Lumbar Spinal Stenosis

Lumbar spinal stenosis is a narrowing of the central canal, the lateral recesses or the intervertebral foramina of the lumbar spine that compresses the cauda equina or the nerve roots. Its typical symptom is neurogenic claudication: leg pain, numbness or heaviness on standing and walking that eases with sitting or bending forward. It is the commonest reason for spinal surgery in people over 65 years.

MRI evidence of stenosis is present in about 20% of people over 60 years, and symptoms occur in a smaller proportion. The usual level is L4 to L5, then L3 to L4 and L2 to L3. The acquired degenerative form is by far the commonest; developmental stenosis (short pedicles, achondroplasia), spondylolisthesis, previous surgery, epidural lipomatosis, Paget disease and ossification of the ligamentum flavum are other causes.

The natural history is mixed: about a third improve, half stay unchanged, and 15 to 30% worsen over 4 years. Complications are loss of walking distance, falls, chronic pain, reduced independence, and, rarely, cauda equina syndrome.

Pathophysiology.

Loss of disc height, disc bulge, facet joint hypertrophy, thickening of the ligamentum flavum and osteophytes reduce the dural sac cross-sectional area (under 75 mm2 is severe; an anteroposterior canal diameter under 10 mm is absolute stenosis). Extension and standing reduce the canal further, and flexion widens it, which explains the postural pattern. Walking raises the metabolic demand of the roots while venous congestion and ischaemia reduce supply.

Pain, numbness, tingling or weakness in the buttocks, thighs or legs (usually both legs) on standing or walking, relieved within minutes by sitting or leaning forward (the patient may walk bent over or prefer a shopping trolley or cycling). Low back pain is common. Weakness of foot dorsiflexion and falls may follow. Bladder, bowel or saddle symptoms indicate cauda equina syndrome.

Examination between symptoms is often normal. Look for symptoms provoked by lumbar extension or after walking, reduced ankle reflexes, sensory loss in a root pattern, weakness after exercise, and normal foot pulses. Check the hips, peripheral nerves and posture.

• MRI of the lumbar spine: central, lateral recess and foraminal stenosis, dural sac cross-sectional area, nerve root crowding (the sedimentation sign), facet and ligamentum flavum changes, and grading of central stenosis from A to D.
• Standing flexion and extension radiographs for instability and spondylolisthesis; CT or CT myelography when MRI is contraindicated.
• Electromyography and nerve conduction studies to separate peripheral neuropathy and multilevel radiculopathy; ankle brachial pressure index or arterial duplex for vascular claudication.
• Bone density measurement before fusion; blood tests: HbA1c, vitamin B12, full blood count, renal function.
• Function scores (Oswestry Disability Index, walking distance on a treadmill) to track treatment.

Differential diagnosis.

• Vascular claudication (pain on walking relieved by standing still, reduced pulses, independent of posture).
• Peripheral neuropathy, diabetic amyotrophy and hip osteoarthritis.
• Lumbar disc herniation, trochanteric bursitis and tumour.
• Spinal arteriovenous fistula and myelopathy.

Non-operative care is first line for most patients. Surgery relieves leg symptoms more reliably than non-operative treatment over 1 to 2 years, when symptoms are disabling.

Non-operative treatment (3 to 6 months).

