Spinal Stenosis
Summary
Lumbar Spinal Stenosis (LSS) is a degenerative narrowing of the spinal canal, lateral recess, or neural foramina, leading to compression of the neural elements. It is the leading cause of spinal surgery in patients >65. The classic symptom is Neurogenic Claudication: leg pain/heaviness precipitated by walking and relieved by flexion (sitting or leaning forward). This differentiates it from Vascular Claudication (relieved by standing still). Pathology involves a triad: Disc Bulge (Anterior), Facet Hypertrophy (Lateral), and Ligamentum Flavum Buckling (Posterior), transforming the canal into a "Trefoil" (cloverleaf) shape. Management ranges from conservative (Epidurals) to surgical Decompression (Laminectomy). [1,2,3]
Key Facts
- The "Shopping Trolley Sign": 90% of patients find relief by leaning forward. Flexion increases canal diameter by stretching the Ligamentum Flavum. Extension (walking downhill) buckles it inward, worsening symptoms.
- The "Simian Stance": Patients walk with a stooped posture (hips and knees flexed) to maximize canal capacity.
- Neurogenic vs Vascular:
- Vascular: "I have to stop and stand still." (Pulses absent).
- Neurogenic: "I have to sit down or bend over." (Pulses present).
Clinical Pearls
"The Bicycle Test": A patient who cannot walk 100 yards but can cycle 5 miles has Spinal Stenosis. Cycling maintains a flexed spine (canal open). Vascular patients cannot cycle due to metabolic ischemia.
"Degenerative Spondylolisthesis": Stenosis often comes with a slip (usually L4 on L5). Why? The facet joints, which normally stop the slide, are worn out. These patients often need FUSION added to their decompression.
"It's Arthritis of the Spine": Explaining it as "internal arthritis" is less terrifying to an 80-year-old than "spinal compression".
Demographics
- Age: >60 years.
- Prevalence: 20-30% of asymptomatic elderly have radiological stenosis. Treat the patient, not the MRI.
- Risk Factors:
- Congenital Short Pedicles (starts symptoms earlier, e.g., 40s).
- Acromegaly / Paget's Disease (rare causes).
The "Trefoil" Canal
The normal canal is oval. In stenosis, it becomes triangular (Trefoil) due to encroachment from three sides:
- Anterior: Disc bulge / Osteophytes.
- Posterior: Ligamentum Flavum Hypertrophy (main dynamic factor).
- Posterolateral: Facet Joint Facet cysts/spurs.
Classification (Schizas - MRI T2 Axial)
- Grade A: CSF visible. Mild/Moderate.
- Grade B: Rootlets occupy whole sac.
- Grade C: Rootlets indistinguishable (No CSF). Severe.
- Grade D: Extreme compression. "Bone on Bone" appearance.
Symptoms
Signs
Imaging
- MRI Lumbar Spine: Gold Standard.
- Assess canal cross-sectional area (<100mm² = Stenosis. <75mm² = Severe).
- Look for "Sedimentation Sign" (Rootlets normally float to back in supine; with stenosis, they stay clumped).
- X-Ray (Standing):
- Crucial for Spondylolisthesis.
- Flexion/Extension views: Check for instability (does the slip move?). Instability = Fusion required.
LEG PAIN / CLAUDICATION
↓
NEUROGENIC OR VASCULAR?
(Pulses / Bicycle Test / Stoop)
┌────────────┴────────────┐
VASCULAR NEUROGENIC
(Refer Vasc) ↓
CONSERVATIVE CARE
(Flexion Physio / Analgesia)
↓
SYMPTOMS LIMIT LIFESTYLE?
┌───────────┴───────────┐
NO YES
↓ ↓
MONITOR MRI SPINE
↓
SEVERE STENOSIS?
┌──────┴──────┐
INJECTION SURGERY
(Epidural) (Decompression)
↓ ↓
RELIEF? INSTABILITY?
