondylolisthesis (vertebral slippage)
  • Spinal trauma or prior surgery
  • Inflammatory and rheumatologic diseases
  • Congenital conditions such as achondroplasia

Epidemiology

• LSS affects approximately 103 million people worldwide and 11% of older adults in the United States.¹ Radiologic evidence of narrowing can be found in up to 20% of people over 60. Interestingly, many individuals with imaging findings of stenosis remain asymptomatic.
• Genetic predisposition has also been identified, with certain gene variants linked to disk degeneration and ligament thickening.²

Pathophysiology

• As the IV discs lose height and hydration, weight-bearing shifts to the posterior elements, causing facet joint overload and ligamentum flavum thickening. These changes gradually reduce the canal’s diameter.³
• Symptoms result from both mechanical compression of nerve roots and vascular compromise, leading to ischemia and neurogenic pain. The combination of static compression (anatomical narrowing) and dynamic compression (postural changes) explains why symptoms worsen with standing and extension and improve with flexion.³

Clinical Presentation

• The hallmark symptom of LSS is neurogenic claudication: pain, numbness, or weakness in the legs that worsens with walking or lumbar extension and improves with sitting or leaning forward.^1-3
• Other common features include:
  • Low back pain
  • Bilateral leg discomfort, often asymmetric
  • Tingling or weakness
  • Postural adaptation to relieve pressure (the “shopping cart sign”)
• Severe cases may progress to cauda equina syndrome or conus medullaris syndrome, presenting with bladder or bowel dysfunction, saddle anesthesia, and bilateral leg weakness. These presentations constitute a surgical emergency.²

Diagnostic Evaluation

Diagnosis is based on clinical findings supported by imaging:^1-3

• X-rays: reveal bone spurs, disk height loss, or vertebral slippage.
• Computed tomography scans: assess bony canal dimensions.
• Magnetic resonance imaging is the gold standard, offering detailed visualization of soft tissues and nerve compression. Typical findings include reduced canal diameter (less than 10 mm for severe stenosis).
• Electromyography and nerve conduction studies can help distinguish LSS from peripheral neuropathy or plexopathy.

Anesthetic Considerations

• Patients with preexisting spinal stenosis present unique challenges for anesthesia providers, particularly regarding neuraxial techniques.⁴

Neuraxial Anesthesia in Patients with Spinal Stenosis

• A landmark 15-year retrospective study from Mayo Clinic evaluated 937 patients with preexisting spinal stenosis or lumbar radiculopathy who received neuraxial anesthesia.⁴ Key findings include:
  • Block success rate: 97.2%, comparable to the general population.
  • Neurologic complication rate: 1.1% (95% CI: 0.5% to 2.0%), which is higher than the general population.
  • Risk factors for complications: multiple neurologic diagnoses and compressive radiculopathy increased risk.

Clinical Implications

• Preoperative neurologic examination should be documented thoroughly to establish baseline deficits.
• Informed consent should include a discussion of the increased risk of neurologic complications.
• Consider general anesthesia as an alternative when multiple risk factors are present.
• Lower local anesthetic doses may be required due to reduced epidural space volume.
• Technical difficulties may be encountered due to degenerative changes, calcified ligaments, and osteophytes.
• Postoperative neurologic monitoring is essential to detect new or worsening deficits.

Management Strategies

• Treatment aims to relieve pain, improve function, and prevent progression. Management generally follows a stepwise approach:^1-3

Conservative Care

• Lifestyle modification, posture correction, and weight management are the cornerstones of conservative management.
• Nonsteroidal anti-inflammatory drugs and pain control. There is limited evidence for long-term use.
• Physical therapy focuses on flexion-based and core-strengthening exercises.
• Epidural steroid injections can provide short-term (weeks to months) relief of leg-dominant symptoms by reducing nerve inflammation, but do not correct the underlying stenosis.
• Benefits are variable and generally temporary; injections are typically used to improve function or delay surgery. There is limited evidence for long-term effectiveness.

Minimally Invasive Procedures

• Interspinous spacers to limit extension.
• Radiofrequency ablation for facet-mediated pain.
• Percutaneous decompression for hypertrophied ligamentum flavum.

Surgical Decompression

• Laminectomy (open or minimally invasive) remains the standard for severe or refractory cases.
• Fusion may be added when spinal instability or spondylolisthesis is present.
• Studies show that surgery offers significant improvement in pain and function compared with nonoperative management, although benefits may diminish over time.¹

Prognosis

• The outlook for mild to moderate LSS is generally favorable, with many patients improving through conservative measures alone. However, 20% to 40% eventually require surgery within 10 years.^1,2
• Outcomes depend on symptom severity, preoperative functional status, and psychosocial factors such as depression or smoking. Surgical decompression provides lasting pain relief in most patients, though spinal balance may decline years after the procedure.

Complications

• Untreated or severe LSS can lead to:2
  • Chronic pain and mobility loss
  • Muscle atrophy
  • Depression and reduced quality of life
  • Neurologic emergencies (cauda equina syndrome)
• Surgical complications, though uncommon, include infection, hematoma, dural tears, and iatrogenic instability.