What is Sciatica
Sciatica is pain radiating down the leg below the knee in the distribution of the sciatic nerve, indicating nerve root compromise from mechanical pressure or inflammation—it is a symptom of lumbar radiculopathy, not a specific diagnosis. 1
Core Definition and Pathophysiology
Sciatica represents a symptom complex resulting from nerve root irritation, most commonly caused by lumbar disc herniation, with both compression and inflammation playing critical roles in producing symptoms. 2, 3
Over 90% of symptomatic lumbar disc herniations occur at the L4/L5 and L5/S1 levels. 1
The pathophysiology involves proinflammatory substances (particularly TNF-alpha) secreted by the nucleus pulposus that cause nerve root pain, especially when mechanical injury is present. 3
Clinical Presentation
Pain Characteristics
The defining feature is pain radiating from the lower back through the buttock and down the posterior thigh, extending below the knee into the foot and toes in the sciatic nerve distribution. 1, 4
Pain often has a neuropathic quality with burning, electric sensations, or dysesthesia. 1
Symptoms are typically aggravated by spinal flexion/extension, walking, or running. 1
Neurological Findings
Sensory deficits occur in the affected dermatome (L4, L5, or S1 distribution). 1
Motor weakness corresponds to the affected nerve root:
- L4: knee strength deficits
- L5: great toe and foot dorsiflexion weakness
- S1: foot plantarflexion weakness 1
Reflex changes include diminished or absent ankle reflex (particularly with S1 involvement). 1
Diagnostic Approach
Diagnosis is primarily clinical, based on history and physical examination findings. 2, 4
The straight-leg-raise test has 91% sensitivity but only 26% specificity for herniated disc. 1, 5
The crossed straight-leg-raise test is more specific (88%) but less sensitive (29%). 1, 5
Critical Red Flags Requiring Urgent Evaluation
Urinary retention (90% sensitivity for cauda equina syndrome—a medical emergency). 1
Fecal incontinence or bowel dysfunction. 1
Rapidly progressive or severe neurological deficits. 1
Important Clinical Pitfalls
Do not confuse sciatica with referred pain from the lower back that does not follow nerve root distribution—true sciatica must radiate below the knee. 1, 2
Psychosocial factors and emotional distress are stronger predictors of outcomes than physical examination findings or pain severity. 1
Consider alternative diagnoses including spinal stenosis (pseudoclaudication relieved by sitting) and piriformis syndrome. 1, 6