(Y/N) (Spondylo)
┌──────┴──────┐
NO YES
↓ ↓
LAMINECTOMY FUSION
1. Conservative
- Physio: Core stability. Flexion exercises (Posterior pelvic tilt). Avoid Extension (McKenzie extensions make it worse!).
- Epidural Steroid Injections:
- Reduces venous congestion/edema.
- Good for short term relief (3 months). Does not alter long-term progression.
2. Surgical: Decompression (Laminectomy)
- Indication: Failure of conservative care. Poor Quality of Life (QoL). Walking distance <100m.
- Procedure:
- Laminectomy: Remove Spinous Process + Lamina + Ligamentum Flavum.
- Laminotomy / Fenestration: Less invasive. Just "undercutting" the lamina.
- Success: Good for leg pain (80%). Unpredictable for back pain.
3. Surgical: Fusion
- Indication: Stenosis WITH Instability (Degenerative Spondylolisthesis > Grade 1 or movement on dynamic X-rays).
- Why?: Removing the lamina/facets in an already slippery spine causes massive slip post-op. You must fuse it (TLIF/PLIF) to lock it.
Dural Tear
- Incidence: 5-10% (Higher in revision). The dura is often thin and stuck to the ossified ligamentum flavum.
- Repair: Suture + Patch. Bed rest 24-48h.
Adjacent Segment Disease
- Fusion increases stress on the level above. 10-20% risk of needing surgery at the next level over 10 years.
The Weinstein Trial (SPORT) - 2008
- Comparison: Surgery vs Non-Op for LSS.
- Finding: Surgery group showed significantly greater improvement in pain and function at 2 and 4 years.
- Conclusion: Unlike disc herniation (where patients get better anyway), stenosis is mechanical and structural. It rarely improves spontaneously. Surgery is superior for QoL.
The Maine Lumbar Spine Study
- Showed that 8-10 year outcomes for surgery were better than non-op, but the gap narrowed over time due to re-stenosis or other age-related comorbidities.
What is Spinal Stenosis?
Think of your spine like a pipe carrying a cable (the nerve). Over time, "limescale" (bone spurs) and "sludge" (thick ligaments) block the pipe. When you stand up, it pinches the cable.
Why does bending forward help?
Bending forward is like un-kinking a hosepipe. It opens up the channel and lets the blood flow to the nerves again. That's why you can lean on a shopping trolley for an hour, but can't walk upright for 5 minutes.
The Surgery
It is called "Decompression". We essentially act like a plumber rodding out the drain. We remove the bone spurs and thick ligaments from the back of the spine to give the nerves breathing room.
- Weinstein JN, et al. Surgical versus nonsurgical therapy for spinal stenosis. N Engl J Med. 2008.
- Schizas C, et al. Qualitative grading of severity of lumbar spinal stenosis based on the morphology of the dural sac on magnetic resonance images. Spine. 2010.
- Katz JN. Lumbar spinal stenosis. N Engl J Med. 2008.
Q1: What is the "Sedimentation Sign" on MRI? A: In a normal supine MRI, nerve rootlets sink to the bottom of the dural sac (dorsally) due to gravity. In severe stenosis, they remain suspended or clumped in the middle because there is no room to settle. Positive sign = Severe stenosis.
Q2: Why do we avoid extension exercises in Stenosis? A: Extension buckles the hypertrophied Ligamentum Flavum anteriorly into the canal, further narrowing the diameter and worsening symptoms. Flexion exercises are prescribed. This is the opposite of Disc Herniation (where McKenzie extension pushes the disc forward away from the nerve).
Q3: When would you add Fusion to Decompression? A: If there is evidence of instability (Spondylolisthesis), specifically if there is dynamic instability on flexion/extension views (>3-4mm translation), or if the decompression requires excessive facet resection (>50% bilateral) which would destabilize the spine iatrogenically.
(End of Topic)