• Education, flexion based exercise, walking programmes, cycling, a walking frame or trolley, weight loss, physiotherapy.
• Paracetamol 1 g orally every 6 hours as needed (maximum 4 g daily; 3 g daily when weight is under 50 kg, with chronic alcohol use or hepatic impairment).
• Ibuprofen 400 mg orally every 8 hours with food (maximum 1200 mg daily) or naproxen 500 mg orally every 12 hours with food (maximum 1000 mg daily) for up to 2 weeks at a time.
• Add omeprazole 20 mg orally once daily in patients over 65 or with ulcer risk.
• Avoid NSAIDs with eGFR under 30 mL/min/1.73 m2, peptic ulcer, heart failure, uncontrolled hypertension or anticoagulant use.
• Gabapentin 300 mg orally at night, increased by 300 mg every 1 to 3 days to 300 to 600 mg three times daily (maximum 3600 mg daily; reduce at creatinine clearance under 60 mL/min).
• Or pregabalin 75 mg orally at night or twice daily, increased after 3 to 7 days to 150 mg twice daily (maximum 300 mg twice daily; reduce with renal impairment).
• Benefit is modest and falls risk rises with age.
• Duloxetine 30 mg orally once daily for 1 week, then 60 mg once daily (maximum 120 mg daily); avoid with monoamine oxidase inhibitors, uncontrolled hypertension, and creatinine clearance under 30 mL/min.
• Epidural steroid injection (transforaminal dexamethasone 8 to 10 mg, non-particulate, or interlaminar triamcinolone 40 mg) under image direction gives temporary relief, usually for several weeks to a few months.
• No more than 3 in 12 months and at least 2 to 4 weeks apart.
• Avoid with infection, uncontrolled diabetes (blood glucose rises for 3 to 5 days), and unheld anticoagulants (hold apixaban or rivaroxaban for 72 hours and warfarin for 5 days with INR under 1.5).
• Calcitonin has weak evidence and is not used routinely.

Surgery (disabling claudication or radiculopathy after 3 to 6 months, progressive weakness, cauda equina syndrome).

• Decompression: laminectomy, or bilateral decompression through a unilateral approach (laminotomy), preserving the facet joints and the pars where possible.
• Decompression with instrumented fusion for spondylolisthesis, scoliosis, instability, a recurrent stenosis, or when facet resection is extensive.
• Interspinous process spacers are used in selected patients with mild, flexion relieved symptoms at one or two levels; reoperation rates are higher than with decompression.
• About 60 to 70% have lasting improvement at 2 to 5 years. Complications: dural tear 5 to 10%, infection 1 to 3%, epidural haematoma, neurological injury, venous thromboembolism, and repeat surgery in 10 to 20% by 5 to 10 years.

Operative antibiotic prophylaxis.

• Cefazolin 2 g intravenously (3 g when weight is 120 kg or over) within 60 minutes before incision as a single dose (repeat after 4 hours or blood loss over 1500 mL).
• With severe penicillin allergy, vancomycin 15 mg/kg intravenously starting 90 to 120 minutes before incision as a single dose, with levels and creatinine checked in prolonged cases.

Tranexamic acid (fusion).

• Tranexamic acid 15 mg/kg (maximum 1 g) intravenously over 10 minutes before incision, repeated once after 3 hours if bleeding continues (maximum 2 g).
• Avoid with a history of thromboembolism, active intravascular clotting, seizures, or recent coronary stent; reduce the dose at creatinine clearance under 50 mL/min.

Thromboprophylaxis.

• Mechanical prophylaxis and early mobilisation.
• Enoxaparin 40 mg subcutaneously once daily started 24 to 48 hours after surgery once haemostasis is secure and continued for 7 to 14 days (20 mg once daily at creatinine clearance under 30 mL/min; check the platelet count on days 5 to 14).

Analgesia after surgery.

• Paracetamol 1 g orally every 6 hours.
• Oral morphine 5 to 10 mg every 4 hours as needed for up to 3 to 5 days (start 2.5 to 5 mg with age over 75 or eGFR under 30 mL/min/1.73 m2).
• Laxative; avoid NSAIDs after fusion until union is expected.

Monitoring. Walking tolerance, pain and neurological state at each visit. After surgery, review at 2 weeks, 6 weeks, 3 months and 12 months; radiographs after fusion. Glucose in diabetes after injections.

Referral and escalation. Refer to a spinal service for symptoms that limit daily activity despite 3 to 6 months of treatment, or progressive weakness. Emergency referral for cauda equina syndrome (urinary retention, saddle anaesthesia, faecal incontinence, bilateral progressive weakness) with urgent MRI.

Special groups.

• Older and frail patients: minimally invasive decompression with limited blood loss; consider frailty, cognition and falls.
• Diabetes: neuropathy may confound the diagnosis; control glucose before surgery and injections.
• Anticoagulated patients: plan the interruption of therapy with the prescribing team.
• Kidney impairment: avoid NSAIDs, reduce gabapentin, pregabalin and morphine doses, and adjust enoxaparin.